Materials

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11 pages, 1109 KiB

Open AccessCommunication

Impact of Cerium Oxide on the State and Hydrogenation Activity of Ruthenium Species Incorporated on Mesocellular Foam Silica

by Kalina Grzelak, Maciej Trejda and Jacek Gurgul

Materials 2022, 15(14), 4877; https://doi.org/10.3390/ma15144877 - 13 Jul 2022

Cited by 2 | Viewed by 1485

Abstract

Herein, the impact of cerium species loaded on mesoporous silica of MCF type on the state and catalytic activity of ruthenium species was studied. Up to 20 wt.% of cerium was incorporated on the silica surface, whereas the same 1 wt.% of Ru [...] Read more.

Herein, the impact of cerium species loaded on mesoporous silica of MCF type on the state and catalytic activity of ruthenium species was studied. Up to 20 wt.% of cerium was incorporated on the silica surface, whereas the same 1 wt.% of Ru loading was applied. The samples prepared were examined by low temperature N₂ adsorption/desorption, XRD, XRF, ICP-OES, XPS and H₂ chemisorption. The catalytic activity of the materials obtained was investigated in the transformation of levulinic acid to γ-valerolactone. It was documented that the presence of Ce favored an increase in the dispersion of ruthenium species, which had a positive impact on the hydrogenation activity for up to 10 wt.% of Ce. Nevertheless, the highest cerium loading had a negative influence on the textural parameters of the support. Full article

(This article belongs to the Special Issue Feature Paper in Section Catalytic Materials)

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20 pages, 5433 KiB

Open AccessArticle

Femtosecond Laser-Ablated Copper Surface as a Substrate for a MoS₂-Based Hydrogen Evolution Reaction Electrocatalyst

by Ramūnas Levinas, Asta Grigucevičienė, Tadas Kubilius, Aidas Matijošius, Loreta Tamašauskaitė-Tamašiūnaitė, Henrikas Cesiulis and Eugenijus Norkus

Materials 2022, 15(11), 3926; https://doi.org/10.3390/ma15113926 - 31 May 2022

Cited by 6 | Viewed by 2028

Abstract

One of the methods to improve the performance of a heterogeneous electrocatalyst is the dispersion of a catalytic material on a suitable substrate. In this study, femtosecond laser ablation was used to prepare very rough but also ordered copper surfaces consisting of vertical, [...] Read more.

One of the methods to improve the performance of a heterogeneous electrocatalyst is the dispersion of a catalytic material on a suitable substrate. In this study, femtosecond laser ablation was used to prepare very rough but also ordered copper surfaces consisting of vertical, parallel ridges. Then, a molybdenum sulfide coating was electrochemically deposited onto these surfaces. It was observed by profilometry that the average roughness of the surface after coating with MoS₂ had decreased, but the developed surface area still remained significantly larger than the projected surface area. The electrodes were then used as an electrocatalyst for the hydrogen evolution reaction in acidic media. These were highly efficient, reaching 10 mA cm⁻² of HER current at a −181 mV overpotential and a Tafel slope of ~39 mV dec⁻¹. Additionally, scanning electrochemical microscopy was used to observe whether hydrogen evolution would preferentially occur in certain spots, for example, on the peaks, but the obtained results suggest that the entire surface is active. Finally, the electrochemical impedance spectroscopy data showed the difference in the double-layer capacitance between the ablated and non-ablated surfaces (up to five times larger) as well as the parameters that describe the improved catalytic activity of fs-Cu/MoS₂ electrodes. Full article

(This article belongs to the Special Issue Feature Paper in Section Catalytic Materials)

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19 pages, 30517 KiB

Open AccessArticle

Bacteria and Soil Enzymes Supporting the Valorization of Forested Soils

by Agata Borowik, Jadwiga Wyszkowska and Jan Kucharski

Materials 2022, 15(9), 3287; https://doi.org/10.3390/ma15093287 - 4 May 2022

Cited by 8 | Viewed by 2185

Abstract

To decompose forest biomass, microorganisms use specific enzymes from the class of oxidoreductases and hydrolases, which are produced by bacteria and soil fungi. In post-agricultural forest soils, bacteria adapt more easily to changing ecological conditions than fungi. The unique features of bacteria, i.e., [...] Read more.

