Analysis and process evaluation of metal dopant (Zr, Cr)-promoted Ga-modified ZSM-5 for the oxidative dehydrogenation of propane in the presence and absence of CO2

Abstract

A systematic study of the comparative performances of 4% Ga-, 4% Zr-, and 1% Cr-impregnated H-ZSM-5 catalysts for oxidative dehydrogenation of propane in the presence and absence of CO₂ is presented. It was found that methane, ethene, propene, butene, pentene, and BTX are the major products from all of these catalysts at various reaction temperatures (400-550 °C), WHSV, 4 kg_cat s mol_C3H8 ^-1 and feed gas, C₃H₈/N₂ = 2.5/97.5 and C₃H₈/CO₂/N₂ = 2.5/5/92.5; flow rate, 75 mL min^-1 under atmospheric pressure for 10 h. The combination of material characterization and catalytic testing revealed that Ga-, Zr-, and Cr-doped H-ZSM-5 are excellent catalysts for this process, helping to achieve around 61% CO₂ conversion. The co-doped Ga/H-ZSM-5 catalysts significantly enhanced the activity (65% propane and 61% CO₂ conversion at 550 °C) among all the tested catalysts, with approximately 100% total selectivity 62% towards BTX and 26% towards propene, but with lower selectivity for methane, ethene, and pentene (i.e., light hydrocarbons). TPR profiles indicated that the redox cycle between Cr(iii)O₆ and Cr(vi)O₄ played an important role in the dehydrogenation of C₃H₆ over Cr/Zr-Ga/H-ZSM-5. CO₂ could oxidize a part of the Cr(iii) species to Cr(vi) species under the reaction conditions used.