Microsoft Word - 02Revised.doc CHEMICAL ENGINEERINGTRANSACTIONS VOL. 55, 2016 A publication of The Italian Association of Chemical Engineering Online at www.aidic.it/cet Guest Editors:Tichun Wang, Hongyang Zhang, Lei Tian Copyright © 2016, AIDIC Servizi S.r.l., ISBN978-88-95608-46-4; ISSN 2283-9216 Low-Temperature Catalytic Reaction over Manganese- Cerium Composite Oxide Supported on Titania Rongzhi Zhao, Raorui Liang, Suqin Li*, Cunyi Song University of Science and Technology Beijing lisuqin@metall.ustb.edu.cn A series of catalysts of manganese-cerium (Mn-Ce) active components supported on TiO2 prepared through sol-gel process were used for low-temperature catalytic reduction of NO with ammonia as reductant. The catalysts were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that the particle size of the catalysts is smaller and the active components are highly dispersed on the support. Doping Ce exhibited an inhibitory effect on the crystal transition of TiO2 from anatase to rutile phase. Furthermore, the TiO2 support got the entire anatase phase at 450°C, with an improved the property of the catalyst. The catalyst with the highest activity was obtained with a mass Ce(0.8)-Mn/TiO2 ratio of 0.15, and calcinated at 450°C, providing 99.01% NO conversion at 140°C at a high space velocity of 67, 000 h-1. With the increasing of Ce-Mn loading amount and Ce/Mn molar ratio, the NO conversion increased firstly and then decreased. With the increasing of NH3/NO molar ratio in inlet flue gas, NO conversion increased firstly and then tended to be stable. . 1. Introduction NOx (nitrogen oxides) is one of the main pollutants in the atmosphere, which on atmospheric pollution caused by the main influence is NO and NO2. More than 95% of NOx is NO in atmosphere, NO2 accounts for the proportion to be very small. 90% of NOx in flue gas is NO (Chen et al., 2010). So, the removal of NO is the most important in the prevention and treatment of nitrogen oxides. Selective catalytic reduction method refers to the NH3 and other reducing agents restore the NOx to N2 selectively under the action of certain temperature and catalyst. At present, the most mature commercial catalyst in the SCR method of industrial application is to add a certain amount of MoO3 or WO3 (Jung and Grange, 2001) on the basis of the V2O5/TiO2, so as to carry out the modification of the catalyst. However, the temperature of catalyst activities between 350°C and 400°C Celsius, so that the SCR device must be placed before the air pre heater, which will cause the high sulfur and high sulfur dust in the flue gas have a huge impact on catalyst activity and catalyst life (Shen et al., 2006). However, with the successful industrialization of Calcium-BasedSemi-Dry Method of Sintering Flue Gas Desulphurization Technology, the flue gas outlet temperature of sintering flue gas is about 80~150°C. Therefore, it has become a hot spot and key point of the Study on denitrification of sintering flue gas to seek the catalyst of high efficiency at low temperature, especially in the temperature range of 80~150°C. In recent years, researchers at home and abroad have carried out a lot of research on the low temperature SCR catalyst carrier and catalyst active constituent. The catalyst with transition metal was found to have good catalytic performance in low temperature and the better one is Mn oxide (Park et al., 2001; Gong and Ralph, 2003; Imen et al., 2016; Pragya and Vasanthakumari, 2016). Studies showed that Ce can transfer electrons and ions in the catalytic reaction because of its oxygen storage, so that the active component of Ce-Mn which is obtained after doping as an auxiliary agent displayed out better catalytic activity (Gong and Ralph, 2003; Liu et al., 2006; Shen et al., 2010). Because the anatase TiO2 has a larger specific surface area and active site, which the stability of sulfate on the surface of is much lower than the other metal oxides. So TiO2 is difficult to happen sulfation reaction and its curing is reversible (Boningari and Panagiotis, 2011; Leonardo et al., 2014). Other studies have indicated that the vulcanization of TiO2 can enhance the catalytic activity, so it not only has a strong ability to anti sulfur poisoning, but also can play a protective role of the active component of the load DOI: 10.3303/CET1655002 Please cite this article as: Zhao R.Z., Liang R.R., Li S.Q., Song C.Y., 2016, Low-temperature catalytic reaction over manganese-cerium composite oxide supported on titania, Chemical Engineering Transactions, 55, 7-12 DOI:10.3303/CET1655002 7 (Saur et al., 1986). Therefore, many scholars use anatase TiO2 as a carrier to load other metal oxides which mixed Mn as catalysts for selective catalytic reduction at low temperature. In addition, MnOX-TiO2, CeO2- MnOX-TiO2 and V2O5-MnOX-TiO2 catalysts prepared by sol gel method were reported. The addition of Ce and V could inhibit the transformation of TiO2 from anatase to rutile. With the addition of the active component, the specific surface area of the catalyst and the pore volume will increase .Through the activity tests showed that the catalytic effect has been greatly improved (Wu et al., 2011). In this paper, the reaction temperature is set at 80~140°C according to the semi dry sintering flue gas desulfurization process exit temperature. TiO2 carrier was prepared by gel sol method, and the active component of Ce-Mn was prepared by impregnation method. Evaluation of the catalytic activity of NO by low temperature catalytic reduction of NH3, and research for the impact of the catalyst poisoning and activity about the high oxygen and high humidity condition of sintering flue gas. . 