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Article

Advanced PtCo Catalysts Based on Platinum Acetate Blue for the Preferential CO Oxidation in H2-Rich Mixture

by
Marina Shilina
1,*,
Irina Krotova
1,
Sergey Nikolaev
1,
Natalia Cherkashina
2,
Igor Stolarov
2,
Olga Udalova
3,
Sergey Maksimov
1 and
Tatiana Rostovshchikova
1
1
Chemistry Department, Lomonosov Moscow State University, 119991 Moscow, Russia
2
Kurnakov Institute of General and Inorganic Chemistry, RAS, 119991 Moscow, Russia
3
Semenov Federal Research Center for Chemical Physics, RAS, 119991 Moscow, Russia
*
Author to whom correspondence should be addressed.
Catalysts 2024, 14(8), 484; https://doi.org/10.3390/catal14080484 (registering DOI)
Submission received: 28 June 2024 / Revised: 23 July 2024 / Accepted: 26 July 2024 / Published: 28 July 2024
(This article belongs to the Section Catalytic Materials)
Browse Figures
Review Reports Versions Notes

Abstract

:
Preferential oxidation of carbon monoxide (CO-PROX) in H2-rich mixture is an effective way of hydrogen purification for fuel cells. High-performance PtCo/ZSM-5 catalysts with reduced Pt loading for this process were prepared using polynuclear platinum acetate complex known as platinum acetate blue (PAB) of the empirical formula Pt(CH3COO)2.5 as a novel precursor. The impregnation of HZSM-5 (Si/Al = 15 and 28) with PAB and its decomposition at 200 °C resulted in the stabilization of highly dispersed Pt0 and PtOx species on the zeolite surface. The catalytic properties were improved by the addition of Co(CH3COO)2 followed by calcination at 450 °C. Produced materials were studied by SEM, TEM, EDX, XPS, and DRIFTS methods and tested in a CO-PROX reaction. The relationship between the synthesis conditions, structure, and catalytic behavior of composites is discussed in this paper. The synergistic effect of Pt and Co was observed when they both were located together in zeolite channels. The Pt-Co interaction provides new active catalytic sites and prevents platinum aggregation during the process. Due to this, the 100% CO conversion in the wide temperature range from 50 to 130 °C is achieved for PtCo/ZSM-5 catalysts (Si/Al = 15), which is the best result compared to low-loaded Pt catalysts prepared with traditional precursors.

1. Introduction

Oxidation of carbon monoxide remains one of the most studied reactions due to its enormous fundamental and applied significance [1,2,3,4,5]. Recently, special attention from researchers has been attracted to the preferential oxidation of CO in H2-rich gas mixture (CO-PROX). It is an effective way to carry out hydrogen purification from CO impurities for the application in fuel cells [6,7,8]. Catalysts for this process should be active, selective, and stable in the temperature range of 65–85 °C corresponding to the operating window of fuel cells [9]. Supported nanoparticles of noble metals are widely used in the oxidation of CO, among them, Pt-based catalysts are the most suitable for the CO-PROX process [10,11,12,13]. The rational design of catalysts with reduced noble metal loading for CO oxidation remains an urgent task, the solution of which requires knowledge of the process mechanism and the nature of active centers. With a decreasing of metal loading, metal dispersity, electronic state, and catalytic behavior varies greatly [14,15,16]. The choice of a suitable support and synthesis conditions along with a chemical precursor for introducing the active metal becomes of great importance [17,18,19,20].
Oxide supports seem to be promising candidates for stabilizing highly dispersed particles of the active phase, even for single atoms and small clusters due to strong metal–oxide interactions [21,22,23,24]. To prepare high-performance Pt-based catalysts for CO-PROX, different metals (Ni, Fe, Ce, Co, and etc.) or oxides are additionally introduced as promoters [25,26,27,28]. Among them, cobalt oxides should be noted due to their own high activity [4,29,30,31] and a strong synergistic effect with platinum [32,33,34].
Zeolites are considered as the prospective supports for the formation and stabilization of highly dispersed active species with the controllable electronic states of metals for different redox reactions [35,36,37,38,39,40]. The type of framework and the Si/Al ratio influence the catalyst structure and catalytic properties [41,42,43]; in CHA zeolite, the activity in the CO oxidation increased with decreasing pore size and an optimal Si/Al molar ratio of 17 [44]. The use of BEA to stabilize Pd nanoparticles led to their almost complete oxidation and low activity in the CO oxidation compared to Pd/ZSM-5 [45]. The high performance of ZSM-5 zeolites modified by platinum metal groups in the oxidation reactions is due to a synergistic effect of metals and acid sites of zeolites [46,47,48]. Acid sites on the zeolite surface favor the formation and stabilization of highly dispersed MeOx particles that play an important role in the oxidation of both CO and hydrocarbons [45,49].
Different types of Pt-modified zeolites have been used for CO-PROX [6,50,51,52], and transition metals or oxides are used as promotors to improve catalytic performance [53,54,55,56,57] To achieve the high activity of bimetallic catalysts, it is necessary to ensure their maximum proximity on the surface of the support. In the case of low-loaded catalysts, the procedure for introducing active components is of great importance; the original method of laser electrodispersion (LED) was applied for the selective deposition of highly dispersed Pt particles on the zeolite surface and Co pre-modified ZSM-5 with Si/Al of 15, 28, and 40 [51,53]. Pt- and PtCo-ZSM-5 with low Si/Al of 15 and 28 were more efficient in CO-PROX. The use of such zeolites provides the best conditions for Pt and Co interaction and improved catalytic properties. This fact, along with the known data that both noble and transition metal-modified ZSM-5 were more active in the CO oxidation compared to alumina and BEA supported catalysts [45,58], is the background of this work. However, the question of the influence of the Si/Al ratio in zeolite on the catalytic performance of PtCo/ZSM-5 prepared by the traditional method of impregnation in CO-PROX remains not entirely clear.
In this work, the polynuclear Pt9(CH3COO)23 complex known as platinum acetate blue (PAB) was used as a novel precursor for Pt loading in zeolite. This X-ray amorphous substance of the empirical formula Pt(CH3COO)2.5 was synthesized and characterized as has been described previously [59]. ZSM-5 zeolite with Si/Al = 15 and 28 was used for the preparation of Pt and PtCo catalysts. The impregnation of ZSM-5 with PAB and its two-step decomposition at 200 and then at 300 °C results in the stabilization of highly dispersed PtOx species on the zeolite surface. The properties of Pt-modified zeolite were improved by the addition of Co(CH3COO)2 followed by calcination at 450 °C. Prepared materials with reduced 0.1–0.2 wt% Pt were studied by SEM, TEM, EDX, XPS, and DRIFTS methods and tested in the CO-PROX reaction. The relationships between synthesis conditions, structure and catalytic behavior of composites were found. The best synergistic effect of Pt and Co was observed when they both were located together on the surface of a zeolite with Si/Al = 15, which has the highest acidity.

2. Results

2.1. Catalytic Performance in the Preferential CO Oxidation in H2-Rich Mixture

2.1.1. Pt-Modified Zeolites

The catalytic characteristics (X150; Xmax, and Tmax) in the CO-PROX reaction for all Pt-modified zeolites with a different Si/Al ratio and Pt loading activated by different ways (a–c) are given in Table 1. Synthesis conditions, in particular, the heat treatment regime, have a strong impact on catalytic behavior. As can be seen from the table, Pt/Z samples on both zeolites (Z-15 and Z-28) with the same 0.1% Pt content heated at 200 °C (a) are more active compared with samples calcined at 300 °C (b). However, a change in the heat treatment regime has a different effect on Pt zeolites with different Si/Al ratio. With decreasing the heat treatment temperature from 300 °C to 200 °C X150 increases 2 times for 0.1 Pt/15 and only 1.5 times for 0.1 Pt/Z-28.
A change in the Pt content from 0.1 to 0.2 wt% has only a little effect on the efficiency of catalysis. The catalytic activity improves markedly with increasing platinum content to 0.6 wt%. In this case, it is possible to achieve a quite high conversion above 90% already at 150 °C. Unexpectedly, it turned out that the efficiency of catalysts with less than 0.2 wt% platinum content can be enhanced by sequential heat treatment at 200 and then at 300 °C (c). Figure 1 (curves 1, 2) shows a comparison of temperature dependencies of the CO conversion for samples 0.2 Pt/Z-15(a) and (c), obtained by calcination at 200 °C (a), and additionally activated at 300 °C (c). The effect of catalyst activation after additional heat treatment (c) is manifested to a greater extent for Pt/Z-15. It can be seen from the comparison of X150 and Xmax for 0.2 Pt/Z-15 and 0.2 Pt/Z-28 activated at different modes. The X150 value increases from 19 to 57% for 0.2 Pt/Z-15 when replacing mode (a) with (c), while for 0.2 Pt/Z-28, this value only increases from 17 to 35 %. After the two-step activation (c) of 0.2 Pt/Z-15, the Xmax value also increases by almost 1.5 times. It can be seen that catalysts operate quite stably; the maximum conversion only slightly increases in cooling mode for both Pt/Z-15 and Z-28 samples.
The influence of the Si/Al ratio in zeolite on the activity of Pt/Z catalysts can be clearly seen in Figure 1 (curves 2, 3), which shows the temperature dependences of CO conversion on catalysts with different aluminum contents. It can be seen that the activity of Pt/Z-15 composites is a little higher than Pt/Z-28. However, the Xmax value is lower for the sample with a smaller Si/Al ratio. Apparently, more active catalysts for oxidation of CO are also more active in the side reaction of the hydrogen oxidation. When a certain temperature is reached, the CO conversion reduces due to the high rate of this unwanted process.
According to their catalytic characteristics in the CO-PROX reaction, Pt-modified zeolites with a reduced platinum content (0.1–0.2%) prepared using PAB as a precursor are comparable or slightly inferior to supported Pt catalysts obtained by means of laser electrodispersion from Pt0 or by support impregnation using traditional Pt precursors [51]. Their catalytic activity may be further improved by the additional introduction of cobalt cations onto the surface of Pt/Z samples.

