Abstract
Oxygen vacancy in ceria-based support is a dominate factor for catalyzing the water gas shift reaction by faster a redox cycle between Ce4+ and Ce3+ which is one of the elementary step in WGS reaction mechanism. Therefore, in this work, CeO2-based support was incorporation by Sm ion in order to produce the oxygen vacancy defect site. Ce1-xSmxO2 (x = 0.010, 0.050, and 0.10 at%) mixed oxide supports were synthesized by urea gelation to investigate the role of Sm addition into ceria-based support on surface, structural and redox properties which was altered to their catalytic activities. XRD and Raman spectroscopy results indicated the incorporation of Sm3+ into CeO2 lattice which gave rise to unit cell enlargement and led to structural distortions inside CeO2 which produced strain and unbalanced charge and then finally facilitated oxygen vacancy formation. XANES and EXAFS results also evidenced the replacement of Sm3+ into Ce4+ site in CeO2 lattice. H2-Temperature programmed reduction and temperature-resolved X-ray absorption spectroscopy (under reduction condition) were employed to investigate the reducibility of Ce1-xSmxO2 supports. XANES spectra of Ce L3 edges displayed lower surface reduction temperature (Ce4+ to Ce3+) which corresponded to H2-TPR results. The results of catalytic activity tests for water gas shift reaction showed that the activity of 1 wt%Pd/Ce1-xSmxO2 was higher than that of 1 wt%Pd/CeO2. The role of Sm on enhancing WGS reaction rate were to increase CO molecules adsorption by promoting the dispersion of active metal site on catalyst surface and to facilitate the redox cycle between Ce4+ and Ce3+ of ceria support by oxygen vacancies formation. Therefore, combined these two effects the WGS activities were enhanced. Moreover, by using the results from our previous works together with the results from this work, we can evidence that speeding up the different elementary steps in the reaction mechanism, the WGS rate can also be enhanced.
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