Adsorption and reactions of acetaldehyde on platinum(S)-[6(111) .times. (100)]

Abstract

Adsorption and reaction of acetaldehyde with clean and oxygen-predosed Pt(S)-[6(l 11)X(100)] were studied by electron energy loss vibrational spectroscopy (EELS) and temperature-programmed reaction spectroscopy (TPRS). Acetaldehyde adsorption at 95 K on the clean surface produced a multilayer structure with vibrational bands characteristic of solid acetaldehyde. This condensed phase desorbed near 133 K leaving an adsorbed layer showing a major binding state of 58 kJ g-mol'1 2and a minor state of 70 kJ g-mol"1. The vibrational spectra and characteristic pattern of H2 evolution obtained upon heating the chemisorbed layer above 300 K indicated the conversion of the acetaldehyde surface complex to ?)3-ethylidyne. The ethylidyne species dehydrogenated to gaseous hydrogen and surface carbon above 450 K. In a separate reaction path, acetaldehyde underwent decarbonylation near 290 K to produce adsorbed CO and methane, which desorbed in a reaction-limited peak at 317 K. Vibrational features suggestive of a surface acetyl species were observed below 290 K. Evidence was also obtained for acetaldehyde adsorbed molecularly in 1 configurations. Similar results were obtained for acetaldehyde on the Pt-(S)-[6(l 11)X(100)] surface in the presence of preadsorbed atomic oxygen, indicating the absence of direct attack of acetaldehyde by oxygen. This contrasts with the nucleophilic attack on the carbonyl carbon observed previously on copper and silver surfaces.

Catalytic Deoxygenation of Methyl-Octanoate and Methyl-Stearate on Pt/Al2O3

“…That is, indirectly via octanoic acid or directly from methyl octanoate. The metal-catalyzed decarbonylation of one-oxygen-containing compounds such as aldehydes, alcohols and ketones to the corresponding hydrocarbons with one C less than the parent oxygenated feed is a well-known reaction [26,27]. Similar results were found by Murzin in the conversion of ethyl stearate (C 18 ) over Pd/C catalysts in presence of H 2 , yielding mostly n-heptadecane [7].…”

Density-functional theory studies of acetone and propanal hydrogenation on Pt(111)

“…33,34 Electron energy loss vibrational spectroscopy ͑EELS͒ studies of acetaldehyde adsorption on Pt(S) -͓6(111)X(100)͔ show formation of acetyl surface species at 137 K while C-C bond cleavage reactions occur at higher temperatures. 35 Similarly, adsorbed propanal can lose a hydrogen atom bonded to the carbonyl, leading to adsorbed propionyl species and adsorbed H atom. This adsorbed propionyl species is shown in Fig.…”

Catalytic degradation of oxygenates in Fischer–Tropsch aqueous phase effluents to fuel gas via hydrodeoxygenation over Ru/AC catalyst

“…51 The acyl species decarbonylates by C-C bond scission to liberate CO and an alkane of one carbon less than the starting acyl. In addition, McCabe et al 52 have also verified that acetaldehyde can be decomposed or decarbonylated to generate methane and CO over Pt single crystals. Recently, CO and methane were also found to be the predominant products in vapor-phase hydrogenation of acetic acid and decomposition of ethanol on both Ru 53 and Pt 54 surfaces.…”