Stabilization of active sites in alloyed Pd–Rh catalysts on γ-Al2O3 support

• Alloyed Pd–Rh catalyst is more stable than the mechanical mixture.
• Pd2+ active sites in Pd and Rh–Pd catalysts are studied using spin probes.
• Rh diffusion from the surface into the bulk of Al2O3 is studied by PL.
• Electron-donor sites are essential for stabilization of active Pd2+ ions.

Active components for three-way catalysts containing alloyed Pd–Rh particles with the concentration of the components 0.12 and 0.08 wt.%, respectively, were synthesized and studied. The properties of these materials were compared with those of supported catalysts containing one or two precious metals (PM) prepared by mechanical mixing of the components with the same concentrations of PM. The stability of the samples was estimated by in situ prompt thermal aging (PTA) procedure. Photoluminescence (PL) and electron paramagnetic resonance (EPR) were used to show the importance of intrinsic sites of the support in stabilization of single-metal and alloyed Pd-containing clusters with high catalytic activity in CO oxidation. Substantial mutual effect of Pd and Rh in the alloyed particles was revealed. It prevents Pd-containing particles from sintering and hinders diffusion of Rh3+ ions into the bulk of the support at high temperatures. The spin probe technique was used to demonstrate that the alloy formation permits one to improve significantly the catalyst stability to reduction.

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