The Mechanism of Alkane Selective Oxidation by the M1 Phase of Mo–V–Nb–Te Mixed Metal Oxides: Suggestions for Improved Catalysts

Abstract

Abstract.We report here first principles predictions (density functional theory with periodic boundary conditions) of the structures, mechanisms, and activation barriers for the catalytic activation and functionalization of propane by the M1 phase of the Mitsubishi-BP America generation of Mo-VNb-Te-O mixed metal oxide (MMO) catalysts.Our calculations show that the Reduction-coupled Oxo Activation (ROA) principle, which we reported at Irsee VI to play the critical role for the selective oxidation of n-butane to maleic anhydride by vanadium phosphorous oxide (VPO), also plays the critical role for the MMO activation of propane, as speculated during Irsee VI. However for MMO, this ROA principle involves Te=O and V rather than P=O and V.The ability of the Te=O bond to activate the propane CH bond depends sensitively upon the number of V atoms that are coupled through a bridging O to the Te=O center. Based on this ROA mechanism, we suggest synthetic procedures aimed at developing a single phase MMO catalyst with dramatically improved selectivity for ammoxidation. We also suggest a modified single phase composition suitable for simultaneous oxidative dehydrogenation (ODH) of ethane and propane to ethene and propene, respectively, which is becoming more important with the increase in petroleum fracking. Moreover, we also suggest some organometallic molecules that activate alkane CH bonds through the ROA principle.

Probing the Positions of TeO Moieties in the Channels of the MoVNbTeO M1 Catalyst: A Density Functional Theory Model Study

“…Since the discovery of the MoVNbTeO mixed-metal oxide catalyst [3], significant effort was devoted in understanding this catalyst. Studies in this field range from synthesizing MoVNbTeO and its variants [9][10][11], characterizing the structure of these materials [12][13][14][15][16][17][18][19][20], elaborating the catalytic mechanism [21][22][23], to elucidating how the metal centers and V 5+ /V 4+ pairs are distributed in the material [24][25][26][27][28]. It is well accepted that the V 5+ species are responsible for activating the alkanes over this catalyst [21,27,29,30], yet clarifying their location remains as one of the challenges.…”

Quantum mechanics based mechanisms for selective activation of hydrocarbons by mixed metal oxide heterogeneous catalysts – A tribute to Robert Grasselli

“…Progress is promising and indeed we have nowbeen able to use DFT theory to establish the nature of the active site of the M1 phase that activates propane to propene, which we find that involves a (Te=O)-O-(V=O)-O-(Te=O) trimer site (with Te+4) with additional nearby Mo=O sites replaced by V=O. [12,13] We have also established the nature of the M2 phase that activates propene to form allyl and subsequently acrylonitrile. This also involves Te=O sites, with (with Te+4).…”

“…[14] These studies suggest modifications in the M1 catalyst that might lead to a single phase catalyst capable of highly selective propane to acrylonitrile. [13] However no one has yet tested this published mechanism. No doubt if Grasselli was still active with his premier research group, these ideas would already have been tested.…”

Atomic Imaging of Molybdenum Oxide Nanowires with Unique and Complex Periodicity by Advanced Electron Microscopy

“…Therefore, molybdenum oxide at the nanoscale has been significantly used as a catalyst because of its large surface area that promotes the reaction . In the catalytic field, elements such as V, W, Nb, and Te are usually substitutional or interstitial to the Mo site, resulting in the M1, M2, and Mo 5 O 14 -type structures with different functions. − M1 (space group 32, Pba 2) and M2 (space group 25, Pmm 2), which are both orthorhombic structures, originated from the Mo 5 O 14 structure due to structural deformation. , Thus, a systematic study of the Mo 5 O 14 structure would realize the structural motif of molybdenum oxide-based catalysts and help understanding of the bonding relationship for selective oxidation. In fact, the Mo 5 O 14 structure was found by Kihlborg et al in 1964, having a tetragonal structure (space group 127) of MoO 6 octahedra and MoO 7 pentagonal bipyramids .…”