Investigations of the Effect of H2 in CO Oxidation over Ceria Catalysts

The preferential CO oxidation (so-called CO-PROX) is the selective CO oxidation amid H2-rich atmospheres, a process where ceria-based materials are consolidated catalysts. This article aims to disentangle the potential CO–H2 synergism under CO-PROX conditions on the low-index ceria surfaces (111), (110) and (100). Polycrystalline ceria, nanorods and ceria nanocubes were prepared to assess the physicochemical features of the targeted surfaces. Diffuse reflectance infrared Fourier-transformed spectroscopy (DRIFTS) shows that ceria surfaces are strongly carbonated even at room temperature by the effect of CO, with their depletion related to the CO oxidation onset. Conversely, formate species formed upon OH + CO interaction appear at temperatures around 60 °C and remain adsorbed regardless the reaction degree, indicating that these species do not take part in the CO oxidation. Density functional theory calculations (DFT) reveal that ceria facets exhibit high OH coverages all along the CO-PROX reaction, whilst CO is only chemisorbed on the (110) termination. A CO oxidation mechanism that explains the early formation of carbonates on ceria and the effect of the OH coverage in the overall catalytic cycle is proposed. In short, hydroxyl groups induce surface defects on ceria that increase the COx–catalyst interaction, revealed by the CO adsorption energies and the stabilization of intermediates and readsorbed products. In addition, high OH coverages are shown to facilitate the hydrogen transfer to form less stable HCOx products, which, in the case of the (110) and (100), is key to prevent surface poisoning. Altogether, this work sheds light on the yet unclear CO–H2 interactions on ceria surfaces during CO-PROX reaction, providing valuable insights to guide the design of more efficient reactors and catalysts for this process.

Highly stable bimetallic Au–Cu supported on Al2O3 for selective CO oxidation in H2-rich gas: effects of Cu/Au atomic ratio and sensitive influence of particle size

The effects of Au/Cu atomic ratio and thermal pretreatment on the catalytic performance of AuxCuy/Al2O3 for PROX were studied. The reduced AuxCuy/Al2O3 catalysts display higher catalytic activity and stability than the calcined catalysts.

Effect of Calcination Temperatures of Cu/CeO2-Containing Co on Physiochemical Properties and Catalytic Activity to Selective CO Oxidation

The CuO/CeO2-Co3O4 catalysts were prepared via co-precipitation at different calcination temperatures and evaluated catalytic activities in the reaction of selective CO oxidation. The catalysts were characterized by BET, XRD and FESEM-EDX techniques. As determined by BET studies, the catalysts have type IV adsorption isotherm which indicated mesoporous structure. An increase in calcination temperatures decreased the specific surface areas of the catalysts. XRD was used for determination of crystallite sizes of each oxide. It was found that CuO and Co3O4 existed in highly dispersed at every calcination temperatures. For CeO2, an increase in calcination temperatures increased the crystallite sizes. Surface morphology of the catalysts was also investigated by FESEM. The catalyst calcined at 500°C showed the highest performance to completely convert CO to CO2 at 150°C. Furthermore, the effect of CO2 and H2O to activity of catalyst was studied. The result showed that both CO2 and H2O has negative effect to activity of catalyst. CO conversion and selectivity decreased to 93.8% and 48.5% at 210°C, respectively. This may be due to the adsorption of CO2 and H2O molecules on active site and due to the reverse water gas shift reaction occurred at temperature above 190°C.