Group V transition metal oxide cluster reactions: An approach to elucidating the physical basis of heterogeneous catalysis

Transition metal oxides are widely used as catalysts in industrial processes. However, the mechanisms by which these catalysts function and the structure-reactivity relationships are not well understood. A novel technique to understanding the catalytic activity of transition metal oxides is to examine the chemistry of gas-phase transition metal oxide clusters. Reactivity studies of metal oxide clusters are carried out using a triple quadrupole mass spectrometer or a guided ion beam mass spectrometer coupled with a laser vaporization source. Group V transition metal oxide clusters are the focus of this thesis because of their importance in catalytic reactions.; Before reactivity investigations were performed, the formation and collision-induced dissociation (CID) of group V transition metal oxide cluster cation and anions were examined using a guided ion beam mass spectrometer in order to gain some insight into cluster structure. The reactions of tantalum oxide cluster ions with 1,3-butadiene, 1-butene, and benzene were examined using a triple quadrupole mass spectrometer. The major product observed during the reactions of certain tantalum oxide cluster cations with 1,3-butadiene and 1-butene was a C-C activation product, Ta_xO_yC₂H₄+. From these investigations it was found that the extent to which Ta_xO _y+ activate the C-C bonds of 1,3-butadiene, 1-butene, and benzene depends upon the size and degree of coordinative saturation of the cluster.; Additionally, the reactions of group V transition metal oxide cluster ions with n-butane were investigated using a guided ion beam mass spectrometer in order to determine the reactivity of metal oxide cluster ions with a saturated hydrocarbon. The major reaction channels observed during the reaction of certain stoichiometric niobium and tantalum oxide cluster cations include association of n-butane (M_xO _yC₄H₁₀+), C-C activation (M _xO_yC₂H₄+), loss of an oxygen atom (M_xO_y−1+), and dehydration (M_xO_y−1C₄H₈+).; Finally, the reactions of group V transition metal oxide cluster ions with ethane and ethylene were investigated using a guided ion beam mass spectrometer. The major reaction channels observed during the reactions of C₂ hydrocarbons with M_xO_y+ were association and oxygen transfer. The studies reveal that the identity of the metal, charge state, cluster stoichiometry, and geometric structure strongly influence the ability of the metal oxide cluster to transfer an oxygen atom to the neutral C₂ hydrocarbon. (Abstract shortened by UMI.)...