2.1.2. Bimetallic PtCo Catalysts

Temperature dependencies of the CO conversion in CO-PROX for mono- and bimetallic catalysts are compared in Figure 2. The synergism of Co and Pt action in bimetallic PtCo/Z-15 catalysts is clearly visible.
The catalytic characteristics for PtCo/Z samples containing 2.5 Co, wt% and different Pt contents on zeolites with Si/Al = 15 and 28 are given in Table 2. It can be seen that the addition of cobalt allows not only to achieve 100% CO conversion in the presence of hydrogen, but also to significantly reduce the temperature at which maximum conversion is achieved. Depending on the catalyst composition the CO oxidation with 100% conversion occurs in a wide temperature range of 50–130 °C.
It should be noted that the Si/Al ratio related to zeolite acidity significantly affects the activity of bimetallic PtCo composites, as in the case of monometallic samples (Table 1). The data in Table 2 show that an increase in the platinum content by two times (from 0.1 to 0.2 wt%) in the catalysts with the same cobalt content (2.5 wt%) has a different effect on the catalytic parameters of the composites on Z-15 and Z-28. In the first case, the T100 temperature decreases from 90 °C for 0.1 PtCo/Z-15 to 50 °C with an increase in the Pt loading. The temperature window for 100% CO conversion expands by 20 degrees, and ∆T100 becomes 50–110 °C for 0.2 PtCo/Z-15. On the contrary, for zeolites with a higher Si/Al ratio (PtCo/Z-28), an increase in the Pt loading from 0.1 to 0.2 wt% leads to the reduction of ∆T100 from 70–110 °C up to 70–90 °C.
Thus, the two 0.2 PtCo/Z-15 and 0.1 PtCo/Z-28 systems turned out to have the best performance in the CO-PROX reaction. The inherent acidic properties of ZSM-5, associated with the presence of aluminum atoms in its framework, significantly affect the catalytic performance of Pt and PtCo zeolites. Probably, the interactions of Pt and Co precursors with the acidic sites of zeolite determine the catalyst structure, which will be confirmed below using physicochemical methods.

2.2. DRIFT Spectroscopy of the Adsorbed CO

To study the electronic and coordination state of platinum and cobalt on the zeolite surface, the DRIFT spectroscopy of adsorbed carbon monoxide was used (Figure 3a–c). This method is widely used to study a supported catalyst because of the high sensitivity of CO stretching frequency to the structure of the binding sites [60,61,62,63,64,65,66,67]. There are well-established values for the vibrational frequency on supported Pt catalysts [14,60,62,63,64]. When CO is adsorbed on oxidized cationic Pt sites, its values lie in the range above 2100 cm−1, and can be blue-shifted to 2170 cm−1 depending on the cation charge and support [60,62,63]. When CO is adsorbed on Pt-metal particles, the vibrational frequency is red-shifted and decreases from 2100 to 2020 cm−1 when passing from isolated platinum atoms to small clusters. In addition, the cluster formation is accompanied by the appearance of additional bands (below 2000 cm−1) associated with the bridging adsorption of CO on several neighboring Pt atoms at once [14,65].
In the spectra of CO adsorbed on monometallic 0.2 Pt/Z-15 at various pressures (Figure 3a), along with absorption bands of 2215 cm−1 and 2186 cm−1, corresponding to the Lewis acid centers of zeolite [60,61], new bands are observed in the region of 2160–2000 cm−1. They are absent in the spectra of the original zeolite at these CO pressures, and belong to platinum mono- and polycarbonyls in various oxidation states [62,63]. Thus, weak absorption bands observed in the regions of 2128 cm−1 and 2100 cm−1 in spectrum 1, obtained with a low dose of introduced CO (0.5 µmol/g), may correspond to mono- and bicarbonyls Pt+ cations. At the same time, linear adsorption of CO on isolated platinum atoms or Ptδ+ can also appear in the region of 2090–2100 cm−1 [18,64]. With an increase in the amount of introduced CO (spectra 2, 3), the intensities of the observed bands raise and additional absorption appears in the region of 2166 cm−1, associated with the formation of Pt+ tricarbonyls [63,64]. Apparently, under experimental conditions, the partial reduction of platinum under the influence of CO already occurs at room temperature. This is clearly visible in spectrum 4, Figure 3, recorded after the introduction of large doses of CO (up to 4 kPa) and its subsequent removal by evacuation. The shape of spectrum 4 is significantly different: in its low-frequency region, new broad absorption bands appear at 2027 and 1975 cm−1, corresponding to linear and bridging adsorption of CO on metal–platinum clusters, respectively [18,64,65]. In addition, spectrum 4 also contains CO bands at 2128 and 2097 cm−1 associated with adsorption on single cations and platinum atoms, observed in spectra 1–3.
Thus, the 0.2 Pt/Z-15 catalyst originally includes oxidized and partially reduced platinum in an atomically dispersed state. However, in a CO atmosphere, a further reduction of platinum occurs with the formation of metal clusters and nanoparticles.
The Co introduction into Pt/Z increases the resistance of platinum to aggregation. Figure 3b shows the spectra of CO adsorbed on the 0.2 PtCo/Z-15 sample under the same conditions as for the monometallic one. The observed intense wide band with a maximum at 2205 cm−1 corresponds to the adsorption of CO on cobalt cations located in the ion-exchange positions of the zeolite, mainly in the form of isolated Co2+ ions and a small fraction of oxocations [30,60,61,66]. In this case, the platinum absorption bands are not recorded with a small dose of added CO (spectrum 1). With increasing pressure (spectra 2, 3), new relatively small absorption bands appear in the low-frequency region of the spectrum (2150–2000 cm−1). They may belong not only to the platinum carbonyls discussed above, but also to the carbonyls of Co+ cations. The latter can arise under the influence of CO as a result of the reduction of [Co-O-Co]2+ oxocations and appear as absorption bands of Co+(CO) (2113 cm−1), Co+(CO)2 (2113, 2043 cm−1), and Co+(CO)3 (2137, 2088, 2080 cm−1) [30,66,67]. The contribution of platinum carbonyls to the broad absorption band in this region can be revealed by analyzing spectra taken at different CO pressures (Figure 3b).
A broad band at 2100 cm−1 observed in spectra 2, 3 of the 0.2 PtCo/Z-15 sample (Figure 3b), similar to that in the spectra of 0.2 Pt/Z-15 (Figure 3a), and associated with the adsorption of CO on Ptδ+, may partially overlap with one of the Co+(CO)3 bands at 2091 cm−1. After removing excess CO (spectrum 4), the vibration bands of Co+ tricarbonyls (2137 and 2090 cm−1) disappear, increasing the intensity of the band of Co+ mono- and bicarbonyls at 2113 cm−1. At the same time, the intensity of the band at 2100 cm−1, related to the adsorption of CO on Ptδ+, remains almost unchanged.
Figure 3b (inset) shows a comparison on an enlarged scale of the spectra of mono- and bimetallic Pt-containing composites obtained at a residual CO pressure of 0.05 kPa (spectra 4 of Figure 3a,b). If in the spectrum of Pt/Z, oxidized forms of platinum (2160–2124 cm−1) are clearly visible in addition to partially reduced platinum Ptδ+ (2100–2090 cm−1), then for the bimetallic PtCo/Z composite, the analysis of bands in this region becomes difficult due to an overlap with the intense band at 2205 cm−1. However, it is clear that the ratio of the intensities of the bands at 2128 and 2100 cm−1 in this case is lower than in the 0.2 Pt/Z sample. In addition, no formation of platinum nanoparticles is observed in the spectrum of PtCo/Z (bands below 2090 cm−1). By this means, the Co introduction in the Pt-modified zeolite prevents the formation of platinum nanoparticles on the surface.

