Study On Denitrification Catalysts Based On Hexaaluminate

Nitrogen oxides (NOX) are very important pollutants in the atmosphere, which have great harmful effect on ecological environment, economic development and human health. There are many types of NOX, but air pollution mainly caused by NO, NO2, and N2O. Currently, catalytic decomposition is an effective way to remove N2O, which usually is a by-product in petrochemical industry. Selective catalytic reduction (SCR) method is often used to remove NO in the flue gas of coal combustion power plant. Hexaaluminate catalyst has been extensively researched in recent years because it is a kind of high thermal stability catalyst materials with higher catalytic activities under high temperature environment.In this paper, a series of transit metal-doped hexaaluminate catalysts were prepared by co-precipitation. And hexaaluminate-supported Fe2O3 catalyst has been prepared by incipient wetness impregnation method. The catalysts were characterized by XRD, H2-TPR, BET, TG-DSC and other means. The catalytic denitrification activities of the samples were examined in a miniature reaction rig. (1) The performances of hexaaluminate catalysts for N2O direct decomposition were studied.Ba series hexaaluminates BaMxAl12-xO19-δ(M=Cu, Co; x=1,2,3,4), were prepared. These compound crystal structure was much complex and their catalytic activity was poor. At the same time, experimental results showed that there was a great amount of NO in the decomposition products when N2O decomposition over BaCoxAl12-xO19-δcatalyst, which concentration was up to 1000ppm.La series of hexaaluminate catalysts expressed advanced N2O direct decomposition activity. Perfect hexaaluminate phase was found in LaCuAl11O19-δcatalyst, which also had better activity for N2O decomposition. LaCuxM1-xAl11O19-δ(x=0.2,0.4,0.6,0.8) was prepared by doping metal elements Mn and Fe in Cu-doped hexaaluminate. Their activities of N2O decomposition were higher than single Cu doped hexaaluminate and NO concentration in the exhaust gas decreased at some extent. When CH4 was added in the process of N2O decomposition over LaCu0.4Fe0.6Al11O19-δ, conversion rate of N2O was increased and the concentration of by-product NO was decreased ulteriorly.(2) NO catalytic reduction activities were studied over hexaaluminate under CH4 atmosphere.LaFeAl11O19-δwas prepared by co-precipitation with ammonium carbonate as precipitant. The precursor was precipitated at 60℃for 3h and then was calcinated at 1200℃for 4h. The characterized results showed that LaMAl11O19-δ(M was Mn, Cu and Fe) expressed perfect hexaaluminate phase and the catalyst samples had higher catalytic activity. The results showed that the optimal doping amount of Mn, Cu and Fe is 1,1 and 2, respectively.Bi-metal doped catalysts LaMMAl10O19-δwere also formed complete hexaaluminate phase under calcinated at 1200℃for 4h. They showed high specific surface area and good catalytic activity. Comparison with single Mn or Fe-doped catalysts, catalytic activities of LaMnCuAl10O19-δand LaFeCoAl10O19-δhad significantly improved. In the series of LaCuxFe1-xAl11O19-δsamples, the catalyst with x=0.8 had a better activity for N2O decomposition and its activation energy was about 90.52 kJ·mol-1.(3) Investigation on NO catalytic reduction over hexaaluminate supported iron catalysts.Incipient wetness impregnation method was employed to prepared 3wt% load Fe2O3 on LaAl12O19-δcatalyst. The precursor was calcinated at 600℃for 4h to form a high dispersed Fe2O3 on the hexaaluminate carrier surface with a higher specific surface area. Experiment of NO reduced reaction with CH4 as reductant showed that the catalyst catalytic activity was excellent, which temperature of T10% and T90% were 490℃and 589℃, respectively.100 hours continuous lifetime experiment indicated that no obvious activity decline was observed.