Hua-Qing Yang

Methane activation by naked Ni0 atom: a theoretical study

Abstract The reactions between Ni (d 10 1 S) and CH 4 have been carried out at the B3LYP/6-311+G(2d, 2p) and B3LYP/6-311++G(3df,2p) theoretical levels. The reaction path in which the intermediates transfer from one to another via transition state is rationalized by their structures and natural bond orbital analysis. The reactions of Ni+CH 4 →NiCH 2 +H 2 , Ni+CH 4 →NiCH 3 +H and Ni+CH 4 →NiH +CH 3 are predicted to be endothermic, and the reaction Ni+CH 4 →NiH +CH 3 is the easiest to occur.

Theoretical study of the catalytic oxidation mechanism of 5-hydroxymethylfurfural to 2,5-diformylfuran by PMo-containing Keggin heteropolyacid

The mechanism for the aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) catalysed by PMo-containing Keggin heteropolyacid (H3PMo12O40) has been systematically investigated at the M06/6-31++G(d,p), Lanl2dz level in dimethylsulfoxide. For H3PMo12O40 in dimethylsulfoxide, the most stable species was [PMo12O40]3−, which was the catalytic active species for the aerobic oxidation of HMF to DFF. Over the [PMo12O40]3− active species, the reaction of 2HMF + O2 → 2DFF + 2H2O was associated with three successive reaction stages: the oxidation of the first HMF to DFF by [PMo12O40]3−, the import of O2 to form the peroxide [PMo12O41]3− and the oxidation of the second HMF to DFF by [PMo12O41]3−, regenerating [PMo12O40]3−. The oxidation of each HMF involves two main reaction steps: the cleavage of the O–H bond in the hydroxyl group and cleavage of the C–H bond in the methylene group of HMF. The turnover frequency determining the transition state was the first-step C–H bond cleavage in the methylene group of HMF with a rate constant of kH = 1.345 × 108 exp(−153 476/RT), while the turnover frequency determining the intermediate was representative of the HMF-containing molecular complex on [PMo12O40]3−. The value of the kinetic isotope effects (kH/kD) is predicted to be about 4.2–5.9 over the temperature range 373–433 K. This study provides an insight into the catalytically crucial step in the oxidation of HMF to DFF.

Activation of Propane C-H and C-C Bonds by Gas-Phase Pt Atom: A Theoretical Study

The reaction mechanism of the gas-phase Pt atom with C3H8 has been systematically investigated on the singlet and triplet potential energy surfaces at CCSD(T)//BPW91/6-311++G(d, p), Lanl2dz level. Pt atom prefers the attack of primary over secondary C-H bonds in propane. For the Pt + C3H8 reaction, the major and minor reaction channels lead to PtC3H6 + H2 and PtCH2 + C2H6, respectively, whereas the possibility to form products PtC2H4 + CH4 is so small that it can be neglected. The minimal energy reaction pathway for the formation of PtC3H6 + H2, involving one spin inversion, prefers to start at the triplet state and afterward proceed along the singlet state. The optimal C-C bond cleavages are assigned to C-H bond activation as the first step, followed by cleavage of a C-C bond. The C-H insertion intermediates are kinetically favored over the C-C insertion intermediates. From C-C to C-H oxidative insertion, the lowering of activation barrier is mainly caused by the more stabilizing transition state interaction ΔE≠int, which is the actual interaction energy between the deformed reactants in the transition state.

Theoretical investigation on copper hydrides catalyzed hydrosilylation reaction of 3-methylcyclohex-2-enone: mechanism and ligands' effect

The mechanism of the hydrosilylation reactions of 3-methylcyclohex-2-enone with tetramethyldisiloxane (TMDS) catalyzed by (Ph3P)CuH and (IPr)CuH has been investigated by DFT. The catalytic cycle is composed of two steps: the addition of the copper hydrides to the CC bond in the substrate, and the regeneration of the copper hydrides assisted by TMDS. The calculations indicate that the catalyst recovery step is the rate-determining step. The assistances of IPr and Ph3P ligands to the CuH catalysts make the transition state structures compact and stable. The steric bulk of the ligands could help to stabilize the central Cu atom and promote the coordination of the central Cu atom with the substrate. The higher nucleophilicity of the catalysts and the stronger interaction of the ligands with the central Cu atom make the catalysts interact more easily with the substrate. The hydrosilylation reaction proceeds more favorably when catalyzed by (IPr)CuH as compared to (Ph3P)CuH.

