Effect Of Calcination Treatment On Catalytic Performance Of Pd-Cu/APT For CO Oxidation At Ambient Temperature

CO oxidation at low (ambient) temperature is involved in industry, aerospace, military, environmental protection and every aspects of human life, including civilian and military CO gas masks, automobile cold start exhaust control, and CO elimination in narrow living spaces such as submarine, aircraft. In the aspect of academic study CO oxidation at low (ambient) temperature has been regarded as a probe reaction to show the relationship between surface properties, grain size, morphology, exposed crystal surface, crystalline phases and the catalytic performance. Therefore, CO catalytic oxidation at low (ambient) temperature has important practical value and extensive theoretical significance. CO oxidation at low (ambient) temperature is a hot issue in catalytic field.The supported Wacker catalyst is rich of Cl", while water vapor molecules involve in Wacker catalytic reaction. The supported Wacker catalyst not only exhibits a high catalytic activity for CO oxidation but also possess much higher water resistance, anti-halide poisoning in the presence of water vapor and the organic halide at room temperature compared with oxide catalyst and precious catalyst. Affected by the preparation methods, reaction conditions, activated carbon or alumina supported Wacker catalyst exists poor stability such as Cu species decomposition resulted from calcination at high temperature and Cu active phase aggregation and phase transition in catalytic reaction process. Studies have shown that supports and pretreatment conditions have an important influence on the formation, structure and stability of the active phase. In the previous work, natural attapulgite (APT) as a carrier, we have investigated preparation and catalytic performance of Pd-Cu/APT catalyst.Based on our previous research, the effect of calcination temperature on chemical and physical properties, phase structure and performance of the catalyst for CO oxidation at ambient temperature was investigated by FT-IR,XRD, TEM, N2-physisorption, TG-DTA, H2-TPR and H2-TPR-MS. The possible reason for deactivation of the Pd-Cu/APT catalyst was suggested by structure characterization of fresh and deactivated catalysts. In view of the deactivated reason, catalyst can be able to regenerate by calcination treatment. The effects of different regeneration conditions (the regeneration temperature, regeneration time, regeneration atmosphere) on the catalytic activity of Pd-Cu/APT catalyst were investigated. At last, storage stability of the catalyst was studied. The main results were as follows:1. The effect of calcination temperature on catalytic performance of Pd-Cu/APT catalyst for CO oxidationThe calcination temperatures have an obvious impact on structure of support and Cu species active phase. The results show that as the calcination temperature increase, structure and texture of the catalysts changed which are caused by desorption of water in the support. Cu species change from Cu(OH)Cl to CuO gradually, while interactions between highly dispersed Pd and Cu species increase firstly and then decrease. The catalyst calcined at 300℃ possess the highest surface area, dispersed Cu(OH)Cl, and strong interaction between Pd species and Cu species. Under the reaction conditions of CO 0.5%, GHSV 6000 h-1, water content 3.3% and ambient temperature, the catalyst is able to maintain its activity for CO complete oxidation more than 800 min. Calcination temperatures higher or lower than 300℃ cause the catalytic performance to decrease.2. The investigation of reason for deactivation and regeneration technological conditions for Pd-Cu/APT catalystCharacterization results of the fresh and deactivated Pd-Cu/APT catalysts indicate that, on the one hand, water vapor in the feed gas adsorbs on surface of catalyst and interacts with support to improve crystallinity of support. Then specific surface area of the catalyst reduces slightly, resulting in Cu active species slight aggregation, thus inhibited reducibility of the catalyst significantly. On the other hand, excess water vapor condensed on surface of support covers the active centers, resulting in reduction of the catalytic activity. Deactivated catalyst which is treated 30 min at 150℃ without any atmosphere obtains the best catalytic activity. Pd-Cu/APT catalyst stored after 7 months has an excellent activity and exhibits good storage stability.