Study On Preparation And Catalytic Performance Of HXSM-5 Catalyst For Decomposition Of N₂O

Nitrous oxide（N₂O）is one of the main greenhouse gases at present,its greenhouse potential value is more than 300 times that of carbon dioxide,and the global total amount of N₂O is increasing at a certain rate every year.In this thesis,the preparation and performance of HZSM-5 catalysts for decomposition of nitrous oxide（N₂O）were studied.The decomposition reaction process of nitrous oxide on Cu/HZSM-5 catalyst was investigated by in-situ infrared spectroscopy.The intrinsic kinetics of catalytic decomposition of nitrous oxide was also measured.Exploratory research was carried out for effects of single-component transit metal oxide active component and preparation method on the activity of HZSM-5 supported catalyst.And based on this work experiments were conducted for decomposition of nitrous oxide on composite bicomponent transit metal oxides catalysts.The experimental results showed that the single-component copper oxide catalyst（labeled Cu₈/HZSM-5）with the molecular sieve carrier of silica-to-aluminum ratio of 27 and loading of 8%of copper oxide possessed the highest activity.Nitrous oxide was completely decomposed at 404?C.By optimizing the preparation conditions,the optimal catalyst prepared condition was calcinated at 420?C for 4 h.The catalyst Cu₈/HZSM-5 had the best activity and nitrous oxide was completely decomposed at396?C.The hydrothermal stability test of the molecular sieve catalyst sample Cu₈/HZSM-5 was carried out in feed gas with 9%water vapor.The result showed that the catalyst still maintained good catalytic activity for 10 h running experiment.At 400?C,100 h continuous thermal stability test revealed that the decomposition rate of nitrous oxide was always maintained above 95%.Based on the Cu/HZSM-5 catalyst sample prepared in the laboratory with silicon-to-aluminum ratio of 27 and loading of 8%Cu O,the single-factor experimental study was performed.The result exhibited that optimal molding conditions for industrial-scale molding catalysts were that the glue concentration was 2%,the ratio of water to powder was 1.4 m L·g^-1,the dosage of binder was 30%,and the dosage of extrusion aid was 8%.The mechanical strength of the prepared industrial shaped catalyst was 187N·cm^-1.The completely decomposed of nitrous oxide was observed at temperature of488?C on this industrial scale catalyst.Further orthogonal experiments were conducted with four-factor and three-level molding conditions.It was determined that the amount of binder had the greatest effect on the mechanical strength of the catalyst,followed by the amount of extrusion aid,the glue concentration,and the ratio of water to powder.In-situ infrared experiments were carried out based catalyst sample Cu₈/HZSM-5with the silicon-to-aluminum ratio of 27 prepared in the laboratory.Four different gas atmospheres were designed,namely N₂O,N₂O+O₂,N₂O+NO,N₂O+NO+O₂.In-situ infrared spectroscopy was used to analyze the adsorption of gas on the catalyst at different time and temperature.The phenomena of desorption of the nitrous oxide molecular was observed for various situations on the catalyst.The analysis results showed that there were three kinds of adsorption modes for nitrous oxide molecules on the surface of Cu₈/HZSM-5,i.e.physical adsorption,weak chemical adsorption,and chemical adsorption（stronger）respectively.With the increase of system temperature,the N₂O molecules physically and weakly adsorbed on Cu₈/HZSM-5 would be partially desorbed from catalyst surface.During the catalytic decomposition reaction of nitrous oxide,N₂O molecule was adsorbed on the surface of the catalyst firstly to form N₂O^*.Then adsorbed oxygen（O^*）and N₂ were generated.Third step was the generation of free O₂ from active oxygen atoms adsorbed on the active sites and oxygen molecule desorbed to the gas stream.Under the conditions of this experiment,O₂ was the zero-order reaction during the catalytic decomposition of N₂O,which had little effect on the reaction.NO had obvious promoting effect on N₂O catalytic decomposition reaction.It was recyclable during the catalytic decomposition of nitrous oxide.The intrinsic kinetics was investigated for the decomposition of N₂O catalysed by the Cu₈/HZSM-5 catalyst with silicon to aluminum ratio of 27.The experimental results showed that in the case of eliminating internal and external diffusion,the N2O decomposition reaction was determined to be of first-order with respect to nitrous oxide.The activation energy of the reaction was 115.15 k J·mol^-1.And parameters of the reaction kinetic equation were determined through experiments under the experimental conditions.