Platinum Metals Rev., 2001, 45, (1), 40
Ammonia Reactions on Ruthenium
Studying ammonia (NH3) decomposition helps in understanding the kinetics of NH3 synthesis and contributes towards cleaning up NH3 emissions from sewage and activated sludge. For nearly a century iron catalysts have been used to synthesise NH3 from hydrogen (H2) and nitrogen (N2). However, ruthenium (Ru) materials are now replacing them. The major drawback of Ru catalysts is H2 poisoning, as H2 retards the dissociative adsorption of N2, which is the rate determining step in NH3 synthesis. As cerium oxide (CeO2) can stabilise noble metal dispersion and improve H2 poisoning, it has been used as a catalytic support to promote N2 activation or NH3 synthesis.
Scientists from Osaka Municipal Technical Research Institute, Japan, have now used Ru and CeO2 to prepare a catalyst which decomposes NH3 with high activity (K. Hashimoto and N. Toukai, J. Mol. Catal. A: Chem ., 2000, 161, (1-2), 171-178). The catalyst consists of Ru-CeO2 highly dispersed in Y-form zeolite (YZ). Ru-CeO2/YZ works at conditions where YZ and CeO2 are inactive.
The catalyst contained (in wt.%): 64.0 SiO2, 19.5 Al2O3, 10.2 CeO2 and 1.9 Ru. The decomposition rate was first order in NH3. The Ru particles loaded on CeO2/YZ reduce inhibition of the decomposition rate by H2.
IR spectra for the catalyst showed that NH3 decomposition at 300°C proceeded via formation of intermediate species, such as Ru−NH3, Ru−NH2, Ru−N2 and Ru−H on the Ru surface.