Au-Rh and Au-Pd Nanoalloys supported on well-defined Rutile Titania Nanorods for Aromatics Hydrogenation Applications

摘要

TiO_2-supported bimetallic Au-Rh and Au-Pd nanocrystals were synthesized using both impregnation and colloidal approaches employing HAuCl_4 and RhCl_3 as precursors. The as-obtained bimetallic catalysts were then supported onto TiO_2 rutile nanorods in order to provide catalytic systems with well-defined metal-support interactions for HRTEM characterization. The results revealed the superiority of the colloidal approach over the impregnation technique to obtain bimetallic nanoparticles (4 nm in size) with tunable composition. However, for Au-Rh/TiO_2, optimization of the procedure of the sol immobilization onto the TiO_2 support was required to avoid possible Rh re-dissolution. Preparation of Au-Pd/TiO_2 followed the same procedure but with more acidic conditions necessary to perform immobilization on the support. UV-vis spectroscopy and XRD results suggest formation of a Rh-rich shell over an Au core center for Au-Rh NPs, while Au-Pd NPs present a pure alloy structure. Au-Rh/TiO_2 was used for performing the high-pressure hydroconversion of tetralin in the presence or not of H_2S. The results indicate a strong thioresistance induced by the addition of Au to Rh.