Theoretical study on the gas-phase reaction mechanism between rhodium monoxide and methane for methanol production

The gas‐phase reaction mechanism between methane and rhodium monoxide for the formation of methanol, syngas, formaldehyde, water, and methyl radical have been studied in detail on the doublet and quartet state potential energy surfaces at the CCSD(T)/6‐311+G(2d, 2p), SDD//B3LYP/6‐311+G(2d, 2p), SDD level. Over the 300–1100 K temperature range, the branching ratio for the Rh(4F) + CH3OH channel is 97.5–100%, whereas the branching ratio for the D‐CH2ORh + H2 channel is 0.0–2.5%, and the branching ratio for the D‐CH2ORh + H2 channel is so small to be ruled out. The minimum energy reaction pathway for the main product methanol formation involving two spin inversions prefers to both start and terminate on the ground quartet state, where the ground doublet intermediate CH3RhOH is energetically preferred, and its formation rate constant over the 300–1100 K temperature range is fitted by kCH3RhOH = 7.03 × 106 exp(−69.484/RT) dm3 mol−1 s−1. On the other hand, the main products shall be Rh + CH3OH in the reactions of RhO + CH4, CH2ORh + H2, Rh + CO +2H2, and RhCH2 + H2O, whereas the main products shall be CH2ORh + H2 in the reaction of Rh + CH3OH. Meanwhile, the doublet intermediates H2RhOCH2 and CH3RhOH are predicted to be energetically favored in the reactions of Rh + CH3OH and CH2ORh + H2 and in the reaction of RhCH2 + H2O, respectively.

Computational investigation on stereochemistry in titanium-salicylaldehydes-catalyzed cyanation of benzaldehyde.

Theoretical simulation on the enantioselective cyanation of benzaldehyde over titanium-salicylaldehyde catalysts is performed with B3LYP//ONIOM methods. The calculations predict that the attack of cyanide to adsorbed benzaldehyde is the rate-determining step for the entire reaction. The stereochemistry of the titled reaction might be controlled not only by the attack directions of cyanide to benzaldehyde but also by different coordination modes of benzaldehyde to the chiral catalysts. In addition, to evaluate the accuracy of the employed method, the stereoselectivities of the reactions with five different chiral ligands are theoretically predicted. The theoretical predictions are qualitatively in agreement with experiments, and a linear relationship between calculated Delta DeltaG(double dagger) and experimental ones is obtained, especially for the reactions using the ligands with a single chiral center.

Catalytic reduction of NO by CO on Rh4+ clusters: a density functional theory study

An extensive study was conducted to explore the catalytic reduction of NO by CO on Rh4+ clusters at the ground and first excited states at the B3LYP/6-311+G(2d), SDD level. The main reaction pathway includes the following elementary steps: (1) the coadsorption of NO and CO; (2) the recombination of NO and CO molecules to form CO2 molecules and N atoms, or the decomposition of NO to N and O atoms; (3) the reaction of the N atom with the second adsorbed NO to form N2O; (4) the decomposition of N2O to N2 molecules and O atoms; and (5) the recombination of O atoms and CO to form CO2. At low temperatures (300–760 K), the turnover frequency (TOF)-determining transition state (TDTS) is the simultaneous C–O bond formation and N–O bond cleavage, with a rate constant (s−1) of kPs = 4.913 × 1012  exp(−272 724/RT). The formation of CO2 should originate in half from the reaction between the adsorbed CO and NO. The presence of CO in some degree decreases the catalytic reduction temperature of NO on the Rh4+ clusters. At high temperatures (760–900 K), the TDTS is applied to the N–O bond cleavage, with a rate constant (s−1) of kPa = 6.721 × 1015  exp(−318 376/RT). The formation of CO2 should stem solely from the surface reaction between the adsorbed CO and the O atom, the latter originating from NO decomposition. The bridge NbRh4+ is thermodynamically preferred. Once the bridge NbRh4+ is formed, N2O- and NCO-contained species are predicted to exist, which is in good agreement with the experimental results.