To decompose forest biomass, microorganisms use specific enzymes from the class of oxidoreductases and hydrolases, which are produced by bacteria and soil fungi. In post-agricultural forest soils, bacteria adapt more easily to changing ecological conditions than fungi. The unique features of bacteria, i.e., tolerance and the ability to degrade a wide range of chemical compounds, prompted us to conduct research that contributes to the improvement of the broadly understood circular management of biomass production and economic efficiency. This study aimed to analyze changes in the microbiological activity and the activities of dehydrogenases, catalase, β-glucosidase, urease, arylsulfatase, acid phosphatase, and alkaline phosphatase in the soil sampled from under Picea abies (Pa), Pinus sylvestris (Ps), Larix decidua (Ld), Quercus robur (Qr), and Betula pendula (Bp), after 19 years. The control object was unforested soil. The studies allowed one to demonstrate the relationship between the activity of soil enzymes and the assemblages of culturable microorganisms and bacteria determined by the metagenomic method and tree species. Thus, it is possible to design the selection of tree species catalyzing enzymatic processes in soil. The strongest growth promoter of microorganisms turned out to be Quercus robur L., followed by Picea abies L., whereas the weakest promoters appeared to be Pinus sylvestris L. and Larix decidua M. Full article

(This article belongs to the Special Issue Feature Paper in Section Catalytic Materials)

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19 pages, 2871 KiB

Open AccessEditor’s ChoiceArticle

Low Metal Loading (Au, Ag, Pt, Pd) Photo-Catalysts Supported on TiO₂ for Renewable Processes

by Francesco Conte, Ilenia Rossetti, Gianguido Ramis, Cyril Vaulot, Samar Hajjar-Garreau and Simona Bennici

Materials 2022, 15(8), 2915; https://doi.org/10.3390/ma15082915 - 15 Apr 2022

Cited by 10 | Viewed by 2858

Abstract

Photo-catalysts based on titanium dioxide, and modified with highly dispersed metallic nanoparticles of Au, Ag, Pd and Pt, either mono- or bi-metallic, have been analyzed by multiple characterization techniques, including XRD, XPS, SEM, EDX, UV-Vis and N₂ adsorption/desorption. Mono-metallic photo-catalysts were prepared [...] Read more.

Photo-catalysts based on titanium dioxide, and modified with highly dispersed metallic nanoparticles of Au, Ag, Pd and Pt, either mono- or bi-metallic, have been analyzed by multiple characterization techniques, including XRD, XPS, SEM, EDX, UV-Vis and N₂ adsorption/desorption. Mono-metallic photo-catalysts were prepared by wet impregnation, while bi-metallic photocatalysts were obtained via deposition-precipitation (DP). The relationship between the physico-chemical properties and the catalyst’s behavior for various photo-synthetic processes, such as carbon dioxide photo-reduction to liquid products and glucose photo-reforming to hydrogen have been investigated. Among the tested materials, the catalysts containing platinum alone (i.e., 0.1 mol% Pt/TiO₂) or bi-metallic gold-containing materials (e.g., 1 wt% (Au_xAg_y)/TiO₂ and 1 wt% (Au_xPt_z)/TiO₂) showed the highest activity, presenting the best results in terms of productivity and conversion for both applications. The textural, structural and morphological properties of the different samples being very similar, the main parameters to improve performance were function of the metal as electron sink, together with optoelectronic properties. The high activity in both applications was related to the low band gap, that allows harvesting more energy from a polychromatic light source with respect to the bare TiO₂. Overall, high selectivity and productivity were achieved with respect to most literature data. Full article

(This article belongs to the Special Issue Feature Paper in Section Catalytic Materials)

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13 pages, 3890 KiB

Open AccessArticle

Organo-Nanocups Assist the Formation of Ultra-Small Palladium Nanoparticle Catalysts for Hydrogen Evolution Reaction

by Erik Biehler, Qui Quach, Clay Huff and Tarek M. Abdel-Fattah

Materials 2022, 15(7), 2692; https://doi.org/10.3390/ma15072692 - 6 Apr 2022

Cited by 8 | Viewed by 2437

Abstract

Ultra-small palladium nanoparticles were synthesized and applied as catalysts for a hydrogen evolution reaction. The palladium metal precursor was produced via beta-cyclodextrin as organo-nanocup (ONC) capping agent to produce ultra-small nanoparticles used in this study. The produced ~3 nm nanoparticle catalyst was then [...] Read more.

