Morphological effects of the nanostructured ceria support on the activity and stability of CuO/CeO₂ catalysts for the water-gas shift reaction

Abstract

Three CuO/CeO2 catalyst with different morphologies of ceria, namely nanospheres, nanorods and nanocubes, were synthesized and used to catalyze the water-gas shift (WGS) reaction. The reactivity tests showed that the Cu supported on the ceria nanospheres exhibited both the highest activity and superior stability when compared with the nanocube and nanorod ceria catalysts. Operando X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) methods were used to characterize these catalysts in their working state. High resolution electron microscopy (HRTEM, STEM) was used to look at the local atomic structure and nano-scale morphology. Our results show that the morphology of the ceria support, which can involve different crystal faces and concentrations of defects and imperfections, has a critical impact on the catalytic properties and influences: (1) the dispersion of CuO in the as-synthesized catalyst; (2) the particle size of metallic Cu upon reduction during the WGS reaction, (3) the stability of the metallic Cu upon variations of temperature, and (4) the dissociation of water on the ceria support. The nanosphere ceria catalyst showed an excellent water dissociation capability, the best dispersion of Cu and a strong Cu-Ce interaction, therefore delivering the best performance among the three WGS catalysts. The metallic Cu, which is the active species during the WGS reaction, was more stabilized on the nanospheres than on the nanorods and nanocubes and thus led to a better stability of the nanosphere catalyst than the other two architectures. Each catalyst exhibited a distinctive line-shape in the 800-1600 cm(-1) region of the DRIFTS spectra, pointing to the existence of different types of carbonate or carboxylate species as surface intermediates for the WGS.

Morphology-Dependent Properties of Cu/CeO2 Catalysts for the Water-Gas Shift Reaction

“…Therefore, the obtained CeO 2 samples are ideal supports to investigate the crystal-plane effect on catalytic performance. Similar to the literature [21], the nanoshaped CeO 2 supports inherit their authentic morphologies after the loading of Cu. CuO particles were not resolvable from the TEM images because of the high dispersion of minute particles as well as the low contrast between the CuO and CeO 2 supports.…”

“…The bands at 3729, 3686, and 3635 cm −1 can be assigned to mono, double, and triple coordinated hydroxyl [21]. At 250 °C, a strong broad band of hydroxyl centered at 3700 cm −1 was observed due to the strong interaction between hydroxyls through hydrogen bonding.…”

“…The surface areas of the cubes, rods, and octahedras were 30.34, 81.90, and 100.01 m 2 /g, respectively. The specific surface areas appeared to affect the concentration of the centers for anchoring small particles on the oxide support and further determine the dispersion of CuO [21]. The CeO2-C, with the largest particle size and the lowest specific surface, may lead to the formation of large particles of crystalline CuO, while the other supports tend to show good Cu dispersion and high catalytic activity.…”

Effects of Morphology of Cerium Oxide Catalysts for Reverse Water Gas Shift Reaction

“…Theoretical simulations predicted increasing catalytic activity of ceria nanorods in CO oxidation with increasing lattice microstrain [60]. It has been suggested that increasing microstrain enhances active metal-ceria support interaction, resulting in improved dispersion of the active phase, stabilization of the active metal species in a lower valence state and enhanced overall reducibility [27,61]. Supported ceria cubes were moreover reported to possess lower lattice microstrain and corresponding lower catalytic activity in WGS compared to rods [27].…”

Room Temperature Synthesis of Ceria by the Assisted of Cationic Surfactant and Aging Time

“…Ceria is typically used for active support, as numerous research findings have indicated that such a characteristic is due to strong metal-ceria surface defects bonding, which stabilises the metal catalyst [18][19][20][21][22]. In this situation, ceria-metal interface will exist through oxygen migration from the support to the metal and vice versa, resulting in an enhanced surface reaction (e.g.…”