中央研究院 原子與分子科學研究所

To develop promising dual atom catalysts (DACs) for enhancing valuable C₂₊ products in CO₂ electroreduction (CO₂RR), we need a molecular level understanding of the interaction between reaction intermediates, metal atoms, and substrates. NiMn on graphitic carbon nitride (g-C₃N₄) was experimentally reported to be an efficient CO₂RR catalyst. Here, we studied the origin of its activity. We used integrated crystal orbital Hamiltonian population (ICOHP) analysis along the reaction coordinate of the carbon-carbon (C-C) coupling reaction to understand how the electronic structures of NiMn doped on pristine (NiMn@g-C₃N₄) and N-vacancy graphitic carbon nitride (NiMn@V-g-C₃N₄) affect the reaction. NiMn@V-g-C₃N₄ selectively produces ethanol at low limiting potential -0.55 V and a low kinetic barrier (0.78 eV) for *CO+*CHO→*COCHO. At this step, electron donation from the NiMn in the N-vacancy to the adsorbate is essential. Tricoordinated Ni atom at the vacancy site has a stable oxidation state 0 with a fully filled 3d¹⁰ configuration, while Mn atom takes +2 oxidation state with a half-filled 3d⁵ configuration. ICOHP shows that these electronic configurations result in a moderate binding strength of key intermediates near the Ni while facilitating the flexible change in Mn-C to Mn-O binding for producing *COCHO, thus promoting the formation of ethanol. 

We report a type of highly efficient double hydrogen atom transfer (DHAT) reaction. The reactivities of 3-aminopropanol and 2-aminoethanol towards Criegee intermediates (syn- and anti-CH₃CHOO) were found to be much higher than those of npropanol and propylamine. Quantum chemistry calculation has confirmed that the main mechanism of these very rapid reactions is DHAT, in which the nucleophilic attack of the NH₂ group is catalyzed by the OH group which acts as a bridge of HAT. Typical gas-phase DHAT reactions are termolecular reactions involving two hydrogen bonding molecules; these reactions are typically slow due to the substantial entropy reduction of bringing three molecules together. Putting the reactive and catalytic groups in one molecule circumvents the problem of entropy reduction and allows us to observe the DHAT reactions even at low reactant concentrations. This idea can be applied to improve theoretical predictions for atmospherically relevant DHAT reactions.

Two-dimensional covalent organic frameworks (2D COFs) featuring periodic frameworks, extended π-conjugation and layered stacking structures, have emerged as a promising class of materials for photocatalytic hydrogen evolution. Nevertheless, the layer-by-layer assembly in 2D COFs is not stable during the photocatalytic cycling in water, causing disordered stacking and declined activity. Here, we report an innovative strategy to stabilize the ordered arrangement of layered structures in 2D COFs for hydrogen evolution. Polyethylene glycol is filled up in the mesopore channels of a β-ketoenamine-linked COF containing benzothiadiazole moiety. This unique feature suppresses the dislocation of neighbouring layers and retains the columnar π-orbital arrays to facilitate free charge transport. The hydrogen evolution rate is therefore remarkably promoted under visible irradiation compared with that of the pristine COF. This study provides a general post-functionalization strategy for 2D COFs to enhance photocatalytic performances.

CO₂ conversion to valuable products on ZnO (0001) monolayer doped by transition metals (TM-ZnO where TM is Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) was investigated by density functional theory calculation. The results show that doping TMs can reduce the overpotential for CO₂ reduction reaction (CRR) compared to pristine ZnO. Significantly, the oxidation state of TMs by different d-orbital occupancy results in a change of the electronic properties of the catalysts, leading to a difference in reactivity, reaction pathway, and selectivity of the final products. Early TMs (Sc to Cr) showing oxidation state 3⁺ prefer CH₄ as a product while late TMs (Mn to Cu) showing oxidation state 2⁺ can make HCOOH. Remarkably, Co-ZnO can produce HCOOH with ultra-low overpotential at 0.02 V and can further produce CH₃OH with an overpotential of only 0.45 V. Therefore, Co-ZnO monolayer is suggested as a promising CRR catalyst for experimental research. This work sheds light on the rational design of low-cost metal oxides with high stability, activity, and product selectivity for CRR and other reactions.

To gain an understanding of the substitution effect for the unimolecular reaction rate coefficients for Criegee intermediates (CIs), we performed ab initio calculations for CH₂OO, CH₃CHOO, (CH₃)₂COO, CH₃CH₂CHOO, CH₂CHCHOO and CHCCHOO. The energies of the CIs, products and transition states were calculated with QCISD(T)/CBS//B3LYP/6-311+G(2d,2p), while the rate coefficients were calculated with anharmonic vibrational correction by using second order vibrational perturbation theory. It was found that for single bonded substitutions, the hydrogen transfer reaction dominates for the syn-conformers, while the OO bending reaction dominates for the anti-conformers. However once a double bond or a triple bond is added, the OO bending reaction dominates for both syn and anti-conformers. The rate coefficients for OO bending reaction show a significant increase when adding a methyl group or ethyl group. On the other hand, the addition of unsaturated vinyl and acetylene groups usually results in a slower thermal decomposition compared to the saturated substitution. Interestingly, for syn_Syn-CH₂CHCHOO, a special five member ring closure reaction forming dioxole was calculated to have an extremely fast rate coefficient of 9312 s^-1 at room temperature.

In this study, we performed ab initio calculations and obtained the bimolecular rate coefficients for the CH₂OO/CH₃CHOO reactions with H₂O/(H₂O)₂. The energies were calculated with QCISD(T)/CBS//B3LYP/6-311+G(2d,2p) and the partition functions were estimated with anharmonic vibrational corrections by using the second order perturbation theory.  Furthermore, we directly measured the rate of CH₂OO reaction with water vapor at high temperatures (348 and 358 K) to reveal the contribution of water monomer in the CH₂OO decay kinetics. We found that the theoretical rate coefficients reproduce the experimental results of CH₂OO for a wide range of temperatures. For anti- (syn-) CH₃CHOO, we obtained theoretical rate coefficients of 1.60×10^-11 (2.56×10^-14) and 3.40×10^-14 (1.98×10^-19) cm³ sec^-1 for water dimer and monomer reactions at room temperature.  From the detailed analysis on the quantum chemistry and approximations for the thermochemistry calculation, we conclude that our calculated values should be within a factor of 3 of the correct values.  Furthermore, at [H₂O]=1×10¹⁷ to 5×10¹⁷ cm^-3, we estimate that the effective first-order rate coefficients for CH₂OO, anti- and syn-CH₃CHOO reactions with water vapor will be ~10³, ~10⁴, and ~10¹ s^-1, respectively. Thereby, for Criegee intermediates (CIs) with a hydrogen atom on the same side as the terminal oxygen atom, the reaction with water vapor will likely dominate the removal processes of these CIs in the atmosphere.