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Article

Highly Dispersed Pt Nanoparticles on N-Doped Ordered Mesoporous Carbon as Effective Catalysts for Selective Hydrogenation of Nitroarenes

by
Yao Sheng
1,
Xinrui Lin
1,
Xueguang Wang
1,*,
Xiujing Zou
1 and
Chunlei Zhang
2,*
1
State Key Laboratory of Advanced Special Steel, School of Materials Science and Engineering, Shanghai University, 99 Shangda Road, BaoShan District, Shanghai 200444, China
2
Education Ministry Key Lab of Resource Chemistry, Shanghai Key Laboratory of Rare Earth Functional Materials, College of Chemistry and Materials Science, Shanghai Normal University, 100 Guilin Road, XuHui District, Shanghai 200234, China
*
Authors to whom correspondence should be addressed.
Catalysts 2020, 10(4), 374; https://doi.org/10.3390/catal10040374
Submission received: 5 March 2020 / Revised: 22 March 2020 / Accepted: 23 March 2020 / Published: 31 March 2020
(This article belongs to the Section Catalytic Materials)
Browse Figures
Versions Notes

Abstract

:
Highly-dispersed Pt nanoparticles supported on nitrogen-modified CMK-3 mesoporous carbon (Pt/N-CMK-3) were first fabricated by a two-step impregnation route. The influences of N content on the catalyst porous structure, Pt nanoparticle size, surface properties, and interaction between Pt species and the support were investigated in detail using N2 sorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectra (XPS). The N species acted as anchoring sites for the stabilization of Pt particles. Benefiting from the formation of ultrafine metal nanoparticles, the Pt/N-CMK-3 exhibited excellent catalytic activity and selectivity for the selective hydrogenation of nitro aromatics to the corresponding anilines with hydrogen. The Pt/N-CMK-3 catalyst could be reused eight times and keep its catalytic performance.

Graphical Abstract

1. Introduction

Substituted aromatic amines are crucial industrial intermediates for the production of various fine chemicals, such as dyestuffs, agrochemicals, pharmaceuticals, and polymers, and most of them are synthesized by catalytic reduction of corresponding nitro aromatics [1,2,3]. Particularly, sheterogeneous catalytic reduction over supported metal catalysts as an environment-friendly and efficient protocol attracts much interest [4,5]. The selective reduction of nitro aromatics over supported metal catalysts was widely adopted with different hydrogen sources, such as hydrazine hydrate, sodium borohydride, gas hydrogen, formic acid, ammonia borane, and so on [6,7,8,9]. Among them, H2, a low cost, non-toxic, and the cleanest hydrogen donor, is recognized as the most ideal reducing agent for the hydrogenation of nitro aromatic compounds in industrial production.
Heterogeneous noble metal-based catalysts such as Ru, Rh, Pt, and Pd have been reported to be efficient for the hydrogenation of nitroarenes [10,11]. Downsizing the noble metal particles to a few nanometers can dramatically improve their catalytic activity, due to the increasing surface-to-atom ratio [12,13]. However, the supported small metal nanoparticles often suffer from serious aggregation because of the high surface energy [14,15,16]. In addition, it remains challenging to keep other reducible groups, especially the halogen groups (F, Cl, Br, and I), intact at high conversion rates when using noble metal catalysts with H2 as the hydrogen source [17,18,19]. Generally, the catalytic performance is closely linked to the metal particle sizes, the structure or surface properties of the support, and the interaction effect between the metal and support. The activity and selectivity of the catalyst for the hydrogenation of nitroarenes could be modified by preparation method, thermal treatment, and element doping [20,21,22].
Mesoporous materials are considered as the ideal choices as catalyst supports due to their large surface areas, tunable pore size, and thermal and chemical stability [23,24,25]. Particularly, functionalized supports, such as nitrogen doped mesoporous carbon, have received great interest because the incorporation of N atoms into mesoporous carbon frameworks not only alters the mechanical and electronic properties, and the surface chemical states, of carbon materials, but also is efficient for the stabilization of the metal nanoparticle [26,27].
In the present work, we report for the first time an N-doped ordered mesoporous carbon fabricated by using a simple impregnation step with 2-methylimidazole as an ideal nitrogen source (N-CMK-3-x, where x represents the 2-methylimidazole amount). The N-CMK-3 supports act as efficient catalytic supports to disperse and stabilize ultrafine Pt nanoparticles. The as-prepared Pt/N-CMK-3 catalysts exhibited highly efficient catalytic activity and chemoselectivity for the hydrogenation of nitro aromatics into corresponding anilines with H2 under room temperature. Of particular importance, was that the Pt/N-CMK-3 was rather stable without any leaching of metal nanoparticles and could be reused for the selective hydrogenation of nitrobenzene.

