Effects of Cesium and Chlorine on Butadiene Adsorption on Ag/α-Al2O3 Catalysts

The selective epoxidation of conjugated olefins containing allylic substituents and epoxidation of propylene in the presence of butadiene

“…As the feed concentration of C 4 H 6 increases from zero to 0.9 mol%, the selectivity to PO increases from approximately 2.5 to 40%. The concurrent decrease in C 3 H 6 conversion indicates that C 4 H 6 is much more strongly adsorbed on the Ag-O surface sites than C 3 H 6 , consistent with the observations of Vannice and co-workers [24]. At C 4 H 6 levels as low as 0.2 mol%, the conversion of C 3 H 6 is lowered by more than 50% even though the ratio of C 3 H 6 /C 4 H 6 = 30.…”

“…The situation for ethylene oxide formation is the expected relationship of feed concentration to selective product formation where there is a parallel reaction pathway for nonselective product formation (CO 2 /H 2 O in the case of olefin epoxidation). Vannice and co-workers [24] have also observed that the integral heats of adsorption of butadiene on O-covered Ag catalysts are much stronger than ethylene adsorption on the same surfaces, presumably due to the conjugated olefin structure of butadiene. These results, coupled with the direct relationship of EpB selectivity and butadiene feed concentration, strongly suggest that adsorbed C 4 H 6 stabilizes EpB or its precursor against over oxidation to CO 2 and H 2 O.…”

Adsorption of 1,3-butadiene on supported and promoted silver catalysts

“…Badani et al measured integral heats of adsorption, Q ad , at 300 K for BD on unpromoted and promoted Ag/α-Al 2 O 3 catalysts [26]. Irreversibly adsorbed butadiene was more weakly bound on O-covered surfaces than on reduced Ag surfaces, but the amount of irreversibly adsorbed BD was higher on O-covered catalysts than on reduced catalysts.…”

The influence of chemical transport via vapour phase on the properties of chloride and caesium-doped V–Fe mixed oxide catalysts in the oxidation of butadiene to furan

“…Furthermore, chloride and caesium are well-known promoters for alumina-supported silver epoxidation catalysts [10][11][12][13]. Extensive studies of the heat of adsorption of oxygen and butadiene on unpromoted and chloride and caesium promoted Ag/Al 2 O 3 showed an influence of both promoters on the interaction between the reactants and the surface of the silver particles [12,13].…”

“…Extensive studies of the heat of adsorption of oxygen and butadiene on unpromoted and chloride and caesium promoted Ag/Al 2 O 3 showed an influence of both promoters on the interaction between the reactants and the surface of the silver particles [12,13]. Different models were proposed to explain the role of the promoters such as: i) modification of the properties of the surface by electronic interactions between the promoters and the surface, ii) influence on the surface structure; iii) formation of Cs-O or Cs-Ag-O compounds and iv) blocking of unselective sites by chloride formation.…”