Powder Catalysts Research Articles

Photocatalytic activity of Co3O4@C enhanced by induction of amorphous cobalt-based MOF

A series of Co3O4@C-N (N = 1, 2, 3) composite photocatalysts were prepared by simple agitation and pyrolysis for degradation of organic dyes. The hollow macroscopic spherical structure of Co3O4@C-2 was constructed by adjusting the pyrolysis time. Compared with pure Co3O4, the carbon composite Co3O4@C-2 significantly enhanced light absorption in the UV and visible range, improved the electron transport efficiency and prevented the necessary photoexcited electron-hole pair recombination. Hence, the photocatalytic degradation rate of methylene blue (MB, 20 mg/L) reached 100% in 120 min under UV–vis light irradiation. Under the coupling of Co3O4 and graphitized carbon, Co3O4@C-2 obtained high structural stability, good reusability and low biotoxicity. Scavenging experiments and ESR test showed that •O2- radical was the active species for MB removal. After six cycles of tests, the photocatalytic efficiency of Co3O4@C-2 remained at 90.42%. The macroscopic spherical structure Co3O4@C-2 effectively avoids the problem of dispersion and recovery of powder catalyst, which also paves a path for the designing of candidate commercial photocatalyst with high efficiency and low consumption.

Vegetable Oil Hydrogenation over Pt Monolithic and Powder Catalysts: Experimental and Modeling Study

AbstractA complete kinetic study was performed for the hydrogenation of vegetable oil using a powder and a monolithic Pt catalyst. The experimental studies were carried out at a wide interval of H2 pressure, temperature, and catalyst loading using Pt/γ‐Al2O3 powder catalyst in a slurry reactor and Pt/Al2O3/Al‐structured catalyst in a monolithic stirrer reactor. The mathematical model for the reactors includes the hydrogenation and isomerization reactions, the external gas‐liquid and liquid‐solid mass transfer as well as the internal mass transfer. Four kinetic models were evaluated for both catalysts. The best fit of the experimental data was obtained by adopting a Langmuir‐Hinshelwood kinetic model for the liquid reactant and a dissociative adsorption and zero‐order reaction for H2.

Powdered MnySb1–yOx Catalysts for Cerium-Mediated Oxygen Evolution in Acidic Environments

MnySb1–yOx powders with a series of compositions were evaluated as catalysts for chemical water oxidation in aqueous perchloric, sulfuric, or methanesulfonic acid. O2(g) evolved spontaneously over MnySb1–yOx catalyst powders that had been suspended in solutions that were pre-loaded with Ce4+ ions. The rate of O2 evolution depended on the amount, as well as the oxidation state, of the Mn in the powder. The highest O2 evolution rate was observed from the most Mn-rich catalyst, which had an effective surface oxidation state of Mn2.9+ in its rest state. The facile synthetic accessibility of such catalysts in powder form constitutes a step toward replacing Ir or Ru in Ce-mediated oxygen evolution in decoupled water splitting systems, as well as toward developing inks of earth-abundant catalysts for preparation of catalyst-coated membranes used in conventional proton-exchange membrane electrolyzers.

Enhanced photoelectrochemical degradation of toxic tetracycline by Au nanoparticles modified Co doped Fe2O3 electrode under mild conditions

• Novel Au modified Co doped Fe 2 O 3 photoelectrode was designed and synthesized. • Doping Co and surface Au reduced pairs recombination and promoted conductivity. • This photoelectrode showed good activity and reusability to tetracycline degradation. • Generated hydroxyl and superoxide radical played critical roles to the degradation. The accumulation of Tetracycline (TCH) in water damages the ecosystem and endanger human health. Although traditional Fenton reactions can degrade the antibiotics effectively, introduced strong oxidants and irrecoverable catalyst powders during the catalytic process bring new environmental problems. In this paper, novel Au nanoparticles modified Co doped Fe 2 O 3 (Au/Co:Fe 2 O 3 ) composited electrodes were prepared for the photoelectrochemical degradation of TCH under mild conditions. Due to the significantly reduced recombination of photogenerated electron-hole pairs and promoted electrical conductivity, Au/Co:Fe 2 O 3 electrode exhibited removal efficiency of 75 % for 180 min without any additional oxidants at low potential. Moreover, the Au/Co:Fe 2 O 3 also showed excellent reusability and long-term stability. Under light irradiation, generated O 2 − and OH species played critical roles in the degradation of TCH.

