(630e) Oxidative Coupling of Methane Using Layered, Ruddlesden–Popper (R-P) Oxides

With recent increases in shale gas fracking, the need for direct conversion of methane to higher value chemicals and fuels has become important.¹ A feasible approach for conversion of methane to C₂₊ hydrocarbons is oxidative coupling of methane (OCM), which involves the conversion of methane in the presence of oxygen at elevated temperatures to higher molecular weight hydrocarbons (e.g., the formation of ethylene: 2CH₄ + O₂ => C₂H₄ + 2H₂O). While promissing, achieving high yields toward C₂₊ hydrocarbons remains a challenge due to the formation of thermodynamically more favorable products, such as CO₂ and CO. A previously demonstrated approach to improve product selectivity at high operating temperatures involves the use of membrane plug flow reactors, where an oxygen-ion conducting membrane is employed to separate the methane and oxygen streams.² In these systems, oxygen is activated to oxygen ions on one side of the membrane, followed by transport of oxygen ions through the membrane to the methane side, where they react to form C₂₊ hydrocarbons. The commonly used membranes for this process are based on perovskite structures. While promising, perovskites suffer from instability and limited oxygen transport rates through the membrane. In this study, we focused on utilizing layered oxides belonging to the Ruddlesden–Popper (R–P) phases (A_n+1B_nO_3n+1 (n=1, 2..)) as potential catalysts/membranes for OCM. These oxides have significant potential for implemention in membrane reactors since they exhibit high oxygen diffusion properties and thermal stabilities in catalytic processes.^3,4 Here, we reported the performance of the La-Mg series, composed of La_1.4Sr_0.6Al_0.6Mg_0.4O₄ (LSAM), La_1.4Ba_0.6Al_0.6Mg_0.4O₄ (LBAM), La_1.4Sr_0.6Ga_0.6Mg_0.4O₄ (LSGM), and La_1.4Ba_0.6Ga_0.6Mg_0.4O₄ (LBGM). The catalysts are synthesized via a modified sol-gel method and initial catalytic tests are conducted using packed-bed reactors to assess potential for implementation in membrane reactors.

References

1. Wang, B. et al. Catal. Today 285, 147 (2017)
2. Lancaster Farrell, B., Igenegbai, V. O. & Linic, S. ACS Catal. (2016)
3. Gu, X. K. et al. J. Am. Chem. Soc. 140, 8128 (2018)
4. Das, A., Xhafa, E. & Nikolla, E. Catal. Today 277, 214 (2016)