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Investigating the operation parameters for ammonia synthesis in dielectric barrier discharge reactors

Plasma-assisted nitrogen fixation has been considered a potential green alternative for conventional Haber–Bosch process and has recently received a lot of attention. Ammonia synthesis in nonthermal plasma reactors at atmospheric pressure has been investigated in this research with a 5% Ru/α-Al2O3 catalyst. The operating parameters including feed molar ratio, flow rate, applied voltage, discharge power and argon dilution were investigated to provide information for optimization of NH3 concentration and energy consumption. Difference between the blank reactor and the catalyst-packed reactor were presented with a discussion on their own optimal parameters. The optimal feed gas ratio (N2:H2) for blank reactor and the catalyst-packed reactor are 1:3 and 2:1 correspondingly. Higher flow rate resulted in a lower NH3 concentration and energy consumption in both blank reactor and the catalyst-packed reactor. Ammonia concentration of 1.49% was achieved in a catalytic DBD reactor with 120 ml min−1, 2:1 N2/H2 feed gas ratio and 38.4 W discharge power, corresponding to the energy consumption of 32.39 MJ mol−1. The discharge power and the reactor temperature is important to the synthesis of ammonia in catalytic DBD reactor and the effect of heat build-up in the reactor on NH3 concentration was observed. Argon addition improved the conversion of nitrogen and hydrogen at a cost of energy consumption and production rate in both blank and catalyst-packed reactor, but it is more beneficial for increasing the conversion of reactants in the case of catalytic DBD reactor.