Design And Preparation Of Promoted Gold Nanoparticle Catalyst For Selective Oxidation Reactions

The selective oxidation reaction plays an important role in petrochemical production given its products are widely used as fine chemical intermediates and organic solvents.However,selective oxidation products are more active than raw materials and prone to excessive oxidation reaction,producing large amount of by-products and causing waste of resources and serious environmental pollution.It has been proved that gold nanoparticle?NP?catalysts have excellent oxidation activity and are widely used in the selective oxidation of benzyl alcohol and cyclohexane.However,the gold nanoparticles have high surface energy,so it is easily aggregated and inactivated in the reaction and even dissociate from the support,causing the loss of active components.Meanwhile,the low selectivity of target products on high active gold NP catalyst is still a problem.In the view of above questions,in this work,palladium,platinum,tin oxides,molybdenum oxides were applied as promoter to modify gold NP catalyst based on our previous research work.The impact of different promoters and its content on surface structure,stability and catalytic performance of catalyst were extensively investigated.Au-Pd/MCF and Au-Pt/MCF catalysts were designed and synthesized with noble metal Pd and Pt as promoters,respectively.The obtained catalysts were characterized by XRD,XPS,UV-Vis,TEM and chemisorption techniques,and further applied for partial oxidation of benzene alcohol and cyclohexane.UV-Vis and XRD characterization results show that Au-Pd and Au-Pt noble metal alloy catalysts are formed.XPS results show that there are electrons transfer between Au and promoter?Pd,Pt?atoms.The benzyl alcohol and cyclohexane partial oxidation results indicate that introducing Pd significantly enhanced the activity of gold NP catalyst,and 0.4%Au-0.6%Pd/MCF catalyst exhibited the highest activity.XPS results confirms that 0.4%Au-0.6%Pd/MCF catalyst contains large amounts of Au^0*or Au^?+species which are corresponding to the excellent partial oxidation performance of gold-palladium catalysts.It was also found that the presence of palladium oxides on the catalyst surface significantly inhibit the catalytic activity of Au-Pd catalysts.It was found that introducing Pt atoms inhibited the catalytic activity of Au NP catalyst because the presence of Au^?-and Pt^?-which are not as active as Au^0*or Au^?+species.Au-Pt alloy NP catalysts exhibited a relative low catalytic activity for partial oxidation reaction,but a high selectivity towards useful products were obtained.Meanwhile,transition metal oxides such as tin oxide and molybdenum oxide were introduced into gold NP catalyst as promoter and the effect of promoter to partial oxidation performance was investigated.The introduction of a small amount of tin oxide?such as 0.2wt%?led to the alternation of surface electronic structure of gold NPs and improved the catalytic performance of the gold catalyst.However,as the content of tin oxide increased,which may cover the active sites and lead to the aggregation of gold NPs,and further reduce the catalytic activity of gold catalysts.The introduction of molybdenum oxide does not change the surface electronic structure of gold NPs,but leads to the aggregation of gold NPs and covers the surface active sites,resulting in a low catalytic activity.as the content of molybdenum oxide increases in the catalyst.