Plasma-catalytic ammonia synthesis on Ni catalysts supported on Al2O3, Si-MCM-41 and SiO2

Plasma-catalytic synthesis of ammonia has the potential to store hydrogen on a decentralized scale under mild conditions by consuming the distributed renewable energy power. Suitable catalyst supports can promote plasma-catalytic ammonia synthesis (PCAS). The impact of the support (Al2O3, Si-MCM-41 and SiO2) on the performance of the Ni catalysts for PCAS was investigated under ambient pressure without heating under various N2:H2 ratios, discharge powers, and flow rates. Results indicated that Ni/Al2O3 (Ni-Al) had an energy yield of 0.47 g NH3/kWh at an NH3 concentration of 13,670 ppm or 1.15 g NH3/kWh at an NH3 concentration of 3086 ppm and Ni/Si-MCM-41 (Ni-SiM) had a highest ammonia production rate of 6311 mu mol/(gcat & sdot;h) with the NH3 concentration and energy yield closed to those of Ni-Al. The performances of the Ni-Al and Ni-SiM catalysts were maintained for at least 50 h, and the structures of the catalysts undergoing the 50-h reaction did not change significantly. The role of the support was revealed via several characterizations, suggesting that the number of weak acid sites, Ni dispersion, and Ni -support interactions of the catalysts, which are vital for PCAS, can be affected by the type and structure of the support. In situ and ex situ spectral measurements for some important species in PCAS were performed to test the hypothesis that the reaction takes place over the catalyst and in the gas phase. According to the in -situ DRIFTS in the N2-H2 plasma, ex -situ N 1s oS, and NH3-TPD, it was speculated that the generated NH3 absorbed on the weak acid site could desorb in a timely manner to accelerate the regeneration of the active sites of the catalyst in the N2-H2 plasma, which resulted in a higher ammonia concentration for PCAS.