Ultra-small palladium nanoparticles were synthesized and applied as catalysts for a hydrogen evolution reaction. The palladium metal precursor was produced via beta-cyclodextrin as organo-nanocup (ONC) capping agent to produce ultra-small nanoparticles used in this study. The produced ~3 nm nanoparticle catalyst was then characterized via X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-Vis), and Fourier transform infrared spectroscopy (FTIR) to confirm the successful synthesis of ~3 nm palladium nanoparticles. The nanoparticles’ catalytic ability was explored via the hydrolysis reaction of sodium borohydride. The palladium nanoparticle catalyst performed best at 303 K at a pH of 7 with 925 μmol of sodium borohydride having an H₂ generation rate of 1.431 mL min⁻¹ mL_cat⁻¹. The activation energy of the palladium catalyst was calculated to be 58.9 kJ/mol. Full article

(This article belongs to the Special Issue Feature Paper in Section Catalytic Materials)

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11 pages, 2894 KiB

Open AccessEditor’s ChoiceArticle

Improved Methane Production by Photocatalytic CO₂ Conversion over Ag/In₂O₃/TiO₂ Heterojunctions

by Patricia Reñones, Fernando Fresno, Freddy E. Oropeza and Víctor A. de la Peña O’Shea

Materials 2022, 15(3), 843; https://doi.org/10.3390/ma15030843 - 22 Jan 2022

Cited by 7 | Viewed by 2935

Abstract

In this work, the role of In₂O₃ in a heterojunction with TiO₂ is studied as a way of increasing the photocatalytic activity for gas-phase CO₂ reduction using water as the electron donor and UV irradiation. Depending on the [...] Read more.

In this work, the role of In₂O₃ in a heterojunction with TiO₂ is studied as a way of increasing the photocatalytic activity for gas-phase CO₂ reduction using water as the electron donor and UV irradiation. Depending on the nature of the employed In₂O₃, different behaviors appear. Thus, with the high crystallite sizes of commercial In₂O₃, the activity is improved with respect to TiO₂, with modest improvements in the selectivity to methane. On the other hand, when In₂O₃ obtained in the laboratory, with low crystallite size, is employed, there is a further change in selectivity toward CH₄, even if the total conversion is lower than that obtained with TiO₂. The selectivity improvement in the heterojunctions is attributed to an enhancement in the charge transfer and separation with the presence of In₂O₃, more pronounced when smaller particles are used as in the case of laboratory-made In₂O₃, as confirmed by time-resolved fluorescence measurements. Ternary systems formed by these heterojunctions with silver nanoparticles reflect a drastic change in selectivity toward methane, confirming the role of silver as an electron collector that favors the charge transfer to the reaction medium. Full article

(This article belongs to the Special Issue Feature Paper in Section Catalytic Materials)

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18 pages, 20344 KiB

Open AccessArticle

Photocatalytic Degradation of 4,4′-Isopropylidenebis(2,6-dibromophenol) on Sulfur-Doped Nano TiO₂

by Joanna B. Kisała, Gerald Hörner, Adriana Barylyak, Dariusz Pogocki and Yaroslav Bobitski

Materials 2022, 15(1), 361; https://doi.org/10.3390/ma15010361 - 4 Jan 2022

Cited by 12 | Viewed by 2096

Abstract

In present work, we examine the photocatalytic properties of S-doped TiO₂ (S1, S2) compared to bare TiO₂ (S0) in present work. The photocatalytic tests were performed in alkaline aqueous solutions (pH = 10) of three differently substituted phenols (phenol (I), 4,4′-isopropylidenebisphenol [...] Read more.

In present work, we examine the photocatalytic properties of S-doped TiO₂ (S1, S2) compared to bare TiO₂ (S0) in present work. The photocatalytic tests were performed in alkaline aqueous solutions (pH = 10) of three differently substituted phenols (phenol (I), 4,4′-isopropylidenebisphenol (II), and 4,4′-isopropylidenebis(2,6-dibromophenol) (III)). The activity of the catalysts was evaluated by monitoring I, II, III degradation in the reaction mixture. The physicochemical properties (particle size, ζ-potential, E_bg, Eu, E⁰_cb, E⁰_vb, σ_o, K_L) of the catalysts were established, and we demonstrated their influence on degradation reaction kinetics. Substrate degradation rates are consistent with first-order kinetics. The apparent conversion constants of the tested compounds (k_app) in all cases reveal the sulfur-loaded catalyst S2 to show the best photocatalytic activity (for compound I and II S1 and S2 are similarly effective). The different efficiency of photocatalytic degradation I, II and III can be explained by the interactions between the catalyst and the substrate solution. The presence of bromine substituents in the benzene ring additionally allows reduction reactions. The yield of bromide ion release in the degradation reaction III corresponds to the Langmuir constant. The mixed oxidation-reduction degradation mechanism results in higher degradation efficiency. In general, the presence of sulfur atoms in the catalyst network improves the degradation efficiency, but too much sulfur is not desired for the reduction pathway. Full article

(This article belongs to the Special Issue Feature Paper in Section Catalytic Materials)

