Studies Of Electrochemical Conversion Of Light Alkanes On Platinum Single Crystal Surface

Alkanes and olefins are primary energy resources and industrial substrates in modern society.Related studies have attracted enormous interest in the field of energy and catalysis.Electrochemical methods not only provide an efficient tool of transfer energy to activate inert substrate but also can help control the reaction rate and degree by altering the electrode potential,making electrochemistry a promising way of utilizing alkanes and olefins.However,due to the inert nature of alkanes and the selectivity of the olefin oxidation,the development and practical application of alkanes and olefins electrochemistry are still limited.Therefore,design and developing the electrocatalyst of alkanes and olefins conversion with high activity and understanding its underlying reaction mechanism became the key to study alkane and olefins electrochemistry.This thesis studied the interaction of methane,ethane and propane,ethylene with platinum and palladium-based on well-defined model single crystal electrode and characterization techniques like cycle voltammetry(CV),in situ FTIR spectroscopy and NMR spectroscopy.Along with DFT calculations,the sensitivity of the surface reaction and the reaction mechanism was revealed,providing a theoretical guidance for the rational design of alkanes and olefins electrocatalysis.The main works are summarized as below:1、The electrochemical features of methane on platinum single crystal electrode in acidic aqueous solutions have been explored.The results show that the electrochemical conversion of methane on platinum is highly sensitive to its surface structure.Among three basal planes of platinum,only Pt(100)can activate methane at an appreciable rate at room temperature.Also,the reactivity decreases gradually with the decrease of atom number of Pt(100)terrace width,with a Pt(100)terrace width of at least 5 atoms can effectively catalyze the conversion of methane.In situ FTIR spectroscopy results show that methane mainly converted to multiple site bond CO on Pt(100),which later completely oxidized to CO2 at high potentials.Combined with DFT calculations and the experiment of 13CH3CH2OH electrooxidation,the results show that the high activity of Pt(100)results from its low energy barrier of coupling surface CHx and surface oxygen.2、The interaction of ethane and propane with Pt(100)has been studied.The results show that the oxidation of ethane and propane on Pt(100)displaying four characteristic oxidation peaks.By altering adsorption potentials,scan rate and reaction temperature,combining the results of in situ FTIR spectroscopy,the basic process of ethane and propane conversion on Pt(100)were revealed.Besides,the study of step surface containing Pt(100)terrace shows that the electrooxidation of ethane and propane with platinum is also surface-structure sensitive.Decoration of Pt(100)surface by Sn and Ru atom shows that the adatom mostly hinders the reaction of alkanes by taking up the active site of Pt(100).The product of ethane and propane electrooxidation has also been revealed by NMR analysis.3、The electrochemical features and mechanism of ethylene reaction on platinum and palladium have been studied.The activity of ethylene and the adsorption potentials is closely connected on platinum while not on palladium.High reactivity towards the conversion of surface CHx making Pt(100)a robust catalytic surface for ethylene conversion.While high reactivity of Pt(111)at low potential can only show when the electrode was activated at a high potential of 1.1v.In situ FTIR spectroscopy shows that linearly-bonded and bridge-bonded CO and a few vinylidene species were produced on Pt(100)while two kinds of vinylidene with different configurations were produced on Pt(110)and Pt(111),the vinylidene turns into oxygenated species at higher potentials.The reaction of ethylene on Pd(100)and Pd(111)didn’t show much differences,producing acetaldehyde rather than CO at higher potentials.This thesis provided a fundamental understading over the electrochemical reaction of alkanes and olefins on noble metal catalysts and is of great importance to the catalyst design and mechanism analysis on alkane and olefin electrochemistry.