A Study of the Increase in Selective Catalytic Reduction (SCR) Activity Of

Korean J. Chem. Eng., 27(4), 1220-1225 (2010) DOI: 10.1007/s11814-010-0215-6 RAPID COMMUNICATION A study of the increase in selective catalytic reduction (SCR) activity of the V/TiO2 catalyst due to the addition of monoethanolamine (MEA) Phil Won Seo*, Sung Su Kim**, and Sung Chang Hong***,† *Department of Chemical and Biological Engineering, Korea University, 1, 5-Ga, Anam-dong, Sungbuk-gu, Seoul 136-701, Korea **Department of Environmental Engineering, Graduate School of Kyonggi University, ***Department of Environmental Energy Systems Engineering, Kyonggi University, 94 San, Iui-dong, Youngtong-gu, Suwon-si, Gyeonggi-do 442-760, Korea (Received 11 November 2009 • accepted 16 February 2010) Abstract−Experiments were conducted to evaluate the effect of adding ethanol amine during the preparation of a V/TiO2 catalyst to remove nitrogen oxide (NOx) by selective catalytic reduction (SCR). The catalyst added monoethanolamine (MEA) had the highest NOx conversion among all the neutralization reagents tested, and the optimum MEA concentration was determined to be 10%. The catalyst-added MEA had a large amount of lattice oxygen, which was determined in the O2 on/off experiment. In addition, it also displayed a high reoxidation rate in the O2 reoxidation experiment. In the XPS analysis, the superior redox properties of the catalyst-added MEA were shown to be caused by the presence of Ti+3, a non-stoichiometric species. Key words: SCR, Monoethanolamine, Non-stoichiometric, V/TiO2, Redox INTRODUCTION the NH3-SCR through the impregnation method, outstanding response activation was obtained with complete dissolution of NH4VO3 and 5+ 4+ NOx, along with sulfur oxides, is the cause of acid rain, which reduction of V to the V state under acidic conditions where the leads to corrosion processes and the pollution of soil and water. More- pH was approximately 2.5. Lee [9] reported that in catalysts impreg- over, it reacts with moisture and hydrocarbons in the atmosphere to nated with vanadium, a higher level of activation was observed in create a photochemical smog and depletes the ozone layer, ultimately catalyst that did not contain OA relative to catalysts containing OA, having a great damaging effect on the human body [1]. Among the and that the response activation differed in accordance with the pH methods developed for removing NOx emitted from such stationary established at the time the catalyst was prepared. Also, Roozeboom sources of pollution, SCR using NH is the most promising. The major et al. [10] prepared V2O5 based catalysts by ion exchange, passing a SCR reactions are as follows. NH4VO3 solution at pH 4 through a bed of support material. Ciam- belli et al. [11] examined methods of removing NOx from V2O5/TiO2 4NO+4NH3+O2→4N2+6H2O(1) catalysts by varying the pH in the range of 2.86-10 using HNO3 2NO2+4NH3+O2→3N2+6H2O(2)and NH4OH. According to the results of this study, the rate of NOx conversion improved markedly with an increase in pH. Therefore, The SCR reaction is a process that removes NO through the chem- x it can be concluded that pH influences the activation of the cata- ical reactions (1)-(2), whereby the catalyst is installed within the lysts at the time the catalyst is prepared. passageway through which the emitted gases pass through, and NH 3 Therefore, in this study, we investigated the impact that acidic is sprayed in front of the catalyst [2]. and alkaline conditions have on SCR activity during the production The core technology involved in the SCR process using NH is 3 of the V/TiO catalyst for SCR by preparing catalysts in which OA based on catalyst technology. In preparation of the V/TiO catalyst, 2 2 and other neutralization reagents such as NH OH, MEA, diethano- ammonium metavanadate (AMV, NH VO ), is commonly used as 4 4 3 lamine (DEA) and triethanolamine (TEA) have been added. We vanadium source, and oxalic acid (OA, (COOH) ) is added to increase 2 determined the optimum quantity of the neutralization reagents that the solubility of AMV [3-5]. Solutions of AMV with OA become resulted in catalysts with superior activity. In addition, through O acidic in the atmosphere, and its pH is around 2.1-2.5. Among the 2 on/off experiments, reoxidation experiments and XPS analysis, we other additives included during the production of the catalyst, etha- also examined the causes for the activation of the prepared catalyst. nol amine functions to elevate the pH, thereby limiting corrosion of the equipment by OA and changes in the surface properties of EXPERIMENTAL the catalyst [6,7]. Economidis et al. [8] reported that, when producing catalysts for 1. Catalyst Preparation