Au_n团簇催化水煤气变换反应机理的密度泛函理论研究

Reaction mechanism of water gas shift reaction Au_n clusters:A density functional theory study

利用密度泛函理论(DFT)研究了Au10、Au13和Au20三类团簇的稳定性和对水煤气变换(WGSR)反应的催化活性,考察了各物质在Aun团簇上的吸附行为和微观反应机理。结果表明,三类Aun团簇的稳定性顺序为Au10<Au13<Au20,而Aun团簇中电子离域性及吸附能力大小趋势为Au13>Au10>Au20。在三类Aun团簇上,水煤气变换反应的控速步骤均为H2O的解离,但其反应机理路径有所不同。Au10团簇上为羧基机理,COOH*中间体直接解离;Au13团簇上为氧化还原机理,两个OH*发生歧化反应;Au20团簇上为羧基机理,COOH*和OH*发生歧化反应。通过对三类团簇上的最佳反应路径进行比较发现,Au13团簇在低温下具有较好的催化活性。

The stability and catalytic activity of Au10,Au13 and Au20 clusters in water gas shift reaction（WGSR） were investigated by density functional theory（DFT）; the adsorption behavior of reaction species and the reaction mechanism of WGSR on various Aun clusters were explored. The results indicated that the stability of three Aun clusters follows the order Au10 Au13 Au20,whereas their electron delocalization and adsorption capacity decreases in the sequence of Au13 Au10 Au20. Three Aun clusters exhibit the same rate-determining step for WGSR,i.e. H2 O dissociation; however,they are quite different in the actual reaction routes. Over Au10 cluster,the WGSR reaction follows the carboxyl mechanism, characterized by the direct dissociation of COOH＊; over Au13 cluster,the redox mechanism applies,suggested by the disproportionation of two OH＊;over Au20 cluster, the WGSR reaction proceeds via the carboxyl mechanism, represented by the disproportionation of COOH＊ and OH＊. A comparison for the optimal reaction paths over three Aun clusters suggests that the Au13 cluster has the highest catalytic activity in the WGSR reaction at low temperature.