Effects of cesium and chlorine on oxygen adsorption on promoted Ag/α-Al2O3 catalysts Original Research Article

Integral heats of oxygen adsorption were measured at 443 K on unpromoted and promoted Ag/α-Al2O3 catalysts. Two unpromoted catalysts with average Ag particle sizes of about either 200 or 300 nm were utilized while the promoted catalysts had particle sizes in the range of 250–350 nm. The promoted catalysts were prepared with either CsNO3 to study the effect of cesium, or CsCl to study the combined effect of cesium and chlorine. For both groups, the Cs content was around either 400 or 1200 ppm. Following a low-temperature pretreatment involving calcination at 523 K and reduction in H2 at 473 K, the catalysts were characterized by volumetric measurements of oxygen chemisorption and subsequent hydrogen titration at 443 K. Unlike the unpromoted catalysts, the promoted samples exhibited varying amounts of reversible oxygen adsorption with a maximum of 30% reversible adsorption on a 1174 ppm Cs-only promoted catalyst; however, the presence of only Cs at either loading altered the total oxygen uptake by only ±10% compared to the unpromoted catalyst. Regardless, the H2/(O2)irrev titration ratio was close to the stoichiometric ratio of 2.0 except for the catalyst with the highest Cl content. With this latter sample, there was additional hydrogen uptake beyond the titration of adsorbed oxygen. Several cycles of pretreatment/adsorption measurements were needed to ‘stabilize’ these catalysts and obtain reproducible results.