Construction Of Pt-Ni Bimetallic Catalysts And Study On Their Catalytic Performance For Hydrogen Production By Steam Reforming Of Ethanol

As the most potential clean energy,hydrogen energy plays a dominant role in the future energy structure.Because of its advantages of renewable raw materials and high efficiency of hydrogen production,ethanol steam reforming?ESR?will become one of the mainstream of hydrogen energy production.However,due to the complexity of the reforming process,factors such as carrier,component selection,metal dispersion and reaction conditions of the catalyst all may affect the catalytic performance of the catalyst.Therefore,how to build cheap,high efficiency,low energy consumption,high thermal stability catalyst has become a hot spot in this field,which also has an important theoretical and guiding significance for the development of hydrogen production technology.In this paper,we mainly studied the construction of various catalyst structures and their reaction performance,which uses Pt and Ni bimetallics as active components to promote the breaking of C-C bond and C-H bond,in the meanwhile CeO₂ with the ability of oxygen storage on the surface,and the highly chemically stable SiO₂ were used as carrier.The structure construction and reaction performance of various catalysts were studied,and the effects of CeO₂ particle size,metal content and different catalyst structure on the reaction performance in the reforming process were revealed.The key research and conclusions are as follows:1.A series of Pt-Ni/CeO₂ bimetallic catalysts were prepared by incipient-wetness impregnation with different sizes of the nanospherical cerium oxide that was prepared by hydrothermal crystallization as carrier,and its application in the reaction of ESR was investigated.The physical and chemical properties and the reducibility of the catalysts were analyzed by various characterization methods.Moreover,we further studied the catalytic activity and thermal stability of the catalysts in-depth.The results show that there are more Ce³⁺active sites in the CeO₂ of small particles,which can achieve high oxygen storage capacity;and its anchorage effect is conducive to the dispersion and stabilization of active metals,exhibiting relatively good catalytic performance.When using 2Pt-6Ni/CeO₂?50 nm?as the catalyst,after 10 h of reaction under reaction temperature of 450°C and the molar ratio of water to alcohol keeping6:1,it showed that the conversion of ethanol did not change obviously,and the selectivity of hydrogen remained about 70%,meanwhile the selectivity of byproduct CO was 1.5%,with the presence of trace amounts of acetaldehyde molecules.This can be attributed to the synergistic effect between the Pt and Ni active components.Pt can promote the decomposition and dehydrogenation of ethanol.In addition to the strong C-C bond breaking ability,Ni component also has a definite activity on water gas shift reaction and methane reforming,which can reduce the content of CO and CH₄ in the product as well.Meanwhile,the presence of Pt improves the dispersion of the Ni component.In addition,CeO₂with high oxygen activity also promoted the dissociation of ethanol and vapor,overcoming the carbon deposition on the metal surface,and the interaction with Pt and Ni promoted the catalytic performance of the catalyst to some extent.2.Using St?ber method to synthesize high specific surface silicon spheres,carrying CeO₂ on its surface,combining the advantages of two materials to prepare CeO₂/Si O₂ composite carrier,bimetallic catalyst Pt-Ni/CeO₂/SiO₂ was finally constructed by adopting impregnation method.The surface properties and catalytic performance of composites with different Ce/Si ratios were investigated.The results indicate that the catalyst prepared from 30Ce/Si samples as composite supports by multiple characterization analysis has spherical shape,no obvious agglomeration,and the particle size is about 500 nm,in which Pt and Ni metal components are highly dispersed.Furthermore,synthesized catalysts also has mesoporous structure,high specific surface,thermal stability and other advantages.And the Pt-Ni/Ce O₂/SiO₂ catalyst at450°C for 20 h without significant deactivation.,ethanol is almost completely conversion,and H₂ selectivity is up to about 70%,showing good catalytic performance.This is attributed to the advantages of the high specific surface area of the composite carrier,which not only improves the dispersion of the metal components,but also enhances the interaction and synergy between the carrier and the metal.At the same time,the anti-carbon deposition ability of CeO₂ particles in the composite carrier is much higher than that of CeO₂ in mechanical mixing,which is favorable for improving the reaction activity and thermal stability.3.A special yolk-shell type Pt-CeO₂@Ni-SiO₂ catalyst was successfully constructed by the improved St?ber method,which was applied to the ESR reaction efficiently.The composite structure was discussed and analyzed in combination with various characterization methods.The results show that the catalyst has a special core-shell structure,excellent dispersion,particle size of about 330 nm,Si O₂ shell coating uniform and thickness of about 30 nm,with high specific surface,good crystallinity,uniform dispersion of metal components.At the same time,the Pt-CeO₂@Ni-SiO₂ catalyst has a H₂selectivity of up to 66%at a low temperature of 400°C.The ethanol conversion is close to 100%and maintains no change for 28 h,showing excellent catalytic performance.This is attributable to the yolk-shell structure can sufficiently promote the utilization of the active component,and the metal Ni on the shell of the catalyst can also perform multiple purifications on H₂.In addition,the structure can effectively prevent the loss of internal components,and the mobility of the core phase increases the interaction between CeO₂ and Pt,which is conducive to promoting CO conversion,and thus obtaining a higher H₂ yield.