2.3. Microscopic Studies

SEM microphotographs and EDA data of 0.2 Pt/Z-15 and 0.2 PtCo/Z-15 (Figure S1) show that both Pt and Co are uniformly distributed on the zeolite surface, and their locations in the bimetallic catalyst practically coincide. Typical TEM microphotographs of initial and spent Pt-modified ZSM-5 are shown in Figure 4 on the example of 0.6 Pt/Z-28 along with corresponding histograms of particle size distribution. It can be seen (Figure 4a) that the sample contains ultrafine gray objects with a size of about 100–200 nm. The interplanar distance for regions of ordered atoms on the gray surface is 10.3 Å, which is close to that in the ZSM-5 (200) face (JCPDS 29-1257, d = 9.93 Å). Such areas were present in all studied samples and will not be noted further. Dark particles on the zeolite surface can be associated with platinum species according to EDA spectra (Figure S2). In the HRTEM micrograph of the initial catalyst (Figure 4b), the interplanar spacing for regions of ordered atoms on the particle surface is 2.6 Å (Figure 4b), which is close to that in the PtO (111) face (JCPDS 47-1171, d = 2.67 Å). But in the spent sample (Figure 4d), the interplanar distance for regions of ordered atoms for dark particles becomes only 2.2 Å (Figure 4d), which is close to that in the Pt(111) face (JCPDS 70-2057, d = 2.25 Å). This indicates a reduction in platinum oxide during catalytic tests in the H2 rich mixture. As one can see from the comparison of histograms of particle size distribution for the initial and spent samples (Figure 4c,f), an average particle size increases from 2 to 3.5 nm during catalytic tests, and, in addition, a number of large (<15 nm) particles are formed. This is in good agreement with DRIFTS data indicating the further reduction and agglomeration of platinum in monometallic samples in the CO atmosphere.
Typical TEM microphotographs of initial bimetallic samples on ZSM-5 with different Si/Al ratios are compared in Figure 5 on the example of 0.2 PtCo/Z-15 and 0.2 PtCo/Z-28. There are dark species on the surface of both zeolites, but their number on the surface of Z-28 is much higher. On some particles, it is possible to distinguish regions of ordered atoms with the interplanar distance on the surface of nanoparticles being 2.2 Å (Figure 5b,e,f), which is close to that in the Pt(111) face (JCPDS 70-2057, d = 2.25 Å). This distinguishes such samples from monometallic ones, where the interplanar distance of 2.6 Å was found (Figure 4b) corresponding to PtO.
As evidenced by the SEM-EDA data (Figure S1c–f), Pt and Co are located in bimetallic catalysts on the same surface areas. This is also confirmed by TEM-EDA element maps and spectrum shown in Figures S3 and S4. By this means, highly dispersed species in TEM images may be associated not only with Pt but also with Co-containing particles. Moreover, it is difficult to distinguish them based on the interplanar distances, because some of them are very close, for example, interplanar distances between 2.0 and 2.9 Å are also typical for Co3O4 (JCPDS 00-042-1467). However, it is more likely that small dark images irregularly located on the zeolite surface (Figure 5c–f) correspond to Pt nanoparticles with a similar size as in monometallic samples. Low-contrast highly dispersed spherical species are likely related to the Co counter ions (bare Co2+ ions or [Co-O-Co]2+ oxocations) originally located in zeolite channels [30]. This is consistent with the DRIFT spectroscopic data showing that the main cobalt state is Co2+. It is known that sintering and migration of the Co counter–ions/aggregates to the zeolite grain periphery may occur due to zeolite reconstruction under the exposure of high-energy TEM beam [68]. Because of this, the Co species of 2 nm uniformly distributed over the zeolite also become visible in the TEM images. For this reason, it is not possible to correctly estimate the particle size distribution of Pt for bimetallic samples.
TEM microphotographs of the 0.2 PtCo/Z-15 sample after DRIFT spectroscopic and catalytic studies are given in Figure 6. Most images are similar to those shown in Figure 5a,c,e for the initial sample. They contain only small species (about 2 nm) with different contrast. But, along with highly dispersed particles, larger aggregates consisting of closely located small crystallites become clearly visible in some microphotographs (Figure 6c,d). In accordance with interplanar distances between 2.2 and 2.8 Å obtained for some regions of ordered atoms, they can be attributed to Pt and Co mono- or bimetallic species. It is important to note that large dark particles of 3–4 nm in size, as in the case of the monometallic Pt sample, are not visible in these images (Figure 6) after spectroscopic and catalytic studies. As it was shown by means of DRIFTS, the Co introduction onto the surface of the Pt-modified zeolite prevents the formation of platinum nanoparticles on the surface. Due to the large excess of cobalt, the probability of Co and Pt proximity and their interaction with each other in zeolite channels should be very high.

2.4. XPS Studies

To study the features of the Pt electronic states in catalysts, XPS spectra of Pt/Z were compared with the PAB spectrum. In the survey, XPS spectrum (Figure S5) of PAB lines of carbon, oxygen, and platinum are observed; the high-resolution spectra of the elements (Pt4f and C1s) are presented in Figure 7; the results of their decomposition into components are given in Table 3.
A doublet with the binding energy of the Pt4f7/2 component equal to 74.2 eV is observed in the Pt4f XPS spectrum of PAB (Figure 7a). This binding energy corresponds to the oxidized state of platinum, but it is difficult to determine the degree of its oxidation. Moreover, the binding energy of this line depends not only on the oxidation state of platinum, but also on its local environment. A similar 74.1 eV binding energy of the Pt4f7/2 line was found for the trivalent platinum complex [Pt2(EtCS2)4I2] [69]. At the same time, the binding energies of the Pt4f7/2 line for PtO2 oxide also corresponds to the range of 74.1–75.0 eV [70]. In accordance with the rather narrow Pt4f7/2 lines in the spectrum, we can conclude that the platinum blue acetate includes only one electronic state of Pt with the oxidation degree higher than Pt(II). The component in the C1s XPS spectrum (Figure 7b) with a binding energy of 288.7 eV was attributed to COO− groups. The ratio of the COO− group and Pt lines is about 2.5; all oxygen lines in the spectrum also are attributed to COO− groups. These data are in good agreement with the synthesized Pt9(CH3COO)23 complex associated with the Pt(CH3COO)2.5 empirical formula [59].
In the survey XPS spectra (Figure S5) of all synthesized catalysts, lines of carbon, oxygen, silicon, platinum, cobalt, and aluminum are observed. In contrast to the PAB spectrum, the Pt4f spectra of the Pt/Z samples (Figure 8) include three components corresponding to different electronic states of the metal. The binding energies for the platinum lines were interpreted, assuming the presence of platinum in the metallic Pt0 and two oxidized Pt2+ and Pt4+ states based on the data [70]. The spectra decomposition was performed, taking into account an overlapping of the Pt4f and Al2p lines as described in [53]. Oxidized Pt species may be associated not only with platinum oxides but also with the chemical Pt–Ox–Al interaction [71]. The binding energies of the Pt4f7/2components, the fractions of Pt atoms in various states obtained from the spectra decomposition as well as the ratios of elements on the sample surface are given in Table 4 and Table 5 for Pt/Z and PtCo/Z catalysts, respectively, before and after testing in CO-PROX.
As can be seen from Table 4 for the 0.2 Pt/Z-15 catalyst, a two-stage heat treatment (c) at 200 °C and then at 300 °C increases the fraction of metallic platinum on the surface in comparison with heating only at 200 °C (a). At the same time, part of the platinum remains in an oxidized state; the simultaneous presence of metallic and oxidized Pt states favors the catalytic oxidation [53]. The oxidized platinum weakens unwanted CO adsorption and promotes oxidation. Also, two-stage processing slightly increases the total platinum content on the surface. These factors improved the catalytic performance as can be seen from Table 1 and Figure 1. Increasing the platinum content to 0.6% leads to significant preservation of the oxidized state of platinum. This is in good agreement with TEM microphotographs (Figure 4b) where interplanar spacing for regions of ordered atoms on the particle surface was 2.6 Å that is close to PtO(111).
The introduction of cobalt into Pt/Z samples has little effect on the electronic state of platinum as can be seen from Table 5. In addition, the electronic states of both metals are close on Co/Pt zeolites with different Si/Al ratios. Cobalt in all cases is predominantly in the Co2+ state, which indicates its distribution in the form of cations or oxocations inside the zeolite channels that is consistent with DRIFTS and TEM data and our previous results [30,72]. The only difference deals with the element content on the zeolite surface. First, it should be noted that the platinum content on the surface is significantly reduced in the presence of cobalt. It may be that platinum, when interacting with cobalt, penetrates deep into the zeolite channels. Next, if the ratio of metals on a Z-15 zeolite is close to a given bulk atomic value (Co/Pt = 40), then the surface of the Z-28 zeolite is enriched with cobalt. This is due to the difference in Co/Al ratio in these samples. Surface cobalt oxide may form with increasing this value [30,72].
After catalytic tests, the proportion of metallic platinum in the Pt/Z samples increases noticeably. The Pt reduction with the formation of larger metal nanoparticles under reaction conditions was confirmed by TEM data (Figure 4d). In the bimetallic 0.2 PtCo/Z-15 sample, the Pt0 fraction also increases after catalysis in contrast to another 0.2 PtCo/Z-28 composite with lower Al content. The oxidized platinum in catalyst can be reduced not only with CO molecules, but also with the participation of Co2+ cations. This process becomes more likely when both Pt2+ and Co2+ are in close proximity within the zeolite channels as it was found previously [53]. The use of a more acidic zeolite Z-15 with higher Al proportion promotes this interaction, increasing the possibility of more cations of both metals entering the zeolite channels. As a result, the probability of interaction between cobalt and platinum cations in the zeolite channels and partial reduction of the latter increases. Close contact with cobalt cations ensures the preservation of the isolated state of platinum atoms without the formation of agglomerates, which is confirmed by the DRIFTS of adsorbed CO data (Figure 3). Changes in the electronic state of cobalt due to interaction with platinum are not very noticeable due to its large excess. The slightly increased amount of Co3+(35%) in the 0.2 PtCo/Z-28 sample is likely associated with the formation of a surface Co3O4 oxide.