Adsorption and in-situ photocatalytic Fenton multifield coupled degradation of organic pollutants and coking wastewater via Fe[sbnd]BiOBr modification of three-dimensional graphene aerogel

Both adsorption and advanced oxidation processes can achieve rapid removal of organic pollutants. Based on this, FeBiOBr was modified on the surface of three-dimensional graphene aerogel (3D rGA) to construct FeBiOBr/rGA composites. Using the surface adsorption properties of graphene to quickly adsorb pollutants, combined with photocatalytic Fenton degradation by FeBiOBr catalysts, the adsorption and in-situ photocatalytic Fenton multifield coupled degradation system was constructed by the consistency of adsorption and catalytic degradation sites. Experimental results showed that FeBiOBr/rGA has a 2.92-fold increase in the adsorption capacity for phenol compared with bulk rGA. Meanwhile, the degradation rate constant was 2.7 times higher than that of FeBiOBr because of the excellent electrical conductivity of graphene. In addition, it also exhibited excellent COD and TOC removal performance for different phenolic and coking wastewaters. The effects of graphene content, catalyst dosage, H2O2 concentration and other factors on the adsorption-catalytic degradation activity of the synergistic system were further investigated. Based on the influence of active species, the mechanism of FeBiOBr/rGA composite adsorption and in-situ catalytic degradation multifield coupling removal of pollutants was proposed. In addition, the 3D rGA could effectively solve the problem of difficult recycling of powder catalysts and has significant practical application potential.

Relating extrusion as a method of bifunctional catalysts synthesis and their catalytic performance

Although catalyst shaping by extrusion has been industrially applied for decades to suppress the pressure drop, much less emphasis was put on fundamental understanding of extrusion for catalytic pastes and its effect on the properties of the final catalyst bodies. During recent years intensive research efforts have been put on synthesis of extrudates by systematically varying different synthesis parameters, methods of metal modifications, different types of binders and correlating extrudate properties with their performance in several catalytic reactions. The synthesis method of extrudates can have a large impact on properties, relevant for catalysis, including acidity/basicity, the metal location and the particle size as well as textural properties, which can differ from the properties of the corresponding powder catalysts. Furthermore, a binder can interact with the support changing physico-chemical and catalytic properties. The current review summarizes recent developments related to shaping of catalysts by extrusion addressing also such advanced methods to investigate diffusion of liquid reactants inside the extrudates and interconnectivity of pores, as pulse gradient field NMR spectroscopy and fluorescent probe analysis respectively.

Monolith or Powder: Improper Sample Pretreatment May Mislead the Understanding of Industrial V2O5-WO3/TiO2 Catalysts Operated in Stationary Resources.

Although various characterizations are widely applied to commercial V2O5-WO3/TiO2 catalysts, the influence of the catalyst physical structure, i.e., monolith or powder, on the characterization results has not been investigated. Several important catalytic behaviors and phenomena were observed in this study using V2O5-WO3/TiO2 monolithic catalysts employed for over 5000 h in various stationary flue gases, and many of the results were only observable on monolithic catalysts, such as depth-dependent distribution of external elements, penetration of As2O3, and the formation of Tl2O-TiO2 p-n junctions. If the monolith is ground into powder states, it will alter or destroy the catalyst surface and remove important clues closely related to catalytic performance under working conditions. The redox and acidity properties of V2O5-WO3/TiO2 obtained from powder samples may be significantly different from their true state under working conditions, resulting in a misperception of catalyst performance. Therefore, a cautious pretreatment should be taken into careful consideration when analyzing commercial honeycomb V2O5-WO3/TiO2 catalysts.

Catalytic debromination of waste brominated resin by co-pyrolysis with Pd-containing spent automotive catalysts

A "treating the wastes with wastes" approach was provided in this study, where spent automotive catalysts were added into waste brominated resin for debromination by co-pyrolysis. Spent automotive catalyst in this study was the Pd-only ternary automotive catalyst and the content of Pd was 493.89 μmol/kg. The proportions of Pd(0) and Pd(Ⅱ) in spent automotive catalyst were 86.37% and 13.63%, respectively. Wrapped Pd invalidated the catalytic effect of automotive catalyst. The debromination rate of brominated resin could be increased from 12.73% to 66.86% after co-pyrolysis with spent automotive catalyst powder at 260°C. The catalytic debromination of Pd on brominated resin relied on the oxidative addition and decomposition reactions. Aryl bromides in 2,2′,4,4′-tetrabromodiphenyl ether would be attacked by Pd in turn according to the higher positive charge. This work contributes scientific information and approach to the reuse of spent automotive catalysts and the safe disposal of brominated resin together.

