Comparative study of adsorption and reaction sites heterogeneity on alumina- and silica-supported (10 %Со+0.5 %Pd) catalyst surfaces during CO hydrogenation reaction

Adsorption and reaction sites heterogeneity on alumina- and silica-supported Co-Pd catalysts in the reaction of CO hydrogenation are discussed. Adsorption sites can act as reaction sites if exhibiting essential and indispensable properties. Various techniques were used to investigate the catalysts. Characterization of adsorption sites as reaction centres was done based on linearly adsorbed CO species. Increased adsorption energy on alumina-supported metal, so-called adsorption strength, supposed diminished amount of linear adsorbed CO. The linear CO species was not largely present and adsorption site strength, respectively adsorption bond strength, was rated average. Plenty of surface hydrogen species did not facilitate hydrogenation because the sites responsible for adsorption were of relatively mean to high strength. Adsorption sites on SiO 2 -supported metal particles were stronger than those operating on matching Al 2 O 3 -supported samples, and processes of adsorption, dissociation, and hydrogenation on the surface were mostly well balanced. Generally, adsorption sites for linear CO species as reaction centres were not much active in CO dissociation and hydrogenation. Methane band intensity in the infrared spectra of alumina-supported catalysts increased with reaction time that means domination of linear CO species is not an obstacle to CO hydrogenation run on other active sites. With silica-supported samples, adsorption sites working as reaction entities diminished their activity in CO hydrogenation with time to participate in water-gas shift reaction as getting more advantageous. The results obtained are compared and discussed with recently reported study of titania-supported Co-Pd catalysts. • Adsorption sites can act as reaction sites if they possess necessary properties. • Atop CO adsorption site is an ineffective site upon dissociation and hydrogenation. • Own site activity in CO hydrogenation can be reduced with time by promoting WGSR.