| The catalytic synthesis of low carbon mixed alcohols from carbon monoxide hydrogenation is one of the challenging and attractive subjects in the field of C1 chemistry. With the complicated process catalytically, the investigation into reaction mechanism has been an important point of improving the all-round catalytic performance of catalysts. In this thesis, the influence of the preparation variable (mainly calcinations temperature) on the structural and catalytic properties of samples, thus the interaction between copper and zirconia, and then alkali metals, especially K were introduced into CuZrO2-based methanol synthesis catalysts in order to produce mixed alcohols due to its strong ability to promote carbon chain growth. Meanwhile, palladium was added as an effective promoter into this system to increase the activity of both un-doped and K-doped catalysts. A series of characterization techniques including BET, X-ray diffraction (XRD), temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) were employed to investigate the effect of potassium, palladium promoters on the surface structure, physical properties, the activation of CO and H2. Correlation between the structural properties and the catalytic activity was established based on the research of a series of experimental results. Some basic questions about catalysis science, such as the relations between structure and performance, metal-support interaction and synergistic effect between the modifiers were studied. The main contents of the thesis are as follows:1. After studying the effect of calcination temperature on the catalytic performance of CuZrO2 catalysts, it showed that copper was highly dispersed on the support of ZrO2 when the catalysts were calcined at appropriate temperature, enhancing the synergic effect and thus promoting the spillover of intermediates between the copper and ZrO2. However, copper begins to aggregate and ZrO2 crystallize as the excess calcination temperature, leading to the low catalytic activity.2. Carbon monoxide conversion and alcohol time-space yield was improvedmarkedly with the addition of a low concentration of precious metal Pd. TPR and TPD results revealed that Pd enhanced copper oxide reduction while Cu inhibits reduction of Pd species; simultaneously, the presence of palladium improved the adsorption and activation of CO molecular adsorbed on the surface of catalyst. The importance of the palladium incorporated to the CuZrO2 catalyst in determining the catalytic activity was related to the relative ease with which hydrogen is dissociated on the Pd particles and then spilt over the Cu and ZrO2 phase of the base catalyst, and the stronger capability of activating CO molecular.3. After investigating the influence of the different alkali metal promoters on the catalytic performance of the samples, it was found Li to be as the best promoter in terms of catalytic activity of alcohols synthesis and, from the selectivity of C2+OH point of view, Cs is an optimism modifier. As a matter of fact, K promoter was used more frequently as a doper economically.4. It was observed that K component appears to enhance the selectivity of C2+OH significantly with the lower catalytic activity simultaneously. Furthermore, overall performance of catalyst was found to depend strongly on the amounts of K impregnated. Generally, optimum K promoter concentration was about 2.5% by weight. It was proposed that the balance between the acid and base sites was regulated by the addition of K favoring the surface chain growth reaction. On the other hand, the presence of K inhibits CuO reduction, blocks surface Cu atoms, and therefore leads to the poor activity of catalysts for alcohols synthesis.5. The effective coupling effect of potassium and manganese, which was controlled by the loadings content of K, that is, the ratio of K to Mn, enhanced the capacity of carbon chain growth of catalysts and thus increased selectivity of C2+OH of catalytic product. Moreover, with the increase of K content... |
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