Effects of acidity and combination of Ga and Pt on catalytic behavior of Ga-Pt modified ZSM-5 catalysts in benzene alkylation with pure propane

Alkylation of benzene with pure propane under flow condition has been investigated on a series of monometal gallium and bimetal gallium-platinum modified H-ZSM-5 zeolites with different acidity. The catalysts have been intensively characterized by XRD, XPS, TPR and IR spectroscopy. The chemical states of Ga and Pt have been studied and correlated with catalytic performances of these materials. The coke deposition on catalysts has been evaluated. It was found that the catalytic activity, product distribution and reaction path depend strongly on zeolite acidity and Pt content. With increasing the Si/Al ratio, the benzene conversion decreases and products distribution changes. Main reaction products for high acidity catalysts (lower Si/Al ratio) are toluene, ethylbenezene (EB) and xylenes, indicating that the cracking of propane is favored over its dehydrogenation. For the samples with low acidity, the formation of cumene and propylbenzenes (PrBz) is enhanced. Bimetal GaPt samples show high catalytic activity and selectivity to cumene. Pt promoted Ga-ZSM-5 catalysts show low concentration of coke like polyolefines and polycondensed aromatics, because platinum has a role of the entrance for hydrogen spillover which prevents or moderates coke deposition. Bimetal GaPt samples could be very efficient catalysts for cumene production from benzene alkylation using propane as alkylating agent. It is established that part of platinum in the bimetal samples is in zero valent state and most probably form big metal particles. (C) 2004 Elsevier B.V. All rights reserved.