The effect of promoters (Ce, K, La, Mg, and Mn) on the catalytic properties of Ni/Al2O3 catalysts prepared by incipient wetness impregnation method (imp) were investigated in carbon dioxide hydrogenation at 500 ºC and 1 atm. All the promoted Ni/Al2O3 catalysts exhibited in higher CO2 conversion than the non-promoted ones, which may be attributed to their higher reducibility and higher number of active Ni species. All the Ni-based catalysts showed CH4 selectivity nearly 100%. The effect of preparation method was further investigated on K and Ce promoted Ni/Al2O3 catalysts by comparing the solid-state reaction method (ss) with and without dry ball milling and the imp method. The imp_Ni-K/Al2O3 was found to be the most efficient catalyst giving the highest CO2 conversion at 82.03%. According to the CO chemisorption results, the amounts of nickel active sites of the non-promoted ss_Ni/Al2O3 catalysts were lower than the ones prepared by impregnation but when dry ball milling was applied in the preparation of Ni/Al2O3 catalysts by ss method, the CO2 conversion increased. The main differences in the characteristics of the catalysts prepared by solid-state reaction and impregnation were probably the Ni particle sizes and the location of Ni particles on the support. The XPS results suggest that nickel oxide particles were deposited on the external surface of the alumina supports when prepared by the ss method. The best performance among the ss catalysts was obtained over the bm_Ni-Ce/Al2O3 with CO2 conversion as 81.16%, which were comparable to the imp_­­Ni-K/Al2O3. The catalysts performances were correlated well with high Ni %dispersion and the amount of Ni active sites.

Thesis (M.Eng.)--Chulalongkorn University, 2014