Study On Methane Redox Characteristics Based On Cu/Al₂O₃ Catalyst

Methane is widely distributed in China,with large reserves and more environmental protection.Using methane as reducing gas to reduce nitrogen oxide gas which is extremely harmful to human body and the environment has more advantages and great research value compared with NH3.Although methane is relatively more environmentally friendly,the pollution caused by low concentration methane emitted by valve air(VAM),exhaust gas of internal combustion engine and insufficient combustion of gas-fired boiler can not be ignored.Therefore,this paper also studied the catalytic reduction of NO and catalytic oxidation characteristics of methane under the action of catalyst.At present,the catalytic activity of Cu/Al2O3 catalyst is relatively low,and Cu/Al2O3 catalyst can not be used as more effective carrier for methane oxidation,but its catalytic activity and dispersion efficiency need to be further improved.Therefore,this paper studied and improved the Cu/Al2O3 catalyst from the three directions of support,modification of metal additives and active components,and studied the reaction mechanism of methane catalytic reduction of NO,in order to further improve the methane catalytic activity of Cu/Al2O3 catalyst.This paper studies as follows:Firstly,copper based catalysts with different supports(Al2O3,ZSM-5,Ti2O3,ZrO2 and SiO2)were prepared and tested for catalyst efficiency.The test results showed that when CH4 was used as reducing agent,the NO reduction efficiency of the catalyst was Cu/Al2O3>Cu/ZSM-5>Cu/ZrO2,while the order of catalytic oxidation reaction between methane and oxygen was opposite,Cu/ZrO2>Cu/ZSM-5>Cu/Al2O3,It shows that there is a competitive relationship between the catalytic oxidation of methane and the reduction of NO by methane,which inhibits the NO reduction by methane efficiency of the catalyst to a certain extent.Cu/TiO2 and Cu/SiO2 catalysts have little efficiency in the reduction of NO by methane and the catalytic oxidation of methane.At the same time,the effects of calcination temperature and inlet methane concentration on the efficiency of Cu/Al2O3 catalyst were tested.Cu based catalyst Cu/SMA(a)(a=10,20,30)was prepared with nano alumina with different particle sizes(10nm,20nm,30nm)as the carrier.The test results show that Cu/SMA(20)catalyst with 20nm alumina as the carrier has the best catalytic activity.Secondly,Cu-M/SMA(20)(M=Co,Ni,Ce,Mn)catalysts modified by different transition metal elements(Co,Ni,Ce,Mn)were prepared.The test results showed that the efficiency order of methane reduction of NO under the catalyst was Cu-Ce/SMA(20)>Cu-Co/SMA(20)>CuNi/SMA(20)>Cu/SMA(20)>Cu-Mn/SMA(20),The order of catalytic oxidation of methane is CuMn/SMA(20)>Cu-Co/SMA(20)>Cu-C e/SMA(20)>Cu-Ni/SMA(20)>Cu/SMA(20).The experimental and characterization results show that the addition of Mn promotes the catalytic oxidation reaction between methane and oxygen and inhibits the reaction of NO reduction by methane.the addition of Ce cooperates with the active component Cu to form Cu2+Ce3+?Cu++Ce4+cycle enhances the NO reduction efficiency of the catalyst.The experimental results show that with the increase of Ce content,the catalytic reduction efficiency of methane first increases and then decreases,while the catalytic oxidation of methane shows an upward trend with the increase of Ce content.Finally,a series of nano-sized copper oxide with adjustable particle size were prepared.It was found that the addition of EG could effectively refine the particle size of copper oxide.The prepared nano-sized copper oxide with different particle sizes is loaded on the previously selected alumina support surface with particle size of 20nm and tested.The test results show that with the decrease of the particle size of copper oxide,the catalytic reduction of NO by methane and the catalytic oxidation efficiency of methane of the catalyst first increase and then decrease.The characterization results show that with the decrease of the particle size of copper oxide,it can be better dispersed on the surface of alumina support,However,the smaller the particle size,it will also cause the blockage of the pore opening of the catalyst support and reduce the exposed active reaction sites,which will affect the catalytic efficiency.Therefore,different pretreatment methods are used to adjust the catalyst channels.The test results show that H2 pretreatment at appropriate temperature and acid treatment at appropriate concentration can play the role of regulating the catalyst carrier channels to a certain extent,release the blocked channels of the catalyst to a certain extent,and improve the catalytic efficiency.Among them,the effect of acid treatment catalyst is better than H2 pretreatment.In conclusion,it provides a good idea for the catalytic reduction of methane and the use of Al2O3 catalyst,which provides a better idea for the oxidation and reduction of methane.