Experimental and theoretical studies of reactions of neutral vanadiumand tantalum oxide clusters with NO and NH 3

Reactions of neutral vanadium and tantalum oxide clusters with NO, NH 3 , and an NO / NH 3 mixture in a fast flow reactor are investigated by time of flight mass spectrometry and density functional theory (DFT) calculations. Single photon ionization through a 46.9 nm (26.5 eV) extreme ultraviolet (EUV) laser is employed to detect both neutral cluster distributions and reaction products. Association products VO 3 NO and V 2 O 5 NO are detected for V m O n clusters reacting with pure NO, and reaction products, TaO 3 , 4 ( NO ) 1 , 2 , Ta 2 O 5 NO , Ta 2 O 6 ( NO ) 1 - 3 , and Ta 3 O 8 ( NO ) 1 , 2 are generated for Ta m O n clusters reacting with NO. In both instances, oxygen-rich clusters are the active metal oxide species for the reaction M m O n + NO → M m O n ( NO ) x . Both V m O n and Ta m O n cluster systems are very active with NH 3 . The main products of the reactions with NH 3 result from the adsorption of one or two NH 3 molecules on the respective clusters. A gas mixture of NO : NH 3 (9:1) is also added into the fast flow reactor: the V m O n cluster system forms stable, observable clusters with only NH 3 and no V m O n ( NO ) x ( NH 3 ) y species are detected; the Ta m O n cluster system forms stable, observable mixed clusters, Ta m O n ( NO ) x ( NH 3 ) y , as well as Ta m O n ( NO ) x and Ta m O n ( NH 3 ) y individual clusters, under similar conditions. The mechanisms for the reactions of neutral V m O n and Ta m O n clusters with NO / NH 3 are explored via DFT calculations. Ta m O n clusters form stable complexes based on the coadsorption of NO and NH 3 . V m O n clusters form weakly bound complexes following the reaction pathway toward end products N 2 + H 2 O without barrier. The calculations give an interpretation of the experimental data that is consistent with the condensed phase reactivity of V m O n catalyst and suggest the formation of intermediates in the catalytic chemistry.