Effect Of Preparation Method On Catalytic Performance Of Pd-Cu/APT For Low-temperature CO Oxidation

CO oxidation at low temperature is involved in CO gas masks, CO gas sensors, automobile cold start exhaust control, purification of hydrogen for proton exchange membrane fuel cells (PEMFCs), CO2 laser, the reduction of harmful components in tobaccoand CO elimination in narrow living spaces such as submarine, aircraft. In the aspect of academic study CO oxidation at low temperature has been regarded as a probe reaction to show the relationship between exture, structure, morphology, surface properties and the catalytic performance. So CO catalytic oxidation at low temperature has important practical value and extensive theoretical significance.The supported Wacker catalyst contains much 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. In the past few decades, there are a lot of reports about the influence of support, addition agent, reaction conditions and reaction mechanism on the catalytic performance of supported Wacker catalyst. In recent years, some researchers paid attention to developing a suitable preparation method to promote the catalytic performance. In our previous work, natural attapulgite (APT) as a carrier, we have investigated the influence of active component proportion, the addition of Cu2(NO)3 addition agent and calcination temperature on the structure and CO catalytic oxidation performance of Pd-Cu/APT catalyst.Based on our previous research, the effect of preparation method (impregnation method and evaporation ammonia method) on chemical and physical properties, phase structure and performance of the catalyst for CO oxidation at low temperature was investigated by FT-IR, XRD, TEM, N2-physisorption and H2-TPR. Furthermore, the catalysts prepared by different ammonia concentration were characterized in detail, and the effect of ammonia concentration on the catalytic performance of cataltst made by the evaporation ammonia method was also discusseddepthly. The main results were as follows:1. Effect of preparation method on the catalytic activities of Pd-Cu/APT catalysts for low-temperature CO oxidationUnder the reaction conditions of CO 0.5%, GHSV 6000 h-1, water content 3.3% and ambient temperature, the initial CO conversion over catalyst made by evaporation ammonia method can reach 100%, and has almost no change in 160 min. However, the initial CO conversion over catalyst made by impregnation method is less than 10%, lower than the catalytic performance of catalyst made by evaporation ammonia method significantly. The characterization results show that the Cu species exist as CuCl2·2H2O on catalyst made by impregnation method, while the Cu species mainly exist as Cu2(OH)3Cl nanoplatelet on catalyst made by evaporation ammonia method. The Cu2(OH)3Cl nanoplatelet has strong interaction with Pd species and the APT support, and shows better reduction property. So, the catalyst prepared by evaporation ammonia method shows higher catalytic activity than that prepared by impregnation method.2. Effect of ammonia concentration on the catalytic activity of Pd-Cu/APT via ammonia evaporation for CO oxidationUnder the reaction conditions of CO 1.5%, GHSV 6000 h-1, water content 3.3% and room temperature, the initial CO conversion of catalyst made by appropriate ammonia concentration (adding 10 ml NH3·H2O) can reach 70%, while the initial CO conversions of catalyst made by low ammonia concentration (adding 5 ml NH3·H2O) and high ammonia concentration (adding 15 ml NH3·H2O) are only 20% and 30% resectively. The results showed that under the condition of low or high ammonia concentration, the CuO phase was the main Cu species, and there was only small quantity of Cu2(OH)3Cl on the Pd-Cu/APT, which leaded to poor catalytic activity. The appropriate ammonia concentration facilitated the formation of stable Cu2(OH)3Cl, and the high dispersed degree, nanoplatelet morphology and strong interaction between Pd species and Cu2(OH)3Cl significantly promoted the catalytic performance.