Autocatalytic Surface Hydroxylation of MgO(100) Terrace Sites Observed under Ambient Conditions

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• 作者：John T. Newberg ; David E. Starr ; Susumu Yamamoto ; Sarp Kaya ; Tom Kendelewicz ; Erin R. Mysak ; Soeren Porsgaard ; Miquel B. Salmeron ; Gordon E. Brown ; Jr. ; Anders Nilsson ; Hendrik Bluhm
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：July 7, 2011
• 年：2011
• 卷：115
• 期：26
• 页码：12864-12872
• 全文大小：963K
• 年卷期：v.115,no.26(July 7, 2011)
• ISSN：1932-7455

文摘

We have investigated the reaction of water vapor with the MgO(100) surface using ambient pressure X-ray photoelectron spectroscopy (AP-XPS), which permits the study of the chemical composition of the MgO/water vapor interface at p(H₂O) in the Torr range. Water dissociation on thin MgO(100) films of 4鈥?.5 monolayers (ML) grown on Ag(100) was studied under isobaric conditions at p(H₂O) ranging from 0.005 to 0.5 Torr and temperatures from 380 to 鈭?0 掳C, up to a maximum relative humidity (RH) of 20%. At RH < 0.01% dissociative adsorption occurs only at defect sites (0.08 ML), while terrace sites remain unreactive toward water dissociation. In the range 0.01 < RH < 0.1% there is an abrupt onset of dissociative adsorption at terrace sites which saturates at 1 ML at 0.1% RH, and is accompanied by an increase in molecular water adsorption. At 20% RH there is 1 ML of molecularly adsorbed water interacting with a fully hydroxylated interface on MgO(100). The observed onset of hydroxylation near 0.01% RH is suggested to be due to water molecules aggregating at the surface, leading to an autocatalytic dissociation of water at MgO(100) terrace sites.