Effect Of Hydroxyl At Halloysite Surface And Distribution Of CeO₂ Facets On Structure And Catalytic Performance Over Copper-cerium Catalysts

Proton exchange membrane fuel cells（PEMFCs）are new power generation devices that convert chemical energy into electrical energy.The Pt electrode of PEMFCs is very sensitive to CO and easily poisoned in hydrogen-rich fuel.The CO content in hydrogen fuel is reduced to about1%,through reforming of hydrocarbons and water-gas shift reaction.Preferential oxidation of CO（CO-PROX）is an effective method to reduce CO content from 1%to below 100 ppm.Due to the redox property and high oxygen storage capacity of CuO/CeO₂ catalysts,it has potential applications in CO-PROX.However,the reducibility of the copper species in the CuO/CeO₂ easily leads to poor stability.Researches show that the hydroxyl on the catalyst surface can promote the formation of bicarbonate species during CO-PROX reaction to accelerate reaction rate.Moreover,CeO₂ supports exposing specific facets are beneficial to stabilize Cu⁺and then improve the stability of the catalysts.Herein,hydroxyl-rich halloysite（HNTs）materials and CeO₂ exposing to specific facets are selected as supports to improve the stability of the catalysts.Further research is conducted to analyze the catalytic mechanism.The specific research contents are as follows:The halloysite support was etched by molten salt method,and then copper and cerium species were loaded on hydroxyl-rich support surface.The effect of hydroxyl on the distribution of active components and catalytic performance was analyzed by series of characterization techniques and catalytic activity tests.The results show that the hydroxyl groups on the inner surface of halloysite contribute to the dispersion of CuO_x and CeO_2-x species on the support surface.During the CO-PROX conditions,Cu⁺-CO carbonyl species form on the catalyst surface,which trends to occur CO oxidation reaction.Simultaneously,the formation of bicarbonate species accelerate the reaction rate of CO oxidation,further improving the catalytic performance of CO-PROX reaction.A series of CuO/CeO₂ catalysts with different morphologies were prepared by impregnation and hydrothermal methods.And the controllability of active component distribution was realized through regulation of facets.It is found that the nano-spherical CuO/CeO₂ catalyst prepared by hydrothermal by impregnation methods has high specific surface area,mainly exposing（111）and（100）facets,accompanied by a small amount of（110）facets.This combination of facets makes CuO_xspecies highly dispersed on the surface of CeO₂ support.And the surface contains a high proportion of Ce³⁺species,which is beneficial to the formation of oxygen defects and the stability of Cu⁺ions.The nano-spherical CuO/CeO₂ catalyst exhibites 100%CO conversion and selectivity at 95 ℃ in CO-PROX reaction,and the complete CO conversion temperature window is 95-215 ℃.