Effects of regeneration cycles on heptane-H-2 reactions over Pt-Re/Al2O3 catalysts

Alumina-supported Re, Pt and Pt-Re catalysts have been used to catalyse rea ctions of heptane-H-2 mixtures as a probe of sulfur-free Pt-Re/Al2O3 cataly st structure after a series of pretreatments involving oxidation-reduction and oxychlorination-reduction regeneration cycles. Catalyst activities and selectivities for aromatization, cyclization, hydrogenolysis and isomerizat ion reactions are discussed in relation to CO and H-2 chemisorption, IR and X-ray absorption near-edge spectroscopy (XANES) data and were consistent w ith alloying of Pt and Re with Re surface enrichment on the alloy particles . Surface enrichment of Re was greater in the absence rather than the prese nce of Cl in the catalyst pretreatment. Both oxidation-reduction and oxychl orination-reduction completely removed deposited coke from used catalysts b ut the addition of Cl maintained higher metal surface area and catalytic ac tivity.