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15 pages, 2217 KiB

Open AccessEditor’s ChoiceArticle

Engineering Commercial TiO₂ Powder into Tailored Beads for Efficient Water Purification

by George V. Theodorakopoulos, Fotios K. Katsaros, Sergios K. Papageorgiou, Margarita Beazi-Katsioti and George Em. Romanos

Materials 2022, 15(1), 326; https://doi.org/10.3390/ma15010326 - 3 Jan 2022

Cited by 8 | Viewed by 2358

Abstract

In this study, efficient commercial photocatalyst (Degussa P25) nanoparticles were effectively dispersed and stabilized in alginate, a metal binding biopolymer. Taking advantage of alginate’s superior metal chelating properties, copper nanoparticle-decorated photocatalysts were developed after a pyrolytic or calcination-sintering procedure, yielding ceramic beads with [...] Read more.

In this study, efficient commercial photocatalyst (Degussa P25) nanoparticles were effectively dispersed and stabilized in alginate, a metal binding biopolymer. Taking advantage of alginate’s superior metal chelating properties, copper nanoparticle-decorated photocatalysts were developed after a pyrolytic or calcination-sintering procedure, yielding ceramic beads with enhanced photocatalytic and mechanical properties, excellent resistance to attrition, and optimized handling compared to powdered photocatalysts. The morphological and structural characteristics were studied using LN₂ porosimetry, SEM, and XRD. The abatement of an organic pollutant (Methyl Orange, MO) was explored in the dark and under UV irradiation via batch experiments. The final properties of the photocatalytic beads were defined by both the synthesis procedure and the heat treatment conditions, allowing for their further optimization. It was found that the pyrolytic carbon residuals enabled the adhesion of the TiO₂ nanoparticles, acting as binder, and increased the MO adsorption capacity, leading to increased local concentration in the photocatalyst vicinity. Well dispersed Cu nanoparticles were also found to enhance photocatalytic activity. The prepared photocatalysts exhibited increased MO adsorption capacity (up to 3.0 mg/g) and also high photocatalytic efficiency of about 50% MO removal from water solutions, reaching an overall MO rejection of about 80%, at short contact times (3 h). Finally, the prepared photocatalysts kept their efficiency for at least four successive photocatalytic cycles. Full article

(This article belongs to the Special Issue Feature Paper in Section Catalytic Materials)

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15 pages, 3500 KiB

Open AccessFeature PaperArticle

Platinum Nanoparticles Modified Copper/Titanium Electrodes as Electrocatalysts for Borohydride Oxidation

by Aldona Balčiūnaitė, Aušrinė Zabielaitė, Daina Upskuvienė, Loreta Tamašauskaitė-Tamašiūnaitė, Irena Stalnionienė, Leonas Naruškevičius, Jūratė Vaičiūnienė, Algirdas Selskis, Remigijus Juškėnas and Eugenijus Norkus

Materials 2021, 14(24), 7663; https://doi.org/10.3390/ma14247663 - 12 Dec 2021

Cited by 2 | Viewed by 2453

Abstract

In this study, sodium borohydride oxidation has been investigated on the platinum nanoparticles modified copper/titanium catalysts (PtNPsCu/Ti), which were fabricated by employing the electroless copper plating and galvanic displacement technique. ICP-OES, XRD, FESEM, and EDX have been used to characterize PtNPsCu/Ti catalysts’ composition, [...] Read more.

In this study, sodium borohydride oxidation has been investigated on the platinum nanoparticles modified copper/titanium catalysts (PtNPsCu/Ti), which were fabricated by employing the electroless copper plating and galvanic displacement technique. ICP-OES, XRD, FESEM, and EDX have been used to characterize PtNPsCu/Ti catalysts’ composition, structure, and surface morphology. The oxidation of sodium borohydride was examined on the PtNPsCu/Ti catalysts using cyclic voltammetry and chrono-techniques. Full article

(This article belongs to the Special Issue Feature Paper in Section Catalytic Materials)

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22 pages, 3314 KiB

Open AccessArticle

Ce-Containing MgAl-Layered Double Hydroxide-Graphene Oxide Hybrid Materials as Multifunctional Catalysts for Organic Transformations

by Alexandra-Elisabeta Stamate, Octavian Dumitru Pavel, Rodica Zăvoianu, Ioana Brezeştean, Alexandra Ciorȋță, Ruxandra Bȋrjega, Katja Neubauer, Angela Koeckritz and Ioan-Cezar Marcu

Materials 2021, 14(23), 7457; https://doi.org/10.3390/ma14237457 - 4 Dec 2021

Cited by 9 | Viewed by 3137

Abstract

The combination of layered double hydroxides (LDH) with graphene oxide (GO) enables the formation of nanohybrids with improved properties. This work focuses on the structural and catalytic properties of Ce-containing MgAl LDH-GO composites bearing different concentrations of GO in the range of 5–25 [...] Read more.