Graphitic carbon nitride thin films for light-induced photocatalysis in a slit geometry microreactor

A combination of a photocatalysis and a micro-flow technology provides a highly capable tool for the design and utilisation of functional thin films. Here, they are represented by graphitic carbon nitride films, potentially used for photo-oxidations in environmental chemistry or for hydrogen evolution by water splitting. The optimised synthesis involves a study of the role of monomers, solvents, calcination temperatures, particle size, etc., in respect of the achieved photocatalytic activity. Films were prepared from the mixture of milled powder catalysts and a binder, dried, and subjected to post-processing treatments (post annealing, plasma application). The intended functionality was assessed in two types of reactions, photo-oxidation of a fluorescent dye, Rhodamine B, and photo-oxidation of a common antibiotic, Tetracycline. The performance was compared for the bulk catalyst, and for the thin film. In either case, the same part of light spectrum, concentrations, and other conditions were applied. However, for the thin films, a special experimental setup was utilised. It had the appearance of a micro-flow apparatus designed as a slit geometry photo-microreactor. Comparison of the two different reaction systems revealed the advantages of the thin film catalyst, which was immobilised directly on the photo-microreactor wall. The specific rate constant was more than 50 times higher in this arrangement for both model reactants. In addition, thin films of g-C3N4 were stable and well adherent during the microreactor tests with the repetitive reaction cycles. Plasma treatment considerably increased the hydrophilicity of the dried thin films, which resulted in their substantially higher photoactivity.

Design order macro-meso porous structure monolithic Co3O4/SiO2 catalyst via a novel 3D printing for the highly efficient catalytic combustion of toluene

The shortcomings of Co-based powder catalysts such as amorphous susceptibility to loss and high influence by pressure drop have become the key factors affecting their catalytic activity. In this paper, two methods were proposed to prepare novel monolithic Co3O4/SiO2 catalysts by 3D direct ink writing (DIW) technology: (1) one-step method of printing the active component with supports, (2) two-step method of printing the support first, and then loading the active components. The results showed that the monolithic catalyst prepared by the two-step method possessed more abundant Co3+ and lattice oxygen (Olatt) species than the one-step method, which jointly promoted the catalytic conversion of toluene. However, the catalyst printed by the one-step method had a stronger interaction between the active component and the support, showing better thermal stability and water resistance. In addition, the SiO2 support (the calcined product after SiO2 ink printing) enhances the activity, stability, compression resistance, while the N–SiO2 support (the calcined product after SiO2 precursor ink printing) can effectively prevent blockage of the pore structure by the binder and increase physical properties such as pore volume and specific surface area of Co3O4/SiO2 catalyst.

Using Atomic Layer Deposition (ALD) to Immobilize Molecular Catalysts on Solid Powder Supports

While homogeneous molecular catalysts are valued for their high reaction specificity, they are not as easily recoverable at industrial scales as heterogeneous catalyst powders that can be rapidly separated from the reaction solution. Here, we will discuss a new approach using atomic layer deposition (ALD) to immobilize molecular catalysts onto heterogeneous powder supports to achieve this combination of selectivity and recoverability. In this presentation, we demonstrate applicability using a non-noble metal (nickel) molecular catalyst to do Suzuki carbon-carbon cross-coupling reactions. Due to extremely short catalyst lifetimes caused by dimerization, this catalyst exhibits limited catalytic reactivity under homogeneous conditions. However, when heterogenized and immobilized, product yields of over 90% can be achieved in aqueous conditions, and the catalytic activity is preserved through over five hundred recovery and wash cycles. Following this work, we will also report on how modification of the ALD surface chemistry and number of ALD cycles affect catalytic performance.

