Comparative study of aromatization selectivity during N-heptane reforming on sintered Pt/Al₂O₃ and Pt-Re/Al₂O₃ catalysts

BACKGROUND: The metal dispersed over a support can be present as small crystallites with sizes less than 5 nm. The smaller crystallites favour aromatization while larger crystallites favour cracking/hydrogenolysis. Sintering results in the agglomerization of smaller metal crystallites. Correlation of size with aromatization selectivity was investigated.RESULTS: The primary products of n-heptane reforming on fresh Pt were methane, toluene, and benzene, while on fresh Pt-Re, the only product was methane. Both catalysts exhibited enhanced aromatization selectivity at different oxygen sintering temperatures. The reaction products ranged from only toluene at 500 °C sintering temperature to methane at a sintering temperature of 650 °C with no reaction at 800 °C for the Pt/Al₂O₃ catalyst. On Pt-Re/Al₂O₃ catalyst, methane was the sole product at a sintering temperature of 500 °C while only toluene was produced at a sintering temperature of 800 °C.CONCLUSION: This is the first time that sintering has been used to facilitate aromatization of supported Pt and Pt-Re catalysts. A superior selectivity behaviour associated with bi-metallic Pt catalysts is established. It was found that no reaction occurred on Pt catalyst after sintering at 800 °C whereas sintering Pt-Re at 800 °C promoted aromatization solely to toluene. Copyright © 2008 Society of Chemical Industry