Structure and surface properties of ceria-modified Ni-based catalysts for hydrogen production

Series of Ni catalysts supported on alumina and mixed xCeO2-Al2O3 oxides with different CeO2 content (1–12 wt%) were prepared by impregnation method. The effect of CeO2 loading on the structure and catalytic properties of supported Ni catalysts in dry methane reforming was studied. The texture, structure and surface properties of the catalysts in their calcined, reduced and used state were studied by using different techniques such as: adsorption-desorption isotherms, XRD, UV–vis DRS, XPS, Raman, H2-TPR, EPR, TPO and TEM. Variation in the electronic environments of the cerium and nickel as a function of the CeO2 content and pretreatment was observed for CeO2-containing Ni catalysts. The couples Ni2+/Nio and Ce3+/Ce4+ were detected in the oxidic, reduced and spent ceria-loaded Ni catalysts. CeO2-containing Ni catalysts exhibited higher activity and stability with time on stream relative to that of alumina-supported Ni. The obvious difference in the behaviors of Ni/xCeO2-Al2O3 and Ni/Al2O3 was related to the difference in their dispersions. Small nanoparticles of 4.7–6.3 nm were observed for CeO2-modified catalysts assuring their high activity and resistance to carbon deposition. The highest activity and stability of Ni catalyst with 6 wt.% CeO2 was due to the higher electron density and accessibility of the active sites caused by the close contact between nickel and cerium species. While, Ni/Al2O3 catalyst exhibited low activity and carbon resistant due to the agglomeration of nickel particles up to 20 nm.