(Invited) Bipolar Membranes with a 3D Junction of Interlocking Electrospun Fibers

Bipolar membranes (BPMs), typically laminated layers of anion-exchange and cation-exchange polymers, have the unique capability of splitting water at a potential near 0.83 V. Such membranes are used in electrodialysis membrane separation processes. They also have applications in water electrolyzers, CO2 electrolysis cells, and self-humidifying fuel cells. We report here on recent developments regarding BPMs with a high interfacial area, 3D nanofiber junction.Membranes were prepared by first creating a bipolar junction layer, by the simultaneous electrospinning of anion-exchange and cation-exchange polymers, with the addition of catalyst nanoparticles to facilitate water splitting. Solvent vapor exposure and hot-pressing closed all interfiber pores, to create a dense film of interpenetrating and interlocking nanofibers of positively and negatively charged polymers. In one fabrication method, dense films of solution cast anion and cation-exchange polymers were hot-pressed onto the opposing surfaces of the junction layer to create a tri-layer BPM. Membranes were also fabricated by electrospinning all three layers of the BPM: first spinning anion-exchange fibers, followed by dual fiber spinning with catalyst spraying, and then spinning only cation-exchange fibers. Solvent exposure and hot-pressing closed all interfiber voids.BPMs were made with a junction layer 12-15 mm thick, where the total membrane thickness was 50-80 mm. Membranes were prepared with both hydrocarbon and fluoropolymer ionomers, e.g., sulfonated poly(ether ether ketone) or perfluorosulfonic acid as the cation-exchange polymer and either quaternized poly(phenylene oxide), AEMIONä (an imidazolium-based polymer sold by Ionomr Innovations, Inc.), or PiperION (a poly(aryl piperidinium) from Versogen) as the anion-exchange polymer. A variety of different junction layer catalysts powders were examined, including Al(OH)3 and graphene oxide. Membranes were evaluated in an H-cell for the collection of steady-state current-voltage data and in a flow cell for long-term constant current water splitting (electrolysis) operation, typically with an aqueous Na2SO4 electrolyte. The 3D junction membranes performed exceptionally well: (i) the water splitting potential was low (near the expected value of 0.83 V), (ii) the transmembrane voltage drop was small at high currents (e.g., a voltage drop of 1.1 V up to 1.1 A/cm2), and (iii) the extended bipolar reaction zone for water splitting with interlocking fibers allowed for high current density operation with no evidence of membrane degradation.In this talk, the effect of membrane composition (the type/amount of anion and cation exchange polymers and choice of catalyst) and structure (the thickness of the layers) on short-term and long-term membrane performance will be discussed. Results will be presented for operating the bipolar membrane in water splitting and water generation modes.

Simultaneous hypercrosslinking and functionalization of polyHIPEs for use as coarse powder catalyst supports

Porous polymers offer desirable properties for heterogeneous catalysis, such as excellent stability, high active site density, and reusability. However, their synthesis is often complicated, requiring expensive reagents and laborious synthetic processes. We produce organophosphorus functionalized polyHIPEs by the polymerization of particle and surfactant stabilized water-in-styrene/divinylbenzene high internal phase emulsion templates, followed by post-functionalization using low-cost hypercrosslinking strategies. Three hypercrosslinking approaches were investigated, including knitting with an external crosslinker, solvent stitching and Scholl coupling reaction. Each approach’s ability to simultaneously create micro/mesoporosity and incorporate organophosphorus moieties into the polyHIPE structure as catalyst anchor sites were assessed, introducing surface areas of up to 410 m2/g and phosphorus concentrations of up to 7.4 wt%. After Pd-loading, the polyHIPEs displayed outstanding catalytic performance in a Suzuki-Miyaura coupling reaction, reaching turnover frequencies of 5722 h−1. The coarse powder form of the polyHIPEs allowed for simple catalyst recovery from the reaction mixture for reuse.

Tailoring soft-flexible negative Poisson's ratio support to boost photocatalytic efficiency: From dissociation to anchoring

