Abstract
CeO2 nanooctahedrons, nanorods, and nanocubes were prepared by the hydrothermal method and were then used as supports of Cu-based catalysts for the water-gas shift (WGS) reaction. The chemical and physical properties of these catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption/desorption, UV-Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR) and in situ diffuse reflectance infra-red fourier transform spectroscopy (DRIFTS) techniques. Characterization results indicate that the morphology of the CeO2 supports, originating from the selective exposure of different crystal planes, has a distinct impact on the dispersion of Cu and the catalytic properties. The nanooctahedron CeO2 catalyst (Cu-CeO2-O) showed the best dispersion of Cu, the largest amount of moderate copper oxide, and the strongest Cu-support interaction. Consequently, the Cu-CeO2-O catalyst exhibited the highest CO conversion at the temperature range of 150–250 °C when compared with the nanocube and nanorod Cu-CeO2 catalysts. The optimized Cu content of the Cu-CeO2-O catalysts is 10 wt % and the CO conversion reaches 91.3% at 300 °C. A distinctive profile assigned to the evolution of different types of carbonate species was observed in the 1000–1800 cm−1 region of the in situ DRIFTS spectra and a particular type of carbonate species was identified as a potential key reaction intermediate at low temperature.
Highlights
Proton exchange membrane fuel cells (PEMFC), for which hydrogen is the most suitable reactant, have been extensively reported as promising mobile power sources to generate electricity for automotive applications [1]
A distinctive profile assigned to the evolution of different types of carbonate species was observed in the 1000–1800 cm−1 region of the in situ diffuse reflectance infra-red fourier transform spectroscopy (DRIFTS) spectra and a particular type of carbonate species was identified as a potential key reaction intermediate at low temperature
Three types of CeO2 supports with different morphologies/crystal planes (CeO2 -R, CeO2 -C, and CeO2 nanoparticles (CeO2 -O)) were synthesized and used as supports of Cu-based catalysts for the water-gas shift (WGS)
Summary
Proton exchange membrane fuel cells (PEMFC), for which hydrogen is the most suitable reactant, have been extensively reported as promising mobile power sources to generate electricity for automotive applications [1]. The water-gas shift (WGS) reaction, which can provide hydrogen and eliminate the CO impurity to protect the Pt anodes from poisoning, is regarded as a promising process to obtain pure hydrogen for PEMFC. The WGS processes applied in industry mainly include high-temperature WGS processes using commercial FeOx -CrOx catalysts and low-temperature WGS processes using Cu/ZnO/Al2 O3 catalysts [2]. These commercially available WGS catalysts are usually inadequate for specific applications in PEMFC, due to several universal drawbacks, e.g., low catalytic efficiency, relatively high operation temperature, as well as strict pretreatment procedures and their pyrophoric nature [3]. Cerium oxide (CeO2 ), due to its unique features (e.g., high oxygen storage capacity (OSC), rich oxygen vacancies, strong interaction with active metals, and ease of change between Ce3+ and Ce4+ ), has been regarded and extensively used as a versatile and excellent support for transition metal [4,5]
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