Infra-red spectra of acetylene on γ-alumina and γ-alumina-supported platinum, and effect of sulphur compounds

Abstract

The i.-r. spectra of the surface species formed by the initial adsorption of acetylene on γ-alumina and γ-alumina-supported-platinum were obtained at room temperature. The adsorption of acetylene on γ-alumina resulted in weak and strong adsorbent-adsorbate interactions. The bands at 3260, 2697, 2680, 2665, 2640, 2167 and 1945 cm^–1 were due to weakly held acetylene. The bands at 3305 and 2000 cm^–1 were due to strongly held acetylene on the γ-alumina surface. The adsorption of acetylene on supported platinum resulted in a sharp band at 1690 cm^–1. Hydrogenation of acetylene adsorbed on the γ-alumina surface was greatly facilitated by the presence of platinum.

Addition of H₂S and COS to the system resulted in poisoning of the adsorbents due to the dissociation of these sulphur compounds and the subsequent formation of (Al₂O₃)·S_x and PtS_x complexes. Poisoning substantially reduced acetylene adsorption on the γ-alumina and platinum. There was no evidence to show the adsorption of acetylene on poisoned sites. This system illustrated that both the catalyst and the catalyst support are susceptible to sulphur poisoning.