Catalytic activity of Pt-Re-Pb/Al_2O_3 naphtha reforming catalysts

摘要

The main purpose of the naphtha reforming process is to obtain high octane naphtha, aromatic compounds and hydrogen. The catalysts are bifunctional in nature, having both acid and metal sites. The metal function is supplied by metal particles (Pt with other promoters like Re, Ge, Sn, etc.) deposited on the support. The influence of the addition of Pb to Pt-Re/Al_2O_3 naphtha reforming catalysts was studied in this work. The catalysts were prepared by co-impregnation and they were characterized by means of temperature programmed reduction, thermal programmed desorption of pyridine and several test reactions such as cyclohexane dehydrogenation, cyclopentane hydrogenolysis and n-heptane reforming. Results: It was found that Pb interacts strongly with the (Pt-Re) active phase producing decay in the metal function activity. Hydrogenolysis is more affected than dehydrogenation. Part of the Pb is deposited over the support decreasing the acidity and the strength of the most acidic sites. Conclusion: The n-heptane reforming reaction shows that Pb modifies the stability and selectivity of the Pt-Re catalysts. Small Pb additions increase the stability and greatly improve the selectivity to C_7 isomers and aromatics while they decrease the formation of low value products such as methane and gases.