Switchover of Reaction Mechanism for the Catalytic Decomposition of HCOOH on a TiO2(110) Surface

详细信息    查看全文

• 作者：Yohei Uemura ; Toshiaki Taniike ; Mizuki Tada ; Yoshitada Morikawa ; Yasuhiro Iwasawa
• 刊名：Journal of Physical Chemistry C
• 出版年：2007
• 出版时间：November 8, 2007
• 年：2007
• 卷：111
• 期：44
• 页码：16379 - 16386
• 全文大小：658K
• 年卷期：v.111,no.44(November 8, 2007)
• ISSN：1932-7455

文摘

Catalytic decomposition of HCOOH on a TiO₂(110) surface switches over between unimolecular dehydration(HCOOH H₂O + CO) and bimolecular dehydrogenation (HCOOH H₂ + CO₂), depending on the reactionconditions. As the dehydration and dehydrogenation reactions proceed on acidic and basic oxide catalystsurfaces, respectively, the aspect observed on the same single crystal surface seems to be not compatiblewith the conventional acid-base catalysis concept. To clarify the origin of the switchover of the acid-basecatalysis, the reaction mechanism of the HCOOH dehydrogenation was studied by density functional theory(DFT) calculations. It was concluded from the DFT calculations together with the rate equation andexperimentally determined activation energy that the bimolecular dehydrogenation proceeds between a stronglyadsorbed bridging formate anion and a weakly adsorbed HCOOH molecule by cooperative catalysis of threeadjacent surface Ti⁴⁺ ions as Lewis acidic sites on the surface. This mechanism is entirely different from theprevious dehydration mechanism that the dehydration occurs on an oxygen point defect (basic character)formed in situ by H₂O desorption from two OH under the catalytic dehydration reaction conditions. Thus, theTiO₂(110) surface provides two kinds of active sites for the HCOOH decomposition in a manner differentfrom the traditional acid-base catalysis concept.