2. Results and Discussion

2.1. Catalyst Characterization

N2 adsorption–desorption isotherms and corresponding pore size distribution profiles of the CMK-3, Pt/CMK-3, and Pt/N-CMK-3-x samples were recorded. As depicted in Figure 1a, all of the Pt/N-CMK-3-x samples exhibited typical IV isotherms with distinct hysteresis at relative higher pressure (P/P0 > 0.4), ascribing to the characteristics of mesoporous structure, similar to that of the CMK-3 support. This result demonstrated that the mesoporous structure of CMK-3 was still kept after being incorporated with Pt, C, and N components. The similar pore size distributions of the samples in Figure 1b also proved this point, and the pore sizes were primarily in the range of 3–4 nm. The detailed textural parameters and physical properties of the samples are shown in Table 1. With the increased amount of 2-methylimidazole, the specific surface area, pore volume, and pore size of the Pt/N-CMK-3-x showed a remarkable decline, implying the successful incorporation of C and N from the pyrolysis of 2-methylimidazole. The final contents of Pt and N in the samples were determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and CHN elemental analyzer (Table 1). As can be seen, the Pt contents were all located at 1.90 ± 0.05 wt%, while the N contents showed obvious increase from 2.1 to 3.5 wt% with increasing the amount of 2-methylimidazole. However, when the amount of 2-methylimidazole was continuously increased, the Pt/N-CMK-3-3 showed only a small increase in N contents about 0.2 wt%. Maybe the excess 2-methylimidazole did not incorporate in the CMK-3 frameworks, due to N loss during the synthesis at 800 °C.
The XRD patterns of the CMK-3 and Pt/N-CMK-3 materials are displayed in Figure 2. All samples showed broadened diffraction peaks at 2θ = 43°, indicating the presence of graphitic carbon. For the Pt/CMK-3 catalyst, an obvious diffraction peak at 2θ = 39.8° was assigned to (111) lattice planes of metal Pt (PDF 70–2431). When the N species were incorporated in the matrix, the diffraction peak for metal Pt became weak and wide. As the N content was further increased, the diffraction peak of Pt (111) in Pt/N-CMK-3-2 and Pt/N-CMK-3-3 was disappeared completely, indicating that the Pt species were highly dispersed in the N-CMK-3 matrix. These results revealed that the incorporation of N in the carbon matrix benefited the dispersion of Pt nanoparticles on the surface, due to the complexing and stabilizing effect.
Figure 3 presents the representative TEM images of the Pt/CMK-3 and Pt/N-CMK-3-x samples. All the samples displayed obvious order pore channels, similar to pure CMK-3 (not shown). For Pt/CMK-3, plenty of darker metal nanoparticles with average particle sizes of 5.5 nm were distributed on the support. As the N species were introduced, the average size of Pt nanoparticles was remarkably decreased to 2.9 nm in Pt/N-CMK-3-1, which was attributed to the significant role of N in anchoring metal particles. It can be seen from Table 1 that the Pt particle sizes of Pt/N-CMK-3 and Pt/N-CMK-3-1 counted by TEM were approximately equal to the mean sizes of Pt crystallites by XRD. When the N contents were continuously increased, the mean sizes of the Pt particles reached a minimum value of about 1.2 nm in Pt/N-CMK-3-2 catalyst. These results, in agreement with the XRD result in Figure 2, confirmed that the N content had significant effects on the sizes of metal Pt crystallites or particles formed, which will be analyzed in detail in subsequent XPS analysis. In addition, the high-angle annular dark-field scanning TEM (HAADF-STEM) and the elemental mapping images demonstrated that Pt and N species were uniformly dispersed in Pt/N-CMK-3-2 (Figure 3e).
The valence states of Pt and N types of the prepared materials were characterized by XPS spectra. As depicted in Figure 4a, the Pt 4f XPS spectra of Pt/CMK-3 showed symmetric doublet peaks at the binding energy of 71.7 and 75.2 eV, respectively, which were attributed to Pt0. However, this binding energy value was higher than the binding energy of bulk Pt (4f7/2 = 71.2 eV) [28,29,30], indicating the interaction between Pt particles and the CMK-3. When the CMK-3 support was treated with 2-methylimidazole and the N species were introduced into the matrix, the binding energies of Pt0 4f were shifted to higher values with increasing N content, implying the existence of an interaction effect between Pt and N species due to a charge-transfer. The N species in the Pt/N-CMK-3-2 was further identified by the N 1s XPS spectrum in Figure 4b. Three peaks at 397.5, 399.4, and 400.7 eV were assigned to pyridinic-type, pyrrolic-type, and graphitic-type N [31,32,33,34], respectively. It has been reported that the pyrrolic and pyridinic N sites act as anchoring sites for the stabilization of Pt particles and suppressing their agglomeration [35,36]. The relative peak area percentage of each type of N in Pt/N-CMK-3-x catalysts is listed in Table 2. The surface N compositions were close to those determined by the CHN elemental analyzer in Table 1. When the N content was increased, the relative peak intensity for graphitic N was strengthened, and in the meanwhile, the relative peak intensity for pyrrolic N was found to be decreased. However, the peak intensities for the pyridinic N showed no obvious change. Therefore, the total content of pyrrolic and pyridinic N for the Pt/N-CMK-3-2 showed a maximum value, due to the combination of the two factors of the increases in N contents and the decrease in pyrrolic N on the catalyst surfaces.