Highly efficient catalysts have been developed and obtained excellent performance in the laboratory environment. However, there is a huge gap between the laboratory and industry. The high request of recyclability and stability determine that the traditional powder catalyst cannot be directly applied. On the other hand, catalyst anchoring is a promising strategy to solve this problem. Here, novel flexible supports with different negative Poisson's ratios (NPR) were fabricated to obtain enhanced photocatalytic and mechanical property by 3D printing, and were furtherly modified by Ag nanowires, TiO 2 and metallization. The largest specific surface area is up to 2.66 m 2 g −1 which is because of the relatively smooth surface of the support. The NPR support modified by TiO 2 completely degraded the dye solution within 75 min, resulting from the improved site for CdS to load. Part of the TiO 2 formed heterojunction with CdS, but the content was too small to significantly enhance the transfer of electron-hole pairs. After ten cycles, the residual catalytic performance remained 71.25%− 75.32%, which is mainly from the weak binding of CdS. The mechanical properties were significantly improved by adding TiO 2 by almost 4 times than that of pure Polyurethaneacrylate (PUA), resulting from the pinning effect from the nano particles. The proposed strategy offers new perspectivity of coupling delicately efficient photocatalyst and flexible support for the large-scale industrial application.

Magnetically recyclable MXene derived N-doped TiO2@C@Fe3O4 nanosheets for enhanced degradation of organic pollutants via photo-Fenton

We synthesized the magnetic recyclable Ti3C2 derived N-TiO2@C@Fe3O4 for photo-Fenton degradation of organic pollutants through high-temperature calcination and solvothermal methods. Ti3C2 was first calcined into TiO2@C with a homogeneous titanium source and a two-dimensional carbon framework. Then the magnetic nanoparticles (Fe3O4) were loaded by solvothermal method, which effectively solved the problem of repeated circulation of powder catalysts. N-TiO2@C@Fe3O4 could be used as an excellent co-catalyst to improve the decomposition efficiency of H2O2 in advanced oxidation processes (AOPs). This significantly reduced the amount of H2O2 and Fe2+ in the photo-Fenton system. The N-TiO2@C@Fe3O4 photo-Fenton system could degrade 96.5% of Rhodamine B (RhB) within 300 s and maintain a recycling rate of more than 90% after 10 cycles. This system also had favorable applicability to the same wastewater of antibiotics. This mechanism was proposed that the N-TiO2@C@Fe3O4 photo-Fenton system activated H2O2 to generate hydroxyl radicals (·OH) and superoxide radicals (·O2−) to further attack RhB. This research provided novel insights for the photo-Fenton collaborative catalytic system to achieve advanced oxidation treatment of pollutants in the water environment.

A low-cost and eco-friendly powder catalyst: Iron and copper nanoparticles supported on biochar/geopolymer for activating potassium peroxymonosulfate to degrade naphthalene in water and soil.

A low-cost and environment-friendly biochar/geopolymer composite loaded with Fe and Cu nanoparticles (Fe-Cu@BC-GM) was prepared by impregnation-calcination using lignin and kaolin as precursors. SEM, FTIR and XRD analysis suggested that the Fe-Cu@BC-GM had a certain pore structure, rich functional groups and stable crystal structure. The obtained Fe-Cu@BC-GM was used as the catalyst of potassium peroxymonosulfate (PMS) for remediation of wastewater and soil polluted by naphthalene (NAP). Experimental results indicated that Fe-Cu@BC-GM exhibited outstanding catalytic performance, and the maximum degradation rate of NAP in water and soil reached 98.35% and 67.98% within 120min, respectively. The XPS measurement confirmed the presence of successive Fe (Ⅲ)/Fe (Ⅱ) and Cu(Ⅱ)/Cu(Ⅰ) redox pairs cycles on the surface of Fe-Cu@BC-GM, which made Fe (Ⅲ) and Cu(Ⅰ) continuously generated Fe (Ⅱ) activating PMS to produce SO4·- and ·OH for the degradation of NAP. The effects of Fe-Cu@BC-GM/PMS system on plant toxicity were evaluated by analyzing the degradation intermediates and bioassay of mung bean. It was proved that the Fe-Cu@BC-GM/PMS system could degrade NAP into less toxic intermediates, and the seed germination rate, root and stem length of mung bean after soil remediation were not notably different from those of the uncontaminated soil. This work opened new prospect for the application of geopolymer in degradation of persistent organic pollutants (POPs) and provided a cost-effective option for the remediation of the persistent organic pollutants contaminated water and soil.

