Shape effects of ceria nanoparticles on the water-gas shift performance of cuox /ceo2 catalysts

T1EDK-00094 UIDB/EQU/50020/2020 UIDB/00511/2020 CEECINST/00102/2018 UIDB/50006/2020 UIDP/50006/2020 DL 57/2017The copper–ceria (CuOx /CeO2 ) system has been extensively investigated in several catalytic processes, given its distinctive properties and considerable low cost compared to noble metal-based catalysts. The fine-tuning of key parameters, e.g., the particle size and shape of individual counterparts, can significantly affect the physicochemical properties and subsequently the catalytic performance of the binary oxide. To this end, the present work focuses on the morphology effects of ceria nanoparticles, i.e., nanopolyhedra (P), nanocubes (C), and nanorods (R), on the water–gas shift (WGS) performance of CuOx /CeO2 catalysts. Various characterization techniques were employed to unveil the effect of shape on the structural, redox and surface properties. According to the acquired results, the support morphology affects to a different extent the reducibility and mobility of oxygen species, following the trend: R > P > C. This consequently influences copper–ceria interactions and the stabilization of partially reduced copper species (Cu+ ) through the Cu2+ /Cu+ and Ce4+ /Ce3+ redox cycles. Regarding the WGS performance, bare ceria supports exhibit no activity, while the addition of copper to the different ceria nanostructures alters significantly this behaviour. The CuOx /CeO2 sample of rod-like morphology demonstrates the best catalytic activity and stability, approaching the thermodynamic equilibrium conversion at 350◦ C. The greater abundance in loosely bound oxygen species, oxygen vacancies and highly dispersed Cu+ species can be mainly accounted for its superior catalytic performance.publishersversionpublishe

Effect of support nature on the cobalt-catalyzed CO2 hydrogenation

CO2 hydrogenation to value added chemicals/fuels has gained considerable interest, in terms of sustainable energy and environmental mitigation. In this regard, the present work aims to investigate the CO2 methanation performance of cobalt-based catalysts supported on different metal oxides (MxOy: CeO2, ZrO2, Gd2O3, ZnO) at low temperatures (200–300 °C) and under atmospheric pressure. Various characterization methods, such as N2 adsorption-desorption at −196 °C, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR), were employed to correlate the structural and surface properties of the materials with their catalytic activity. The results revealed a significant impact of support nature on the CO2 hydrogenation performance. The following order, in terms of CH4 yield (YCH4), was recorded at 300 °C: Co/CeO2 (∼96%) > Co/ZnO (∼54%) > Co/G2O3 (∼53%) ∼ Co/ZrO2 (∼53%). On the basis of the characterization results, the superiority of Co/CeO2 catalyst can be mainly ascribed to its enhanced reducibility linked to Co-Ceria interactions. Moreover, Co/CeO2 demonstrated a stable conversion/selectivity performance under subsequent reaction cycles, in contrast to Co/ZnO, which progressively activated under reaction conditions. The latter is related with the modifications induced in elemental chemical states and surface composition of Co/ZnO upon pretreatment in reaction conditions, in contrast to Co/CeO2 sample where a stable surface performance was observedLa hidrogenación de CO 2 a productos químicos/combustibles de valor agregado ha ganado un interés considerable, en términos de energía sostenible y mitigación ambiental. En este sentido, el presente trabajo tiene como objetivo investigar el comportamiento de metanización de CO 2 de catalizadores a base de cobalto soportados sobre diferentes óxidos metálicos (M x O y : CeO 2 , ZrO 2 , Gd 2 O 3 , ZnO) a bajas temperaturas (200– 300 °C) y bajo presión atmosférica. Varios métodos de caracterización, como la adsorción-desorción de N 2 a −196 °C, difracción de rayos X (XRD), espectroscopía de fotoelectrones de rayos X (XPS) y reducción de temperatura programada (TPR), se emplearon para correlacionar las propiedades estructurales y superficiales de los materiales con su actividad catalítica. Los resultados revelaron un impacto significativo de la naturaleza del soporte en el rendimiento de hidrogenación de CO2. El siguiente orden, en términos de producción de CH 4 (Y CH4 ), se registró a 300 °C: Co/CeO 2 (∼96 %) > Co/ZnO (∼54 %) > Co/G 2 O 3 (∼53 %) ∼ Co/ZrO 2 (∼53%). Sobre la base de los resultados de la caracterización, la superioridad de Co/CeO 2El catalizador se puede atribuir principalmente a su mayor capacidad de reducción vinculada a las interacciones de Co-Ceria. Además, Co/CeO 2 demostró un rendimiento de conversión/selectividad estable en los ciclos de reacción posteriores, en contraste con Co/ZnO, que se activó progresivamente en las condiciones de reacción. Esto último está relacionado con las modificaciones inducidas en los estados químicos elementales y la composición superficial de Co/ZnO tras el pretratamiento en condiciones de reacción, en contraste con la muestra de Co/CeO 2 donde se observó un comportamiento superficial establ

