Preparation Of Meso-macroporous Oxide-Graphene Catalysts And Their Application To The Preferential Oxidation Of CO In H₂-rich Gases

The preferential oxidation of CO?CO-PROX?in H₂-rich gas is a key step of hydrogen generator process for proton exchange membrane fuel cells.Recently,the miniaturization of the CO-PROX reactor has been acted as the focus of widespread research.The aim of work is to develop a new catalyst with high catalytic performance,high efficiency,high stability for CO-PROX,as well as to meet the requirements of the miniaturization.Firstly,a chemical and thermal stability tri-block copolymer?P123?and polystyrene?PS?foam were used as the template for the meso-macroporous SiO₂ monoliths.The meso-macroporous SiO₂ possess both macropore that is interconnected through windows and mesoporous channels that are long,parallel and highly ordered.Then a series of high catalystic performance K-Ru/meso-macroporous SiO₂ catalysy,in which K is promoter and Ru is active metal,were prepared and used for the preferential oxidation of CO?CO-PROX?in H₂-rich gases.The catalyst of K-5wt.% Ru/meso-macroporous SiO₂ with molar ratio of K:Ru=5:7 exhibites relatively high activity and selectivity for CO-PROX from 100^-140 oC in reaction gases of 1% CO,1% O₂,50 vol.% H₂ and N2 balance at a high space velocity of 24,000 ml g^-1 h^-1,and also shows excellent catalystic performance for H₂ O and CO₂ resistance.Secondly,a series of K-Ru/meso-macroporous SiO₂ are prepared via four different procedures.The highly dispersed and uniform size Ru nanoparticles were supported on K-promoted meso-macroporous SiO₂ by eliminating the influence of K durning the impregnation.Then,Ru nanoparticles can be highly dispersed on K-promoted meso-macroporous SiO₂ by using the simple impregnation method.The resulted K-Ru/SiO₂ catalyst exhibited very high activity and selectivity for CO-PROX.The particle size has an effect on the selectivity,and the catalyst with the smaller particle size showed better resistance for CO methanation.Among those methods,the K-Ru/SiO₂?SC?with small Ru nanoparticles show the higher activity at low temperature,broader window of CO purification and better resistance for CO methanation in the same test conditions of CO-PROX.The macroporous monolithic GE-macro-mesopore SiO₂ was prepared by imbibing polystyrene foams with silica hydrosols.It possesses the hierarchical porosity,such as interconnected macro pore,highly ordered mesoporous channels,the slit-like pores between GE and SiO₂ and stacking micropore,in which SiO₂ and graphene sheets in the composite are uniformly mixed.Ru nanoparticles with high dispersion were selectively loaded on the surface of the graphene sheets of the composite.The resulted Ru/SiO₂-graphene composite showed excellent catalytic activity,high selectivity and good stability for CO-PROX.The bimetallic Pt-Ni supported on a composite consisted of meso-macroporous SiO₂ and graphene sheet was prepared by a simple sol-gel method combined with impregnation method,which showed excellent low-temperature activity,wide temperature window for purifying CO and very good stability for CO-PROX.In the catalyst,Pt-Ni nanoparticles were supported on the surface of graphene sheets,were in the state of alloy and highly dispersed with size of several nano meters.The high activity of the catalyst is attributed to the formation of Pt-Ni alloy and to Pt?0?enrichment resulted from the electron donating effect from GS and nickel species.The macroporosity of the composite and the mesoporosity of SiO₂ in the composite provided with sufficient passages for the reactant gases to contact Pt-Ni nanoparticles,which is another main reason for the excellent catalytic performance.Such as,the Pt-Ni/graphene-SiO₂ exhibites relatively high activity and selectivity for CO-PROX from 105^-120 oC in reaction gases of 1% CO,1% O₂,50 vol.% H₂,12.5 vol.% CO₂,15 vol.% H₂ and N2 balance at a high space velocity of 24,000 ml g^-1 h^-1,and also shows excellent catalystic performance for H₂ O and CO₂ resistance in the high space velocity.