The combination of layered double hydroxides (LDH) with graphene oxide (GO) enables the formation of nanohybrids with improved properties. This work focuses on the structural and catalytic properties of Ce-containing MgAl LDH-GO composites bearing different concentrations of GO in the range of 5–25 wt.%. The synthesis of the composites was performed by co-precipitating the LDH phase in the presence of GO, while their characterization was performed using XRF, XRD, DRIFT, Raman, SEM, nitrogen adsorption-desorption, and acidity-basicity measurements. The LDH-GO composites, showing redox, basic, and acid catalytic functions, were tested in two different types of organic transformations: (i) Knoevenagel condensation and (ii) one-pot cascade oxidation-Knoevenagel condensation. (i) The cinnamic acid was synthesized by the Knoevenagel condensation of benzaldehyde with diethylmalonate. The composites showed catalytic performances in strong contrast to neat LDH or GO, suggesting a synergistic interaction between the two components. During Knoevenagel condensation, the catalytic activity increased with the GO content in the hybrids up to 15 wt.% and decreased afterwards. (ii) 2-Benzoyl-3-phenylacrylonitrile was synthesized by the aerobic oxidation of benzyl alcohol followed by the Knoevenagel condensation with benzoyl acetonitrile using three different non-polar solvents, i.e., toluene, benzene, and mesitylene. The conversion of benzyl alcohol was higher for the hybrid materials compared to the individual components but decreased with the increase of the graphene oxide concentration. Full article

(This article belongs to the Special Issue Feature Paper in Section Catalytic Materials)

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12 pages, 1382 KiB

Open AccessCommunication

Spherical Silica Modified with Magnesium and Ruthenium—Synthesis, Characterization and Catalytic Properties

by Kalina Grzelak and Maciej Trejda

Materials 2021, 14(23), 7378; https://doi.org/10.3390/ma14237378 - 2 Dec 2021

Cited by 1 | Viewed by 1909

Abstract

The design of different bimetallic catalysts is an important area of catalytic research in the context of their possible applications in the cascade processes, meeting the requirements of the so-called green chemistry. In this study, such catalysts were obtained by the incorporation of [...] Read more.

The design of different bimetallic catalysts is an important area of catalytic research in the context of their possible applications in the cascade processes, meeting the requirements of the so-called green chemistry. In this study, such catalysts were obtained by the incorporation of magnesium species into spherical silica, which was in the next step covered with porous silica and modified with ruthenium species. The structure and chemical composition of the materials obtained were determined by XRD measurements, low temperature N₂ adsorption/desorption, SEM, ICP-OES and XPS methods. The catalytic activities of materials obtained were tested in 2-propanol decomposition and hydrogenation of levulinic acid. The results obtained confirmed the successful coverage of nanospheres with porous silica. A much higher concentration of ruthenium species was found on the surface of the catalysts than in their bulk. The opposite relationship was observed for magnesium species. The modification of nanospheres with silica had a positive effect on the catalytic activity of the materials obtained. For the most active sample, i.e., Ru/NS/3Mg/NS, 49% of levulinic acid conversion in its hydrogenation process was reported with γ-valerolactone as the only product. Full article

(This article belongs to the Special Issue Feature Paper in Section Catalytic Materials)

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11 pages, 8175 KiB

Open AccessArticle

Towards Efficient Acidic Catalysts via Optimization of SO₃H-Organosilane Immobilization on SBA-15 under Increased Pressure: Potential Applications in Gas and Liquid Phase Reactions

by Maciej Trejda, Ada Kaszuba, Ardian Nurwita and Maria Ziolek

Materials 2021, 14(23), 7226; https://doi.org/10.3390/ma14237226 - 26 Nov 2021

Cited by 2 | Viewed by 1445

Abstract

In this paper, the optimization of the synthesis of catalysts based on acidic mesoporous silica of the SBA-15 type by post-synthesis immobilization of 3-(trihydroxysilyl)-1-propanesulfonic acid (TPS) under increased pressure up to 20 bar is reported. Sample structures and composition were examined by XRD [...] Read more.