3. Discussion

The results obtained show that both Si/Al and Pt/Co ratios in catalysts are important factors affecting the distribution and electronic state of metals on the surface of zeolites and, accordingly, their activity in the CO-PROX reaction. An increase in aluminum atoms in the zeolite lattice provides a larger number of ion exchange positions, which facilitates the penetration of a larger number of metal cations (primarily Co) into the zeolite channels [66,72]. The presence of cobalt predominantly in the form of cations in ion-exchange positions of zeolite contributes to a more efficient interaction of platinum and cobalt and stabilization of platinum in a catalytically active PtOδ+ state as it was shown previously [53]. An increase in the amount of platinum introduced into Z-15 (at the same cobalt content) leads to an increase in the number of active centers formed in zeolite channels. Due to the formation of new active sites at the Pt-Ox-Co interfaces, the catalysts with a lower Si/Al ratio provide a larger operating window ∆T100 of 100% CO conversion. At the same time, for the Z-28 zeolite, a large number of Pt0 particles was located on the zeolite surface (Figure 5d–f). As a result, with increasing the platinum loading from 0.1 to 0.2%, only one part of it interacts with cobalt cations in ion-exchange positions. During the spectroscopic and catalytic studies, small platinum and cobalt oxide species become visible (Figure 6b,d), but their interaction on the zeolite surface is probably less effective in catalysis of the CO oxidation in hydrogen excess. Therefore, the 0.2 PtCo/Z-28 composite turns out to be less active than 0.1 PtCo/Z-28. XPS data confirm the different distribution of metals on the surface of zeolites depending on the Si/Al ratio. With the same 2.5% cobalt loading, both Pt and Co contents on the surface of the CoPt composites are lower for Z-15 (Table 5) compared to Z-28. Moreover, it is clear that the platinum content on the surface of both zeolites decreases with the introduction of cobalt, which also indicates an interaction between Pt and Co. Such interaction and the formation of new active centers at the Pt-Ox-Co interfaces provide the synergistic catalytic effect in bimetallic PtCo/Z systems.
The second important aspect of the role of such interaction is related to the fact that there is no agglomeration of platinum during the catalytic process in bimetallic PtCo/Z systems. In this case, although a noticeable reduction in platinum occurs, it remains in a highly dispersed, down to atomic state, difficult to detect by TEM. An important advantage of using PAB as a new precursor for platinum introduction in zeolite is the fact that a large number of highly dispersed partially reduced platinum species is formed during heat treatment. This eliminates the need for an additional stage of platinum reduction, as is the case with the use of other precursors, and creates favorable conditions for the platinum interaction with cobalt. All these factors provide a high efficiency of PtCo/Z catalysts with reduced Pt loading in CO-PROX with the value of ∆T100 between 50 and 130 °C. Similar operating temperature ranges were previously found for low-loaded PtCo/zeolites prepared by a less accessible method of laser electrodispersion [53] or for CeFeOx– supported single atom Pt catalysts [73]. More often, the high CO conversion was achieved only for catalysts with Pt loading of about 1 wt% or higher [20,28,32,33,74].

4. Materials and Methods

4.1. Catalyst Preparation

Platinum blue was synthesized as it was described in [59] using the following materials: hexachloroplatinic(IV) acid H2[PtCl6] × 6H2O] (40% Pt, Sigma-Aldrich, St. Louis, MO, USA), formic acid (90%, Pharmkhim, Moscow, Russia), and glacial acetic acid (99.8% Pharmkhim, Moscow, Russia). HZSM-5 (HZ) zeolites were prepared from NH4ZSM-5 (“Zeolyst”) by the calcination at 550 °C in an air stream for 8 h. Pt-modified zeolites (Pt/Z) were synthesized by the incipient wetness impregnation of dried HZSM-5 with a solution of the desired amount of PAB in glacial acetic acid (99.8% Pharmkhim, Russia). After impregnation, the samples were subjected to heat treatment in three different modes: heating in an oven for 8 h—(a) at 200 °C, (b) at 300 °C, and (c) additional heating at 300 °C (3 h) of the samples already preheated at 200°C. The temperature of 200 °C (a) was chosen as the initial because the decomposition of the platinum acetate complex occurs at this temperature [59]. To select heat treatment conditions that provide the best characteristics of the samples, two more high-temperature modes (b, 300 °C) and (c, 200 + 300,°C) were also tested. The Pt content in zeolites (Si/Al = 15 and 28) varied from 0.1 to 0.6 wt%. The samples were designated, for example, as 0.1 Pt/Z-15 or /Z-28 (a, b, or c) when Pt content was 0.1 wt% for zeolite with Si/Al =15 or 28 depending on the calcination regime (a, b or c).
Cobalt was introduced in 0.1 Pt/Z and 0.2 Pt/Z heated at 200 °C (a) by the incipient wetness impregnation with the aqueous solution of the desired amount of Co(CH3COO)2·4H2O (>99%, IREA2000, Moscow, Russia), then prepared samples were dried for 1 day at room temperature and for 8 h at 120 °C. Finally, the CoPt modified zeolites (Co/Pt/Z) were calcined at 450 °C for 3 h in flowing air. The Co content was 2.5 wt% for all prepared catalysts. The bimetallic samples were designated as 0.1 or 0.2 PtCo/Z-15 or /Z-28 when Pt loading was 0.1 or 0.2 wt% and Si/Al was 15 or 28. All catalysts were stored in air and activated before catalytic tests by heating for 1 h at 350 °C in He.

4.2. Catalyst Characterization

Thermo iCE 3000 spectrometer (Thermo Fisher Scientific Inc., Waltham, MA, USA) was used to analyze Pt and Co contents in the catalysts. The results of AAS measurements agreed with the calculated values.
Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) microphotographs of the samples were recorded using JSM 6000 NeoScope and JEOL JEM 2100F/UHR instruments (JEOL, Tokyo, Japan) integrated with a JEOL JED-2300 Analysis Station Plus EDX system. Sample preparation for TEM studies and image analysis were described in detail [45]. The average particle size was determined from the particle size distribution histograms obtained by processing approximately 300 particle images. Interplanar distances (d) were determined using the ImageJ 1.47 program (https://imagej.nih.gov/ij/download.html, accessed on 10 July 2021). The lattice d-spacing values were calculated from the fast Fourier transformation (FFT) patterns for planes visible in high-resolution TEM images. The crystal structures of the ordered atomic domains were identified using the ICDD data base (https://www.icdd.com, accessed on 10 July 2021).
X-ray photoelectron spectroscopy (XPS) study was performed on an Axis Ultra DLD spectrometer (Kratos Analytical Limited, Manchester, UK) with a monochromatic Al Kα source (hν = 1486.7 eV, 150 W) at a transmission energy of 160 and 40 eV as described in [53]. The energy scale of the XPS spectra was preliminarily calibrated using the characteristic Si 2p peak at 103.6 eV.
Diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) studies of adsorbed CO were performed on an Infralum FT-801 Fourier spectrometer (Russia) with a diffuse reflectance accessory (Lyumeks–Sibir’) in the 900–6000 cm−1 range (4 cm−1 resolution, 256 scans). Catalyst pellets were placed in a quartz tube with the CaF2 optical window and heated at a rate of 10 °C/min to 400 °C and then kept at this temperature for 100 min. Spectra of adsorbed CO were recorded at room temperature at equilibrium gas pressure and varied from 0.1 to 4.4 kPa as well as at a residual pressure of 0.05 kPa after evacuation. The IR spectra were transformed into the Kubelka–Munk function [75]:
F(R) = a/s,
where a is the absorption and s is the scattering.

4.3. Catalytic Tests

The catalytic oxidation was performed at 50–250 °C with the initial gas mixture CO:O2:H2:He = 1:1:49:49 (v/v) in a fixed-bed quartz reactor in the flow regime as was described [53]. Heating–cooling cycles were carried out, temperature was changed in steps of 20 °C, and each temperature was maintained for 20 min; 250 mg of catalyst (40–60 mesh fraction) mixed with an equivalent amount of quartz sand was used. The composition of the gas mixture at the reactor outlet was analyzed using a Crystal 2000 chromatograph (Chromatec SDO JSC, Mariy El, Russia) equipped with a thermal conductivity detector (flow rate 10 cm3 min−1). A small amount of methane (<3%) was found in the reaction products for monometallic Pt/Z catalysts. When bimetallic CoPt/Z catalysts were used, no methane was detected. The catalytic activity was assessed from the temperature dependences of the CO conversion. The CO conversion at a given T°C temperature (XT, %), the maximum conversion (Xmax, %), as well as temperatures corresponding to 50% and Xmax, % (T50 and Tmax, respectively) were used. The temperature to achieve 100% CO conversion (T100) and the operating window ΔT100 of the 100% conversion of CO in the PROX were also estimated for the most active catalysts.

