Ethanol Conversion on Cyclic (MO₃)₃ (M = Mo, W) Clusters

Abstract

The reactions of ethanol (CH 3 CH 2 OD) over cyclic (MO 3 ) 3 (M = Mo, W) clusters were studied experimentally and computationally. The cyclic clusters were prepared by sublimation of MoO 3 and WO 3 powders in a vacuum. To evaluate the cluster activity in dehydration, dehydrogenation, and condensation reactions, they were suspended in an ethanol matrix on an inert substrate, graphene monolayer on Pt(111). The reaction products formed upon heating were followed and quantified using temperature-programmed desorption. The experimental results were corroborated using coupled cluster CCSD(T) calculations at DFT optimized geometries that provide quantitative molecular-scale information on the reaction mechanisms. The dehydration and dehydrogenation of ethanol probe both the Lewis/Brønsted acid/ base and redox properties of the metal centers. The overall conversion of the alcohol is governed by the Lewis acidity of the metal center, and product selectivities, as determined by the relative weights of dehydrogenation and dehydration, are governed by the reducibility of the metal center.

Unravelling Mechanistic Aspects of the Gas‐Phase Ethanol Conversion: An Experimental and Computational Study on the Thermal Reactions of MO2+ (M=Mo, W) with Ethanol

“…Comparing the reactivity of molybdenum and tungsten dioxides cations toward ethanol with that of neutral isolated (MoO 3 ) 3 and (WO 3 ) 3 clusters,, some dissimilarities are observed. While the ethanol conversion is governed overall by the Lewis acidity of the metal center, the preference of neutral (MoO 3 ) 3 for oxidative dehydrogenation, that is, acetaldehyde formation, and the bias for dehydration, that is, ethene formation, in the case of (WO 3 ) 3 can be explained by the different reducibility of the metal center.…”

“…Related to this, a closer inspection of the reactions of WO 3 films with propanol has revealed that alcohol dehydration proceeds efficiently only on O=W VI =O sites, whereas isolated W=O sites were shown to be inactive . In addition, Dixon and co‐workers have studied the ethanol conversion over cyclic neutral (MO 3 ) 3 (M=Mo, W) gas‐phase clusters, unravelling the chemical selectivity toward oxidative dehydrogenation to acetaldehyde and toward dehydration, respectively.…”

Kinetics and mechanisms of alcohol dehydration pathways on alumina materials

“…Computational chemistry studies on other metal oxides (WO 3 and MoO 3 ) also show the involvement of di-alcohol species in reactions suggesting that this observation is broadly applicable to metal oxides. 58,59 The existence of analogous surface sites on all alumina catalysts can be inferred from the similarity of the observed pressure dependences and the commonality of the underlying mechanism and resulting rate expression for ethene formation. In a recent report, Hu et al 60 noted that γ-Al 2 O 3 samples treated at different temperatures (773-1373 K) result in various polymorphs of alumina (γ-, δ-, θ-, and α-Al 2 O 3 and their mixtures).…”

High hydrogen storage capacity in calcium‐decorated silicene nanostructures

“…It is clear that the Ca-decorated silicene sheet is metallic, in contrast to the zero-band-gap feature of silicene. Additionally, a small gap of about 106 meV is opened up at the Dirac point due to the breakage of the symmetry of the two sublattices of silicene [43][44][45][46][47].…”