2.2. Catalytic Reaction

Nitrobenzene was first conducted as a model compound over the Pt/N-CMK-3-2 to optimize the reaction conditions, and the results are listed in Table 3. Firstly, the hydrogenation of nitrobenzene with H2 was investigated in different solvents. All the solvents like ethylacetate, toluene, ethyl ether, methanol, and ethanol showed excellent catalytic activity, but ethanol (nitrobenzene/ethanol = 4:1 (mmol mL−1)) gave the highest nitrobenzene conversion (entries 1–7). Secondly, the results showed that the nitrobenzene conversion steadily increased with increasing H2 pressure from 0.5 to 2 MPa, indicated that the H2 pressure influenced the dissolution of H2 in the solvent. The reaction rate did not change obviously when increasing H2 pressure from 2 to 6 MPa (entry 5 and entries 10,11), implying the absence of a hydrogen transport limitation at high pressure. Finally, the nitrobenzene conversion continually increased with the temperature without loss of selectivity (100%) (entries 12–14).
We compared the initial conversions of nitrobenzene as a model compound over Pt/N-CMK-3-x catalysts with H2 in ethanol for 10 min at 40 °C, and the results are summarized in Table 4. As can be seen, the CMK-3 and N-CMK-3-2 materials provided no activity (entries 1 and 2). When the CMK-3 was treated with 2-methylimidazole, the Pt/N-CMK-3-1 showed a nitrobenzene conversion of 8.0%, which was much higher than that of Pt/CMK-3 (3.9%). The Pt/N-CMK-3-2 with the minimum particle size showed the highest nitrobenzene conversion. The turnover frequencies (TOFs) for the Pt/N-CMK-3-2 exhibited high values of 18,819 h−1. However, when the N content was further increased, the initial conversions of nitrobenzene of Pt/N-CMK-3-3 showed a decline. These variations matched well with the results of TEM. These results demonstrated that the activity of the Pt/N-CMK-3-x for the selective hydrogenation of nitrobenzene was significantly influenced by the N content inducing changes in the size of the Pt nanoparticles.
The scope of Pt/N-CMK-3-2 in hydrogenation of nitroarenes, a series of nitro compounds with diverse substituent groups, were tested under the optimized reaction conditions, and the results are summarized in Table 5. To our great delight, the Pt/N-CMK-3-2 exhibited high activity and selectivity for the hydrogenation of substituted nitroarenes. Apart from nitrobenzene (Table 5, entry 1), the substituted nitrobenzenes having nonreducible groups like –CH3, –NH2, and CH3O– were also furnished with excellent yield (>99%) (entries 2–7). It has been reported that supported noble catalysts, such as Pt, Pd, Rh, etc., display poor chemoselectivity to the hydrogenation of the nitro group when halogen groups exist in the same molecule [37]. Herein, no obvious dehalogenation product was observed in the selective hydrogenation of the halogen-substituted nitroarenes (entries 8–13). Moreover, other reducible groups such as –COOCH2CH3, –COOH, –CN, and –CHO on the nitrobenzene were also well tolerated to give the corresponding amines in high selectivity (entries 14–17). Also, for heterocyclic nitroarenes containing N element, full conversion and high selectivity of >99.0% was achieved (entries 19–22). In contrast, the hydrogenation of p-chloronitrobenzene over Pt/CMK-3 showed not only low catalytic activity but also poor selectivity (entry 23). The high chemoselectivity of the Pt/N-CMK-3-2 catalysts for the hydrogenation of nitroarenes to anilines was likely due to the higher reactivity of nitro group than other functional groups.
The stability and reusability of the Pt/N-CMK-3-2 catalyst were further investigated by the hydrogenation of nitrobenzene at 40 °C. As presented in Figure 5, the Pt/N-CMK-3-2 exhibited a nitrobenzene conversion of 80.1% in the first cycle. After completion of the reaction, the catalyst was separated by filtration, washed with ethanol three times, and dried overnight at 60 °C. Then the recovered catalyst was directly used for the next run without any reactivation or purification. The nitrobenzene conversion remained at 78.7% for the eight runs, and the aniline selectivity was kept at 100%. After each cycling reaction, the Pt contents in the product solution were determined by ICP-AES. It was found that the solution hardly contained the Pt element (<1 ppm). As can be seen in Table 1, the total Pt content in the spent Pt/N-CMK-3-2 was 1.86 wt%, which was very close to that of before the reaction. It was demonstrated that the Pt/N-CMK-3-2 possessed good recyclability and has great potential for practical applications in the selective hydrogenation of nitroarenes in the future.

3. Experimental Section

3.1. Chemicals

All chemicals were purchased and used without further purification. Pluronic P123 (EO20PO70EO20) and tetraethylorthosilicate (TEOS) were bought from Sigma-Aldrich Reagent (Shanghai, China). Chloroplatinic acid hexahydrate (H2PtCl6·6H2O), 2-methylimidazole, all nitro compounds, and solvents were supplied by Sinopharm Chemical Reagent Co., Ltd (Shanghai, China).

