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Isotope substitution, a fascinating tool of physical chemistry, has been broadly applied in the research field of heterogeneous catalysis. In general, due to the differences in the mass-related atomic vibrational frequencies and zero-point energy of isotopic molecules, the apparent isotope effect (AIE) or observed kinetic isotope effect (observed KIE) from isotope substitution examination could provide unique knowledge regarding the reaction rate and mechanism of a catalytic reaction, such as the rate-determining step, key reaction intermediate, or catalyst design and synthesis. However, the treatment of the AIE is not as straightforward as the isotopic switch experiment, and needs sufficient care and comprehensive identification to deal with the influences from the equilibrium isotope effects (EIEs) of quasi-equilibrium elementary steps, kinetic isotope effect (KIE) of the pseudo rate-determining step, transition states, intrinsic reaction barriers, etc. Fundamentally, the key factors affecting the AIE could be the partition function part and the zero-point energy part of each single elementary step. Theoretically, the classification of the KIE could be based on the quantity of KIE (including normal KIE and inverse KIE) or the molecular transformation (including primary KIE, secondary KIE, tunneling KIE, and solvent KIE) involved. This article presents a recap of the fundamental concepts and relations of KIE, EIE and AIE, and a concise review on the selected applications of isotope effects throughout heterogeneous catalysis. Lastly, the meaningful perspectives regarding the critical factors that impact the AIE and the appropriate treatment of the AIE are discussed meticulously. [ABSTRACT FROM AUTHOR]

The electrochemical nitrogen reduction reaction (NRR) is emerging as a promising sustainable technique that can convert nitrogen (N2) to ammonia (NH3) under ambient conditions. However, the selectivity and electrocatalytic activity of the NRR obtained experimentally to date are still unsatisfactory. As a consequence, it remains a technical challenge to develop scalable, low-cost, and efficient NRR electrocatalysts. Herein, we present an oxygen vacancy (VO)-rich two-dimensional gold (Au)/titanium dioxide (TiO2) hybrid that acts as an advanced NRR electrocatalyst under ambient conditions. Electrocatalytic testing demonstrated that the Au/TiO2 hybrid catalyst delivered a promising NH3 yield of 64.6 μg h−1 mg−1 cat and a high faradaic efficiency of 29.5% at −0.40 V versus the reversible hydrogen electrode in acidic media. Experimental findings and theoretical calculations demonstrate that the strong electron-donating effect of VO in TiO2 was essential for N2 activation. Meanwhile, the introduction of Au promotes both the electrochemical and thermodynamic rate-limiting steps by adjusting the electronic structure of the active sites. Together, these effects greatly facilitate the activation and reduction of N2 under ambient conditions. The specific catalyst design strategy in our work represents an alternative avenue to produce other two-dimensional electrocatalysts with high NRR activity and selectivity through rational structural engineering. [ABSTRACT FROM AUTHOR]

Recently discovered homogeneous frustrated Lewis pairs (FLPs) have attracted much attention for metal-free catalysis due to their promising potential for the activation of small molecules (e.g., H2, CO, CO2, NOx and many others). Hence, a wide range of these homogeneous FLPs have been extensively explored for many advanced organic syntheses, radical chemistry and polymerizations. In particular, these FLPs are efficiently utilized for the hydrogenation of various unsaturated substrates (e.g., olefins, alkynes, esters and ketones). Inspired by the substantial progress in these homogeneous catalytic systems, heterogeneous FLP catalysts, including semi-solid and all-solid catalysts, have also emerged as an exciting and evolving field. In this review, we highlight the recent advances made in heterogeneous FLP-like catalysts and the strategies to construct tailorable interfacial FLP-like active sites on semi-solid and all-solid FLP catalysts. Challenges and outlook for the further development of these catalysts in synthetic chemistry will be discussed. [ABSTRACT FROM AUTHOR]

Dissociation of O2 into atomic oxygen is a significant route for O2 activation in metal-catalyzed oxidation reactions. In this study, we systematically investigated the mechanisms of O2 dissociation and the promoting role of water on nine transition metal (Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, and Au) surfaces. It was found that on clean metal surfaces, the dissociation of O2 was most favorable on Co(0001) and most difficult on Au(111), according to the free energy barriers of Co (0.03 eV) ＜ Rh (0.20 eV) ＜ Ni (0.26 eV) ＜ Cu (0.45 eV) ＜ Ir (0.62 eV) ＜ Pd (0.65 eV) ＜ Pt (0.92 eV) ＜ Ag (1.07 eV) ＜ Au (2.50 eV). With the involvement of water, O2 and H2O formed an O2…H2O complex via hydrogen bonding interactions, being accompanied by an increased co-adsorption free energy of 0.17–0.52 eV and a more activated O–O bond. More importantly, the introduction of water reduced the barriers of O2 dissociation on all the nine metal surfaces, with the reduction of the free energy barrier ranging from 0.03 eV on Co(0001) to 1.05 eV on Au(111). The intrinsic reasons for the promotional role of water are attributed to the hydrogen bonding effect between O2 and H2O and the electronic modification effect induced by the water–surface interaction. These results provide a fundamental understanding of the catalytic role of water in O2 dissociation on the transition metal surfaces and may be helpful in the rational design of new efficient catalysts for the oxidation reactions using molecular oxygen or air. [ABSTRACT FROM AUTHOR]