5. Conclusions

Advanced PtCo/ZSM-5 (Si/Al = 15 and 28) catalysts for CO-PROX were prepared using platinum acetate blue (PAB) of the empirical formula Pt(CH3COO)2.5 as a novel precursor for the zeolite impregnation. The PAB decomposition at a two-step heat treatment at 200 °C and then at 300 °C results in the stabilization of highly dispersed Pt0 and PtOx particles on the zeolite surface. The properties of Pt-modified zeolite were significantly improved by the additional impregnation with Co(CH3COO)2. The best synergistic effect of Pt and Co was observed when they both were located together on the zeolite with the highest acidity when Si/Al = 15. The reasons are the interaction of Co oxocomplexes with platinum in the zeolite channels and the formation of new active sites for the CO oxidation at the Pt-Ox-Co species. PtCo/ZSM-5 catalysts with only 0.1–0.2 wt.% Pt are extremely effective for hydrogen purification. In the H2 excess, they provide the 100% CO conversion in the wide temperature range from 50 to 130 °C that corresponds to the tolerable CO values (below10 ppm) for the hydrogen-rich electrode side of proton exchange membrane fuel cells (PEMFC). Such a synthetic strategy to reduce metal loading can be considered as a useful approach towards designing high-performance zeolite-based noble metal catalysts.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/catal14080484/s1, Figure S1: SEM micrographs and EDA maps and EDA spectrum for samples: (a,b) 0.2 Pt/Z-15; (c–f) 0.2PtCo/Z-15; Figure S2: TEM microphotographs and the EDA spectra obtained from the locations marked on the microphotographs of the initial (a,b) and spent (c,d) 0.6 Pt/Z-28 samples; Figure S3: SEM micrographs and EDA maps of initial samples: (a–c) 0.2 PtCo/Z-15; (d–f) 0.2 PtCo/Z-28; Figure S4: TEM microphotograph of the 0.2 PtCo/Z-28 (a) and the EDA spectra obtained from the location 1 and 2 marked on the microphotograph (b,c); Figure S5: Survey XPS spectra of the PAB and all PtCo/Z catalysts.

Author Contributions

Conceptualization, methodology, and validation, M.S. and T.R.; formal analysis, S.N., N.C., and I.S.; investigation, O.U., I.K., and S.M.; writing—original draft preparation, T.R.; writing—review and editing, M.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The original data presented in the study are openly available in https://istina.msu.ru.

Acknowledgments

This work regarding the synthesis and characterization of precursors was supported by the Ministry of Science and Higher Education of the Russian Federation as part of the State Assignment of the Kurnakov Institute of General and Inorganic Chemistry of the Russian Academy of Sciences. The synthesis and structural studies of catalysts were performed within the framework of the State Assignment to the Lomonosov Moscow State University (Project No. AAAAA21-121011590090-7). Catalysts were tested within the framework of the State Assignment to the Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences (Project No. 122040500058-1, Physics and Chemistry of New Nanostructured Systems and Composite Materials with Desired Properties). Structural studies were carried out using the equipment purchased within the framework of the Lomonosov Moscow State University Development Program. The authors are grateful to K. Maslakov for helping in carrying out these studies.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

