Restructuring of AuPd Nanoparticles Studied by a Combined XAFS/DRIFTS Approach

Abstract

The use of AuPd nanoparticles in catalysis is widespread, with the activity being attributed to their precise structural properties. We demonstrate the restructuring of AuPd nanoparticles under CO oxidation conditions using a combined XAFS/DRIFTS approach. The fresh catalyst exhibits PdO islands at the surface of the nanoparticles, which are reduced under reaction conditions, a process observed via both DRIFTS and Pd K-edge XAFS measurements. From the EXAFS analysis alone the nanoparticles were observed to have a Au rich core with an outer region of intimately mixed Au and Pd atoms. This structure was found to remain mostly unaltered throughout reaction. However, the DRIFTS spectra showed that although Au was present on the surface during the initial stages of reaction the surface rearranged just before light-off, and contained only Pd atoms thereafter. This study highlights the advantage of this combined approach, where both the surface structure and local environment of the constituent metals can be probed simultaneously, allowing a complete picture of the restructuring of these bimetallic particles to be obtained under reaction conditions.

Recent Advances in the Gold-Catalysed Low-Temperature Water–Gas Shift Reaction

“…There was also no enhancement in catalyst stability after 16 h on-stream in any of the bimetallic catalysts. Additionally, it has been shown that CO preferentially binds to Pd over Au, which could potentially passivate the Au [64,65]. These findings are in contrast to an earlier DFT study that predicted Au/Pd catalysts to be highly active for the LTS reaction.…”

Intensification studies of heterogeneous catalysts: probing and overcoming catalyst deactivation during liquid phase operation

“…83 Microscopic methods such as (S)TEM, 84 can readily demonstrate that active site reorganization occurs. Restructuring of nanoparticles of AuPd has also been studied by combined EXAFS/DRIFTS, 85 and (pulse) chemisorption studies 86 can also be used to readily identify sintering events. Where reorganisation is related to the oxidation or reduction of a particular phase, e.g.…”

Boosting the Characterization of Heterogeneous Catalysts for H2O2 Direct Synthesis by Infrared Spectroscopy

“…Restructuring (and degradation [13]) phenomena occurring on the metal nanoparticles under reaction conditions could be monitored using a combined XAFS/DRIFTS or FTIR transmission approach, as proposed by Gibson et al for AuPd bimetallic catalysts during CO oxidation [123].…”