Spectroscopic identification of adsorbed species derived from adsorption and decomposition of formic acid, methanol, and formaldehyde on cerium oxide

Abstract

The surface species formed from adsorption and decomposition of HCOOH, CH 3OH, and HCHO over dehydroxylated cerium oxide have been identified using in situ Fourier transform infrared spectroscopy at temperatures from 300 to 673 K. Bidentate and unidendate formate species were formed upon adsorption of HCOOH at 300 K. It is suggested that the two types of formate species originated from dehydroxylation and deprotonation of the formic acid on the surface. The formate species decompose above 473 K in uacuo and subsequently leave a residue of carbonate and isolated OH groups on the surface. At least two kinds of surface methoxy species with characteristic IR bands in the regions 2950-2780 and 1100-1030 cm −1 were detected when cerium oxide was exposed to CH 3OH at 300 K. These methoxy species were partly oxidized to form formate species by oxygenation of cerium oxide at 473 K. Dioxymethylene species together with formate species were produced from adsorption of HCHO on cerium oxide at 300 K. Upon warming the samples to 373 K, IR bands due to the dioxymethylene species nearly disappeared while bands of the methoxy species emerged. Band intensities of both dioxymethylene and methoxy species increased markedly when cerium oxide was partially reduced prior to the adsorption. It is concluded that the methoxy and formate species are produced mainly via Cannizzaro reaction, particularly on partially reduced cerium oxide.