On the promotion effect of cesium on butadiene epoxidation with Ag/α-Al2O3 catalysts

Cs-promoted Ag/α-Al2O3 catalysts prepared via thermal decomposition of Ag oxalate or reduction of Ag nitrate have been studied. XRD and hydrogen titration showed an increased Ag dispersion in oxalate-derived catalysts, and TEM revealed a domain structure of Ag particles, with the size of the particles being essentially independent of the conditions of thermal treatments. According to TEM and XRD, the Cs content (500–1,500 ppm) did not influence Ag particle sizes but high Cs loading stabilized the domains during high-temperature treatments. EDX did not reveal enrichment of Ag surface with Cs and indicated predominantly uniform distribution of the promoter, at least in high-loading samples. The yield of butadiene oxide was a strong function of Cs content, and typical volcano-shaped dependence has been observed for catalysts at the steady state. However, the catalysts approached the steady state quite differently, the changes in the yield with time-on-stream being dependent on the Cs loading and catalyst pretreatments. While high-loading samples displayed some activation, the low-loading ones showed deactivation. The reasons are discussed.