H 2 production from reactions between water and small molybdenum suboxide cluster anions

Abstract

Reactions between molybdenum suboxide cluster anions, Mo(x)O(y)(-) (x=1-4; y < or = 3x), and water (H(2)O and D(2)O) have been studied using mass spectrometric analysis of products formed in a high-pressure, fast-flow reactor. Product distributions vary with the number of metal atoms in the cluster. Within the MoO(y)(-) oxide series, product masses correspond to the addition of one water molecule, as well as a H/D exchange with MoO(4)H(-). Within the Mo(2)O(y)(-) oxide series, product evolution and distribution suggest sequential oxidation via Mo(2)O(y)(-)+H(2)O/D(2)O-->Mo(2)O(y+1)(-)+H(2)/D(2) reactions for y<5, while for Mo(2)O(5)(-), Mo(2)O(6)H(2)/D(2)(-) is produced. Mo(2)O(6)(-) does not appear to be reactive toward water. For the Mo(3)O(y)(-) oxide series, sequential oxidation similarly is suggested for y<5, while Mo(3)O(5)(-) reactions result in Mo(3)O(6)H(2)/D(2)(-) formation. Mo(3)O(6)(-) appears uniquely unreactive. Mo(3)O(7)(-) and Mo(3)O(8)(-) react to form Mo(3)O(8)H(2)/D(2)(-) and Mo(3)O(9)H(2)/D(2)(-), respectively. Lower mass resolution in the Mo(4)O(y)(-) mass range prevents unambiguous mass analysis, but intensity changes in the mass spectra do suggest that sequential oxidation with H(2)/D(2) evolution occurs for y<6, while Mo(4)O(y+1)H(2)/D(2)(-) addition products are formed in Mo(4)O(6)(-) and Mo(4)O(7)(-) reactions with water. The relative rate constants for sequential oxidation and H(2)O/D(2)O addition for the x=2 series were determined. There is no evidence of a kinetic isotope effect when comparing reaction rates of H(2)O with D(2)O, suggesting that the H(2) and D(2) losses from the lower-oxide/hydroxide intermediates are very fast relative to initial reaction complex formation with H(2)O or D(2)O. The rate constants determined here are two times higher than those determined in identical reactions between W(2)O(y)(-)+H(2)O/D(2)O.

Insight into ethylene interactions with molybdenum suboxide cluster anions from photoelectron spectra of chemifragments

“…We have observed kinetically trapped, thermodynamically unfavored structures resulting from cluster-water and cluster-alcohol reactions in the previous studies. 26,28,31,49,50 In combination with the observations listed in the previous paragraphs, the new results from this current study evoke a picture of π-electron donation to Mo centers, with adjacent Mo− −H or H− −O− −Mo bond formation, and kinetically controlled fragment formation. A similar mechanism has been invoked in the oxidative dehydrogenation of alkanes over bulk MoO 3 .…”

RH and H2 Production in Reactions between ROH and Small Molybdenum Oxide Cluster Anions

“…37 In particular, sequential oxidation of the lower oxides via Mo x O y − + ROH → Mo x O y+1 − + RH was observed, and addition products formed via Mo x O y − + ROH → Mo x O y+1 RH − were observed for the higher oxide clusters. However, there are a few key differences.…”

“…Additionally, in Figure 4b, a low-intensity product peak with mass corresponding to Mo 4 36,37 To compare those rate constants to the rates of Mo x O y − + ROH reactions, the same analysis will be applied here. Individual oxide peaks in the x = 2 and 3 manifolds of Mo x O y − vary as a function of alcohol (ROH) number density present in the reactor.…”

“…The HO−H bond dissociation energy is 1.17 eV higher than the CH 3 −OH bond dissociation energy, which may explain why abstraction products were not observed in the cluster−water reactivity studies. 36,37 The most predominant product peak, …”

Interaction of TiO+ with water: infrared photodissociation spectroscopy and density functional calculations

“…10 The reactions between vanadium oxide ions and water were also investigated by Ma et al 11 and Li et al 12 using fast flow reactor experiments and density functional calculations. Jarrold and co-workers investigated the reactions of water with tungsten oxides [13][14][15] and molybdenum oxides 16 using a high-pressure fast-flow reactor combined with a time-of-flight mass spectrometer. Zhou and co-workers conducted matrix isolation spectroscopic studies of water adsorption on platinum oxides, 17 tantalum oxides and niobium oxides.…”