Studies On Mechanism Of Catalytic Coupling Reaction Of CO And Effect Of Impurities On Catalyst's Activity

Since the 1980's, new synthesis technology of diethyl oxalate (DEO) by catalytic coupling reaction of CO in gaseous phase at normal pressure has become one of important projects of C1chemical process in the world. For the industrialization of this new synthesis technology and the fundamental research on the catalytic reaction , this paper has performed a series of fundamental research on the surface structure of the catalyst, and the mechanism of the catalytic reaction and the catalyst deactivation caused by impurities in the raw gas. The surface structure of the Pd system catalyst first was studied by temperature programmed reduction (TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy(TEM) measurement. The average value of Pd particles was found to be about 8nm,but the promoter-Fe is highly dispersed on the surface of the supporter. It was thought that a ideal catalytic structure, supported Pd catalyst with filling the promoter-Fe, is formed on the surface of Pd system catalyst. A series of studies on the mechanism of CO coupling reaction to DEO were made by using in situ infrared spectroscopy and XPS methods and so on. The adsorption of reactant-ethyl nitrite on the catalyst at reaction temperature was found to play a role in accelerating ethyl nitrite decomposition and the product of ethyl nitrite decomposition was confirmed to oxidize the active component-Pd0 to Pd2+. The steps of the reaction mechanism were proposed and the mechanism phenomenon, such as CO insertion, was explained in the light of the principle of the soft-hard acid and alkali. In this thesis, the effect of oxygen, ammonia and hydrogen on the activity and selectivity of Pd system catalyst was also observed respectively and the generation of the catalyst under the condition of industrial production was tested. The mechanism of ammonia poisoning for the catalyst and the parallel deactivation of the catalyst with H2 were proposed on the basis of the results in a series of observational experiments, including XPS characterization of the catalyst. And the reason for oxygen accelerating simultaneously CO coupling main reaction and side reactions was explained from the experimental phenomenon in present work and the results in XPS characterization of the catalyst. In fact, the above mentioned studies on the mechanisms of the catalyst deactivation and the change of the catalyst activity would be helpful to understanding the law of the interaction of active component, promoter and various impurities, and can be regarded as the collateral evidence for the proposed mechanism steps of CO coupling reaction as well.