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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Effect of Steps on the Decomposition of CH_3O at PdZn Alloy Surfaces
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Effect of Steps on the Decomposition of CH_3O at PdZn Alloy Surfaces

机译：台阶对PdZn合金表面CH_3O分解的影响

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The decomposition of methoxide (CH_3O) on a PdZn alloy is considered to be the rate-limiting step of steam re-forming of methanol over a Pd/ZnO catalyst.Our previous density functional (DF) studies (Langmuir 2004,20,8068;Phys.Chem.Chem.Phys.2004,6,4499) revealed only a very low propensity of defect-free flat (111) and (100) PdZn surfaces to promote C-H or C-O bond breaking of CH_3O.Thus,we applied the same DF periodic slab-model approach to investigate these two routes of CH_3O decomposition on PdZn(221) surfaces that expose Pd,(221)~(Pd),and Zn,(221)~(Zn),steps.C-H bond cleavage of CH_3O is greatly facilitated on (221)~(Pd):the calculated activation energy is dramatically reduced,to approx50 kJ mol~(-1) from approx90 kJ mol~(-1) on flat PdZn surfaces,increasing the rate constant by a factor of 10~8.The lower barrier is mainly due to a weaker interaction of the reactant CH_3O and an enhanced interaction of the product CH_2O with the substrate.The activation energy for C-O bond scission did not decrease on the (221)~_Pd) step.On the (221)~(Zn) step,the calculated reaction barriers of both decomposition routes are even higher than on flat surfaces,because of the stronger adsorption of CH_3O.Steps (and other defects) appear to be crucial for methanol steam re-forming on Pd/ZnO catalyst;the stepped surface PdZn(221)~(Pd) is a realistic model for studying the reactivity of this catalyst.
机译：在PdZn合金上甲醇盐（CH_3O）的分解被认为是甲醇在Pd / ZnO催化剂上蒸汽重整的限速步骤。我们以前的密度泛函（DF）研究（Langmuir 2004,20,8068; Phys.Chem.Chem.Phys.2004,6,4499）仅显示了极低的无缺陷平板（111）和（100）PdZn表面促进CH_3O的CH或CO键断裂的倾向。 DF周期性平板模型方法研究CH_3O在PdZn（221）〜（Pd）和Zn，（221）〜（Zn）暴露的PdZn（221）表面上分解的这两种途径.CH_3O的CH键断裂极大地促进了（221）〜（Pd）的计算：计算出的活化能从平坦的PdZn表面上的大约90 kJ mol〜（-1）显着降低到大约50 kJ mol〜（-1），将速率常数增加了一个因子势垒较低，主要是由于反应物CH_3O的相互作用较弱以及产物CH_2O与底物的相互作用增强所致.CO键断裂的活化能在（221）〜_Pd）步骤中没有降低。（221）〜（Zn）步骤中，由于CH_3O的较强吸附，两种分解途径的计算反应势垒甚至比在平坦表面上更高。以及其他缺陷）对于在Pd / ZnO催化剂上甲醇蒸汽重整似乎至关重要;阶梯状表面PdZn（221）〜（Pd）是研究该催化剂反应性的现实模型。

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