In situ formation of catalytically active graphene in ethylene photo-epoxidation

Abstract

Ethylene epoxidation is used to produce 2 × 107 ton per year of ethylene oxide, a major feedstock for commodity chemicals and plastics. While high pressures and temperatures are required for the reaction, plasmonic photoexcitation of the Ag catalyst enables epoxidation at near-ambient conditions. Here, we use surface-enhanced Raman scattering to monitor the plasmon excitation-assisted reaction on individual sites of a Ag nanoparticle catalyst. We uncover an unconventional mechanism, wherein the primary step is the photosynthesis of graphene on the Ag surface. Epoxidation of ethylene is then promoted by this photogenerated graphene. Density functional theory simulations point to edge defects on the graphene as the sites for epoxidation. Guided by this insight, we synthesize a composite graphene/Ag/α-Al2O3 catalyst, which accomplishes ethylene photo-epoxidation under ambient conditions at which the conventional Ag/α-Al2O3 catalyst shows negligible activity. Our finding of in situ photogeneration of catalytically active graphene may apply to other photocatalytic hydrocarbon transformations.

A Green Route for Quick and Kilogram Production of Reduced Graphene Oxide and Their Applications at Low Loadings in Epoxy Resins

“…Raman Analysis : Raman spectroscopy is a powerful tool to examine the defects and disorders in the crystal pattern of materials ,. It is frequently utilized to characterize Graphene and their derivatives [22, 23].…”

“…al. ,. Purified rGO1, rGO2 and rGO4 are not showing additional bands in their Raman spectra, indicating no defect in the crystal lattice of the reduced Graphene Oxide produced by Ball Milling in the presence of activated Zn powder ,.…”

Ammonia Oxidation Enhanced by Photopotential Generated by Plasmonic Excitation of a Bimetallic Electrocatalyst

“…The origin of the LSPR enhancement is elucidated by an additional study. LSPRs excited in the metal NPs decay to form excited electron–hole pairs, which are known to enhance the kinetics of redox reactions . However, there is a process that occurs in parallel: excited electron–hole pairs decay non‐radiatively by electron‐phonon coupling, which results in heating of the NP lattice, and subsequently by phonon‐phonon coupling, which results in the transfer of heat from the heated NP lattice to the surrounding medium.…”

Anion-Exchange-Mediated Internal Electric Field: Boosting Photogenerated Carrier Separation and Utilization

“…During photocatalysis, the separation of electron-hole pairs within the semiconductor catalysts, combined with the following energy transfer processes, can readily generate a large amount of highly active species (such as radicals and singlet oxygen [1][2][3][4] . Notably, these active species could, under green and mild conditions, participate in a variety of organic reactions, including hydrogenation 5,6 , epoxidation 7,8 , alcohol oxidation 9,10 , selective oxidation of aromatic compounds 11,12 , and even some reactions that are rather challenging in thermal catalysis. Yet still, currently for heterogeneous photocatalysts, there exist the common issues of rapid recombination of photocarriers and the resulting low e ciency of carrier separation and utilization, which would hamper the high-performance catalysis of sophisticated organic reactions, and thus their applications have so far been limited primarily to environment-related aspects such as degradation of organics, air puri cation and water photolysis [13][14][15][16][17] .…”