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In the present paper, the mechanisms of N2O reduction by H2 were systemically examined over various polyoxometalate-supported single-atom catalysts (SACs) M1/PTA (M = Fe, Co, Mn, Ru, Rh, Os, Ir, and Pt; PTA = [PW12O40]3-) by means of density functional theory calculations. Among these M1/PTA SACs, Os1/PTA SAC possesses high activity for N2O reduction by H2 with a relatively low rate-determining barrier. The favorable catalytic pathway involves the first and second N2O decomposition over the Os1/PTA SAC and hydrogenation of the key species after the second N2O decomposition. Molecular geometry and electronic structure analyses along the favorable reaction pathway indicate that a strong charge-transfer cooperative effect of metal and support effectively improves the catalytic activity of Os1/PTA SAC. The isolated Os atom not only plays the role of adsorption and activation of the N2O molecule but also works as an electron transfer medium in the whole reaction process. Meanwhile, the PTA support with very high redox stability has also been proven to be capable of transporting the electron to promote the whole reaction. We expect that our computation results can provide ideas for designing new SACs for N2O reduction by using H2 selective catalytic reduction technology.

Anchoring of unimolecular metal oxide onto appropriate supports is a promising and attractive approach for designing efficient metal–oxide-based catalysts from the perspective of economic and environmental sustainability. In the present paper, anchoring of osmium (Os) oxide onto silanol-functionalized polyoxometalates (POMs) to form a single-site supported Os-POM catalyst, in which the isolated osmium tetroxide was tris-grafted on a silanol-functionalized POM platform, has been studied in detail for catalytic oxidation of propylene with dioxygen by using density functional theory (DFT) calculations with the M06L functional. The results derived from the molecular geometry, electronic structure, and OsO bonding feature for this Os-POM catalyst show that (i) rotation of the anionic center subunit of the silanol-functionalized trilacunary POM ligand leads to a coordinated environment conversion from a tetrahedron to a trigonal bipyramid around the transition metal Os center; (ii) a detailed comparison shows that the trigonal bipyramid configuration is the most stable species and provides a large OsO distance and (iii) possesses a matched orbital level for epoxidation of propylene to epoxypropane. The calculated free energy profiles for the epoxidation of propylene show that the rate-determining step is desorption of the first epoxypropane molecule from the Os center. Electronic structure analysis along the reaction pathway shows that the Os-POM catalyst serves as an electrophile, accepting electrons from the propylene π bonding orbital to the π* antibonding orbital of the Os-POM catalyst to break the OsO bond during the oxygen transfer process. Oxygen transfer to the terminal carbon atom of propylene is more favored than the bridging carbon atom because the electron-donating methyl substituent in propylene makes the terminal carbon atom more nucleophilic and accessible for the electrophilic attack by the OsO bond. Cleavage of dioxygen on the Os-POM catalyst is a barrier free process via a quintet-to-singlet state intersystem crossing. The ability of the POM platform to accept and stabilize excess electrons from the Os center effectively promotes the oxygen transfer process, and thus is favorable for epoxidation of propylene by dioxygen.

In the present paper, the reaction mechanism corresponding to activation of hydrogen peroxide (H2O2) by a divanadium–substituted polyoxometalate (POM) [γ–PV2W10O38(μ–OH)2]3– (I) to form catalytic active species, peroxo complex [γ–PV2W10O38(μ-η2,η2–O2)]3– (III), was studied by using the density functional theory (DFT) calculations method with B3LYP functional. The results indicate that coordination of H2O2 to I proceeds via a vanadium–center–assisted proton transfer pathway to remove the first water molecule and form a hydroperoxy intermediate [γ–PV2W10O38(μ–OH) (μ–OOH)]3– (II). And intermediate II occurs through three successive water–assisted proton transfer steps to remove the second water molecule and finally forms catalytic active species. The calculated overall energy profiles show that coordination of H2O2 to vanadium center requires a proton transfer barrier of about 24 kcal mol−1. A detailed comparison of molecular geometries and electronic structure shows that the catalytic active species has a very interesting structural feature, where a superoxide radical (O2− ) was embedded into two vanadium centers, and may be a potential nucleophile. The unique withdrawing electron properties and flexible bonding ability of the γ–Keggin–type POM ligand contribute to the formation of O2− radical. The tunable alternate arrangement of W–O bond series in γ–Keggin–type POM ligand contributes to the flexibility of the γ–Keggin–type POM ligand. Meanwhile, our DFT calculations show a good performance of B3LYP-gauge-independent atomic orbital (IGAIM) method for the calculation of 1H NMR parameters of divanadium-substituted phosphotungstate.

In the present paper, the mechanisms of N