(538a) Oxidative Coupling of Methane with CO2 Using Sr/La2O3 and the Effect of Oxygen Addition

Greenhouse gases such as methane and CO2 are produced in large amounts; methane due to a new method of extraction and CO2 as emission from various industrial processes and vehicles. Converting methane and carbon dioxide into valuable chemicals has been studied for decades as it is both beneficial economically and environmentally. Oxidative coupling of methane with CO2 as oxidant is one reaction where both gases can be used to produce ethylene, a value-added chemical. In this study, strontium-doped La2O3 (Sr/La2O3) catalyst was used to explore its activity for CO2-OCM at various conditions.

In the benchtop experiment, 600mg of pelletized Sr/La2O3 (BET surface area = 4.9m2/g, Johnson Matthey) was packed into a quartz tube reactor (7mm ID). The catalyst activity was studied in three conditions: CH4/CO2 (1/1-2.5), CH4/CO2/O2 (1/1-2.5/0.1), and CH4/O2 (1/0.1). The addition of oxygen was investigated to observe the effect of strong oxidant. The conditions were repeated without catalyst to determine the gas phase reaction. The reactor downstream concentration was analyzed using micro-GC.

The catalyst activity results show that Sr/La2O3 catalyst performed comparably, albeit on the lower activity side, to the catalysts that have been studied for CO2-OCM. At both 875C and 950C, CO2/CH4 ratios higher than 1 led to higher C2 yield, achieving 2.3% at CO2/CH4=2.5 and 2.7% at CO2/CH4=2, respectively. C2 selectivity across all CO2/CH4 ratios and conditions never exceeded 4% due to dominant CO production. With the presence of oxygen, both CO2 conversion CO production decreased and C2 yield increased slightly. The addition of oxygen during the blank tube experiment showed the suppression of CO production at a much greater extent, and more pronounced as the reaction temperature was increased.

This study provides an alternative catalyst for the CO2-OCM reaction. Pelletized Sr/La2O3 showed activity for CO2-OCM reaction and yielded comparable C2 yields to other catalysts. Addition of oxygen to CO2-OCM shows improvement in the catalyst activity and in suppressing the unwanted gas phase reaction. Further investigation is in plan to study the surface morphology change of Sr/La2O3 catalyst during this reaction and also to synthesize CeO2 based catalysts with different metal dopants to study their activity for CO2-OCM.