3.2. Catalyst Preparation

Ordered mesoporous silica SBA-15 was obtained using P123 as a structure directing agent and TEOS as the silica source under acidic conditions according to the document [38]. CMK-3 was prepared using SBA-15 as the template and sucrose as the carbon source, and then was carbonized at 900 °C for 6 h under nitrogen, as described by Ryoo et al. [39]. The silica template was removed using 5 wt% hydrofluoric acid aqueous solutions at room temperature. The CMK-3 product was obtained after filtering, washing, and drying. The N-CMK-3 was prepared by an impregnation method with the following steps: 6 g of CMK-3 and a certain amount of 2-methylimidazole were dissolved in 60 mL deionized water at room temperature; the amount of 2-methylimidazole was 1, 2, and 3 g in the synthesis of N-CMK-3-1, N-CMK-3-2, and N-CMK-3-3, respectively; then, the mixture was stirred at 60 °C and the water was vaporized slowly; and finally, the obtained solid was calcined in N2 atmosphere at 800 °C for 6 h with a heating rate of 2 °C min−1.
Pt/N-CMK-3-x (x represents the amount of 2-methylimidazole with 1, 2, and 3 g) catalyst with 2 wt% of Pt was synthesized by ultrasound-assisted traditional wetness impregnation method. In brief, 6 g of N-CMK-3-x powder and 6.2 mL H2PtCl6·6H2O aqueous solution (0.1 mol L−1) were mixed with deionized water (60 mL) to form a homogeneous suspension under ultrasound conditions. Then, the mixture was stirred at 40 °C until water was evaporated. Finally, the obtained solid was calcined in a flow of 30 vol.% H2 in N2 at 200 °C for 3 h with a ramp rate of 2 °C min−1. For comparison, Pt/CMK-3 was prepared by the identical route.

3.3. Catalyst Characterization

Nitrogen adsorption analysis was carried out at liquid nitrogen temperature (−196 °C) by using an ASAP2020 analyzer (Norcross, GA, USA). Prior to measurement, samples were degassed at 200 °C for 10 h. The specific surface areas of the samples were calculated by the Brunauer–Emmett–Teller (BET) method. The pore volume was calculated at relative pressure P/P0 of 0.991. The pore size distribution plot was calculated using the Barrett–Joyner–Halenda (BJH) formula. The metal Pt loading amount of the catalysts was determined on ICP-AES (Waltham, MA, USA). The N content in the catalysts was measured by using the PerkinElmer 2400 CHN elemental analyzer (Waltham, MA, USA). XRDpatterns were performed on a Rigaku D/MAX-2200 (Billerica, MA, USA) apparatus with a Cu Kα source (40 kV, 40 mA) at room temperature in the 2θ range of 10–90°. Transmission electron microscopy (TEM) and HAADF-STEM micrographs were obtained on a JEM-2010F (JEOL, Beijing, China) with an element energy-dispersive X-ray spectrometer operating at 200 kV. XPS of the catalysts were recorded with an ESCALAB 250xi spectrometer (Thermo Fisher Scientific, Waltham, USA) equipped with Al Kα radiation source (hν = 1486.6 eV). Binding energies of all elements were calibrated by C1s at 284.6 eV.

3.4. Catalytic Reaction and Product Analyses

The chemoselective hydrogenation of nitro aromatics was carried out in a 100 mL stainless-steel autoclave with a stirring controller. In a typical experiment, the autoclave was charged with 80 mmol of nitro aromatics, 40 mg of catalysts, and 20 mL of green solvent ethanol. Before starting the reaction, the reactor was flushed three times with 0.5 MPa of hydrogen to remove the air, and then sealed tight and pressurized to 2 MPa H2. The stirring speed was kept at 800 rpm. Then the hydrogenation reaction was proceeded at 40 °C for a certain time. After the reactor was cooled to room temperature, the remaining H2 was carefully released. One hundred microliters of the mixture were isolated by filtration for further analysis.
Each reaction was repeated more than three times to reach the carbon balance of more than 98% and obtained the nitroarenes conversion with an error ascertained to be within 5%. The qualitative and quantitative analyses of the products were done by gas chromatography (GC)-mass spectrometry (GC-MS, Shimadzu GCMS-QP 2010 Plus, Shanghai, China) and GC (Varian CP-3800, Palo Alto, California, USA) with n-decane as the internal standard.
For the recycling study, the hydrogenation reaction was performed in the same reaction conditions as mentioned above. The catalyst after each run was filtered, and washed several times with ethanol, and dried at 60 °C. Then the recovered catalyst was directly used for the next run without any reactivation or purification. Considering the catalyst loss during the filtration, washing, and drying, the amount of catalyst changed throughout each cycle. However, the Pt/N-CMK-3-2/nitrobenzene/ethanol ratio was always kept the same as it was in the first cycle.

