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水煤气变换反应是一个重要的反应体系,它可以去除H2中少量的CO而被应用在质子膜燃料电池中.然而关于水煤气变换的反应机理还存在一定的争议,为阐明其反应机理,本文采用密度泛函理论PBE方法,金属元素采用Lanl2dz基组,非金属元素采用6-311++G(d,p)基组,对系列二元铜团簇Cu6TM(TM=Co,Rh,Ir,Ni,Pd,Pt,Ag,Au)催化水煤气变换反应机理进行了研究.结果表明:CO分子比H2O分子更容易吸附到团簇上.水煤气变换反应包括三种反应机理:羧基反应机理,氧化还原反应机理,甲酸反应机理,相对应的基元反应分别为CO*+O*→CO2(g),CO*+OH*→COOH*→CO2(g)+H*,和CO*+H*+O*→CHO*+O*→HCOO**→CO2(g)+H*.甲酸根是实验中最可能检测到的中间物,这是由于生成甲酸根有较低的能垒以及甲酸根解离有较高的解离能.Co,Rh,Ni,Pd掺杂在Cu7团簇中对水煤气转化反应的催化效果明显比纯Cu7团簇催化效果好.采用CO的初始消耗率以及最终CO2的产率进一步研究了在Cu6TM(TM=Co,Rh,Ni,Pd)表面甲酸根是反应过程中的旁观者还是一种重要的中间物.计算结果还表明,对于Cu6TM(TM=Ni,Pd),由于CO较低的反应能垒,水煤气变换反应主要按照氧化还原反应机理进行反应,而对于Cu6TM(TM=Co,Rh),水煤气变换反应三种反应机理均可进行反应.本文的结果有助于理解水煤气变换反应和设计更好的催化剂.
Water gas shift reaction is an important reaction system, it can remove a small amount of CO in H2 and is used in proton membrane fuel cells. However, there is still some controversy about the reaction mechanism of water gas shift. To clarify its reaction mechanism, In the PBE method, the Lanl2dz group is used as the metal element and the Cu2TM (TM = Co, Rh, Ir, Ni, Pd, Pt, Ag, Au) catalyzed water gas shift reaction.The results show that CO molecules adsorb to clusters more easily than H2O molecules.Water gas shift reaction includes three reaction mechanisms: reaction mechanism of carboxyl group, redox reaction mechanism , Formic acid reaction mechanism, the corresponding elementary reactions are CO * + O * → CO2 (g), CO * + OH * → COOH * → CO2 (g) + H *, and CO * + H * + O * → CHO * + O * → HCOO ** → CO2 (g) + H *. Formate is the most probable intermediate in the experiment due to lower energy barriers to formate formation and formate dissociation Higher dissociation energy.The catalytic effect of Co, Rh, Ni, Pd doping on the water gas conversion reaction in Cu7 clusters is obviously better than that of pure Cu7 clusters.Using the initial consumption rate of CO And the yield of final CO2 The formate on the surface of Cu6TM (TM = Co, Rh, Ni, Pd) was further investigated as a by-product of the reaction or an important intermediate.The results also show that for Cu6TM (TM = Ni, Pd). Due to the low energy barrier of CO, the water-gas shift reaction mainly reacts according to the redox reaction mechanism, but the three reaction mechanisms of Cu6TM (TM = Co, Rh) and water-gas shift reaction can react. The results help to understand water-gas shift reactions and design better catalysts.