Study On Macroporous Pt/TiO₂ And Pt/CeO₂ Catalysts For Water-Gas Shift Reaction

Water-gas shift (WGS) reaction as a potential pure hydrogen production reaction has recently been attracting rapidly growing interest due to fuel cell power system development, which is considered as a potentially energy source. WGS reaction is a critical process for fuel cell oriented hydrogen production, through which 10¹6%CO can be reduced below 1% and excess H₂ is produced. Supported Pt-based catalysts, especially Pt/TiO₂ and Pt/CeO₂, are promising candidates for WGS reaction owing to their high activity at low-temperature and high stability.The key challenge for fuel cell oriented hydrogen production is the miniaturization of the process, and WGS reactor occupies almost two thirds of the volume in the hydrogen production system from hydrocarbons, so the miniaturization of WGS reactor is of great significance. The aim of this work is to develop novel techniques on WGS reactor miniaturization. Three-dimensionally ordered macroporous (3DOM) Pt/TiO₂ and macroporous - monolith Pt/CeO₂/Al₂O₃ were fabricated by using template method in this work. The so prepared macroporous catalysts were characterized with XRD, TPR, HRTEM, SEM and thermal analysis techniques, and applied to WGS reaction. The relation between catalytic performance and catalyst structure was discussed. The main results and conclusions are as follows:The 3DOM Pt/TiO₂ catalysts exhibited much better catalytic performance than that of both powder and mesoporous Pt/TiO₂ for WGS reaction in 3%CO, 10%H₂O, 87%N₂ feed gases and in the reaction temperature range of 180³60℃, owing to the macroporous structure favoring mass transfer. XPS and catalytic activity results suggested that the active component for the WGS reaction in 3DOM Pt/TiO₂ catalysts was metal Pt which reduced from platinum ions. The results of HRTEM and catalytic stability tests indicated that the sintering of metal Pt particles was the reason for the catalyst deactivation. Chemical adsorption analysis on different 3DOM Pt/TiO₂ catalysts indicated that WGS reaction over the catalysts was structure sensitive. Adding CeO₂ can promote the formation of interaction between Pt and the support. Catalysts with 3DOM structure are potential way to realize the miniaturization of WGS reactor.Macroporous-monoliths of Pt/CeO₂/Al₂O₃ were prepared through inverse concentrated emulsions synthesis route. The macroporous materials exhibited a bimodal meso-macroporosity with macropores in size of 5⁵0μm, as shown in SEM images. The pore size can be adjusted by the volume fraction of dispersed phase and the amount of surfactant added. The macroporous monolith Pt/CeO₂/Al₂O₃ exhibited better catalytic performance that that of micro-channel Pt/CeO₂/Al₂O₃ catalyst for WGS reaction in simulating reformate gases. The converted amount of CO over monolith Pt/CeO₂/Al₂O₃ was much higher than that over micro-channel Pt/CeO₂/Al₂O₃ on per volume of catalysts, showing that the catalysts of the macroporous monolith are promising and much potential materials for the miniaturization of WGS reactor.