Density Functional Studies of Methanol Decomposition on Subnanometer Pd Clusters

Abstract

A density functional theory study of the decomposition of methanol on subnanometer palladium clusters (primarily Pd 4 ) is presented. Methanol dehydrogenation through C-H bond breaking to form hydroxymethyl (CH 2 OH) as the initial step, followed by steps involving formation of hydroxymethylene (CHOH), formyl (CHO), and carbon monoxide (CO), is found to be the most favorable reaction pathway. A competing dehydrogenation pathway with O-H bond breaking as the first step, followed by formation of methoxy (CH 3 O) and formaldehyde (CH 2 O), is slightly less favorable. In contrast, pathways involving C-O bond cleavage are much less energetically favorable, and no feasible pathways involving C-O bond formation to yield dimethyl ether (CH 3 OCH 3 ) are found. Comparisons of the results are made with methanol decomposition products adsorbed on more extended Pd surfaces; all reaction intermediates are found to bind slightly more strongly to the clusters than to the surfaces.

DENSITY FUNCTIONAL THEORY STUDY OF METHANOL ADSORPTION AND DISSOCIATION ON 2Cu/ZnO CATALYST SURFACE

“…Previously, the reaction mechanisms of CH 3 OH dissociation with the C-H, O-H, or C-O bond on the surfaces have been investigated theoretically and experimentally [6,[9][10][11][12][13]. In the present work, we perform only the configuration of site A as initial state (IS A ) to calculate mechanism for CH 3 OH dissociation on 2Cu/ZnO (1010) [25], CuCl(111) [1], and Au(111) [4] surfaces.…”

“…Many previous experiment and calculation investigations of CH 3 OH dissociation on the surfaces suggested that the O-H scission was proposed as the initial dissociation step [4,10], C-H scission was more favorable than O-H scission [11,12], and the C-O scission suggested to be impossible one for both experimental and theoretical studies [9,11,[13][14][15]. However, CH 3 OH dissociation through three routes of bond scission on 2Cu/ZnO   0 1 10 surface in this present works is not still found.…”

“…In addition, it is proven that a catalyst surface with high Cu atom is dispersed on metal oxide surface which it gives higher a conversion and selectivity [10,13,16]. As a result, the target catalyst of 2Cu/ZnO   0 1 10 surface model in which 2Cu supported over ZnO   0 1 10 using well for water gas shift reaction have been studied in our previous works [15].…”

“…The powerful tool of theoretical techniques to understand catalytic reactions on the surface has been known as the density functional theory (DFT) and self-consistent periodic calculations [1,2,13,17,18]. Thus, we employed here to investigate the CH 3 OH adsorption and dissociation on 2Cu/ZnO (1010) catalyst surface.…”

Chemie mit Methan: Studieren geht über Probieren!

“…[80,81] Theoretischen Voraussagen zufolge ist auch die Methanoloxidation auf subnanometergroßen Palladiumclustern energetisch dann günstiger, wenn die Reaktion mit einer C-H-statt mit einer O-H-Bindungsspaltung beginnt. [82] Im Laufe der letzten drei Jahrzehnte wurden viele Gasphasenexperimenten zur mechanistischen Untersuchung der CH 3 OH!CH 2 [86] Beispiele von Gasphasenexperimenten, in denen die Oxidation von Methanol eindeutig mit der Aktivierung einer C-H-Bindung beginnt, sind eher selten. Die Reaktion von Mn(CO) 3 À mit Methanol stellt eine dieser Ausnahmen dar, bei der im ersten Schritt eine C-H-Bindungsaktivierung des Substrats stattfindet; dieser Schritt ist auch geschwindigkeitsbestimmend.…”