Yen-Hsiu Lin Kaito Takahashi* and Jim Jr-Min Lin*
Physical Chemistry Chemical Physics 24, 10439- (2022)
Methyl vinyl ketone oxide (MVKO) and methacrolein oxide (MACRO) are resonance-stabilized Criegee intermediates which are formed in the ozonolysis reaction of isoprene, the most abundant unsaturated hydrocarbon in the atmosphere. The absolute photodissociation cross sections of MVKO and MACRO were determined by measuring their laser depletion fraction at 352 nm, which was deduced from their time-resolved UV-visible absorption spectra. After calibrating the 352-nm laser fluence with the photodissociation of NO2, for which the absorption cross section and photodissociation quantum yield are well known, the photodissociation cross sections of thermalized (299 K) MVKO and MACRO at 352 nm were determined to be (3.02 ± 0.60) × 10−17 cm2 and (1.53 ± 0.29) × 10−17 cm2, respectively. Using their reported spectra and photodissociation quantum yields, their peak absorption cross sections were deduced to be (3.70 ± 0.74) × 10−17 cm2 (at 371 nm, MVKO) and (3.04 ± 0.58) × 10−17 cm2 (at 397 nm, MACRO). These values agree fairly with our theoretical predictions and are substantially larger than those of smaller, alkyl-substituted Criegee intermediates (CH2OO, syn-CH3CHOO, (CH3)2COO), revealing the effect of extended conjugation. With their cross sections, we also quantified the synthesis yields of MVKO and MACRO in the present experiment to be 0.22 ± 0.10 (at 299 K and 30 – 700 Torr) and 0.043 ± 0.019 (at 299 K and 500 Torr), respectively, relative to their photolyzed precursors. The lower yield of MACRO can be related to the high endothermicity of its formation channel.
Pornsawan Sikam, Thanadol Jitwatanasirikul, Thantip Roongcharoen, Nuttapon Yodsin, Jittima Meeprasert, Kaito Takahashi,* Supawadee Namuangruk*
Physical Chemistry Chemical Physics, 24, 12909- (2022).
Single-atom catalyst (SAC) obtained by doping a transition metal (TM) atom to stable monolayers is a promising way to improve CO2 reduction reaction (CRR) performance. In this work, we theoretically investigated the effect of ligand atoms around the doped TM (TM=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) in ZnO and ZnS for promoting CRR performance. We found that the ligand atoms around the TM can influence its oxidation state and the electronic properties of the SACs, thus affecting their CRR activity. Due to the smaller charge transfer between the TM and substrate for TM-ZnS compared to TM-ZnO, the TM binding is weaker for the former. In addition, the more negative charged oxygen ligand atoms in TM-ZnO interact with reaction intermediates, resulting in CRR products with less electron transfer. Pristine ZnS and ZnO monolayers can produce HCOOH but require a high limiting potential (UL) of about -1.2 V. Doping TM can reduce UL while ligand can alter the preferred CRR pathway and product selectivity. We found that Mn-ZnS is selective to CH4 product with a UL of only -0.29 V, which is a nearly 1 V decrease in the UL of ZnS.
Thantip Roongcharoen, Poobodin Mano, Thanadol Jitwatanasirikul, Pornsawan Sikam, Teera Butburee, Kaito Takahashi*, Supawadee Namuangruk*
Applied Surface Science 595, 153527 (2022)
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.
Mei-Tsan Kuo, Kaito Takahashi,* and Jim Jr-Min Lin*
ChemPhysChem
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.
Ting Zhou, Lei Wang, Xingye Huang, Junjuda Unruangsri, Hualei Zhang, Rong Wang, Qingliang Song, Qingyuan Yang, Weihua Li, Changchun Wang, Kaito Takahashi,* Hangxun Xu,* and Jia Guo*
Nature Communications, 12, 3934-
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.
Pornsawan Sikam, Kaito Takahashi, Thantip Roongcharoen, Thanadol Jitwatanasirikul, Chirawat Chitpakdee, Kajornsak Faungnawakij, Supawadee Namuangruk*
Applied Surface Science
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.
Institute of Atomic and Molecular Sciences Academia Sinica
