Plasma Catalytic Conversion of Nitrogen and Hydrogen to Ammonia over Silico Alumino Phosphate (SAPO) zeolites

Abstract Herein, we demonstrate the catalytic activity of microporous Silico Alumino Phosphate (SAPOs) crystals for the assisted plasma synthesis of ammonia. SAPOs can aid as effective catalysts for the synthesis of ammonia via non-thermal plasma using an atmospheric dielectric barrier discharge (DBD) reactor. We studied three prototypical zeolites having crystallographic limiting pore apertures of 3.4 Å (SAPO-56), 3.8 Å (SAPO-34) and 3.9 Å (SAPO-11). We describe a fundamental insight on the effect of the Si/Al ratio and the pore size on ammonia synthesis rate for the different SAPOs. The resultant SAPO-11 displayed ammonia synthesis rates as high as 0.19 micromoles NH3/ min m2 at 20 watts, approximately 1.5 times better compared to other SAPOs. The results indicate that ammonia synthesis is promoted by a lower Si/Al ratio (< 0.25) of the SAPO. Moreover, we observed that SAPO-34 (3.8 Å) and SAPO-11 (3.9 Å) which allow diffusion of N2 (3.6 Å) in to the pores lead to a higher ammonia yield. The lower intensity observed in optical emission spectroscopy (OES) for SAPO-34 suggests the diffusion of plasma activated species onto the surface and the pores. Proving the importance of porosity in plasma catalysis.