Activation of propane C–H and C–C bonds by a diplatinum cluster: potential energy surfaces and reaction mechanisms

The activation mechanism of C3H8 catalyzed by the homonuclear bimetallic Pt2 cluster has been detailedly explored on the singlet and triplet potential energy surfaces at BPW91/aug-cc-pvtz, Lanl2tz level. The C–H bond cleavage channel (dehydrogenation and the release of propylene) is kinetically predominant, whereas the C–C bond cleavage channel (demethanation and the release of ethane) should be ruled out. Furthermore, the release of propylene channel is kinetically favorable, while the dehydrogenation channel is thermodynamically preferable. Besides, both the C–H cleavage intermediate (Pt2H2C3H6b) and the C–C cleavage intermediates (CH3HPt2CHCH3 and CH3PtPtHC2H4) are thermodynamically preferred. The C–H cleavage intermediate (Pt2H2C3H6b) is kinetically favored, while the C–C cleavage intermediates (CH3HPt2CHCH3 and CH3PtPtHC2H4) are kinetically hindered. The homonuclear bimetallic Pt2 cluster toward propane exhibits higher reactivity than the Pt atom, which is in good agreement with the experimental observation.

Theoretical study on the gas‐phase reaction mechanism between palladium monoxide and methane

The gas‐phase reaction mechanism between palladium monoxide and methane has been theoretically investigated on the singlet and triplet state potential energy surfaces (PESs) at the CCSD(T)/AVTZ//B3LYP/6‐311+G(2d, 2p), SDD level. The major reaction channel leads to the products PdCH2 + H2O, whereas the minor channel results in the products Pd + CH3OH, CH2OPd + H2, and PdOH + CH3. The minimum energy reaction pathway for the formation of main products (PdCH2 + H2O), involving one spin inversion, prefers to start at the triplet state PES and afterward proceed along the singlet state PES, where both CH3PdOH and CH3Pd(O)H are the critical intermediates. Furthermore, the rate‐determining step is RS‐CH3PdOH → RS‐2‐TS1cb → RS‐CH2Pd(H)OH with the rate constant of k = 1.48 × 1012 exp(−93,930/RT). For the first CH bond cleavage, both the activation strain ΔE≠strain and the stabilizing interaction ΔE≠int affect the activation energy ΔE≠, with ΔE≠int in favor of the direct oxidative insertion. On the other hand, in the PdCH2 + H2O reaction, the main products are Pd + CH3OH, and CH3PdOH is the energetically preferred intermediate. In the CH2OPd + H2 reaction, the main products are Pd + CH3OH with the energetically preferred intermediate H2PdOCH2. In the Pd + CH3OH reaction, the main products are CH2OPd + H2, and H2PdOCH2 is the energetically predominant intermediate. The intermediates, PdCH2, H2PdCO, and t‐HPdCHO are energetically preferred in the PdC + H2, PdCO + H2, and H2Pd + CO reactions, respectively. Besides, PdO toward methane activation exhibits higher reaction efficiency than the atom Pd and its first‐row congener NiO.

Theoretical study on the gas‐phase reaction mechanism between nickel monoxide and methane for syngas production

The comprehensive mechanism survey on the gas‐phase reaction between nickel monoxide and methane for the formation of syngas, formaldehyde, methanol, water, and methyl radical has been investigated on the triplet and singlet state potential energy surfaces at the B3LYP/6‐311++G(3df, 3pd)//B3LYP/6‐311+G(2d, 2p) levels. The computation reveals that the singlet intermediate HNiOCH3 is crucial for the syngas formation, whereas two kinds of important reaction intermediates, CH3NiOH and HNiOCH3, locate on the deep well, while CH3NiOH is more energetically favorable than HNiOCH3 on both the triplet and singlet states. The main products shall be syngas once HNiOCH3 is created on the singlet state, whereas the main products shall be methyl radical if CH3NiOH is formed on both singlet and triplet states. For the formation of syngas, the minimal energy reaction pathway (MERP) is more energetically preferable to start on the lowest excited singlet state other than on the ground triplet state. Among the MERP for the formation of syngas, the rate‐determining step (RDS) is the reaction step for the singlet intermediate HNiOCH3 formation involving an oxidative addition of NiO molecule into the CH bond of methane, with an energy barrier of 120.3 kJ mol−1. The syngas formation would be more effective under higher temperature and photolysis reaction condition.