Support and crystallite size effects in CO hydrogenation on nickel

Abstract

Adsorption and CO hydrogenation activity/selectivity properties of well-defined Ni SiO 2 , Ni Al 2O 3 , and Ni TiO 2 catalysts representing wide ranges of dispersion and nickel concentration were investigated. CO and H 2 adsorption uptakes were determined for all of the catalysts. The extent of reduction to the metal was also determined for all catalysts by oxygen titration or nickel carbonyl extraction. Specific activities for CO H 2 synthesis were measured for each of the catalysts at 500–550 K and 140 kPa. Effects of strong metal-support interactions are evident in Ni TiO 2 , in well-dispersed Ni Al 2O 3 , and to a lesser extent in very well-dispersed Ni SiO 2 from (i) changes in the nature and stoichiometry of CO and H 2 adsorption and (ii) significant changes in activity and selectivity properties for CO H 2 synthesis with changes in metal dispersion, support, preparation technique, and catalyst pretreatment. Both CO H adsorption ratio and selectivity to C 2+ hydrocarbons increase with increasing metal dispersion in Ni SiO 2 and Ni Al 2O 3 systems, suggesting that metal-support interactions affect selectivity by changing the relative abundance of adsorbed CO and H 2 during reaction.