ChemInform Abstract: Magnetic Resonance Studies of Ammonia Adsorption and Decomposition on Titania-Supported Vanadia Catalysts

Abstract

In-situ proton and deuterion single-resonance NMR techniques were used to study the adsorption and decomposition of ammonia as a function of temperature on a series of V{sub 2}O{sub 5}/TiO{sub 2} catalysts with the weight loading of vanadia ranging from 0 to 6.1 wt % (approximately one monolayer). After analysis of magnetic resonance line shapes, several different molecular species were found to be present on the catalyst surfaces. At low adsorption temperatures on the low-loading samples, the predominant adsorbed species was intact, coordinated ammonia rotating about its C{sub 3} axis. As the weight loading or adsorption temperature was increased, the adsorbed, intact ammonia exhibited an increased H-N-H angle; the total number of protons associated with intact ammonia per gram of sample decreased. At the point where intact ammonia was no longer observed, a new species was observed and assigned to NH{sub 2} moieties. On all samples, ammonium ions were observed at low adsorption temperatures (100{degrees}C) but were found to be easily removed by heating. Their concentration was greater on the higher weight loading samples. The formation of short-lived VOH groups from the protons of dissociated NH{sub 3} was inferred on the higher weight loading samples. Multiple-quantum spin-counting experiments were done tomore » further investigate the nature of the adsorbed species and their groupings on the surfaces. 45 refs., 12 figs., 2 tabs.« less