4. Conclusions

In summary, highly-dispersed Pt nanoparticles supported on nitrogen-modified CMK-3 mesoporous carbon were successfully synthesized by a facile two-step impregnation route. TEM results revealed that ultrafine Pt nanoparticles were uniformly dispersed on the N-doped mesoporous carbon. The prepared Pt/N-CMK-3-2 was found to exhibit much higher catalytic activity for the hydrogenation of various nitro aromatics as compared to the Pt/CMK-3 prepared without the incorporation of N species. The existence of N species in carbon matrix facilitated high metal dispersion and prevented the agglomeration of Pt nanoparticles, due to the interaction effect between Pt and N atoms, which resulted in high catalytic activity. In addition, the Pt/N-CMK-3-2 could completely transform various substituted nitro aromatics to the corresponding aromatic amines with excellent selectivity, even for the case of the halogenated nitrobenzene. The Pt/N-CMK-3-2 catalyst was highly stable and could be reused for the selective hydrogenation of nitrobenzene without obvious loss of catalytic performance.

Author Contributions

Y.S. analyzed the data and wrote the draft of the manuscript; Y.S. and X.L. performed the experiments; X.W. and C.Z. conceived and designed the experiments; X.Z. reviewed and edited the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by National Natural Science Foundation of China (U1860203, 51574164), CAS Interdisciplinary Innovation Team, and the Shanghai Engineering Research Center of Green Energy Chemical Engineering (No. 18DZ2254200).

Acknowledgments

This research was supported by National Natural Science Foundation of China (U1860203, 51574164), CAS Interdisciplinary Innovation Team, and the Shanghai Engineering Research Center of Green Energy Chemical Engineering (No. 18DZ2254200).

Conflicts of Interest

The authors declare no conflicts of interest.