References

  1. Neumann, S.; Gutmann, T.; Buntkowsky, G.; Paul, S.; Thiele, G.; Sievers, H.; Bäumer, M.; Kunz, S. Insights into the reaction mechanism and particle size effects of CO oxidation over supported Pt nanoparticle catalysts. J. Catal. 2019, 377, 662–672. [Google Scholar] [CrossRef]
  2. Lin, J.; Wang, X.; Zhang, T. Recent progress in CO oxidation over Pt-group-metal catalysts at low temperatures. Chin. J. Catal. 2016, 37, 1805–1813. [Google Scholar] [CrossRef]
  3. Freund, H.-J.; Meijer, G.; Scheffler, M.; Schlögl, R.; Wolf, M. CO oxidation as a prototypical reaction for heterogeneous processes. Angew. Chem. Int. Ed. 2011, 50, 10064–10094. [Google Scholar] [CrossRef] [PubMed]
  4. Royer, S.; Duprez, D. Catalytic oxidation of carbon monoxide over transition metal oxides. ChemCatChem 2011, 3, 24–65. [Google Scholar] [CrossRef]
  5. McClure, S.M.; Goodman, D.W. New insights into catalytic CO oxidation on Pt-group metals at elevated pressures. Chem. Phys. Lett. 2009, 469, 1–13. [Google Scholar] [CrossRef]
  6. Park, E.D.; Lee, D.; Lee, H.C. Recent progress in selective CO removal in a H2-rich stream. Catal. Today 2009, 139, 280–290. [Google Scholar] [CrossRef]
  7. Liu, J.; Hensley, A.J.R.; Giannakakis, G.; Therrien, A.J.; Sukkar, A.; Schilling, A.C.; Groden, K.; Ulumuddin, N.; Hannagan, R.T.; Ouyang, M.; et al. Developing single-site Pt catalysts for the preferential oxidation of CO: A surface science and first principles-guided approach. Appl. Catal. B-Environ. 2021, 284, 119716. [Google Scholar] [CrossRef]
  8. Du, X.; Lang, Y.; Cao, K.; Yang, J.; Cai, Y.; Shan, B.; Chen, R. Bifunctionally faceted Pt/Ru nanoparticles for preferential oxidation of CO in H2. J. Catal. 2021, 396, 148–156. [Google Scholar] [CrossRef]
  9. Pourrahmani, H.; Yavarinasab, A.; Siavashi, M.; Matian, M.; Van herle, J. Progress in the proton exchange membrane fuel cells (PEMFCs) water/thermal management: From theory to the current challenges and real-time fault diagnosis methods. Energy Rev. 2022, 1, 100002. [Google Scholar] [CrossRef]
  10. Cao, S.; Zhao, Y.; Lee, S.; Yang, S.; Liu, J.; Giannakakis, G.; Li, M.; Ouyang, M.; Wang, D.; Sykes, E.C.H.; et al. High-loading single Pt atom sites [Pt-O(OH)x] catalyze the CO PROX reaction with high activity and selectivity at mild conditions. Sci. Adv. 2020, 6, eaba3809. [Google Scholar] [CrossRef]
  11. Chen, Y.; Lin, J. Design of efficient noble metal single atom and cluster catalysts toward low-temperature preferential oxidation of CO in H2. Int. J. Hydrogen Energy 2023, 48, 24788–24808. [Google Scholar] [CrossRef]
  12. Mariño, F.; Descorme, C.; Duprez, D. Noble metal catalysts for the preferential oxidation of carbon monoxide in the presence of hydrogen (PROX). Appl. Catal. B-Environ. 2004, 54, 59–66. [Google Scholar] [CrossRef]
  13. Zlotea, C.; Oumellal, Y.; Provost, K.; Morfin, F.; Piccolo, L. Role of hydrogen absorption in supported Pd nanocatalysts during CO-PROX: Insights from operando X-ray absorption spectroscopy. Appl. Catal. B-Environ. 2018, 237, 1059–1065. [Google Scholar] [CrossRef]
  14. Dong, J.; Zhang, Y.; Li, D.; Adogwa, A.; Huang, S.; Yang, M.; Yang, J.; Jin, Q. Reaction-driven evolutions of Pt states over Pt-CeO2 catalysts during CO oxidation. Appl. Catal. B-Environ. 2023, 330, 122662. [Google Scholar] [CrossRef]
  15. Lashina, E.A.; Slavinskaya, E.M.; Stonkus, O.A.; Stadnichenko, A.I.; Romanenko, A.V.; Boronin, A.I. The role of ionic and cluster active centers of Pt/CeO2 catalysts in CO oxidation. Experimental study and mathematical modeling. Chem. Eng. Sci. 2023, 267, 118328. [Google Scholar] [CrossRef]
  16. Feng, C.; Liu, X.; Zhu, T.; Hu, Y.; Tian, M. Catalytic oxidation of CO over Pt/TiO2 with low Pt loading: The effect of H2O and SO2. Appl. Catal. A-Gen. 2021, 622, 118218. [Google Scholar] [CrossRef]
  17. Jing, P.; Gong, X.; Liu, B.; Zhang, J. Recent advances in synergistic effect promoted catalysts for preferential oxidation of carbon monoxide. Catal. Sci. Technol. 2020, 10, 919–934. [Google Scholar] [CrossRef]
  18. Lou, Y.; Xu, J.; Zhang, Y.; Pan, C.; Dong, Y.; Zhu, Y. Metal-support interaction for heterogeneous catalysis: From nanoparticles to single atoms. Mater. Today Nano 2020, 12, 100093. [Google Scholar] [CrossRef]
  19. Lagunova, V.; Filatov, E.; Plyusnin, P.; Kostin, G.; Urlukov, A.; Potemkin, D.; Korenev, S. Metal-oxide catalysts for CO TOX and PROX processes in the Pt-Cr/Mo/W systems. Int. J. Hydrogen Energy 2023, 48, 25133–25143. [Google Scholar] [CrossRef]
  20. Cai, J.; Liu, Z.; Cao, K.; Lang, Y.; Chu, S.; Shan, B.; Chen, R. Highly dispersed Pt studded on CoOx nanoclusters for CO preferential oxidation in H2. J. Mater. Chem. A 2020, 8, 10180–10187. [Google Scholar] [CrossRef]
  21. Nguyen, T.-S.; Morfin, F.; Aouine, M.; Bosselet, F.; Roussert, J.-L.; Piccolo, L. Trends in the CO oxidation and PROX performances of the platinum-group metals supported on ceria. Catal. Today 2015, 253, 106–114. [Google Scholar] [CrossRef]
  22. Qiao, B.; Wang, A.; Li, L.; Lin, Q.; Wei, H.; Liu, J.; Zhang, T. Ferric oxide-supported Pt subnano clusters for preferential oxidation of CO in H2-rich gas at room temperature. ACS Catal. 2014, 4, 2113–2117. [Google Scholar] [CrossRef]
  23. Lang, R.; Du, X.; Huang, Y.; Jiang, X.; Zhang, Q.; Guo, Y.; Liu, K.; Qiao, B.; Wang, A.; Zhang, T. Single-atom catalysts based on the metal-oxide interaction. Chem. Rev. 2020, 120, 11986–12043. [Google Scholar] [CrossRef]
  24. Chen, X.; Chen, J.; Zhao, Y.; Chen, M.; Wan, H. Effect of dispersion on catalytic performance of supported Pt catalysts for CO oxidation. Chin. J. Catal. 2012, 33, 1901–1905. [Google Scholar] [CrossRef]
  25. Mohamed, Z.; Dasireddy, V.D.B.C.; Singh, S.; Friedrich, H.B. The preferential oxidation of CO in hydrogen rich streams over platinum doped nickel oxide catalysts. Appl. Catal. B-Environ. 2016, 180, 687–697. [Google Scholar] [CrossRef]
  26. Niu, T.; Zhao, W.W.; Liu, G.L.; Cao, A.; Zhang, L.H.; Liu, Y. The graphene-meso-macroporous SiO2 supported Pt-Ni alloy nanocatalyst for preferential oxidation of CO in H2-rich gases. Int. J. Hydrogen Energy 2014, 39, 18929–18939. [Google Scholar] [CrossRef]
  27. Zhang, H.; Liu, X.; Zhang, N.; Zheng, J.; Zheng, Y.; Li, Y.; Zhong, C.-J.; Chen, B.H. Construction of ultrafine and stable PtFe nano-alloy with ultra-low Pt loading for complete removal of CO in PROX at room temperature. Appl. Catal. B-Environ. 2016, 180, 237–245. [Google Scholar] [CrossRef]
  28. Wang, C.X.; Zhang, L.; Liu, Y. Aluminumphosphate molecular sieves supported Pt–Co catalysts for the preferential oxidation of CO in H2-rich gases. Appl. Catal. B-Environ. 2013, 136–137, 48–55. [Google Scholar] [CrossRef]
  29. Lukashuk, L.; Föttinger, K.; Kolar, E.; Rameshan, C.; Teschner, D.; Hävecker, M.; Knop-Gericke, A.; Yigit, N.; Li, H.; McDermott, E.; et al. Operando XAS and NAP-XPS studies of preferential CO oxidation on Co3O4 and CeO2-Co3O4 catalysts. J. Catal. 2016, 344, 1–15. [Google Scholar] [CrossRef]
  30. Shilina, M.I.; Rostovshchikova, T.N.; Nikolaev, S.A.; Udalova, O.V. Polynuclear Co-oxo cations in the catalytic oxidation of CO on Co-modified ZSM-5 zeolites. Mater. Chem. Phys. 2019, 223, 287–298. [Google Scholar] [CrossRef]
  31. Eurov, D.A.; Rostovshchikova, T.N.; Shilina, M.I.; Kirilenko, D.A.; Tomkovich, M.V.; Yagovkina, M.A.; Udalova, O.V.; Kaplin, I.Y.; Ivanin, I.A.; Kurdyukov, D.A. Cobalt oxide decorated porous silica particles: Structure and activity relationship in the catalytic oxidation of carbon monoxide. Appl. Surf. Sci. 2022, 579, 152121. [Google Scholar] [CrossRef]
  32. Li, H.; Yu, X.; Tu, S.-T.; Yan, J.; Wang, Z. Catalytic performance and characterization of Al2O3-supported Pt–Co catalyst coatings for preferential CO oxidation in a micro-reactor. Appl. Catal. A-Gen. 2010, 387, 215–223. [Google Scholar] [CrossRef]
  33. Wang, C.; Li, B.; Lin, H.; Yuan, Y. Carbon nanotube-supported Pt-Co bimetallic catalysts for preferential oxidation of CO in a H2-rich stream with CO2 and H2O vapor. J. Power Sources 2012, 202, 200–208. [Google Scholar] [CrossRef]
  34. Nuñez, N.E.; Bideberripe, H.P.; Mizrahi, M.; Ramallo-López, J.M.; Casella, M.L.; Siri, G.J. CO selective oxidation using Co-promoted Pt/γ-Al2O3 catalysts. Int. J. Hydrogen Energy 2016, 41, 19005–19013. [Google Scholar] [CrossRef]
  35. El-Bahy, Z.M.; Alotaibi, M.T.; El-Bahy, S.M. CO oxidation and 4-nitrophenol reduction over ceria-promoted platinum nanoparticles impregnated with ZSM-5 zeolite. J. Rare Earths 2022, 40, 1247–1254. [Google Scholar] [CrossRef]
  36. Yu, Q.; Wu, W.; Wei, J.; Zhang, J.; Zhao, S.; Tang, X.; Yi, H. What is the role of Mn/Al/Pt for ZSM-11 being a good catalytic oxidation catalyst? J. Environ. Chem. Eng. 2023, 11, 110822. [Google Scholar] [CrossRef]
  37. Park, D.C.; Moon, S.; Song, J.H.; Kim, H.; Lee, E.; Lim, Y.H.; Kim, D.H. Widening the operating window of Pt/ZSM-5 catalysts for efficient NOx removal in H2-SCR: Insights from thermal aging. Catal. Today 2024, 425, 114318. [Google Scholar] [CrossRef]
