Elementary reaction

About: Elementary reaction is a research topic. Over the lifetime, 2972 publications have been published within this topic receiving 76110 citations.

Self-adaptive dual-metal-site pairs in metal-organic frameworks for selective CO2 photoreduction to CH4

Abstract: Solar-light-driven reduction of CO2-to-CH4 is a complex process involving multiple elementary reactions and various by-products. Achieving high CH4 activity and selectivity therefore remain a significant challenge. Here we show a bioinspired photocatalyst with flexible dual-metal-site pairs (DMSPs), which exhibit dynamic self-adaptive behaviour to fit mutative C1 intermediates, achieving CO2-to-CH4 photoreduction. The Cu and Ni DMSPs in their respective single-site forms under flexible microenvironment are incorporated into a metal-organic framework (MOF) to afford MOF-808-CuNi. This dramatically boosts CH4 selectivity up to 99.4% (electron basis) and 97.5% (product basis), and results in a high production rate of 158.7 μmol g−1 h−1 with a sacrificial reagent. Density functional theory calculations reveal that the flexible self-adaptive DMSPs can stabilize various C1 intermediates in multistep elementary reactions, leading to highly selective CO2-to-CH4 process. This work demonstrates that efficient and selective heterogeneous catalytic processes can be achieved by stabilizing reaction intermediates via the self-adaptive DMSP mechanism. CH4 selectivity in CO2 photoreduction is a kinetic challenge as a result of the complex pathway involving many intermediates. Here, the authors present dual-metal-site pairs embedded in a metal-organic framework structure with flexible adaptive active sites leading to high CH4 activity and selectivity.

Location of transition states in reaction mechanisms

Abstract: A general method is described for the location of transition states in reaction mechanisms. Transition states for unimolecular and bimolecular reactions can be identified. The procedure is fully automatic, once reactants and products are characterised, and no assumptions as to the geometry of the transition state or of the mechanism are necessary. Examples are given of the Cope and Claisen reactions.

Pulse Radiolysis Studies. I. Transient Spectra and Reaction‐Rate Constants in Irradiated Aqueous Solutions of Benzene

Abstract: The radiation chemistry of aqueous benzene solutions has been studied by the electron‐pulse radiolysis technique. Ultraviolet absorption spectra of some of the transient species have been recorded by synchronized flash‐absorption spectroscopy. The elementary reactions occurring have been observed by fast photoelectric recording of the transient optical density.A transient spectrum having a broad absorption with a strong maximum at 313 mμ has been observed. On the basis of both spectrographic and kinetic evidence this spectrum is assigned to the hydroxycyclohexadienyl radical, (OH)C6H6·. The molar extinction coefficient is estimated to be e3130=3500±800 M—1cm—1. A number of substituted cyclohexadienyl radicals have been observed in aqueous solution as well as in pure benzene and chloro‐benzene. A second transient observed in oxygenated aqueous benzene solution shows an absorption shifted to lower wavelengths. This is attributed to the hydroxycyclohexadienyl peroxy radical, (OH)C6H6O2·.Absolute rate constan...

A first principles study of oxygen reduction reaction on a Pt(111) surface modified by a subsurface transition metal M (M = Ni, Co, or Fe)

Abstract: We have performed first-principle density functional theory calculations to investigate how a subsurface transition metal M (M = Ni, Co, or Fe) affects the energetics and mechanisms of oxygen reduction reaction (ORR) on the outermost Pt mono-surface layer of Pt/M(111) surfaces. In this work, we found that the subsurface Ni, Co, and Fe could down-shift the d-band center of the Pt surface layer and thus weaken the binding of chemical species to the Pt/M(111) surface. Moreover, the subsurface Ni, Co, and Fe could modify the heat of reaction and activation energy of various elementary reactions of ORR on these Pt/M(111) surfaces. Our DFT results revealed that, due to the influence of the subsurface Ni, Co, and Fe, ORR would adopt a hydrogen peroxide dissociation mechanism with an activation energy of 0.15 eV on Pt/Ni(111), 0.17 eV on Pt/Co(111), and 0.16 eV on Pt/Fe(111) surface, respectively, for their rate-determining O2 protonation reaction. In contrast, ORR would follow a peroxyl dissociation mechanism on a pure Pt(111) surface with an activation energy of 0.79 eV for its rate-determining O protonation reaction. Thus, our theoretical study explained why the subsurface Ni, Co, and Fe could lead to multi-fold enhancement in catalytic activity for ORR on the Pt mono-surface layer of Pt/M(111) surfaces.