采用密度泛函理论(DFT)中的B3PW91方法研究了过渡金属Pd8簇催化氢化乙炔的反应机理.研究表明:H2进入Pd8簇后解离成H原子,并且只有当H原子吸附在Pd8簇表面上时,催化氢化反应才能发生.过渡金属Pd8簇催化氢化乙炔的反应机理的研究证实该催化反应从两种反应物出发经过两条不同的反应途径完成催化氢化反应,两种反应物分别为吸附在Pd8簇上的乙炔(Pd8(2H)-CH=CH)和其同分异构体亚乙烯基吸附物(Pd8(2H)-C=CH2).两条途径均为多步连续的加氢反应,不同之处在于从Pd8(2H)-CH=CH出发的为单一路径,解离后的H原子分步依次加成到吸附在Pd8簇上的乙炔中的C原子上,直到反应完成生成乙烷.而从Pd8(2H)-C=CH2出发的路径较为复杂,分别经过两个不同的过渡态和中间体生成次乙基中间体,该过程相对应的反应位垒相差约12.552 kJ·mol-1,说明这两个过渡态同时存在,无先后次序.然后继续加成H原子直到生成乙烷完成反应.同时,两条路径分别形成一系列具有应用价值的C2有机化合物中间体,其中一些中间体通过分子内质子转移相互转化,使得原本独立的两条反应路径联系在一起,成为网状路径.%The mechanism of acetylene hydrogenation catalyzed by Pd8 cluster was investigated by density functional theory (DFT) method at B3PW91/GEN level. The calculation results showed that H2 dissociated into H atoms wherever it adsorbed and the H atoms then adsorbed onto the surface of the Pd8 cluster. The dissociation of H2 is necessary for the hydrogenation of acetylene to ethane catalyzed by the Pd8 cluster. The mechanism of acetylene hydrogenation is dependent on two isomers: acetylene and vinylidene on the Pd8 cluster (Pd8(2H)- CH=CH and Pd8(2H)- C=CH2). The two pathways follow a multistep and successive process to complete the hydrogenation of acetylene. However, a difference exists between Pd8(2H) 8- CH=CH and Pd8(2H) - C=CH2. For the Pd8(2H) - CH=CH pathway, dissociated H atoms add to the C atom of acetylene on the Pd8 cluster in different steps until they produce ethane. The Pd8(2H)- CH=CH2 pathway is complex and proceeds by two different transition states to create ethylidyne, and then H atoms add to the C atom until hydrogenation ceases. Many valuable C2 organic intermediate compounds are produced during the process and some of them transform by proton translocation, which connects the Pd8(2H)-CH=CH and Pd8(2H)-C=CH2 pathways.
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