  38. Wang, X.-F.; Liu, C.-F.; He, L.-C.; Li, B.; Lu, J.-Q.; Luo, M.-F.; Chen, J. Unveiling geometric and electronic effects of Pt species on water-tolerant Pt/ZSM-5 catalyst for propane oxidation. Appl. Catal. A-Gen. 2023, 655, 119108. [Google Scholar] [CrossRef]
  39. Wang, X.; Wang, X.; Yu, H.; Wang, X. The functions of Pt located at different positions of HZSM-5 in H2-SCR Chem. Eng. J. 2019, 355, 470–477. [Google Scholar] [CrossRef]
  40. Zhou, A.; Zhang, J.; Yang, H.; Shang, S.; Zhang, A.; Song, C.; Guo, X. Synergetic and efficient alkylation of benzene with ethane over Pt/ZSM-5 nanosheet bifunctional catalysts to ethylbenzene. Fuel 2023, 342, 127764. [Google Scholar] [CrossRef]
  41. Ma, Y.-K.; Xu, L.-L.; Ouyang, L.-R.; Huang, L.-L.; Jia, A.-P.; Wang, Y.; Lu, J.-Q. Tandem c-cl cleavage and oxidation over Pt/ZSM-5 catalysts for CH2Cl2 deep oxidation: Acidity—Redox synergy, rate—Limiting step, and catalyst stability. Chem. Eng. J. 2023, 476, 146551. [Google Scholar] [CrossRef]
  42. Gao, M.; Gong, Z.; Weng, X.; Shang, W.; Chai, Y.; Dai, W.; Wu, G.; Guan, N.; Li, L. Methane combustion over palladium catalyst within the confined space of MFI zeolite. Chin. J. Catal. 2021, 42, 1689–1699. [Google Scholar] [CrossRef]
  43. Friberg, I.; Clark, A.H.; Ho, P.H.; Sadokhina, N.; Smales, G.J.; Woo, J.; Auvray, X.; Ferri, D.; Nachtegaal, M.; Kröcher, O.; et al. Structure and performance of zeolite supported Pd for complete methane oxidation. Catal. Today 2021, 382, 3–12. [Google Scholar] [CrossRef]
  44. Tian, X.; Shan, Y.; Zhang, J.; Yan, Z.; Sun, Y.; Ding, W.; Yu, Y. The study of Pt/zeolites for CO oxidation: Effects of skeleton structure and Si/Al ratio. Catal. Comm. 2023, 178, 106679. [Google Scholar] [CrossRef]
  45. Rostovshchikova, T.N.; Nikolaev, S.A.; Krotova, I.N.; Maslakov, K.I.; Udalova, O.V.; Gurevich, S.A.; Yavsin, D.A.; Shilina, M.I. ZSM-5 and BEA zeolites modified with Pd nanoparticles by laser electrodispersion. The structure and catalytic activity in CO and CH4 oxidation. Russ. Chem. Bull. 2022, 71, 1179–1193. [Google Scholar] [CrossRef]
  46. Lou, Y.; Ma, J.; Hu, W.; Dai, Q.; Wang, L.; Zhan, W.; Guo, Y.; Cao, X.-M.; Hu, P.; Lu, G. Low-temperature methane combustion over Pd/H-ZSM-5: Active Pd sites with specific electronic properties modulated by acidic sites of H-ZSM-5. ACS Catal. 2016, 6, 8127–8139. [Google Scholar] [CrossRef]
  47. Wang, J.; Guo, X.; Shi, Y.; Zhou, R. Synergistic effect of Pt nanoparticles and micro-mesoporous ZSM-5 in VOCs low-temperature removal. J. Environ. Sci. 2021, 107, 87–97. [Google Scholar] [CrossRef] [PubMed]
  48. Kong, F.; Li, G.; Wang, J.; Shi, Y.; Zhou, R. Promoting effect of acid sites in hierarchical porous Pt/ZSM-5 catalysts for low-temperature removal of VOCs. Appl. Surf. Sci. 2022, 606, 154888. [Google Scholar] [CrossRef]
  49. Daniel, S.; Monguen, C.K.F.; Ayodele, O.B.; Tian, Z.-Y. Tailored synthesized Pt/ZSM-5 catalysts with excellent water vapor stability for low temperature oxidation of CO and C3H6. J. Environ. Chem. Eng. 2023, 11, 109617. [Google Scholar] [CrossRef]
  50. Xu, J.; Xu, X.-C.; Ouyang, L.; Yang, X.-J.; Mao, W.; Su, J.; Han, Y.-F. Mechanistic study of preferential CO oxidation on a Pt/NaY zeolite catalyst. J. Catal. 2012, 287, 114–123. [Google Scholar] [CrossRef]
  51. Shilina, M.I.; Krotova, I.N.; Maksimov, S.V.; Maslakov, K.I.; Nikolaev, S.A.; Udalova, O.V.; Gurevich, S.A.; Yavsin, D.A.; Rostovshchikova, T.N. Total and preferential CO oxidation on low-loaded Pt-HZSM-5 zeolites modified using laser electrodispersion. Russ. Chem. Bull. 2023, 72, 1518–1532. [Google Scholar] [CrossRef]
  52. Sebastian, V.; Irusta, S.; Mallada, R.; Santamaría, J. Selective oxidation of CO in the presence of H2, CO2 and H2O on different zeolite-supported Pt catalysts. Appl. Catal. A-Gen. 2009, 366, 242–251. [Google Scholar] [CrossRef]
  53. Shilina, M.I.; Krotova, I.N.; Nikolaev, S.A.; Gurevich, S.A.; Yavsin, D.A.; Udalova, O.V.; Rostovshchikova, T.N. Highly effective Pt-Co/ZSM-5 catalysts with low Pt loading for preferential CO oxidation in H2-rich mixture. Hydrogen 2023, 4, 154–173. [Google Scholar] [CrossRef]
  54. Malwadkar, S.; Bera, P.; Satyanarayana, C.V.V. Low-temperature preferential CO oxidation in a hydrogen-rich stream over Pt-NaY and modified Pt-NaY catalysts for fuel cell application. Fuel Cells 2023, 23, 15–28. [Google Scholar] [CrossRef]
  55. Jiang, B.; Huang, M.; Cai, D.; Tan, K.B.; Zhan, G. Fabrication of Pt/Co3O4 nanocatalysts based on pollen template for low-temperature CO oxidation. Cat. Commun. 2023, 174, 106597. [Google Scholar] [CrossRef]
  56. Li, C.; Ke, C.; Han, R.; Fan, G.; Yang, L.; Li, F. The remarkable promotion of in situ formed Pt-cobalt oxide interfacial sites on the carbonyl reduction to allylic alcohols. Mol. Catal. 2018, 455, 78–87. [Google Scholar] [CrossRef]
  57. Babucci, M.; Guntida, A.; Gates, B.C. Atomically dispersed metals on well-defined supports including zeolites and metal−organic frameworks: Structure, bonding, reactivity, and catalysis. Chem. Rev. 2020, 120, 11956–11985. [Google Scholar] [CrossRef]
  58. Ivanin, I.A.; Udalova, O.V.; Kaplin, I.Y.; Shilina, M.I. New insights on the Cu-Ce interaction in Cu/Ce catalysts based on ZSM-5 and Beta for the preferential oxidation of carbon monoxide in excess hydrogen. Appl. Surf. Sci. 2024, 655, 159577. [Google Scholar] [CrossRef]
  59. Cherkashina, N.V.; Kochubey, D.I.; Kanazhevskiy, V.V.; Zaikovskii, V.I.; Ivanov, V.K.; Markov, A.A.; Klyagina, A.P.; Dobrokhotova, Z.V.; Kozitsyna, N.Y.; Baranovsky, I.B.; et al. Platinum acetate blue: Synthesis and characterization. Inorg. Chem. 2014, 53, 8397–8406. [Google Scholar] [CrossRef]
  60. Hadjiivanov, K.I.; Vayssilov, G.N. Characterization of oxide surfaces and zeolites by carbon monoxide as an IR probe molecule. Adv. Catal. 2002, 47, 307–511. [Google Scholar] [CrossRef]
  61. Shilina, M.I.; Udalova, O.V.; Nevskaya, S.M. Synergism in the actions of a transition metal cation and a Lewis acid in the liquid and gas phase catalytic conversion of alkanes over modified ZSM5 zeolites under mild conditions. Kinet. Catal. 2013, 54, 691–702. [Google Scholar] [CrossRef]
  62. Chakarova, K.; Mihaylov, M.; Hadjiivanov, K. FTIR spectroscopic study of CO adsorption on Pt–H–ZSM-5. Microporous Mesoporous Mater. 2005, 81, 305–312. [Google Scholar] [CrossRef]
  63. Chakarova, K.; Hadjiivanov, K.; Atanasova, G.; Tenchev, K. Effect of preparation technique on the properties of platinum in NaY zeolite: A study by FTIR spectroscopy of adsorbed CO. J. Mol. Catal. A-Chem. 2007, 264, 270–279. [Google Scholar] [CrossRef]
  64. Aleksandrov, H.A.; Neyman, K.M.; Hadjiivanov, K.I.; Vayssilov, G.N. Can the state of platinum species be unambiguously determined by the stretching frequency of an adsorbed CO probe molecule? Phys. Chem. Chem. Phys. 2016, 18, 22108–22121. [Google Scholar] [CrossRef] [PubMed]
  65. DeRita, L.; Dai, S.; Lopez-Zepeda, K.; Pham, N.; Graham, G.W.; Pan, X.; Christopher, P. Catalyst architecture for stable single atom dispersion enables site specific spectroscopic and reactivity measurements of CO adsorbed to Pt atoms, oxidized Pt clusters, and metallic Pt clusters on TiO2. J. Am. Chem. Soc. 2017, 139, 14150–14165. [Google Scholar] [CrossRef] [PubMed]
  66. Ivanin, I.A.; Krotova, I.N.; Udalova, O.V.; Zanaveskin, K.L.; Shilina, M.I. Synergistic catalytic effect of cobalt and cerium in the preferential oxidation of carbon monoxide on modified Co/Ce/ZSM-5 zeolites. Kinet. Catal. 2021, 62, 798–811. [Google Scholar] [CrossRef]
  67. Hadjiivanov, K.; Tsyntsarski, B.; Venkov, T.; Klissurski, D.; Daturi, M.; Saussey, J.; Lavalley, J.-C. FTIR spectroscopic study of CO adsorption on Co–ZSM-5: Evidence of formation of Co+(CO)4 species. Phys. Chem. Chem. Phys. 2003, 5, 1695–1702. [Google Scholar] [CrossRef]
  68. Chupin, C.; van Veen, A.C.; Konduru, M.; Deprés, J.; Mirodatos, C. Identity and location of active species for NO reduction by CH4 over Co-ZSM-5. J. Catal. 2006, 241, 103–114. [Google Scholar] [CrossRef]
  69. Mitsumi, M.; Murase, T.; Kishida, H.; Yoshinari, T.; Ozawa, Y.; Toriumi, K.; Sonoyama, T.; Kitagawa, H.; Mitani, T. Metallic behavior and periodical valence ordering in a MMX chain compound, Pt2(EtCS2)4I. J. Am. Chem. Soc. 2001, 123, 11179–11192. [Google Scholar] [CrossRef]
  70. Saveleva, V.A.; Papaefthimiou, V.; Daletou, M.K.; Doh, W.H.; Ulhaq-Bouillet, C.; Diebold, M.; Zafeiratos, S.; Savinova, E.R. Operando near ambient pressure XPS (NAP-XPS) study of the Pt electrochemical oxidation in H2O and H2O/O2 ambients. J. Phys. Chem. C 2016, 120, 15930–15940. [Google Scholar] [CrossRef]
  71. Golubina, E.V.; Rostovshchikova, T.N.; Lokteva, E.S.; Maslakov, K.I.; Nikolaev, S.A.; Shilina, M.I.; Gurevich, S.A.; Kozhevin, V.M.; Yavsin, D.A.; Slavinskay, E.M. Role of surface coverage of alumina with Pt nanoparticles deposited by laser electrodispersion in catalytic CO oxidation. Appl. Surf. Sci. 2021, 536, 147656. [Google Scholar] [CrossRef]
