Direct Synthesis of Nitrous Oxide from Nitrogen and Oxygen by Plasma Catalysis Using a Cycled Storage–Discharge Mode: High Selectivity

Compared to the industrial manufacturing process from the decomposition of ammonium nitrate (NH4NO3) that inevitably involves intermediate products (of hydrogen and synthetic ammonia), the direct synthesis route for N2O uses N2 and O2, which is very simple and does not involve any intermediate products. For N2O synthesis, challenges still remain in the direct synthesis from N2 and O2, in particular, with the high selectivity. In terms of the rate-determining step of activation of the inert N2 for direct synthesis of N2O, plasma catalysis is more effective to load electric energies on the N2 molecules than thermal catalysis. Here we report a direct synthesis of N2O from N2 and O2 by plasma catalysis using a cycled storage–discharge (CSD) mode in a dielectric barrier discharge (DBD) reactor with supported catalysts of MnOx/Al2O3. For such a CSD mode, it has two sequential stages in each cycle of the storage of surface-oxygen species only on the catalyst surface generated by oxygen plasma (with a postpurge of nitrogen), followed by the discharge of nitrogen plasma, compared to the normal mode using a mixture of two gases. Under such a CSD mode, it has 6.1 times the selectivity, as high as 91%, of N2O (that far exceeds the literature) compared to the normal mode. This exceptional high selectivity of N2O may be attributed to the outstanding capability of N2 plasma to generate highly reactive nitrogen species that allows efficiently proceeding with surface oxygen on MnOx/Al2O3 catalysts, as well as no extra oxygen species in the gaseous phase (from oxygen plasma of the mixture of two gases) that dismisses the highly reactive nitrogen species (as reductants).