Methanol Adsorption and Dissociation on TiO₂(110) from First Principles Calculations

Abstract

In this work we report on theoretical calculations of methanol adsorption and dissociation on the stoichiometric and defective TiO2(110) surface. The periodic implementation of density functional theory (DFT) with plane waves and pseudopotentials was employed. A supercell made of 4 × 1 unit cells was used to represent the surface, which corresponds to methanol coverage of 0.25 ML. The defective surface was modeled by removing one bridging oxygen from the outermost layer. Several adsorption sites were explored through both static and molecular dynamics calculations. The most stable adsorption site on the defective surface is with the molecule directly adsorbed onto the vacancy, whereas adsorption on titania resembles the stoichiometric case. Our estimated adsorption energies are found to be in agreement with the features observed in previous experimental desorption data. One of the main aims of this study was to determine whether methanol could dissociate on the stoichiometric surface. From static calculations we find that both the molecular and the dissociated state are almost degenerate. In addition, molecular dynamics calculations show that the transition barrier between the two species is small. On the other hand, dissociation on defects is thermodynamically favorable by 0.5 eV. However, dynamic calculations show that in this case the conversion from the molecular to the dissociated state is not straightforward. Implications to these findings are discussed within the text.

Surface photochemistry probed by two-photon photoemission spectroscopy

“…80,81,83 Most DFT calculations show that the transfer of the hydroxyl protons from methanol to the neighboring bridge oxygen sites has a small barrier and the dissociated state of methanol is nearly iso-energetic to the molecular adsorbed state, with the dissociated state being at a slightly higher energy. This suggests that the methanol molecules should be adsorbed on the TiO 2 (110) surface in a molecular form at low temperatures, which is consistent with STM experiments at both room temperature and liquid nitrogen temperature.…”

“…Therefore, the physical and chemical properties of methanol on TiO 2 (110) have been examined in detail both experimentally 29,53,62,[73][74][75][76][77][78][79] and theoretically [80][81][82][83][84] to probe the active sites and relevant reactive structures. Despite this extraordinary effort, central questions remain unresolved, for example, how methanol enhances the photocatalysis of water or how it is eventually photodegraded on TiO 2 .…”

“…As has been reported, the transfer of hydrogen atoms to bridging oxygen sites is much more stable than to the surface in-plane oxygen sites. 81 Therefore, the photochemical changes of methanol on the Ti 5c sites induced by UV irradiation is the photocatalyzed splitting of methanol to formaldehyde with the dissociated hydrogen atoms transferred to the neighboring BBO sites.…”

Effect of defects on photocatalytic dissociation of methanol on TiO2(110)

“…[4][5][6][7][8] Among them, methanol on TiO 2 has attracted much attention in both experimental [9][10][11][12] and theoretical [13][14][15][16][17] investigations because of the remarkable enhancement effect in photocatalyzed hydrogen production in the mixture of methanol with water. 18 Dissociation of methanol on bridge-bonded oxygen vacancy sites (BBOv's) 19 of TiO 2 (110) surfaces has been observed by scanning tunneling microscopy (STM), and this suggests that spontaneous dissociation at these oxygen vacancy sites is possible, in accordance with the recent results of theoretical calculations.…”

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

“…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.…”