The TiO2 used in this study was a commercial TiO2 precursor † o To whom correspondence should be addressed. that was calcined at 500 C. The TiO2 precursor phase was amor- E-mail: [email protected] phous, which was calcined to the crystalline phase. Precursor TiO2 1220 A study of the increase in SCR activity of the V/TiO2 catalyst due to the addition of MEA 1221 Table 1. Experimental condition in a fixed bed reactor Particle size (µm) 297-400 Temperature (oC) 150-400 NOx (ppm) 800 Inlet gas conc. NH3 (ppm) 860 (NH3/NOx=1) (N2 balance) O2 (%)3 H2O (%)6 Space velocity (hr−1) 60,000 Total flow (mL/min) 500 a water bubbler that was maintained at constant temperature. The gas pipe was made of a stainless steel tube. To prevent the forma- tion of salts such as NH4NO3, NH4NO2, which are formed through the reaction between NO and NH3, and also to prevent the conden- sation of moisture in the stainless steel tube, a heating band was wrapped around the tube to maintain a constant temperature of 180 oC. The reactor was a continuous-flow type fixed bed reacting device made with a quartz tube that had an interior diameter of 8 mm and a height of 60 cm. Quartz wool was used to fix the catalyst powder. For measuring the concentration of the reactant and the product, a non-dispersive infra red gas analyzer (Uras10E, Hartman & Braun Co.) was used for NO while NO2 was analyzed using the detector tube (9L, Gas Tec. Co.) located in the exit area of the main reactor. 3. Experimental Procedure and Characterization To maintain the consistency of the filling catalyst, the prepared powder catalyst was made into pallets using 5,000 pounds of powder in a hydraulic press, and then catalyst powder that had a size of Fig. 1. Flow diagram of the procedures use to fabricate the V/TiO2 297-400 µm was selected. catalysts. The experimental conditions are shown in Table 1. The methods used in these experiments were as follows. First, a certain quantity consisted of a pure anatase structure with a specific surface area of of the catalyst was placed in the reactor, and 3% O2/N2 gas was in- 95 m2/g. Vanadium was the active material used, and for all cata- jected into the reactor and maintained at 120 oC for 30 minutes so lysts, an equal quantity of 2% was added. as to remove moisture and impurities from the catalyst surface. When The catalyst used in the present study was prepared by the wet the temperature reached a steady state, other gases were injected impregnation method, and this process is illustrated in Fig. 1. First, into the reactor. The reaction was continued until the concentration the vanadium content in relation to TiO2 was calculated according of the product became consistent, at which time the concentration to the desired composition ratio, and the calculated quantity of AMV was recorded. (Aldrich Chemical Co.) was dissolved in distilled water that was To examine the reoxidation of the catalyst, the catalyst was filled in o o heated to 60 C. At this time, OA (Aldrich Chemical Co.) and neu- the reactor and reduced at 400 C with 0.5% NH3/N2 for 30 minutes. tralization reagents such as MEA, DEA, TEA were added according The SCR reaction was then conducted at the respective temperature to the ratio of weight. The calculated amount of TiO2 was gradually under conditions without oxygen and with NO+NH3 in order to added to the solution while stirring and sufficiently mixing. The reach stabilization. When the reaction was stabilized, 200 ppm O2/ mixed slurry was agitated for 1 hour or more and then the moisture N2 was continuously supplied, while the concentration of NO was was evaporated using a rotary vacuum evaporator at 70 oC. The cata- monitored. o lyst was then further dried in dry oven at 110 C for 24 hours. The The O2 on/off experiment was conducted by supplying NO+NH3+ o dried catalyst was calcined in a tubular furnace at 400 C for 4 hours O2 at a fixed temperature and stably executing the SCR reaction. under air conditions. During the middle of the reaction the O2 supply was momentarily 2. Catalytic Activity Measurement cut off. One hour after the cut-off, O2 was again supplied while the The fixed bed reactor used for the SCR reaction experiment was concentration of the NO was monitored. composed of the gas injection section, the reactor section, and the XPS analysis was conducted with an ESCALAB 210 from VG section that analyzed the reacted gas. The gases supplied into the Scientific, and Al Kα monochromate (1,486.6 eV) was used as an reactor were injected using an MFC (mass flow controller, MKS excitation source. After moisture contained in the catalysts was com- Co.) from each of the cylinders for NO, N2, O2, NH3.

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