2. Experimental section 2.1 Catalyst Preparation Cerium (Ce (NO3)3·6H2O) and manganese acetate (4H2O·C4H6MnO4) were used as precursors in the preparation of active components. The mixing of the solution and the carrier was mixed, and the heating type magnetic mixer was used for stirring for one hour at the temperature of 60 degrees Celsius, so that the active component could be fully contacted with the carrier and the active component was adhered to the surface of the carrier. In the drying oven in 105°C dried in the muffle furnace roasting to 450°C holding 3 h to obtain the Ce-Mn/TiO2 supported catalyst: X%Ce(Y)-Mn/TiO2, Where X% was Ce-Mn/TiO2, Mn, Ce elements of the quality of the sum, said the size of the load Ce-Mn; Y was Ce/Mn molar ratio, which indicated the ratio of cerium and manganese in the catalyst. 2.2 Characterization of catalysts The micro morphology of the catalyst was characterized by the EVO ZEISS 18 scanning electron microscope, and the amplification factor of the scanning electron microscope was 5000 times. The Japanese sample the DMAX-RB kW rotating anode X-ray diffraction phase analysis. Using a copper target (wavelength 0.15406 nm), at 40 kV accelerating voltage, 150 Ma of current intensity, to 10 degrees per minute speed scanning, the scanning range is 2θ= 10 ~ 100º. The specific surface area and pore structure parameters of the catalyst were tested by static nitrogen physical adsorption method using SI QuadraSorb type specific surface and micro hole analyzer. 2.3 Catalyst activity test. The prepared catalyst was used as catalyst, and the particle size of 60~100 was selected as the catalyst for the experiment. 0.5 g samples were used to test the catalytic activity. Test device as shown in Figure 1, the quartz reaction tube diameter of 9 mm, was composed of a vertical pipe type heating furnace, the simulated flue gas composition 0.1%NO, 0.1%NH3, 10%O2, N2 balance, gas flow for 600 ml according to min -1, space velocity of 67000 H-1, reaction temperature was 80 ~ 140°C. 1-N2 Gas Cylinders; 2-O2 Gas Cylinders; 3-NO Gas Cylinders; 4-NH3 Gas Cylinders; 5-Pressure Relief Valve; 6-Flowmeter; 7, 8-Liquid Mixing Heating Device; 9-Preheating Box Type Resistance Furnace; 10- thermometer; 11- Quartz Tube Reactor. Figure 1: Schematic profile of SCR reaction experimental apparatus Determinated NO concentration in import and export using KM900 handheld flue gas analyzer in UK Kane company. Taking into account the adsorption of the catalyst itself on the gas, the initial experiment to the reactor through the NO, to be stable when the outlet concentration, and then through the NH3 to export NO concentration reached a stable after reading the data. Considering gas flow, oxygen and other nonadjustable parameters. When the influence of process parameters on the conversion of NO was studied, these 8 parameters were taken as fixed values, and the effect of the adjustable process parameters on the conversion of NO was studied. 3. Experimental results and discussion 3.1 Effects of different preparation conditions on the catalytic reduction reaction. 3.1.1 Effect of active component loading on catalytic reduction reaction. The experiment, to ensure that other conditions unchanged, selected 80°C, 100°C, 120°C, 140°C four flue gas temperatures, and NO conversion rate and the relationship between the catalyst load was shown in Fig.2. Figure 2: Effect of the catalyst loading on the NO conversion Table 1: The specific surface area and pore volume of the different loading catalysts Sample Surfacearea/(m2·g-1) Pore volume/(×10-2cm3·g-1) Average pore diameter /(nm) TiO2 49 8.17 6.1 5%Mn-Ce(0.2)/TiO2 51 10.25 5.7 15%Mn-Ce(0.2)/TiO2 48 12.96 4.0 20%Mn-Ce(0.2)/TiO2 36 5.85 6.5 25%Mn-Ce(0.2)/TiO2 35 5.74 6.5 The effect of different active component loading on the conversion of NO was demonstrates in Fig.2. The catalyst loading amount was 0, 5%, 10%, 15%, 20% and 25%, and the Ce/Mn molar ratio was 0.2. The specific surface area and total pore volume of the catalyst increases first and then decreases with the increase of catalyst loading, while the average pore size shows the opposite trend in Table 1. It can be seen from the figure that the TiO2 carrier has a certain catalytic performance, at 140°C to about 20%, the load Ce-Mn active component, and the reaction activity is greatly improved. With the increase of the reaction temperature, the catalyst activity of each load is improved, and the maximum amount is over 95%. But when the load capacity reaches 25%, the conversion rate of NO is significantly lower, and the activity is reduced to about 140 at 80%. Analysis shows that the active load increases the catalyst ratio surface area, and corresponding also increases the number of active sites for the surface of the carrier, but load increases to a certain extent, will cause the active sites overlap mutual shading, but the catalytic activity could not be further improve even compared to the previous decreased. This experiment results show that 15% Mn-Ce (0.2) /TiO2 catalyst has the best performance in the test temperature range. The conversion rate of NO is 97.8% at 140°C. So this experiment determines the load of X% is 15%. 3.1.2 Effect of Ce/Mn active components on catalytic reduction reaction. The relationship between the NO conversion rate and the Ce/Mn molar ratio in the catalyst is shown in Figure 3. This part of the experiment is to confirm the effect of the doping modification of Ce on the catalytic performance of the catalyst. Figure 3: Effect of Ce/Mn(molar ratio) in catalyst on the NO conversion 9 Fig. 3 shows the effect of different Ce/Mn molar ratio on the conversion of NO. Under the condition of operating conditions, when the amount of Ce doped in 0.2~1.0 (Ce/Mn molar ratio), all the catalysts in the reaction temperature range of low temperature catalytic reduction activity compared to the Mn/TiO2 catalyst has been greatly improved. Ce (0.8) -Mn/TiO2 catalyst at 80°C NO removal rate is close to 80%, and all of the Ce doped catalyst at 140°C, the catalytic activity was about 95%. The low temperature catalytic reduction activity of this series of catalysts modified by Ce was from low tohigh:Mn/TiO2