Design And Preparation Of Au/Nb-CeO₂ Catalysts And Its Performance In Benzene Combustion Reaction

Catalytic combustion for volatile organic compounds?VOCs?has been the important research subject in environmental management field,among which the heterogenous catalysis study on the building of high-performance catalysts for benzene combustion reaction is of great significance for alleviating air pollution.Au/CeO₂-based catalytic materials have been widely applied to various catalytic fields owing to excellent low-temperature catalytic ability of nano-gold and unique oxygen storage capacity of cerium oxide.To broaden the catalytic application of nano-gold and build the new and highly efficient catalysts,we develop Nb as the promotor firstly to control the physicochemical properties of Au/CeO₂.A series of Au/Nb-CeO₂ catalysts were prepared and then the regulatory effect that Nb has on the interaction between gold and support,the dispersion and valence of gold were investigated.At last,the structure-activity correlation between physicochemical properties of Au/Nb-CeO₂ and catalytic performance for benzene combustion was established.The main research contents are as follows:?1?Firstly,a series of Nb-CeO₂ were synthesized by various methods and Au was then supported on the obtained samples.And then the influence of the two preparation methods on the physicochemical properties and catalytic performance were systematically studied.Also,the regulation of niobium components to Au/Nb-CeO₂ catalytic materials were elaborated.The results show that the catalysts prepared by thermal decomposition method and co-precipitation have good catalytic performance for benzene combustion.The ACN-MM catalysts prepared by thermal decomposition method exhibited much better activity than co-precipitation method mainly because of the improved redox ability of cerium oxide and the enhanced high-dispersion of Au,which are resulted by abundant amorphous NbO_x on the surface.Under the conditions of benzene vapor concentration=1000ppm and space velocity=30000mL/?g?h?,the T_10%and T_90%were 144?and 258?,respectively for benzene combustion reaction.T_90%is about 40?lower than that of undoped Au/CeO₂ catalyst.?2?Next,the influence of Nb,capacity of Au and calcination conditions on the catalysts'property and catalytic performance were systematically investigated on a series of ACN-MM synthesized by thermal decomposition method.On the basis of our findings,it can be concluded that that medium Nb content and Au loading as well as calcination condition were beneficial to the activation process with enhanced redox ability of cerium oxide,the high-dispersion of Au and Lewis acid site on NbO_x.Au/Nb-CeO₂ catalyst with molar ratio of Ce/Nb=15:1,Au loading=3wt%calcined at 400?in air,exhibited the best performance for benzene catalytic combustion.90%of benzene could be converted at 209?on 3wt%Au/Nb-CeO₂,and this is 30 ^o C lower than Au/CeO₂-based catalyst in other related reports.?3?Then,Nb-CeO₂ with various morphologies?rod,broom,spherical and cubic?were synthesized by hydrothermal method and Au was supported on the as-obtained samples.Their performance was further investigated in benzene catalytic combustion.And reaction mechanism of broom ACN-broom with suprior performance was emphatically elaborated.It could be concluded that the rod-like?ACN-bar?and broom-like?ACN-broom?catalysts exhibited better catalytic activity than ACN-MM.The activity decreased in the order of ACN-broom>ACN-bar>ACN-MM>ACN-ball>ACN-cube.T_10%and T_90%for ACN-broom were10?and 30?lower than that of ACN-MM,respectively.The optimum activity of ACN-broom is related to its higher specific surface area,exposed?110?active crystal surface,unique bundle structure,dispersed Nb component and good low temperature redox ability.The higher stability is associated with its strong interaction between Au and Nb-CeO₂.The benzene conversion ratio remains above 90%in 48 h continuous reaction at 230?.