Application Of Anion Radical Emission Materials On Phenol Synthesis And Ethanol Steam Reforming

A novel approach to the phenol synthesis from benzene and hydrogen production from ethanol steam reforming over [Ca₂₄Al₂₈O₆₄]⁴⁺·4O^- (C12A7-O^-) catalyst were investigated by using a flow reactor. In the two reaction systems, the conversion of the reactants and the yield of the products were studied under different conditions. The changes of the catalyst structure before and after the reactions and the intermediates on the catalyst surface and in the bulk were also investigated. The major conclusions have been summarized as follows:1. Study of the one-step synthesis of phenol over C12A7-O^- catalyst1) The preparation and characterization of the catalysts: The C12A7-O^- material was prepared by a solid-state reaction method at a high temperature. The catalyst structure, the intermediates on the catalyst surface and in the bulk was investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Electron Paramagnetic Resonance (EPR).2) One-step synthesis of phenol over C12A7-O^- catalyst: Direct conversion of benzene to phenol by oxygen/water over the synthesized [Ca₂₄Al₂₈O₆₄]⁴⁺·4(O^-) (C12A7-O^-) catalyst was obtained. The benzene conversion of 34 % with phenol selectivity about 90% has been obtained at 565°C and the mixture ratio of C₆H₆:O₂:H₂O = 2:1: 4.8. Carbon formation was found to be negligible after 1000 min's reaction. The synthesis reactions do not destroy the positively charged framework of C12A7-O^-. After the synthesis reactions, part of oxygen species (O^-(cage) and O₂^-(cage)) in the C12A7-O^- bulk were substituted by the species of OH^-(cage). The surface species of OH^-(s) are formed in the synthesis reactions, which are generated by the reactions of O^-(s) with water and benzene. The OH^-(gas-phase) and C₆H₅OH^- (gas-phase) anionic species observed are formed by the surface reactions of O^-(s) with the adsorbed benzene and then desorbed into the gas phase. O^-(s) was suggested as an active species in initiating the benzene conversion process via hydrogen abstraction reaction. Then, the intermediate species C₆H₅OH^- (s) was formed from the phenyl radical C₆H₅(s) and OH^-(s), leading to the formation of phenol by an electron detachment process.2. Study of the hydrogen production from ethanol steam reforming over C12A7-O^-/K catalyst1) The performance of the different catalysts: The hydrogen yield and the ethanol conversion of all the catalysts were studied under the same reaction conditions. It was found that the sample C12A7-O^-/27.3%K possessed the best catalytic performance.2) Ethanol steam reforming over C12A7-O^-/27.3%K catalyst: The present investigation shows that the C12A7-O^-/27.3%K catalyst exhibits high catalytic activity and long stability for the reaction of ethanol steam reforming. The catalyst is very selective to hydrogen production, depending on the experimental conditions. Both the hydrogen yield and the carbon conversion over the C12A7-O^-/27.3%K catalyst were sensitive to temperature, the S/C ratio, the contact time and the potassium-doped content in the catalysts. Carbon formation was found to be negligible even for the molar ratio of H₂O/C₂H₅OH equal to the stoichiometric one. The advantages of the C12A7-O^-/x%K catalyst would be cheap and environmentally friendly, and possessing a long-term stability, which would be useful to the hydrogen production from ethanol steam reforming. Based on the characterization, it was found that the active oxygen species and the doped potassium play important roles in the steam reforming of ethanol over the C12A7-O^-/x%K catalyst.