Role of Cs promotion of Ag/AlOOH catalysts for the epoxidation of 1,3-butadiene: effects on surface acidity and basicity

The epoxidation of 1,3-butadiene to epoxybutene (EpB) was performed in a plug flow reactor using a boehmite-supported silver catalyst with molecular oxygen as the oxidant. Unpromoted silver catalysts exhibited optimum catalytic activity at a silver loading of 15 wt%. Using this experimentally determined silver level, a range of Cs nitrate loadings was incorporated on the Ag/boehmite catalyst to determine which catalyst composition provides the optimum activity. For this study, two catalyst preparations were investigated: (1) simultaneous supporting of silver and Cs nitrate and (2) initial supporting of silver followed by the sequential supporting of Cs nitrate. Reactivity studies have shown that catalysts prepared by simultaneously supporting silver and Cs nitrate are not as effective at enhancing EpB production and catalyst stability compared with catalysts prepared by the sequential supporting method. Adsorption microcalorimetry of CO2 indicates that a portion of the Cs promoter is blocked when simultaneously supporting both Cs and Ag on the support surface. Adsorption microcalorimetry of NH3 and DRIFTS studies have shown that increased Cs loadings result in a reduction in the number of acidic hydroxyl groups present on the catalyst, producing a catalyst that exhibits less deactivation with time-on-stream.