In this paper, the optimization of the synthesis of catalysts based on acidic mesoporous silica of the SBA-15 type by post-synthesis immobilization of 3-(trihydroxysilyl)-1-propanesulfonic acid (TPS) under increased pressure up to 20 bar is reported. Sample structures and composition were examined by XRD measurement, low-temperature N₂ adsorption/desorption and elemental analysis. The catalytic activities of the materials obtained were determined in both gas and liquid phase processes, i.e., by esterification of acetic acid and glycerol dehydration, respectively. The optimum pressure for modification leading to the highest number of acidic sites was found to be 10 bar. The final material was very active and stable in liquid phase processes; however, the stability in the gas-phase process was unsatisfactory due to the loss of sulphonic species from the catalyst surface. Full article

(This article belongs to the Special Issue Feature Paper in Section Catalytic Materials)

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22 pages, 2280 KiB

Open AccessFeature PaperArticle

Adsorption and Oxidation of CO on Ceria Nanoparticles Exposing Single-Atom Pd and Ag: A DFT Modelling

by Vladimir A. Nasluzov, Elena A. Ivanova-Shor, Aleksey M. Shor, Svetlana S. Laletina and Konstantin M. Neyman

Materials 2021, 14(22), 6888; https://doi.org/10.3390/ma14226888 - 15 Nov 2021

Cited by 4 | Viewed by 2408

Abstract

Various CO_x species formed upon the adsorption and oxidation of CO on palladium and silver single atoms supported on a model ceria nanoparticle (NP) have been studied using density functional calculations. For both metals M, the ceria-supported MCO_x moieties are found [...] Read more.

Various CO_x species formed upon the adsorption and oxidation of CO on palladium and silver single atoms supported on a model ceria nanoparticle (NP) have been studied using density functional calculations. For both metals M, the ceria-supported MCO_x moieties are found to be stabilised in the order MCO < MCO₂ < MCO₃, similar to the trend for CO_x species adsorbed on M-free ceria NP. Nevertheless, the characteristics of the palladium and silver intermediates are different. Very weak CO adsorption and the small exothermicity of the CO to CO₂ transformation are found for O₄Pd site of the Pd/Ce₂₁O₄₂ model featuring a square-planar coordination of the Pd²⁺ cation. The removal of one O atom and formation of the O₃Pd site resulted in a notable strengthening of CO adsorption and increased the exothermicity of the CO to CO₂ reaction. For the analogous ceria models with atomic Ag instead of atomic Pd, these two energies became twice as small in magnitude and basically independent of the presence of an O vacancy near the Ag atom. CO₂-species are strongly bound in palladium carboxylate complexes, whereas the CO₂ molecule easily desorbs from oxide-supported AgCO₂ moieties. Opposite to metal-free ceria particle, the formation of neither PdCO₃ nor AgCO₃ carbonate intermediates before CO₂ desorption is predicted. Overall, CO oxidation is concluded to be more favourable at Ag centres atomically dispersed on ceria nanostructures than at the corresponding Pd centres. Calculated vibrational fingerprints of surface CO_x moieties allow us to distinguish between CO adsorption on bare ceria NP (blue frequency shifts) and ceria-supported metal atoms (red frequency shifts). However, discrimination between the CO₂ and CO₃²⁻ species anchored to M-containing and bare ceria particles based solely on vibrational spectroscopy seems problematic. This computational modelling study provides guidance for the knowledge-driven design of more efficient ceria-based single-atom catalysts for the environmentally important CO oxidation reaction. Full article

(This article belongs to the Special Issue Feature Paper in Section Catalytic Materials)

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7 pages, 2004 KiB

Open AccessCommunication

Enhancement of Catalytic Activity and Stability of La_0.6Ca_0.4Fe_0.7Ni_0.3O_2.9 Perovskite with ppm Concentration of Fe in the Electrolyte for the Oxygen Evolution Reaction

by Sergei V. Porokhin, Victoria A. Nikitina and Artem M. Abakumov

Materials 2021, 14(21), 6403; https://doi.org/10.3390/ma14216403 - 26 Oct 2021

Viewed by 1884

Abstract

The catalytic activity and stability of an iron-nickel based oxygen-deficient perovskite for the oxygen evolution reaction (OER) are drastically improved with the ppm additive of Fe ions to the alkaline electrolyte. The enhancement is attributed to a 1–2 nm restructured Ni_0.5Fe [...] Read more.