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Catalysts 10 00374 g001 550
Figure 1. (a) N2 sorption isotherms and (b) pore size distributions of the CMK-3, Pt/CMK-3, and Pt/N-CMK-3-x (x = 1, 2, and 3) samples.
Figure 1. (a) N2 sorption isotherms and (b) pore size distributions of the CMK-3, Pt/CMK-3, and Pt/N-CMK-3-x (x = 1, 2, and 3) samples.
Catalysts 10 00374 g001
Catalysts 10 00374 g002 550
Figure 2. XRD patterns of the CMK-3, Pt/CMK-3, and Pt/N-CMK-3-x (x = 1, 2, and 3) samples.
Figure 2. XRD patterns of the CMK-3, Pt/CMK-3, and Pt/N-CMK-3-x (x = 1, 2, and 3) samples.
Catalysts 10 00374 g002
Catalysts 10 00374 g003 550
Figure 3. TEM images of (a) Pt/CMK-3, (b) Pt/N-CMK-3-1, (c) Pt/N-CMK-3-2, (d) Pt/N-CMK-3-3, and (e) high-angle annular dark-field scanning-transmission electron microscopy (HAADF-STEM) and elemental mapping images of Pt/N-CMK-3-2. The average diameters of the Pt particles were obtained by measuring about 200 clusters for each sample.
Figure 3. TEM images of (a) Pt/CMK-3, (b) Pt/N-CMK-3-1, (c) Pt/N-CMK-3-2, (d) Pt/N-CMK-3-3, and (e) high-angle annular dark-field scanning-transmission electron microscopy (HAADF-STEM) and elemental mapping images of Pt/N-CMK-3-2. The average diameters of the Pt particles were obtained by measuring about 200 clusters for each sample.
Catalysts 10 00374 g003
Catalysts 10 00374 g004 550
Figure 4. (a) Pt 4f XPS spectra of Pt/CMK-3 and Pt/N-CMK-3-x (x = 1, 2, and 3) and (b) N 1s XPS spectra of Pt/N-CMK-3-x (x = 1, 2, and 3).
Figure 4. (a) Pt 4f XPS spectra of Pt/CMK-3 and Pt/N-CMK-3-x (x = 1, 2, and 3) and (b) N 1s XPS spectra of Pt/N-CMK-3-x (x = 1, 2, and 3).
Catalysts 10 00374 g004
Catalysts 10 00374 g005 550
Figure 5. Reuse tests of the Pt/N-CMK-3-2 catalyst. Reaction conditions: 80 mmol nitrobenzene, 40 mg catalyst, 20 mL of ethanol, 40 °C, 2 MPa H2, 1.0 h.
Figure 5. Reuse tests of the Pt/N-CMK-3-2 catalyst. Reaction conditions: 80 mmol nitrobenzene, 40 mg catalyst, 20 mL of ethanol, 40 °C, 2 MPa H2, 1.0 h.
Catalysts 10 00374 g005
Table
Table 1. Pt and N contents, and physical properties of prepared materials.
Table 1. Pt and N contents, and physical properties of prepared materials.
