Benzene Alkylation with Propane over Pt-Modified MFI Zeolites

Abstract

Benzene alkylation with propane has been studied on acidic H-MFI zeolites with SiO2/Al2O3 ratios of 51, 104, and 325, mixed (H-MFI+Pt/CeO2) catalytic systems, and Pt/H-MFI bifunctional catalysts with Pt content of 0.02 and 0.3%. In some of the experiments, Zr2Fe intermetallic compound was added to the catalytic system to ensure H2 removal from the reaction zone. The reaction was carried out at atmospheric pressure, in the temperature range of 573–773 K, C3H8/C6H6=1, and WHSV=0.2–7 h−1. The conversion of propane and selectivity to propylbenzenes was found to increase in the following order of catalytic systems: H-MFI<(H-MFI+Pt/CeO2)<Pt/H-MFI<(Pt/H-MFI+Zr2Fe). The increase of the number of strong Brønsted sites in zeolite led, on one hand, to the increase of propane conversion, but on the other hand, to the decrease of the selectivity to target products, which was due to the cracking of propane and propylbenzenes dealkylation and dismutation. Incorporation of Pt into the catalytic system enhanced propane dehydrogenation at the expense of its cracking and resulted in significant improvement of propane conversion and selectivity to propylbenzenes. Addition of an H2 scavenger allowed a shift of the thermodynamic equilibria and an increase in propane and benzene conversion. The best result was obtained on the (Pt/H-MFI+Zr2Fe) catalytic system with an SiO2/Al2O3 ratio of 325 and a Pt content of 0.22%, on which the yield of propylbenzenes reached 96% with respect to equilibrium and selectivity to propylbenzenes was about 60%. The mechanisms of benzene alkylation with propane operating on various catalysts are discussed.