Gasphasenoxidation von Propan und 1‐Buten durch [V₃O₇]⁺: Wechselspiel von Experiment und Theorie

Abstract

Guter Anfang ist halb gewonnen. Eine Kombination experimenteller und theoretischer Studien zur Dehydrierung von Kohlenwasserstoffen durch [V3O7]+ zeigt eindrucksvoll die entscheidende Rolle der anfänglichen C‐H‐Aktivierung. So erweist sich das einfache Alkan Propan als gänzlich unreaktiv (oben im Bild), während 1‐Buten durch [V3O7]+ rasch oxidiert wird (unten im Bild).

Gas‐Phase Reactivity of Metavanadate [VO3]− towards Methanol and Ethanol: Experiment and Theory

“…[66] The B3LYP functional has been used previously for a range of vanadium oxide systems, and was shown to give reasonable agreement with available experimental data as well as with higher-level theoretical calculations. [19,20,23,24,27,31,32,[67][68][69][70] Calculations were carried out by using the 6-311 + + G** basis sets for H, C and O, and the SDD effective core potential (ECP) and associated basis sets were used for V. [71] The use of an ECP basis set for V was chosen to allow for direct comparison with the heavier Nb centres. Stationary points were characterized by frequency calculations, and unscaled zero-point energies are included for all species.…”

“…These intermediates were approximately modelled by the broken-symmetry DFT approach, [72][73][74][75] based on a procedure used previously for related vanadium oxide centres that were proposed to react by similar hydrogen-atom transfer pathways. [20,40] Projected low-spin energies for broken-symmetry solutions were obtained by spin-projection methods from single-point triplet and broken-symmetry singlet energies at the broken-symmetry singlet geometries; the energies used in these calculations are detailed in the Supporting Information. [20,40,74,75] Spin expectation values S 2 are indicated in the text for these species where appropriate.…”

CH Activation on Aluminum–Vanadium Bimetallic Oxide Cluster Anions

“…Gas-phase clusters have well-defined structures and may have definite active sites that parallel the active sites on the surface of real catalytic systems. Selective activation of C À H bonds by various gas-phase clusters has been extensively studied, and many valuable results have been reported concerning the activations of methane, [4, ethane, [13,34,[37][38][39] propane, [13,34,[37][38][40][41][42] and butane. [13,37,40] However, most of these gas-phase studies were carried out on cationic clusters, [3, 4, 10-11, 14-29, 38-40, 43] and only a few recent studies have focused on anionic clusters.…”

“…Selective activation of C À H bonds by various gas-phase clusters has been extensively studied, and many valuable results have been reported concerning the activations of methane, [4, ethane, [13,34,[37][38][39] propane, [13,34,[37][38][40][41][42] and butane. [13,37,40] However, most of these gas-phase studies were carried out on cationic clusters, [3, 4, 10-11, 14-29, 38-40, 43] and only a few recent studies have focused on anionic clusters. [44][45][46][47] Vanadia supported on alumina (V 2 O 5 /Al 2 O 3 ) has been reported as one of the most active catalytic systems for the selective oxidation of light alkanes and other reactions, and has been widely studied in the condensed phase.…”

“…Keywords: anions · C À H activation · cluster compounds · density functional calculations · radicals work was focused on their reactivities with various molecules. For example, Castleman et al studied the reactivity of vanadium oxide cluster cations with various hydrocarbons and their derivatives with rich findings including the breaking of the CÀC single bond, hydrogen-atom abstraction, oxygen-atom transfer, and breaking of CÀX (X= F, Cl, Br); [72][73][74][75][76][77][78] the Schwarz group studied the interesting CÀH activation by vanadium oxide cluster cations; [21,40] the OHair group studied the reactions of the anionic VO 3 À cluster with methanol and ethanol; [79,80] Bernstein et al studied the C=C bond cleavage on neutral vanadium oxide clusters; [81][82][83] and our group studied the reactions of neutral VO 3 and V 3 O 8 with ethylene. [84,85] In the selective oxidation of light alkanes, vanadium is typically deposited onto high-surface-area support materials such as alumina, silica, titania, and zirconia to increase the number of active sites for obtaining better catalytic activity.…”