键级守恒法研究甲酸在过渡金属上的分解机理

Bond Order Conservation Approach to the Mechanism of Decomposition for Formic Acid over Transition Metals

用键级守恒-Morse势方法研究了甲酸在Ag(111)、Ni(111)和Fe/W(110)面上极低覆盖度及较高覆盖度下的分解机理。计算结果表明,在极低覆盖度下甲酸分解通过HCOO中间体进行,其分解能力依Ag<Ni<Fe/W次序增加。Fe/W上HCOO的C—H、C—O键裂活化垒相差不大,且HCOO可氧化表面。覆盖度较高时,Ag上分解机理无变化,而在Ni、Fe/W上甲酸双分于失水形或表面络合物(HCO*HCOO),随后进一步分解。分解能垒在Ni上较低,有可能呈现自催化行为。

Bond order conservation-Morse potential approach has been used to study the mechanism of decomposition for HCOOH on Ag(111), Ni(111) and Fe/W(110) surface in the two cases of extremely low and higher coverages. The following results have been obtained; In the first case, HCOOH decomposed via intermediate (HCOO(s)) , which proceeds following the order Ag<Ni<Fe/W easily, over Fe/W HCOO oxidizes the surface and the bond scission of C-H and C-O has a small energy barrier difference. In the second case, the mechanism does not change over Ag, but changes over Ni,Fe/W. Two HCOOH molecules form a surface complex (HCO(s) * HCOO(s)) with the loss of water and then decompose further. Over Ni the decomposed reactions have low energy barriers and can show an autocatalytic behavior.