The Mo−V−Te−Nb−O mixed metal oxide catalyst possessing the M1 phase structure is uniquely capable of directly converting propane into acrylonitrile. However, the mechanism of this complex eight-electron transformation, which includes a series of oxidative H-abstraction and N-insertion steps, remains poorly understood. We have conducted a density functional theory study of cluster models of the proposed active and selective site for propane ammoxidation, including the adsorption of propane, isopropyl (CH3CHCH3), and H which are involved in the first step of this transformation, that is, the methylene CH bond scission in propane, on these active site models. Among the surface oxygen species, the telluryl oxo (TeO) is found to be the most nucleophilic. Whereas the adsorption of propane is weak regardless of the MO x species involved, isopropyl and H adsorption exhibits strong preference in the order of TeO > VO > bridging oxygens > empty Mo apical site, suggesting the importance of TeO x species for H abstraction. The adsorption energies of isopropyl and H and consequently the reaction energy of the initial dehydrogenation of propane are strongly dependent on the number of ab planes included in the cluster, which points to the need to employ multilayer cluster models to correctly capture the energetics of surface chemistry on this mixed metal oxide catalyst.

In a case study of organometallic catalytic reactions, this work benchmarks density functional theory calculations on zeolite-supported transition metal complexes. Elementary steps of ethylene dimerization and hydrogenation reactions involving the complex [Rh(C2H4)2(H2)]+, supported on faujasite, were examined by comparing explicit QM (quantum mechanics) cluster models as well as QM/MM (molecular mechanics) embedded models to plane-wave periodic models as reference. Two QM cluster models, 1T and 5T where T refers to tetrahedral units of zeolite, as well as four QM/MM cluster models were explored. For the MM region, the UFF force field was found preferable to the semiempirical method PM6. The embedded cluster models reproduce barriers of C–C and C–H bond formation with deviations from the reference of at most 10 kJ mol–1. With variations of similar size, the effect of embedding on the energetics of the reactions under study is moderate, likely because of the small nonpolar reactants. For elucidating such catalytic reactions at transition metal species in zeolites, cluster models appear equally well-suited as periodic models but computationally advantageous.

A DFT study allows one to understand the selectivity for ethene hydrogenation over dimerization by the well-characterized faujasite-supported [Rh(C2H4)2]+ complex.