Ahmed Alolaywi

King Fahd University, Saudi Arabia

Abstract Title:Oxidative cracking of n-hexane to olefins over VOx/Ce-Al2O3 Catalysts

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This study investigates the kinetics of oxidative cracking of n-hexane to olefins using lattice oxygen of VOx/Ce-Al2O3 catalyst. The TPR/TPO analysis shows a consistent reducibility (79 %) of VOx/Ce-Al2O3 over repeated reduction and re-oxidation cycles. Using NH3-TPD, the total acidity of the sample is found to be 12.2 cm3/g (0.54 mmol/g).  Approximately 22 % of the total acidity results in from the presence of strong acid sites that contributes towards increased selectivity of olefin range products during oxidative cracking. This is also observed during the oxidative cracking of n-hexane in a fluidized CREC Riser simulator. Under the studied reaction conditions, 60% olefin selectivity is achieved at 30% n-hexane conversion. The majority of these olefins come from both cracking and oxidative dehydrogenation (ODH) reactions of alkanes with the catalyst’s lattice oxygen. Based on the experimental observations, a kinetic model is developed considering (i) cracking, (ii) ODH and (iii) catalyst deactivation due to coking and oxygen depletion. The proposed cracking mechanism considers adsorption, C-H and C-C bond fission and desorption as elementary steps and implemented by pseudo steady state hypothesis (PSSH). A Langmuir-Hinshelwood mechanism is found to represent the ODH reactions. The developed model fits the experimental data with favorable statistical indicators. The estimated specific reaction rate constants are also found to be consistent with the product selectivity data.