Reactivities and Collision-Induced Dissociation of Vanadium Oxide Cluster Cations

Abstract

Reactivities and collision-induced dissociation of vanadium oxide cluster cations are investigated using a triple quadrupole mass spectrometer coupled with a laser vaporization source. The dominant peaks in the mass distribution correspond to cluster ions with stoichiometries of (VO 2 ) n (V 2 O 5 ) m (O 2 ) q + . Collision-induced dissociation studies of the vanadium oxide species V 2 O 4-6 + , V 3 O 6-9 + , V 4 O 8-10 + , V 5 O 11-13 + , V 6 O 13-15 + , and V 7 O 16-18 + show that VO 2 , VO 3 , and V 2 O 5 units are the main building blocks for most of these clusters. The reaction pathways observed for these vanadium oxide clusters include molecular association, cracking, dehydration, and oxygenation of the neutral hydrocarbons with the reactivities of specific clusters differing from species to species. For example, V 3 O 7 + is very efficient in the dehydrogenation of 1,3-butadiene and in the cracking of 1-butene. On the other hand, V 3 O 6 + produces only molecular association products with these same reactants. To help explain these differences in reactivity, calculations on the molecular structure of some of these cluster ions were also undertaken, and the findings are presented.

Cluster Structure and Reactions: Gaining Insights into Catalytic Processes

“…1, can serve as model surface sites. These can be readily formed using standard methods from cluster science [13,14].…”

Mass-selected infrared photodissociation spectroscopy of V4O10+

“…However, only scarce experimental information on the spectroscopy and structure of vanadium oxide clusters is available, [4][5][6][7] complicating the interpretation of the gas-phase reactivity studies. [8][9][10][11][12][13][14][15][16][17] Studies of the mass spectral distributions and cluster growth dynamics of vanadium oxide clusters 18,19 and cluster ions 8,12 show that VO 2 , VO 3 , and V 2 O 5 units are the main building blocks for V x O y À/0/+ clusters. Oxygen-rich cluster ions can also contain a weakly bound O 2 species, as was shown in recent collision induced dissociation (CID) and 532 nm photofragmentation studies.…”

“…Oxygen-rich cluster ions can also contain a weakly bound O 2 species, as was shown in recent collision induced dissociation (CID) and 532 nm photofragmentation studies. 7,8 Gas phase reactivity studies indicate that the reactivity of vanadium oxide cluster anions and cations depends on cluster stoichiometry and generally decreases with cluster size. 10,13 However, with the exception of the diatomic VO (see ref.…”

“…Fragmentation of V 4 O 10 + has previously been studied by CID and photofragmentation using 532 nm radiation. 7,8 Single collisions with Xenon atoms lead to O 2 loss already at thermal energies, while other fragmentation channels are only observed at collision energies above 3 eV. Similarly, absorption of a single 532 nm (2.128 eV) photon leads exclusively to O 2 loss, while other fragmentation channels are only observed at higher laser fluences, i.e., under multi-photon absorption conditions.…”

Application of Ion Mobility-Mass Spectrometry to the Study of Ionic Clusters

“…20) Next we show the results of investigation of stable chemical compositions for rst-row transition metal oxide cluster ions. As for the stable composition of the transition metal oxides, there have been several investigations using CID, 21,22) photodissociation 23) and thermal heating. 24) However no de nite was known from such experiments so far.…”