Formation of the rhodium oxides Rh2O3 and RhO2 in Rh/NaY

The oxidation states of Rh in NaY supported catalysts have been studied by temperature programmed reduction (TPR). After calcination of the exchanged catalyst to 380°C, both RhO₂ and Rh₂O₃ are identified, besides small amounts of RhO⁺ and Rh³⁺. Quantitative reduction is possible for samples calcined at temperatures not exceeding 500°C. Re-oxidation of the reduced samples leads to formation of RhO₂ and Rh₂O₃, with negligible protonolysis to Rh³⁺. The dioxide prevails after re-oxidation at 320°C, but the sesquioxide after oxidation at 500°C. In the temperature regime where both oxides coexist the reduction of NO with propane is catalyzed even at an O₂/C₃H₈ ratio of 10. Total oxidation of propane reaches 80% at 350°C.