Edge-rich molybdenum disulfide tailors carbon-chain growth for selective hydrogenation of carbon monoxide to higher alcohols.

Selective hydrogenation of carbon monoxide (CO) to higher alcohols (C2+OH) is a promising non-petroleum route for producing high-value chemicals, in which precise regulations of both C-O cleavage and C-C coupling are highly essential but remain great challenges. Herein, we report that highly selective CO hydrogenation to C2-4OH is achieved over a potassium-modified edge-rich molybdenum disulfide (MoS2) catalyst, which delivers a high CO conversion of 17% with a superior C2-4OH selectivity of 45.2% in hydrogenated products at 240 °C and 50 bar, outperforming previously reported non-noble metal-based catalysts under similar conditions. By regulating the relative abundance of edge to basal plane, C2-4OH to methanol selectivity ratio can be overturned from 0.4 to 2.2. Mechanistic studies reveal that sulfur vacancies at MoS2 edges boost carbon-chain growth by facilitating not only C-O cleavage but also C-C coupling, while potassium promotes the desorption of alcohols via electrostatic interaction with hydroxyls, thereby enabling preferential formation of C2-4OH.

Boosting CO2 Hydrogenation to Formate over Edge-Sulfur Vacancies of Molybdenum Disulfide.

Synthesis of formate from hydrogenation of carbon dioxide (CO2 ) is an atom-economic reaction but is confronted with challenges in developing high-performance non-precious metal catalysts for application of the process. Herein, we report a highly durable edge-rich molybdenum disulfide (MoS2 ) catalyst for CO2 hydrogenation to formate at 200 °C, which delivers a high selectivity of over 99 % with a superior turnover frequency of 780.7 h-1 surpassing those of previously reported non-precious metal catalysts. Multiple experimental characterization techniques combined with theoretical calculations reveal that sulfur vacancies at MoS2 edges are the active sites and the selective production of formate is enabled via a completely new water-mediated hydrogenation mechanism, in which surface OH* and H* species in dynamic equilibrium with water serve as moderate hydrogenating agents for CO2 with residual O* reduced by hydrogen. This study provides a new route for developing low-cost high-performance catalysts for CO2 hydrogenation to formate.

Sensing mechanism of a new fluorescent probe for hydrogen sulfide: photoinduced electron transfer and invalidity of excited-state intramolecular proton transfer.

It is of great significance for biological research to develop efficient detection methods of hydrogen sulfide (H2S). When DFAN reacts with H2S, 2,4-dinitrophenyl ether group acting as an electron acceptor generates a hydroxyl-substituted 2,4-dinitrophenyl ether group, resulting in the disappearance of photoinduced electron transfer (PET), and the new formed DFAH can be observed, while being accompanied by a significant fluorescence. In the present study, the PET sensing mechanism of probe DFAN and the excited state intramolecular proton transfer (ESIPT) process of DFAH have been explored in detail based on the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. Our theoretical results show that the fluorescence quenching of DFAN is caused by the PET mechanism, and the result of ESIPT mechanism is not due to the large Stokes shift fluorescence emission of DFAH. We also optimized the geometric structure of the transition state of DFAH. The frontier molecular orbitals and potential barrier show that the ESIPT process does not easy occur easily for DFAH. The enol structure of DFAH is more stable than that of the keto structure. The absence of the PET process resulted in the enol structure emitting strong fluorescence, which is consistent with the single fluorescence in the experiment. Above all, our calculations are sufficient to verify the sensing mechanism of H2S using DFAN.

A new interpretation of the ESIPT mechanism of 2-(benzimidazol-2-yl)-3-hydroxychromone derivatives.

The present study demonstrates the excited-state intramolecular proton transfer (ESIPT) mechanism of 2-(benzimidazol-2-yl)-3-hydroxychromone (DH3B2) is based on density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. We find that DH3B2-C is the main conformation to occur ESIPT. Moreover, we get the different results of DH3B2 for the ESIPT mechanisms in comparison with the previous reports. We have optimized three isomers (DH3B2-A, DH3B2-B and DH3B2-C), and calculated absorption and fluorescence spectra, which agree well with the experimental data. Furthermore, we prove the hydrogen bond is enhanced in the S1 state by comparing infrared vibrational spectra, the relevant bond length and bond angle. In our calculations, the results of the three levels of calculations (CAM-B3LYP/TZVP, B3LYP/TZVP and PBEPBE/TZVP) indicate that DH3B2-C is the most stable conformation, by compared the single point energy of three isomers. By constructed the potential energy surfaces (PESs), we find the converted relationship among the three isomers; DH3B2-C is the main conformation in which DH3B2 exists. Furthermore, combination with reduced density gradient (RDG) function, the hydrogen bond of DH3B2-C is stronger than that of DH3B2-A and DH3B2-B, which proves that DH3B2-C form is the most favorable form for ESIPT among the three isomers. Meanwhile, we have further investigated the ESIPT mechanisms of DH3B2, via constructing the potential energy curves (PECs). These results have shown that DH3B2-C is easier to ESIPT occur than DH3B2-A and DH3B2-B. Therefore, the proton receptors of the ESIPT are mainly the benzimidazole nitrogen atoms.

Excited-State Proton Transfer Mechanism of 2,6-Diazaindoles·(H2O) n ( n = 2-4) Clusters.

This paper identified a new excited-state proton transfer (ESPT) mechanism for 2,6-diazaindoles (2,6-DAI) in aqueous (H2O) solution based on time-dependent density functional theory. The calculated results show that the excited-state three proton transfer reaction cannot occur because the 2,6-DAI with two water molecules do not form hydrogen bond wires; this finding was different from those reported in previous experiments (Chung et al. J. Am. Chem. Soc. 2017, 139, 6396-6402). 2,6-DAI with three water molecules form 2,6-DAI·(H2O)3 clusters, whereas 2,6-DAI with four water molecules form 2,6-DAI·(H2O)4 cluster. These clusters participate in the ESPT reaction. To determine the ESPT mechanism of 2,6-DAI·(H2O)3 and 2,6-DAI·(H2O)4 clusters, we constructed the potential energy curves of S1 and S0 states. The results confirmed the simultaneous presence of both 2,6-DAI·(H2O)3 and 2,6-DAI·(H2O)4 clusters and only one proton transfer pathway. By calculating the transition states of 2,6-DAI·(H2O)3 and 2,6-DAI·(H2O)4 clusters, we found that the ESPT reaction is a consistent mechanism. Our work investigated the number of water molecules involved in the ESPT and paved the way to further study the intermolecular hydrogen bonding interactions in the biological field.

Sono-desulfurization oxidation reactivities of FCC diesel fuel in metal ion/H2O2 systems.

The objective of this work was to probe experimentally the characteristics of the use of Fe(2+) or Cu(2+) ions in the ultrasound-assisted oxidation desulfurization (UAODS) of diesel fuels and to develop a model that appropriately represented the mechanism. The influence of metal ions (Fe(2+) or Cu(2+)) on aqueous phase pH values of the UAODS of diesel fuels was investigated. The UAODS proceeded rapidly only within a limited pH range from 1.9 to 2.1. It was observed that the UAODS of diesel fuels fitted pseudo-first-order kinetics under our experimental conditions. In UAODS of diesel fuels the apparent reaction rate constants can be greatly enhanced by addition of metal ions and/or using ultrasound. The combination of ultrasound and the metal ions can also reduce the apparent activation energy rapidly. The order of the apparent reaction rate constants in UAODS of diesel fuels is US-Fe(2+)-H(2)O(2) system>US-Cu(2+)-H(2)O(2) system>US-H(2)O(2) system>H(2)O(2) system.