The catalytic activity and stability of an iron-nickel based oxygen-deficient perovskite for the oxygen evolution reaction (OER) are drastically improved with the ppm additive of Fe ions to the alkaline electrolyte. The enhancement is attributed to a 1–2 nm restructured Ni_0.5Fe_0.5O_x(OH)_2-x (oxy)hydroxide layer, as demonstrated with scanning transmission electron microscopy. La_0.6Ca_0.4Fe_0.7Ni_0.3O_2.9 shows almost a four-fold increase in OER activity after Fe addition relative to the as-prepared pristine electrolyte, which demonstrates the low Tafel slope of 44 ± 2.4 mV dec⁻¹ and the superior intrinsic activity of 706 ± 71 A g⁻¹_oxide at 1.61 V vs. RHE. Full article

(This article belongs to the Special Issue Feature Paper in Section Catalytic Materials)

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20 pages, 4200 KiB

Open AccessArticle

Enzymatic Activity and Physicochemical Properties of Soil Profiles of Luvisols

by Anna Piotrowska-Długosz, Mirosław Kobierski and Jacek Długosz

Materials 2021, 14(21), 6364; https://doi.org/10.3390/ma14216364 - 24 Oct 2021

Cited by 27 | Viewed by 2617

Abstract

Most studies on soil enzymes are focused on the upper horizons of the soil profile, even though they transform the soil organic matter at every depth of the soil profile. The aim of this work was to investigate the distribution of β-glucosidase (GLU), [...] Read more.

Most studies on soil enzymes are focused on the upper horizons of the soil profile, even though they transform the soil organic matter at every depth of the soil profile. The aim of this work was to investigate the distribution of β-glucosidase (GLU), nitrate reductase (NR), urease (UR), phosphatase (PHA), dehydrogenase (DHA) and catalase (CAT) activity through 14 trunked soil profiles of the Luvisols formed from a glacial till. The content of microbial biomass carbon (MBC) as well as physicochemical properties such as organic carbon (C_ORG), total nitrogen (N_TOT), available P, K and Mg, soil density and porosity, pH in KCl and fractional composition were also studied. In general, enzymatic activity was highest in the top 30 cm layer of the profiles and decreased progressively towards the deeper horizons. The exceptions were the NR activity, which was active only in the Ap horizon and whose activity decreased sharply to nearly zero in the Bt horizon and parent rock, and the PHA activity, which was highly active even in the parent rock depth. The decreased availability of carbon and nutrients was the main driver of decreases in microbial abundance and enzymatic activity with depth. The enzymatic activity, when expressed on a C_ORG and MBC basis, behaves differently compared to the activity expressed on a soil mass basis. The activity decreased (NR), increased (PHA, UR), showed no clear pattern (GLU) or the changes were not significant (DHA, CAT). The content of C_ORG, N_TOT, K and P_AVAIL generally decreased with depth, while for Mg, there was no clear direction in the profile distribution. Future studies to characterize the substrate distribution within the soil profile and enzyme stability will provide further insight into the controls on nutrient cycling and related enzymes throughout the soil profiles. Full article

(This article belongs to the Special Issue Feature Paper in Section Catalytic Materials)

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19 pages, 3330 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

One-Pot Synthesis of TiO₂-rGO Photocatalysts for the Degradation of Groundwater Pollutants

by Stefano Andrea Balsamo, Roberto Fiorenza, Marcello Condorelli, Roberta Pecoraro, Maria Violetta Brundo, Francesca Lo Presti and Salvatore Sciré

Materials 2021, 14(20), 5938; https://doi.org/10.3390/ma14205938 - 10 Oct 2021

Cited by 16 | Viewed by 2882

Abstract

A non-conventional approach to prepare titanium dioxide-reduced graphene oxide (TiO₂-rGO) nanocomposites based on solar photoreduction is here presented. The standard hydro-solvothermal synthesis of the TiO₂-rGO composites requires high temperatures and several steps, whereas the proposed one-pot preparation allows one [...] Read more.

A non-conventional approach to prepare titanium dioxide-reduced graphene oxide (TiO₂-rGO) nanocomposites based on solar photoreduction is here presented. The standard hydro-solvothermal synthesis of the TiO₂-rGO composites requires high temperatures and several steps, whereas the proposed one-pot preparation allows one to obtain the photocatalysts with a simple and green procedure, by exploiting the photocatalytic properties of titania activated by the solar irradiation. The TiO₂-rGO catalysts were tested in the solar photodegradation of a widely adopted toxic herbicide (2,4-Dichlorophenoxyacetic acid, 2,4-D), obtaining the 97% of degradation after 3 h of irradiation. The as-prepared TiO₂-rGO composites were more active compared to the same photocatalysts prepared through the conventional thermal route. The structural, optical, and textural properties of the composites, determined by Raman, Photoluminescence, Fourier Transform InfraRed (FTIR), UV-vis diffuse reflectance (DRS) spectroscopies, and N₂ absorption-desorption measurements, showed as the solar irradiation favors the reduction of graphene oxide with higher efficiency compared to the thermal-driven synthesis. Furthermore, the possible toxicity of the as-synthesized composites was measured exposing nauplii of microcrustacean Artemia sp. to solutions containing TiO₂-rGO. The good results in the 2,4-D degradation process and the easiness of the TiO₂-rGO synthesis allow to consider the proposed approach a promising strategy to obtain performing photocatalysts. Full article