  72. Shilina, M.; Udalova, O.; Krotova, I.; Ivanin, I.; Boichenko, A. Oxidation of carbon monoxide on Co/Ce-modified ZSM-5 zeolites: Impact of mixed Oxo-Species. ChemCatChem 2020, 12, 2556–2568. [Google Scholar] [CrossRef]
  73. Xiang, G.; Qiu, Z.; Fei, H.; Liu, Z.; Yin, S.; Wu, Y. Synergistic effect of platinum single atoms and nanoclusters for preferential oxidation of carbon monoxide in hydrogen-rich stream. J. Power Sources 2024, 591, 233873. [Google Scholar] [CrossRef]
  74. Navas-Cárdenas, C.; Wolf, E.E.; Benito, N.; Gracia, F. Strong electrostatic adsorption of Pt over CoOx/TiO2 dual-support: Effect of synthesis pH on the catalytic activity for the CO oxidation in presence of hydrogen. Int. J. Hydrogen Energy 2023, 48, 24809–24825. [Google Scholar] [CrossRef]
  75. Boehm, H.-P.; Knözinger, H. Nature and Estimation of Functional Groups on Solid Surfaces. In Catalysis: Science and Technology; Anderson, J.R., Boudart, M., Eds.; Springer: Berlin/Heidelberg, Germany, 1983; pp. 39–207. [Google Scholar] [CrossRef]
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Figure 1. Temperature dependencies of the CO conversion in CO-PROX for Pt-modified zeolites with Si/Al ratio of 15 (1, 2) and 28 (3) after different heating modes—t only 200 °C (1–0.2 Pt/Z-15(a)) and after the additional activation at 300 °C (2–0.2 Pt/Z-15(c); 3–0.2 Pt/Z-28 c); the heating (dashed line) and cooling (solid line) cycles are displayed.
Figure 1. Temperature dependencies of the CO conversion in CO-PROX for Pt-modified zeolites with Si/Al ratio of 15 (1, 2) and 28 (3) after different heating modes—t only 200 °C (1–0.2 Pt/Z-15(a)) and after the additional activation at 300 °C (2–0.2 Pt/Z-15(c); 3–0.2 Pt/Z-28 c); the heating (dashed line) and cooling (solid line) cycles are displayed.
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Figure 2. Temperature dependencies of CO conversion in CO-PROX for mono- (0.2 Pt, wt%—green and 2.5 Co, wt%—blue) and bimetallic catalysts; the heating (dashed line) and cooling (solid line) modes are displayed (two heating–cooling cycles are shown for 0.2 PtCo/Z-15—black symbols represent 1st cycle and red symbols represent 2nd cycle).
Figure 2. Temperature dependencies of CO conversion in CO-PROX for mono- (0.2 Pt, wt%—green and 2.5 Co, wt%—blue) and bimetallic catalysts; the heating (dashed line) and cooling (solid line) modes are displayed (two heating–cooling cycles are shown for 0.2 PtCo/Z-15—black symbols represent 1st cycle and red symbols represent 2nd cycle).
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Figure 3. DRIFT spectra of carbon monoxide adsorbed at RT on monometallic 0.2 Pt/Z-15 (a) and bimetallic the 0.2 PtCo/Z-15 (b) composites at various doses of introduced CO: 0.5 µmol/g (1), equilibrium pressures of 0.9 (2), 2.5 kPa (3), and a residual pressure 0.05 kPa (4). The inset in Figure (b) shows a comparison of spectra 4 from (a,b) on an enlarged scale.
Figure 3. DRIFT spectra of carbon monoxide adsorbed at RT on monometallic 0.2 Pt/Z-15 (a) and bimetallic the 0.2 PtCo/Z-15 (b) composites at various doses of introduced CO: 0.5 µmol/g (1), equilibrium pressures of 0.9 (2), 2.5 kPa (3), and a residual pressure 0.05 kPa (4). The inset in Figure (b) shows a comparison of spectra 4 from (a,b) on an enlarged scale.
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Figure 4. TEM micrographs and particle size distributions of 0.6 Pt/Z-28: (a–c) initial; (d–f) spent.
Figure 4. TEM micrographs and particle size distributions of 0.6 Pt/Z-28: (a–c) initial; (d–f) spent.
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Figure 5. TEM micrographs of initial samples: (a–c) 0.2 PtCo/Z-15; (d–f) 0.2 PtCo/Z-28.
Figure 5. TEM micrographs of initial samples: (a–c) 0.2 PtCo/Z-15; (d–f) 0.2 PtCo/Z-28.
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Figure 6. TEM micrographs 0.2 PtCo/Z-15: (a,b) after DRIFTS studies; (c,d) spent.
Figure 6. TEM micrographs 0.2 PtCo/Z-15: (a,b) after DRIFTS studies; (c,d) spent.
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Figure 7. Pt4f (a) and C1s (b) XPS-spectra of the PAB precursor.
Figure 7. Pt4f (a) and C1s (b) XPS-spectra of the PAB precursor.
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Figure 8. Pt4f XPS-spectra of the initial (a) and spent (b) 0.6 Pt/Z-28 sample. Black curves are the observed spectra (thick lines) and the calculated envelopes (thin lines).
Figure 8. Pt4f XPS-spectra of the initial (a) and spent (b) 0.6 Pt/Z-28 sample. Black curves are the observed spectra (thick lines) and the calculated envelopes (thin lines).
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Table 1. The composition, calcination temperature and catalytic characteristics of Pt/Z catalysts in PROX: CO conversion at 150 °C (X150, %), maximum CO conversion (Xmax, %) and the temperature corresponding to its achievement (Tmax).
Table 1. The composition, calcination temperature and catalytic characteristics of Pt/Z catalysts in PROX: CO conversion at 150 °C (X150, %), maximum CO conversion (Xmax, %) and the temperature corresponding to its achievement (Tmax).
CatalystPt, wt%Si/AlCalcination Temperature,
°C		X150, %Xmax, %Tmax, °C
0.1 Pt/Z-15(a)0.1152001848190
0.1 Pt/Z-15(b)0.115300932210
0.1 Pt/Z-28(a)0.1282001557210
0.1 Pt/Z-28(b)0.1283001052210
0.2 Pt/Z-15(a)0.2152001948190
0.2 Pt/Z-15(c)0.215200 + 3005772170
0.2 Pt/Z-28(a)0.2282001760210
0.2 Pt/Z-28(c)0.228200 + 3003577190
0.6 Pt/Z-28(a)0.6282009292150
Table 2. The compositions and catalytic characteristics in CO-PROX of PtCo zeolites, containing the same 2.5 Co, wt%: temperatures corresponding to 50% and 100% CO conversion (T50 and T100, °C), CO conversion at 70 °C (X70, %), and the operating window ΔT100, °C of the 100% CO conversion.
Table 2. The compositions and catalytic characteristics in CO-PROX of PtCo zeolites, containing the same 2.5 Co, wt%: temperatures corresponding to 50% and 100% CO conversion (T50 and T100, °C), CO conversion at 70 °C (X70, %), and the operating window ΔT100, °C of the 100% CO conversion.
CatalystPt, wt%Si/AlT50 1X70 2T100 1∆T100
0.1 PtCo/Z-150.11573979090–130
0.2 PtCo/Z-150.215661005050–110
0.1 PtCo/Z-280.128651007070–110
0.2 PtCo/Z-280.228691009070–90
1 1st cycle, heating mode. 2 2nd cycle, cooling mode.
Table 3. Binding energies (Eb), corresponding bond types, and fractions of components in XPS spectra of platinum blue acetate (PAB).
Table 3. Binding energies (Eb), corresponding bond types, and fractions of components in XPS spectra of platinum blue acetate (PAB).
SpectrumEb, eVBond TypeFraction, at.%
O1s532.3COO−, O−C35.2
C1s285.0C−C (sp3)37.5
286.4C−O3.3
288.7COO−17.2
Pt4f7/274.2Pt3+, Pt4+6.8
Table 4. Pt4f7/2 binding energies, the fractions of Pt atoms in different states, and the Pt(/Si + Al) ratio on the surface of Pt/Z catalysts.
Table 4. Pt4f7/2 binding energies, the fractions of Pt atoms in different states, and the Pt(/Si + Al) ratio on the surface of Pt/Z catalysts.
Eb, eV71.2–71.372.2–72.473.5–74.0Element
Ratio
SampleConditionsElectronic State, at.%
Pt0Pt2+Pt4+Pt/(Si + Al)
0.2 Pt/Z-15(a)Initial4429270.004
0.2 Pt/Z-15(c)Initial7412140.007
0.6 Pt/Z-28(a)Initial2450260.02
Spent742060.004
Table 5. Pt4f7/2 and Co2p3/2 binding energies, the fractions of Pt and Co atoms in different states, and atomic ratios of elements on the surface of PtCo/Z and Co/Z catalysts.
Table 5. Pt4f7/2 and Co2p3/2 binding energies, the fractions of Pt and Co atoms in different states, and atomic ratios of elements on the surface of PtCo/Z and Co/Z catalysts.
Eb, eV71.2
71.3		72.2
72.4		73.5
74.0		781.6779.8Element Ratio
SampleConditionsElectronic State, at.%
Pt0Pt2+Pt4+Co2+Co3+Pt/(Si + Al)Co/(Si + Al)Co/Pt
0.2 PtCo/Z-15Initial42332574260.0010.04545
Spent65201574260.0010.04444
0.2 PtCo/Z-28Initial40283275250.0010.09393
Spent48282465350.0010.08989
2.5 Co/Z-15Initial---7228-0.045-
1.7 Co/Z-28 1Initial---8317-0.025-
1 data from our previous work [72].
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Shilina, M.; Krotova, I.; Nikolaev, S.; Cherkashina, N.; Stolarov, I.; Udalova, O.; Maksimov, S.; Rostovshchikova, T. Advanced PtCo Catalysts Based on Platinum Acetate Blue for the Preferential CO Oxidation in H2-Rich Mixture. Catalysts 2024, 14, 484. https://doi.org/10.3390/catal14080484

AMA Style

Shilina M, Krotova I, Nikolaev S, Cherkashina N, Stolarov I, Udalova O, Maksimov S, Rostovshchikova T. Advanced PtCo Catalysts Based on Platinum Acetate Blue for the Preferential CO Oxidation in H2-Rich Mixture. Catalysts. 2024; 14(8):484. https://doi.org/10.3390/catal14080484

Chicago/Turabian Style

Shilina, Marina, Irina Krotova, Sergey Nikolaev, Natalia Cherkashina, Igor Stolarov, Olga Udalova, Sergey Maksimov, and Tatiana Rostovshchikova. 2024. "Advanced PtCo Catalysts Based on Platinum Acetate Blue for the Preferential CO Oxidation in H2-Rich Mixture" Catalysts 14, no. 8: 484. https://doi.org/10.3390/catal14080484

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