The Photocatalytic Oxidation Ability of Rb0.9Nb1.625Mo0.375O5.62 with Classic β‐Pyrochlore Structure

AbstractPreviously the non‐cubic β‐pyrochlore polycrystalline compounds Rb0.95NbxMo2‐xO6.475‐0.5x (x=1.31–1.663) have been obtained in the ternary system Rb2O‐Nb2O5‐2MoO3. However, using special synthesis condition leads to the formation of cubic Fd‐3m β‐pyrochlore Rb0.9Nb1.625Mo0.375O5.62 with small size particles and surface area of 15 m2/g. The Rb0.9Nb1.625Mo0.375O5.62 powder has been investigated by X‐ray powder diffraction analysis and scanning electron microscopy with X‐ray microanalysis. The crystal structure refinement has been performed using the Rietveld method. The electronic structure and optical band gap of Rb0.9Nb1.625Mo0.375O5.62 have been studied in comparison to similar non‐cubic composition Rb0.95Nb1.625Mo0.375O5.66. The photocatalytic properties of Rb0.9Nb1.625Mo0.375O5.62 have been investigated on the example for dyes solution oxidation under UV irradiation. The dependence on the photocatalytic properties of dye type and catalyst mass has been studied. It has been observed that the main oxidative species for dye oxidation is hydroxyl radicals. The phase and composition stability of catalyst powder have been confirmed.

Anti-oil-fouling Au/BiOCl coating for visible light-driven photocatalytic inactivation of bacteria

In this work, gold/bismuth oxychloride (Au/BiOCl) nanocomposites with different morphologies were successfully prepared by simple solvothermal method and sodium borohydride reduction method, which exhibited significantly efficient visible-light-driven photocatalytic disinfection for Staphylococcus aureus (S.aureus). Particularly, the flower-like Au/BiOCl nanocomposite showed the highest photocatalytic bactericidal performance among the prepared Au/BiOCl samples. The radical trapping experiments revealed that the hole was the main reactive species responsible for the inactivation of S.aureus over Au/BiOCl composite. The enhanced photocatalytic bactericidal effect could be attributed to the enhanced adsorption intensity of visible light that originated from the surface plasmon resonance (SPR) effect of Au, rapid transfer and space transport of hot electrons caused by the hierarchical structure of BiOCl layered compound. Furthermore, the Au/BiOCl coating prepared on stainless steel wire mesh via in-situ synthesis method exhibited excellent superhydrophilic/underwater superoleophobic performance, which endowed the coating with anti-oil-fouling in water. More importantly, compared with Au/BiOCl powder catalyst, the prepared Au/BiOCl coating with anti-oil-fouling also possessed high photocatalytic bactericidal activity and stable recycling performance.

Elucidating CO2 Hydrogenation over In2 O3 Nanoparticles using Operando UV/Vis and Impedance Spectroscopies.

In2 O3 has emerged as a promising catalyst for CO2 activation, but a fundamental understanding of its mode of operation in CO2 hydrogenation is still missing, as the application of operando vibrational spectroscopy is challenging due to absorption effects. In this mechanistic study, we systematically address the redox processes related to the reverse water-gas shift reaction (rWGSR) over In2 O3 nanoparticles, both at the surface and in the bulk. Based on temperature-dependent operando UV/Vis spectra and a novel operando impedance approach for thermal powder catalysts, we propose oxidation by CO2 as the rate-determining step for the rWGSR. The results are consistent with redox processes, whereby hydrogen-containing surface species are shown to exhibit a promoting effect. Our findings demonstrate that oxygen/hydrogen dynamics, in addition to surface processes, are important for the activity, which is expected to be of relevance not only for In2 O3 but also for other reducible oxide catalysts.

Aufklärung der CO2‐Hydrierung über In2O3‐Nanopartikeln mittels Operando UV/Vis‐ und Impedanzspektroskopie

In2O3 has emerged as a promising catalyst for CO2 activation, but a fundamental understanding of its mode of operation in CO2 hydrogenation is still missing, as the application of operando vibrational spectroscopy is challenging due to absorption effects. In this mechanistic study, we systematically address the redox processes related to the reverse water–gas shift reaction (rWGSR) over In2O3 nanoparticles, both at the surface and in the bulk. Based on temperature-dependent operando UV-vis spectra and a novel operando impedance approach for thermal powder catalysts, we propose oxidation by CO2 as the rate-determining step for the rWGSR. The results are consistent with redox processes, whereby hydrogen-containing surface species are shown to exhibit a promoting effect. Our findings demonstrate that oxygen/hydrogen dynamics, in addition to surface processes, are important for the activity, which is expected to be of relevance not only for In2O3 but also for other reducible oxide catalysts.