Synthesis and high performance of ceria supported nickel catalysts for hydrodechlorination reaction

Catalysts containing 10 wt% Ni supported on CeO2 were prepared by two ways, namely, co-precipitation method using nickel nitrate precursor and impregnation method using nickel nitrate and nickel acetylacetonate as two separate precursors. The catalysts were characterized by pulse chemisorption of H2, X-ray diffraction, and temperature programmed reduction (TPR) techniques and evaluated for the gas phase hydrodechlorination (HDC) of chlorobenzene to benzene in a fixed-bed down-flow glass reactor at 573 K under normal atmospheric pressure. The hydrogen uptake values were used to determine the catalyst properties of Ni/CeO2 like dispersion, metal area, and particle size. Among the two preparatory routes, co-precipitation method gave better catalytic performance in terms of hydrogenation activity, benzene selectivity, and coking resistivity than impregnated Ni/CeO2 catalysts. This may be attributed to high dispersion of smaller NiO crystallites and the appearance of the second reduction peak at a higher temperature (578 K) in TPR profile with co-precipitated Ni/CeO2 catalyst. This indicates that a strong interaction may take place between the NiO crystallites and CeO2 on the surface of co-precipitated Ni/CeO2 catalyst. Contrary to general expectation that the large Ni particles are preferable for HDC reaction, it is observed that smaller metal particles with high dispersion, as in the case of co-precipitated Ni/CeO2 catalyst, promotes better catalyst with longer life.