Preparation Of Pd-Cu/bauxite Catalysts And Their Co Catalytic Oxidation Performance

The catalytic oxidation is considered as a significant way to eliminate CO in many industrial and environmental protection processes, and the design of highly efficient catalysts is the keystone of the research. However, in view of the current research situation, many researchers focus on the study of use synthetic substances as catalyst carries to improve the CO oxidation activity, and there are few reports on using natural resources as catalyst carries in CO oxidation. In fact, natural carriers always show higher activity than synthetic carriers, and the former behave better in reduce the costs. According to the above factors, series of Pd-Cu/bauxite catalysts for CO oxidation reaction have been prepared, employing alkali solution to modify the bauxite which is quite abundant in China to use as carriers and dipping Pd-Cu on the supporters via incipient wetness impregnant method. The catalysts were characterized by XRD, BET, SEM, H2-TPR, CO-TPD and so on. The optimum condition of modification for bauxite carrier was obtained and the influences of the doped copper contents and calcination temperature on the structure and performance of catalysts were investigated systematically, then the preparation parameters were optimized. The main research findings are summarized as follows:1. The best alkali modification conditions of natural bauxite are shown as follows:the bauxite was hydrothermally treated in a 2 M NaOH solution at 120℃ for 36 h, calcined at 450℃ for 2 h. The morphology and texture parameters of bauxite changed a lot after modification. The modified bauxite obtained below optimum condition has a large specific surface area of 174.5 m2·g-1, the pore volume and average pore diameter are 0.25 mL·g-1 and 5.3 nm respectively. Because the alkali hydrothermal process promoted the breaking of Si-O-Al and O-H-0 layer and contributed to improve the specific surface area.2. The optimal copper content of Pd-Cu/bauxite catalysts was investigated. The results indicate that the activity of Pd-Cu/bauxite catalyst increased at first but later decreased, and the catalyst doped with 4wt% of copper shows the highest catalytic activity. It was attributed to that the right amount of palladium and copper species could form a strong interaction to generate a Pd-Cu species. The Pd-Cu species possessed excellent reducibility, large oxygen vacancies and strong capacity of CO adsorption at low temperature, all of the above promoted the catalytic activity. When the copper content up to an excessive level would leads to the formation of bulk CuO, as the bulk CuO was hard to reduce, also, it possessed a small amount of the weak basic sites and a weak capacity of CO adsorption. As a result, the catalytic activity went down.3. The effect of calcination temperature on the structure and performance of Pd-Cu/bauxite catalysts was studied. It was found that the activity of the Pd-Cu/bauxite catalysts reached the maximum at 400℃, and further increasing the calcination temperature, the activity decreased. That’s because the catalysts could get regular morphology to fully contact with the reaction gas at a right calcination temperature, and there existed a strong interaction between the palladium and copper species to help to enhance the capacity of CO adsorption, all of the above contributed to the catalytic activity. When the catalysts calcined at too high a temperature, the active species would sinter and leaded the decreasing of activity.