Preparation And Catalytic Performance Of Pd-cu/Attapulgite Clay Catalyst For CO Catalytic Oxidation

Catalysts eliminating CO at ambient temperature are involved in industry, military, environmental protection and every aspects of human life, such as air-purification devices for respiratory protection in case of danger at mines or in other building; CO gas masks are also available in military; and removing CO in narrow living sapaces like submarine, aircraft, underground fortification and so on. In addition, in the aspect of academic study the CO oxidation has been regarded as a probe reaction to show the relationship between the structure and the performance, and also to investigate the reaction mechanism.The supported wacker catalyst, in which an aqueous solution of PdCl2-CuCl2is active components, exhibits a higher CO catalytic oxidation activity and stability at near room temperature and is stable in the presence of water vapor in the feed gas especially. In the supported PdCl2-CuCl2catalyst system, the characteristic of the supports is also a critical parameter for its catalytic performance. Alumina and active carbon supports are both effective for this kind of reaction system. Since the nature of the support is of crucial importance to the good catalytic performance of the resultant catalysts, the exploration of new catalyst systems with more inexpensive and easier available supports is still a challenge. Attapulgite clay(APT) used as an adsorbent, catalyst and catalyst support shows a good application prospect, due to its unique structure and excellent physicochemical properties.Attapulgite clay was used as support, a series of Pd-Cu/APT catalysts were prepared by wet impregnation method. The activities of these catalysts for CO oxidation were investigated in a fixed-bed continuous flow reactor. And the effects of preparation conditions (preparation method, active component ratio, calcination temperature etc.) on the catalytic performance for CO catalytic oxidation have been studied in this dissertation. On this basis, the structures and surface properties of Pd-Cu/APT catalyst were investigated by N2-physisorption, XRD, H2-TPR, TPD、TG、XPS and FT-IR. The possible reason for high activity of the Pd-Cu/APT catalyst in water vapor was studied by NH3-TPD technique. At last, the influence of technological conditions (such as the pretreatment time of water vapor, space velocity and CO content in feed gas) on the catalytic activity of Pd-Cu/APT catalyst, the intermitted use and the store stability of the catalyst were investigated. The main results were as follows:1. The CO conversion of the Pd-Cu/APT catalyst increases gradually with the reaction time prolonging, though its initial activity is low. The catalytic activity of Pd-Cu/APT is higher than that of Pd/APT and Cu/APT. On the same preparation and reaction conditions, the catalytic activity of Pd-Cu/APT is superior to that of Pd-Cu/C. Meanwhile, compared with Pd-Cu/APT catalyst without calcination, the catalytic activity of Pd-Cu/APT catalyst can be improved obviously via the calcination treatment.2. Characterization results of Pd/APT、Cu/APT and Pd-Cu/APT indicate that copper species of Pd-Cu/APT mainly exist in the form of Cu+, Pd species are highly dispersed, and there is obvious synergistic effect between the Pd and Cu which facilitate the reduction of Cu species. Furthermore, calcination treatment can cause strong interaction between the active species and support in Pd-Cu/APT catalyst.3. The Pd-Cu/APT catalysts pretreated by water vapor or not were characterized by NH3-TPD and the results show that the water vapor pretreatment can enhance the acid of the catalyst, which may promote the CO adsorption and process of reaction. Therefore, the Pd-Cu/APT catalyst exhibits a better CO catalytic oxidation activity in the presence of water vapor.4. The initial activity of the Pd-Cu/APT can be improved to certain extent by extending the water vapor pretreatment time. CO can be converted effectively under the reaction conditions, normal atmosphere, CO content5000ppm, space velocity3000-10000h-1or space velocity 6000h-1,CO content3000-10000ppm. At the same time, the catalyst shows good intermitted use and some short-term store stability, and the deactivated catalyst can be regenerated by heat treatment.