铑催化合成气制乙醇反应中CO断键途径的研究

Abstract

利用程序升温表面反应─红外（TPSr-Ir）动态技术考察CO吸附物种对氢的反应性能并检验表面反应生成的中间物，结果表明线式CO对氢的反应性能高于桥式CO，即线式CO更可能是活性吸附态；表面反应生成了HCO、CH2等中间物.用键级守恒（bOC）-MOrSE势方法计算比较了CO→CH2过程中各可能基元步骤在rH（111）面上的反应活化能和反应热，结果表明CO经其部分氢化物种（如H2CO、HCOH）的氢解反应断裂C─O键在能量上最有利.根据这些实验结果，提出铑基催化剂上合成气转化反应主要按缔合式机理进行；CO的优势断键途径为先部分氢化，而后氢助断键.

The main pathway For C-O bond cleavage in ethanol Formation reaction has been studied by using TPSR-IR dynamic method and Bond-Order-Conservation(BOC)-Morse potential approach.The partially hydrogenated CO species, H CO(1589 cm(-1)),and CH2 species(2933 cm(-1))are simultaneously detected by IR in CO adsorption-TPSR(in H2 Flow) dynamic process over Rh-Mn(1:1)/SiO2 catalyst,and a good correlation between the detected surFace Formyl intensity and the ethanol activity is also observed,implying that Formyl species is a key intermediate in the ethanol synthesis and that C-O bond cleavage occurs From a partially hydrogenated CO species.BOC-Morse potential approach predicts the activation energies For C-O bond cleavage on Rh(111) surFace according to dissociation mechanisms(including direct and hydrogen assisted dissociation of adsorbed CO)and association mechanisms(including direct and hydrogen assisted dissociation of partially hydrogenated CO such as H CO,H2 CO,HCOH),showing that the activation energy For hydrogen assisted dissociation of H2CO(or H COH)is the lowest.Based on the results of IR study and BOC calculation,it may be concluded that C-O bond cleavage occurs via hydrogen assisted dissociation of partially hydrogenated CO species.