Preparation And Catalytic Performance Of Cu-Mn-O Composite Oxide Catalyst For N₂O Catalytic Decomposition

N₂O has once been considered as a kind of gas that is innocuous to the environment and widely applied to the fields such as industry and medical science for a long term.In recent years,with increasingly deepening cognition and research of N₂O,its harm to the environment has obtained a consensus.N₂O can not only damage ozone sphere but it's also a kind of greenhouse gas,and its global warming potential?GWP?is 310 times of CO₂ and 21 times of CH₄.In the Paris Climate Agreement that was passed in December,2015,the emission reductions of six kinds of GHGs?CO₂,CH₄,N₂O,O3,CFCs,PFCs,et al?were enlisted into the framework with a legal binding force.Emission control and elimination of N₂O have become a significant subject with which each country has to face,and research and development of relevant technologies have obtained extensive attention from academic and industrial circles both abroad and home.In many methods of eliminating N₂O,the direct catalytic decomposition method is an economical and effective method,which the characteristic is simpler technological route,lower cost,higher conversion of N₂O and no secondary pollution.In view of the direct catalytic decomposition of N₂O,and its catalytic systems research focused on the noble metal catalyst,zeolite catalyst and metal oxide catalyst.As preparation method of metal oxide catalysts is quite simple,and its composition is easy to be modulated and altered with high catalytic activity,the metal oxide catalyst has won favor from a large number of researchers.Cu-Mn-O composite oxide catalysts not only have higher catalytic activity but they are also cheap and environmentally friendly,so they are widely applied to catalytic combustion of VOCs,WGSR,catalytic synthesis of fine chemicals,etc.However,there are no relevant reports about researches on N₂O catalytic decomposition properties of Cu-Mn-O complex oxide catalysts at the moment.This paper uses Cu?NO₃?2.3H₂O and 50%Mn?NO₃?2 aqueous solution respectively as copper source and manganese source,and K2CO3 as precipitator to prepare the single oxides and Cu-Mn-O composite oxide catalysts by precipitation method and co-precipitation method.The activities of these catalysts for N₂O catalytic decomposition were investigated in a fixed-bed continuous flow reactor.On this basis,the texture strcture,phase composition,surface properties and reducing property of the single oxide catalysts and Cu-Mn-O complex oxide catalysts were investigated by N2-physisorption,XRD,FT-IR,Raman,H2-TPR.Furthermore,the catalysts prepared by different Cu/Mn ratio were characterized in detail,and the effect of Cu/Mn ratio on the catalytic performance of Cu-Mn-O complex oxide catalysts was also discussed depthly.The main results were as follows:1.Catalytic Decomposition of N₂O over Cu,Mn oxide catalystUnder the condition of space velocity of 10000 h^-1,and 0.1%N₂O content,the Cu-Mn-O composite oxides can catalyze NO2 for complete decomposition at 440?,while the reaction temperatures at which the N₂O catalytic and composition conversion rates reached the 100%on the catalyst of the single Cu and Mn oxides were respectively 480?and 500?.Under the same reaction conditions,the catalytic decomposition conversion rate on the catalysts of Cu-Mn-0 composite oxides were markedly higher than the single Cu and Mn oxides.It can be learned from the further characterization results that the single Cu and Mn oxides respectively exist in the phase forms of CuO and Mn₂O₃,and in addition to the formation of the CuMn2O4 spinel phases,there were a certain number of small-grain CuO,which feature more superior reduction performance,thus manifesting the markedly increased the direct catalytic and decomposition activities of N₂O.2.The effects of the Cu/Mn ratio on the structures of the composite oxides and the catalytic and decomposition performances of N₂OWhen the compositions of the reaction raw material gas was 0.1%N₂O,space velocity of 10000 h^-1,and a reaction temperature of 420?,the N₂O catalyst decomposition conversion rate on the Cu1.5Mn1 compound oxides could reach 100%;in contrast,under the same condition of gas components and space velocities,the reaction temperatures for the complete conversions of the N₂O on the Cu2Mnl and Cu1Mn1 compound oxides were respectively 440?and 460?.The sequences of the N₂O catalytic and decomposition activities on the Cu-Mn-0 catalyst of different Cu/Mn ratios were:Cu1.5Mn1>Cu2Mn1>CulMnl.The ratio of Cu/Mn featured significant effects on the on the forms of Cu and Mn species existence,and among them,in the Cu1.5Mn1,for the CuO species that featured the most small grains,the increase of reduction of the Cn/Mn rations can respectively result in the formations of the crystal CuO or the high-diffusion CuO,and it was correlated to the N₂O catalytic and decomposition activities;it was found that the small grain CuO was the main active species that catalyzed the N₂O direct decomposition reactions.