Detailed study of the plasma-activated catalytic generation of ammonia in N2-H2 plasmas

We investigated the efficiency and formation mechanism of ammonia generation in recombining plasmas generated from mixts. of N2 and H2 under various plasma conditions. In contrast to the Haber-Bosch process, in which the mols. are dissocd. on a catalytic surface, under these plasma conditions the precursor mols., N2 and H2, are already dissocd. in the gas phase. Surfaces are thus exposed to large fluxes of at. N and H radicals. The ammonia prodn. turns out to be strongly dependent on the fluxes of at. N and H radicals to the surface. By optimizing the at. N and H fluxes to the surface using an at. nitrogen and hydrogen source ammonia can be formed efficiently, i.e., more than 10% of the total background pressure is measured to be ammonia. The results obtained show a strong similarity with results reported in literature, which were explained by the prodn. of ammonia at the surface by stepwise addn. reactions between adsorbed nitrogen and hydrogen contg. radicals at the surface and incoming N and H contg. radicals. Furthermore, our results indicate that the ammonia prodn. is independent of wall material. The high fluxes of N and H radicals in our expts. result in a passivated surface, and the actual chem., leading to the formation of ammonia, takes place in an addnl. layer on top of this passivated surface. [on SciFinder (R)]