Formaldehyde Polymerization on (WO₃)₃/TiO₂(110) Model Catalyst

Abstract

Polymerization of formaldehyde, H2CO, was studied under ultrahigh vacuum conditions on a model catalyst consisting of monodispersed (WO3)3 clusters anchored on TiO2(110). Formaldehyde oligomers, (H2CO) n , desorbing from the polymer that formed on the catalyst surface are detected between 250 and 325 K in temperature-programmed desorption experiments. At least two monolayers (ML) of H2CO are required on the surface to observe (H2CO) n , desorption and the amount saturates for H2CO coverages in excess of ∼40 ML. The presence of H2CO multilayers is required for the polymerization to take place indicating that it had to occur below 100 K. The saturation amount increases with increasing coverage of (WO3)3 clusters with the highest amount of ∼13 ML observed on 1.2 (WO3)3/nm2. No (H2CO) n desorption was observed on the bare TiO2(110) surface.

Conversion of methanol on rutile TiO2(110) and tungsten oxide clusters: 2. The role of defects and electron transfer in bifunctional oxidic photocatalysts

“…As we have shown recently, this reaction also proceeds via methoxy intermediates, that are, thus, sufficiently available. 15 We also rule out the possible oligomerization of formaldehyde, that was reported at WO 3 catalysts below 100 K. [29][30][31] We do not expect this to be limiting here because the methane desorption proves that remaining methoxy sites are present which indicates that less formaldehyde was produced than on bare TiO 2 . Moreover, Dohna ´lek et al point out, that at least two monolayers of formaldehyde are required to yield reasonable amounts of oligomers.…”

“…Such clusters on various supports were already tested in theoretical and experimental studies for thermal alcohol or aldehyde conversion reactions. [24][25][26][27][28][29][30][31][32] Surprisingly, the photochemistry of these clusters has not been investigated yet although both materials (WO 3 and TiO 2 ) are promising candidates for photochemical reactions. Moreover, the band gap of bulk WO 3 (2.8 eV) is smaller than the one of rutile TiO 2 .…”

Preparation, Characterization, and Catalytic Properties of Tungsten Trioxide Cyclic Trimers on FeO(111)/Pt(111)

“…23À25 Our catalytic studies of (WO 3 ) 3 embedded in an alcohol matrix and/or supported on TiO 2 (110) and Pt(111) demonstrated that the Lewis acid/base chemistry of WdO groups plays a prominent role in alcohol chemistry, leading to formation of alkenes, aldehydes, ketones, and ethers, 13,14 and in the polymerization of formaldehyde. 20,21 To further understand the interactions of (WO 3 ) 3 with oxide supports, we focus on (WO 3 ) 3 cluster deposition on a FeO(111) overlayer grown on Pt(111). 26 In contrast with TiO 2 (110), which has important catalytic properties on its own, we expected the oxygen-terminated FeO(111) surface to be significantly less reactive and therefore ideal as an inert support for our (WO 3 ) 3 clusters.…”

A DFT study of (WO3)3nanoclusters adsorption on defective MgO ultrathin films on Ag(001)

“…[1][2][3] Among them, increasing interest has been devoted to tungsten oxide, which has been found to accelerate many types of reactions, 4 such as alkane isomerization, 5 alkene metathesis, 6 alcohol oxidation, 7 and selective NO reduction. 8 In recent years, tungsten oxides loaded on different supports such as TiO 2 , 9,10 Cu-O 11 and FeO/Pt(111) 12 by direct sublimation of WO 3 have been extensively studied in an attempt to correlate the structure with catalytic performance, like dehydration of 2-propanol, 13 oxidation and reduction of aliphatic alcohols, 14 or polymerization of formaldehyde 15 and acetaldehyde, 16 which has suggested that the catalytic properties of tungsten oxides are strongly inuenced by the support.…”