Energy transfer and catalytic decomposition of ammonia on rhenium at high temperatures

Abstract

Single‐collision energy transfer and catalytic decomposition of NH3 on polycrystallinerhenium at temperatures up to 2300 K were studied with a modulated molecular beammass spectrometer. Internal energy excitation was determined from threshold ionization measurements. The internal energies acquired by NH3 molecules on collision with the heated filament are well correlated with their acquired translational energies. Nitrogen molecules produced in the reaction are vibrationally excited at levels compatible with the filament temperature, in contrast to the results obtained in the reaction on Pt, where significant quantities of highly vibrationally excited N2 molecules were produced. The principal source of N2 in the reaction is the recombination of chemisorbed NH radicals: NHad+NHad→N2+H2. Appearance potential measurements on NH+ 2 show no evidence for evolution of NH2 radicals. At high temperatures (1600–2300 K), H atoms are produced. The reaction mechanisms involved in the decomposition of NH3 are discussed.