(This article belongs to the Special Issue Feature Paper in Section Catalytic Materials)

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19 pages, 3993 KiB

Open AccessArticle

Vanadia–Zirconia and Vanadia–Hafnia Catalysts for Utilization of Volatile Organic Compound Emissions

by Satu Ojala, Tiina Laitinen, Sian Leneuf de Neufville, Mari Honkanen, Minnamari Vippola, Mika Huuhtanen and Riitta L. Keiski

Materials 2021, 14(18), 5265; https://doi.org/10.3390/ma14185265 - 13 Sep 2021

Cited by 3 | Viewed by 1804

Abstract

Utilization is a sustainable and interesting alternative for the destructive treatment of volatile organic compounds due to avoided CO₂ emission. This work concentrates on the development of active and sulfur-tolerant catalysts for the utilization of contaminated methanol. Impregnated and sol–gel prepared vanadia–zirconia [...] Read more.

Utilization is a sustainable and interesting alternative for the destructive treatment of volatile organic compounds due to avoided CO₂ emission. This work concentrates on the development of active and sulfur-tolerant catalysts for the utilization of contaminated methanol. Impregnated and sol–gel prepared vanadia–zirconia and vanadia–hafnia catalysts were thoroughly characterized by N₂ sorption, analytical (S)TEM, elemental analysis, XRD and Raman spectroscopy, and their performances were evaluated in formaldehyde production from methanol and methanethiol mixture. The results showed higher activity of the sol–gel prepared catalysts due to formation of mono- and polymeric vanadia species. Unfortunately, the most active vanadia sites were deactivated more easily than the metal-mixed oxide HfV₂O₇ and ZrV₂O₇ phases, as well as crystalline V₂O₅ observed in the impregnated catalysts. Metal-mixed oxide phases were formed in impregnated catalysts through formation of defects in HfO₂ and ZrO₂ structure during calcination at 600 °C, which was evidenced by Raman spectroscopy. The sol–gel prepared vanadia–zirconia and vanadia–hafnia catalysts were able to produce formaldehyde from contaminated methanol with high selectivity at temperature around 400 °C, while impregnated catalysts required 50–100 °C higher temperatures. Full article

(This article belongs to the Special Issue Feature Paper in Section Catalytic Materials)

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9 pages, 4613 KiB

Open AccessArticle

Irradiance-Controlled Photoassisted Synthesis of Sub-Nanometre Sized Ruthenium Nanoparticles as Co-Catalyst for TiO₂ in Photocatalytic Reactions

by Patricia García-Muñoz, Fernando Fresno, Javier Ivanez and Nicolas Keller

Materials 2021, 14(17), 4799; https://doi.org/10.3390/ma14174799 - 24 Aug 2021

Cited by 1 | Viewed by 1960

Abstract

Photoassisted synthesis is as a highly appealing green procedure for controlled decoration of semiconductor catalysts with co-catalyst nanoparticles, which can be carried out without the concourse of elevated temperatures, external chemical reducing agents or applied bias potential and in a simple slurry reactor. [...] Read more.

Photoassisted synthesis is as a highly appealing green procedure for controlled decoration of semiconductor catalysts with co-catalyst nanoparticles, which can be carried out without the concourse of elevated temperatures, external chemical reducing agents or applied bias potential and in a simple slurry reactor. The aim of this study is to evaluate the control that such a photoassisted method can exert on the properties of ruthenium nanoparticles supported on TiO₂ by means of the variation of the incident irradiance and hence of the photodeposition rate. For that purpose, different Ru/TiO₂ systems with the same metal load have been prepared under varying irradiance and characterized by means of elemental analysis, transmission electron microscopy and X-ray photoelectron spectroscopy. The photocatalytic activity of the so-obtained materials has been evaluated by using the degradation of formic acid in water under UV-A light. Particles with size around or below one nanometer were obtained, depending on the irradiance employed in the synthesis, with narrow size distribution and homogeneous dispersion over the titania support. The relation between neutral and positive oxidation states of ruthenium could also be controlled by the variation of the irradiance. The obtained photocatalytic activities for formic acid oxidation were in all cases higher than that of undecorated titania, with the sample obtained with the lowest irradiation giving rise to the highest oxidation rate. According to the catalysts characterization, photocatalytic activity is influenced by both Ru size and Ru⁰/Ru^δ+ ratio. Full article

(This article belongs to the Special Issue Feature Paper in Section Catalytic Materials)

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