Study Of Nickle-based Perovskite-type Catalysts Forammonia Decomposition At Low Temperature

Proton exchange membrane fuel cell (PEMFC) is the most promising powersource for electric cars as well as portable equipments due to its favorable advantages,such as high efficiency, low weight and less environmental impact.On-site generation of COx-free hydrogen from ammonia decomposition for fuelcell applications has attracted much attention, due to the drive for betterenvironmental protection and energy conversion efficiency.However, ammonia is avery stable molecule that is a reversible decomposition and endothermic reactions thatrequires higher temperatures to be conversed completely. So the catalysts of ammoniaat low temperature is the critical issue.In this study, in light of perovskite oxides having many advantages such asexcellent thermal stability, superior redox properties, great versatility and low cost, aseries of perovskite oxides catalysts would be subjected to ammonia decompositionactivity test.The optimal perovskite would be selected, doped by some metals andloaded on different supports to determine the novel catalyst candidates for theammonia decomposition.A series of ABO3perovskite-type catalysts with different B-site ions (B=Ni, Co,Fe, and Cr) was prepared in ammonia composition and characterized by TPR andXRD, in order to obtain the main factors for ammonia decomposition overperovskite-type catalysts. It was found that Ni-based perovskite has the best catalyticperformance, yielding100%NH3conversion at640℃and10000h-1.According to the activity comparison between LaNiO3and simple oxides NiO,itcould be concluded that the crystal structure of ABO3perovskite had a remarkablepromotion effect on ammonia decomposition process.Furthermore, the ammoniadecomposition activities of La1-xMxNiO3(M=Ce,Ir,Sr; x=0,0.2,0.4,0.6,0.8) was alsoinvestigated, it was obtained that the substitution of Ce for A-site element (La) inLaNiO3would improve significantly the activity in low-temperature range (300-500℃)and high-temperature range (500-750℃), respectively and x=0.4is optimalsubstitution. Ni-based perovskites supported on different supports MgO, SiO2,γ-Al2O3were subjected to activity test of ammonia decomposition to select the optimumsupport which turns out SiO2is the best support. The ratio of SiO2to NiO was a key factor to influence the ammonia decomposition performance. In this study, the bestcatalyst for the ammonia decomposition reaction was LaNiO3supported on SiO2withthe loading of NiO20%, which achieved100%NH3conversion at640℃,same tosingle LaNiO3. Not only the catalytic activity can be improved, but also the amount ofactive component is greatly reduced. Thus it lowers the production costs and ispromising for application. It could be concluded that the ammonia decompositionactivities differs from different structure of SiO2.Due to its mesoporous large specific surface area and ordered mesoporousstructure, the MCM-41molecular sieve is conducive to the dispersion of the activeingredient, increases the effective active sites and improve the reaction capacity of theactive ingredient,thus it shows good catalytic activity in ammonia decomposition.Based on the research above, a novel catalyst,20%La0.6Ce0.4NiO3/MCM-41, isprepared for ammonia decomposition.As a result,it shows good catalytic performanceand ammonia can be completely transformed at536℃.