Characterization of Au-Rh/TiO2 catalysts by CO adsorption; XPS, FTIR and TPD experiments

Abstract

On X-ray photoelectron spectra of the Au-Rh/TiO 2 catalysts the position of Au4f peak was practically unaffected by the presence of rhodium, the peak position of Rh3d, however, shifted to lower binding energy with the increase of gold content of the catalysts. Rh enrichment in the outer layers of the bimetallic crystallites was experienced. The bands due to Au 0 -CO, Rh 0 -CO and (Rh 0 ) 2 -CO were observed on the IR spectra of bimetallic samples, no signs for Rh + -(CO) 2 were detected on these catalysts. The results were interpreted by electron donation from titania through gold to rhodium and by the higher particle size of bimetallic crystallites.

Monitoring in situ the colloidal synthesis of AuRh/TiO2 selective-hydrogenation nanocatalysts

“…63 Acetal formation is also favored by the Lewis acid character of the catalyst. 4 In our case, CO-FTIR has shown the presence of Lewis acidity on the catalysts. It may be associated not only to the TiO 2 support but also to Rh d+ sites (i.e., oxidic Rh species), the amount of which was previously shown to decrease in bimetallics due to Au-induced Rh 0 stabilization.…”

“…Extensive work on this system was performed by Kiss,Óvári and coworkers. [4][5][6][7] Using either chemical or physical preparation techniques, they showed that Au tends to cover the Rh surface. Using scanning transmission electron microscopy (STEM), Chantry et al 8,9 highlighted the tendency of Rh either to deposit in an uneven way on Au nanorods and/or to form mixed alloy layers at the topmost surface depending on kinetic issues during the formation of such nanostructures.…”

“…Next, a 1 wt% aqueous solution of polyvinyl alcohol (PVA, M w ¼ 10 000) was added to the preceding solution while maintaining a mass ratio m PVA /m Au+Rh of 1.2. A solution of 0.1 M NaBH 4 , freshly prepared and kept at 0 C before use, was then dropped under stirring in the solution of metallic precursors with a molar ratio n NaBH4 /n Au+Rh of 5 to ensure a complete reduction of the two metals. Immediately aer NaBH 4 40 is present under our experimental conditions.…”

“…A solution of 0.1 M NaBH 4 , freshly prepared and kept at 0 C before use, was then dropped under stirring in the solution of metallic precursors with a molar ratio n NaBH4 /n Au+Rh of 5 to ensure a complete reduction of the two metals. Immediately aer NaBH 4 40 is present under our experimental conditions. This likely causes the depletion of Rh revealed by elemental analysis of the supported catalysts (see below).…”

Surface species and gas phase products in the preferential oxidation of CO on TiO2-supported Au-Rh bimetallic catalysts

“…The preparation of 1 w.% Au/TiO 2 and 1 w.% Rh/TiO 2 catalysts has been previously published in details (18,19,21). The bimetallic Au -Rh catalysts with three different compositions were produced by impregnating TiO 2 with the mixtures of calculated volumes of HAuCl 4 and RhCl 3 x 3 H 2 O solutions to yield 1 w.% metal content.…”