SamplesPt (wt %)N (wt %)Specific Surface Area (m2 g−1)Pore Volume (cm3 g−1)Pore Size (nm)Pt crystallite Size by XRD (nm)
CMK-3--9791.023.9-
Pt/CMK-31.95-9711.023.95.5
Pt/N-CMK-3-11.922.16200.603.73.0
Pt/N-CMK-3-21.893.55900.523.5-
Pt/N-CMK-3-31.873.75480.493.4-
Spent Pt/N-CMK-3-21.863.55790.513.5-
Table
Table 2. Relative peak area percentage of each type of N in Pt/N-CMK-3-x catalysts.
Table 2. Relative peak area percentage of each type of N in Pt/N-CMK-3-x catalysts.
SamplesNitrogen Content (Atom %) aPyridinic-Type (%) bPyrrolic-Type (%) bGraphitic-Type (%) b
Pt/N-CMK-3-12.09.068.222.8
Pt/N-CMK-3-23.36.957.635.5
Pt/N-CMK-3-33.67.041.951.1
a The N content was determined by XPS. b Data are the percentage of the peak area of the fitted nitrogen in the total area of the N 1s peak.
Table
Table 3. Catalytic performance of Pt/N-CMK-3-2 catalysts for hydrogenation of nitrobenzene a.
Table 3. Catalytic performance of Pt/N-CMK-3-2 catalysts for hydrogenation of nitrobenzene a.
Catalysts 10 00374 i001
EntrySolvent (mL)H2 Pressure (MPa)Temperature (°C)Conv. (%) bSel. (%)
1Ethylacetate (20 mL)24049.2100
2Toluene (20 mL)24025.2100
3Ethyl ether (20 mL)24044.3100
4Methanol (20 mL)24053.7100
5Ethanol (20 mL)24079.5100
6Ethanol (10 mL)24065.1100
7Ethanol (30 mL)24063.6100
8Ethanol (20 mL)0.54024.4100
9Ethanol (20 mL)14056.8100
10Ethanol (20 mL)44080.3100
11Ethanol (20 mL)64081.4100
12Ethanol (20 mL)26098.2100
13Ethanol (20 mL)280100 (0.5 h)100
14Ethanol (20 mL)2100100 (0.2 h)100
a Reaction conditions: 80 mmol nitrobenzene, 40 mg catalyst, 1.0 h. b Actual required reaction time for full conversion of nitrobenzene in parenthesis.
Table
Table 4. Catalytic hydrogenation of nitrobenzene over different catalysts a.
Table 4. Catalytic hydrogenation of nitrobenzene over different catalysts a.
EntryCatalystConv. (%)TOF (h−1) bSel. (%)
1CMK-300-
2N-CMK-3-200-
3Pt/CMK-33.94680100
4Pt/N-CMK-3-18.09750100
5Pt/N-CMK-3-215.218819100
6Pt/N-CMK-3-39.411763100
a Reaction conditions: 80 mmol nitrobenzene, 40 mg catalyst, 20 mL of ethanol, 40 °C, 2 MPa H2, 10 min. b The number of moles of converted nitrobenzene per Pt mole per hour based on the total Pt by ICP in Table 1.
Table
