Sequential Photo-oxidation of Methanol to Methyl Formate on TiO2(110)

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• 作者：Katherine R. Phillips ; Stephen C. Jensen ; Martin Baron ; Shao-Chun Li ; Cynthia M. Friend
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：January 16, 2013
• 年：2013
• 卷：135
• 期：2
• 页码：574-577
• 全文大小：302K
• 年卷期：v.135,no.2(January 16, 2013)
• ISSN：1520-5126

文摘

Methyl formate is produced from the photo-oxidation of methanol on preoxidized TiO₂(110). We demonstrate that two consecutive photo-oxidation steps lead to methyl formate using mass spectrometry and scanning tunneling microscopy. The first step in methanol oxidation is formation of methoxy by the thermal dissociation of the O鈥揌 bond to yield adsorbed CH₃O and water. Formaldehyde is produced via hole-mediated oxidation of adsorbed methoxy in the first photochemical step. Next, transient HCO is made photochemically from formaldehyde. The HCO couples with residual methoxy on the surface to yield methyl formate. Exposure of the titania surface to O₂ is required for these photo-oxidation steps in order to heal surface and near-surface defects that can serve as hole traps. Notably, residual O adatoms are not required for photochemical production of methyl formate or formaldehyde. All O adatoms react thermally with methanol to form methoxy and gaseous water at rt, leaving a surface devoid of O adatoms. The mechanism provides insight into the photochemistry of TiO₂ and suggests general synthetic pathways that are the result of the ability to activate both alkoxides and aldehydes using photons.