On the different roles of isocyanate and cyanide species in propene-SCR over silver/alumina

• Published in: Journal of catalysis 2008-04, Vol.255 (2), p.304-312
• Main Authors: Tamm, Stefanie, Ingelsten, Hanna Härelind, Palmqvist, Anders E.C.
• Format: Article
• Language: English
• Subjects: Catalysis; Catalysts; Chemical reactions; Chemistry; Exact sciences and technology; Gases; General and physical chemistry; NCO; NO x reduction; Propene-SCR; Reaction mechanism; Silver/alumina; Spectrum analysis; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2008.02.019

Silver/alumina is one of the most promising catalyst materials for HC-SCR. The reaction mechanism remains incompletely understood, however. Isocyanate species ( NCO) and cyanide species ( CN), important intermediates in the reaction path in HC-SCR, were investigated by gas-phase FTIR and DRIFT spectroscopy in step-response experiments. In accordance with the literature, the corresponding gas-phase species, HNCO and HCN, were always detected at the same time at the different steps of the experiment; however, the accumulation and consumption of surface NCO and CN species did not show a similar correlation. Consequently, in conflict with the literature, we propose two parallel, independent reaction pathways for NCO and CN species. In one of these reaction pathways, surface nitrates react with C-containing surface species either directly to NCO or via R NO 2 species. In the other pathway, C-containing surface species react with gas-phase NO x or short-lived N-containing surface species to R NO species and subsequently to CN species.