Table 5. Chemoselective hydrogenation of various substituted nitroarenes catalyzed by Pt/N-CMK-3-2 catalyst a.
Table 5. Chemoselective hydrogenation of various substituted nitroarenes catalyzed by Pt/N-CMK-3-2 catalyst a.
EntrySubstrateTime (h)Conv. (%)Sel. (%)
1 Catalysts 10 00374 i0021.5 >99.999.9
2 Catalysts 10 00374 i0032.0>99.999.7
3 Catalysts 10 00374 i0042.0>99.999.5
4 Catalysts 10 00374 i0052.0>99.999.2
5 Catalysts 10 00374 i0064.0>99.999.7
6 Catalysts 10 00374 i0073.0>99.999.9
7 Catalysts 10 00374 i0083.0>99.999.9
8 Catalysts 10 00374 i0093.0>99.999.0
9 Catalysts 10 00374 i0102.5>99.999.7
10 Catalysts 10 00374 i0113.0>99.999.3
11 Catalysts 10 00374 i0123.0>99.999.4
12 Catalysts 10 00374 i0132.5>99.998.5
13 Catalysts 10 00374 i0142.0>99.999.1
14 Catalysts 10 00374 i0154.0>99.999.6
15 Catalysts 10 00374 i0162.5>99.999.1
16 Catalysts 10 00374 i0173.5>99.999.5
17 Catalysts 10 00374 i0184.0>99.998.2
18 Catalysts 10 00374 i0192.0>99.999.0
19 Catalysts 10 00374 i0208.0>99.999.6
20 Catalysts 10 00374 i0215.0>99.999.7
21 Catalysts 10 00374 i0224.0>99.999.7
22 Catalysts 10 00374 i0233.0>99.999.5
23 b Catalysts 10 00374 i0241.535.283.7
a Reaction conditions: 80 mmol substrate, 40 mg catalyst, 20 mL of ethanol, 40 °C, 2 MPa H2. b Performed over Pt/CMK-3.

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Sheng, Y.; Lin, X.; Wang, X.; Zou, X.; Zhang, C. Highly Dispersed Pt Nanoparticles on N-Doped Ordered Mesoporous Carbon as Effective Catalysts for Selective Hydrogenation of Nitroarenes. Catalysts 2020, 10, 374. https://doi.org/10.3390/catal10040374

AMA Style

Sheng Y, Lin X, Wang X, Zou X, Zhang C. Highly Dispersed Pt Nanoparticles on N-Doped Ordered Mesoporous Carbon as Effective Catalysts for Selective Hydrogenation of Nitroarenes. Catalysts. 2020; 10(4):374. https://doi.org/10.3390/catal10040374

Chicago/Turabian Style

Sheng, Yao, Xinrui Lin, Xueguang Wang, Xiujing Zou, and Chunlei Zhang. 2020. "Highly Dispersed Pt Nanoparticles on N-Doped Ordered Mesoporous Carbon as Effective Catalysts for Selective Hydrogenation of Nitroarenes" Catalysts 10, no. 4: 374. https://doi.org/10.3390/catal10040374

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