Influence of pretreatment on the properties of Ag/α–Al2O3 catalysts containing large(± 1 µm) pure and Cs-promoted silver particles. Part 1.—Extent of oxygen and hydrogen sorption and TPD studies

Abstract

In order to elucidate the influence of the pretreatment on the (catalytic) properties of silver catalysts containing large silver particles (± 1 µ m), the interaction of oxygen and hydrogen with reduced and pre-oxidized samples has been investigated. The effect of the presence of caesium on the silver surface has also been investigated. Volumetric (ad)sorption of oxygen and hydrogen, TPD experiments, combined with chemisorption measurements, and electron microscopy were used as characterization techniques.The combined results indicate that the penetration of oxygen into these large silver particles does not occur to any significant extent. When the catalysts are saturated with oxygen, only ca. 40% of the monolayer coverage of oxygen atoms is situated in the subsurface layers.This type of pretreatment exhibited small, but distinct, effects on the uptake of oxygen and hydrogen at 443 K. Higher uptake of oxygen was observed after reduction of the catalyst at more elevated temperatures. The presence of caesium lessens considerably the variation in the uptake.