Hydrogenation Of Carbon Monoxide Catalyzed By ZnO

With modern science and technology developing,the shortage of energy has more and more serious and attracted great attention.Methanol,as an important carbon-to-energy conversion product,has many potential uses in the chemical industry.It can also be used as a clean fuel in the automobile industry.Carbon monoxide hydrogenation is the most traditional way to synthesize methanol,and copper-zinc-aluminum is the commercial catalyst for this reaction.The activation mechanism of carbon monoxide and hydrogen has been much studied on commercial catalysts,but not on on zinc oxide under working conditions.In this thesis,programmed temperature response spectra(TPRS),in situ diffuse reflection Fourier transform infrared(DRIFTS),inelastic neutron scattering(INS),and electron paramagnetic resonance spectra(EPR)and other characterization methods were used to study the activation and reaction of carbon monoxide and hydrogen on ZnO powders and nanoplates under working conditions.The main research results are as follows:(1)Carbon monoxide weakly adsorbs on zinc oxide,and desorbs from the surface at 120 K.Under working conditions,carbon monoxide undergoes a disproportionation reaction on ZnO,generating gaseous carbon dioxide and surface carbon atoms.Meanwhile,carbon monoxide also reacts with residual hydroxyl groups on ZnO to form formate species.(2)Under working conditions,hydrogen adsorption on ZnO forms major irreversibly adsorbed surface hydroxyl and interstitial hydrogen species and minor surface Zn-H species.Surface formate reacts with surface hydroxyl species to produce carbon dioxide and water.Surface active carbon atoms hydrogenate with Zn-H species stepwise to CH(a),CH2(a),CH3(a),and eventually gaseous CH4.(3)Compared with commercial zinc oxide powder,zinc oxide nanoplates exposing a higher proportion of polar Zn-ZnO(0001)and O-ZnO(000-1)surfaces show higher activity in catalyzing the hydrogenation of carbon monoxide to methane.In addition,the effects of different ZnO planes on methanol adsorption and the activation of hydrogen and carbon monoxide were also studied,whose results show that the ZnO polar surface is more avtive than the non-polar surface.These results deepen the fundamental understanding of ZnO-catalyzed hydrogenation reaction of carbon monoxide.