Preparation Of Macroporous Catalysts And Their Application To Preferential Oxidation Of CO In Hydrogen-Rich Gases

Proton exchange membrane fuel cells (PEMFC) with hydrogen as fuel have drawn a lot of attention due to their application in portable, auxiliary and mobile power systems, The practical utility of fuel cells depends on the level of miniaturized hydrogen generator system. The reaction of CO preferential oxide (CO-PROX) is a requisite step of hydrogen generator process. So the miniaturization of the CO-PROX system is a core issue for the commercial utilization of fuel cells.Meso-macroporous alumina supported CuO-CeO₂ catalysts were prepared by citrate, urea combustion and impregnation methods aiming at miniaturizing the reactor of CO-PROX. The effect of loading methods on the microstructure of the catalysts, the interaction between copper and ceria and the catalytic performance for preferential oxidation of CO in hydrogen rich gases was investigated. The results showed that the loading methods markedly influenced the catalyst structure and the catalytic performance. The citrate methods favored the formation of the interaction between copper and ceria. Compared with the urea combustion method, the citrate method led to smaller ceria particles on the alumina support. The meso-macroporous monolithic catalysts prepared by the citrate method maintained the structural characteristics of the highly active CuO-CeO₂ catalysts, The maximum CO conversion reach 99.9% at 163oC (GHSV=1.5×10⁴ h^-1) in the simulated reformate gases containing water and CO2, which suggesting the meso-macroporous alumina monoliths are promising for the application in the compact hydrogen source.The CO-PROX reaction is strongly exothermal and the heat conductivity of catalysts bed imposes a great influence on the catalytic performance. In order to promote the thermal conductivity and prevent the reverse water gas shift reaction (r-WGSR), The metallic copper foams were employed as supports and loaded CeO₂ catalysts by the citrate methods. The monolithic catalysts were tested in the stimulated reformat gas, CO conversion exceeds 99% at 183°C and a high GHSV of 1.0×10⁴ h^-1 In the case of GHSV=7.5×10³ h^-1, the CO conversion reaches 99% at the range of 169-174°C in simulated reformate mixtures.The serious diffusion effect exists from the reactant gas to the catalysts wall of copper foam when the gas flows through the catalysts bed. So the macroporous metallic copper monoliths were prepared by power metallurgy method and employed to promote the mass and heat transfer of catalysts. The macroporous copper monoliths were loaded with copper oxide–ceria catalysts for CO-PROX reaction. The results indicate the monolithic catalysts construction is CuO-CeO₂/Cu–CuO and has good heat conductivity. The catalyst shows very good catalytic performance for CO removal in H2-rich gases, at a high GHSV of 1.0×10⁴ h^-1, CO conversion exceeds 99% at a wide temperature window of 100^-160°C and corresponding selectivities are at the high level of 50 %-90 %. The CO concentrate can be reduced to less than 100 ppm at 185°C in the case of realistic reformate mixtures, which indicating macroporous copper monoliths catalysts with high heat and mass transfer efficiency is preferred for the CO preferential oxidation reaction.In addition, the copper beads were prepared by using resin as templates. The produced metallic beads replicate the shapes and macroporous structures of templates. The porosity is about 60% and the diameter of macropores is in the scale of microns. The copper oxide and ceria catalysts were loaded on the copper beads and evaluated in term of catalytic performance. The results indicate that the maximum conversion of 99% have been achieved in the temperature window of 140^-160 oC at the WHSV 1×10⁴ mL·g^-1·h^-1 in the absent of carbon dioxide and water.