Controlled Synthesis Of Rh-SnO₂ Heteroaggregate Nanocatalysts And Their Application In Catalytic Selective Hydrogenation

This study employed Rh@Sn core@shell nanoparticles as precursors,and in-situ transformed the mentioned precursors into Rh-SnO2 heteroaggregate nanostructures on the supports.The metal-oxide heteroaggregate nanostructures were fully characterized and their applications in catalytic selective hydrogenations of substituted nitroaromatics were investigated.By this work,the correlation of structures-performance is clarified.The detailed achievements are the followings:(1)Dispersed icosahedral Rh nanoparticles are used as precursors,and following deposition of Sn by reduction of stannous 2-ethylhexanoate in the presence of Rh nanoparticles will form Rh@Sn core@shell nanoparticles.Through impregnation of Rh@Sn onto alumina support,calcination at high temperatures and subsequent H2 selective reduction of Rh oxides,the Rh-SnO2 heteroaggregate nanostructures are resulted.A series of characterization techniques such as XRD,HAADF-STEM and XPS confirm that Rh@Sn nanoparticles consist of Rh cores and Sn shells,and Rh-SnO2 heteroaggregates have close-contact metal-oxide nanostructures.(2)Rh-SnO2/Al2O3 catalysts demonstrated superior catalytic performance for selective hydrogenation of substituted nitroaromatics.Compared with the control Rh/Al2O3 catalysts,the catalytic hydrogenation activity and selectivity over Rh-SnO2/Al2O3 are significantly enhanced at the identical reaction conditions.In addition,at an identical Rh loading,the influence of Rh/Sn ratios on the catalytic performance is also investigated.The results indicate that the best catalytic performance is achieved at the ratio of Rh/Sn of 1/1 while too much Sn will cover the Rh surface to decrease the activity and less Sn will lead to insufficient metal-oxide interaction with a decreased activity.It is concluded in this work that the interaction between Rh and SnO2 stabilizes the Rh nanoparticles to decrease the particle agglomeration,and the synergistic effect between Rh and SnO2 enhance the catalytic activity and selectivity.