Stabilization of catalyst particles against sintering on oxide supports with high oxygen ion lability exemplified by Ir-catalyzed decomposition of N2O

Iridium nanoparticles deposited on a variety of surfaces exhibited thermal sintering characteristics that were very strongly correlated with the lability of lattice oxygen in the supporting oxide materials. Specifically, the higher the lability of oxygen ions in the support, the greater the resistance of the nanoparticles to sintering in an oxidative environment. Thus with γ-Al2O3 as the support, rapid and extensive sintering occurred. In striking contrast, when supported on gadolinia-ceria and alumina-ceria-zirconia composite, the Ir nanoparticles underwent negligible sintering. In keeping with this trend, the behavior found with yttria-stabilized zirconia was an intermediate between the two extremes. This resistance, or lack of resistance, to sintering is considered in terms of oxygen spillover from support to nanoparticles and discussed with respect to the alternative mechanisms of Ostwald ripening versus nanoparticle diffusion. Activity towards the decomposition of N2O, a reaction that displays pronounced sensitivity to catalyst particle size (large particles more active than small particles), was used to confirm that catalytic behavior was consistent with the independently measured sintering characteristics. It was found that the nanoparticle active phase was Ir oxide, which is metallic, possibly present as a capping layer. Moreover, observed turnover frequencies indicated that catalyst-support interactions were important in the cases of the sinter-resistant systems, an effect that may itself be linked to the phenomena that gave rise to materials with a strong resistance to nanoparticle sintering

Studies on CuCe0.75Zr0.25Ox preparation using bacterial cellulose and its application in toluene complete oxidation

A series of CuCe0.75Zr0.25Ox catalysts (CCZ) were synthesized based on the environmental‐friendly bacterial cellulose (BC) by using the sol‐gel method. The corresponding synthesis mechanism, physicochemical properties of the catalysts and catalytic performances for toluene oxidation were comprehensively studied. In the presence of BC without sugar, the CCZ−A synthesized by ethanol‐gel exhibits better catalytic activity than the CCZ−W synthesized by water‐gel, which may be due to the different roles of BC in different solvents. However, it is worth noting that the graft copolymerization between BC and active metal (Ce4+, Cu2+) is the same process in both water‐gel and ethanol‐gel. The activity of CCZ‐SW synthesized by water‐gel using BC with sugar is obviously higher than that of CCZ−W and CCZ−A. The temperature of complete degradation of toluene over CCZ‐SW is 205 °C, which is 35 °C lower than that of CCZ−W. The results from BET, Raman and H2‐TPR indicate that the larger the specific surface area, the more oxygen vacancies and better low‐temperature reducibility, that are mainly responsible for the excellent activity of CCZ‐SW. The existence of sugar in BC could hinder the agglomeration of active metal particles during the calcination process. Combined with the results of in situ DRIFT, the adsorbed toluene on the catalyst surface is oxidized into alkoxide, aldehydic and carboxylic acid species as intermediates before the complete oxidation into CO2 and H2O.

A novel magnetic HS−-adsorptive nanocomposite photocatalyst (rGO/CoMn2O4-MgFe2O4) for hydrogen fuel production using H2S feed

Synthesis of low-cost, eco-friendly, semiconducting solar-energy materials with excellent photocatalytic activity [high surface area, good reactant adsorption, photon harnessing in the visible region, and low charge recombination] for application in pollutant conversion to hydrogen is of great importance from environmental remediation as well as green energy and fuel production perspectives. In the present work, a magnetic heterojunction of CoMn2O4/MgFe2O4 and reduced graphene oxide (rGO) was synthesized through a combined Hummers’/hydrothermal method. The obtained nanocomposite (rGO/CoMn2O4-MgFe2O4) was employed for photocatalytic conversion of H2S feed into hydrogen fuel. Adsorption studies in the feed solution proved a good capability for the photocatalyst to adsorb HS− reactant from the reaction medium. This effect was ascribed to the presence of the CoMn2O4 component, serving as a strong bisulfide adsorbent. VSM (vibrating sample magnetometry) analysis revealed that the magnetic property of the photocatalyst was due to the MgFe2O4 component. Photocatalytic investigations showed that the addition of rGO to the CoMn2O4/MgFe2O4 nanocomposite not only improves its reactant adsorption capacity, but also increases the photocatalyst surface area, enhances photon absorption, and suppresses the charge (e/h) recombination, which eventually boosts the photocatalyst activity to produce more hydrogen fuel (∼1.5 times)