Plasma-Assisted Ammonia Synthesis over La2O3 Modified by RF Discharge: Effect of Oxygen Vacancies on N2 Adsorption and Associative Mechanism

Ammonia, owing to its high hydrogen content and low storage cost, has emerged as a novel energy storage carrier for electricity-to-gas conversion. Plasma catalysis shows significant promise for sustainable ammonia synthesis due to its mild reaction conditions and zero carbon emissions. The filled catalyst can further enhance the efficiency of plasma-catalyzed ammonia synthesis. However, the performance of the catalyst needs to be improved, and catalyst modification can be a potential method. In this study, radio frequency discharge plasma was employed to treat the nonprecious metal oxide La2O3, resulting in a plasma-assisted ammonia synthesis rate of 35.37 μmol/g/min. This rate is 16.5% higher than the untreated sample (30.36 μmol/g/min) and surpasses that of typical catalysts such as Al2O3 (29.14 μmol/g/min) and MoO2 (24.97 μmol/g/min). Characterization results from EPR and N2-TPD revealed that radio frequency plasma treatment significantly increased oxygen vacancy content on La2O3 surface and promoted N2 chemisorption. We employed density functional theory to further investigate the effect of oxygen vacancies on charge transfer and electronic structure during N2 adsorption process. Subsequently, we calculated the reaction paths of N2 under dissociative and associative mechanisms. Treating La2O3 with radiofrequency plasma serves as a crucial strategy for enhancing the efficiency of plasma-catalyzed ammonia synthesis.