A commercial V2O5-WO3/TiO2 catalyst used at an NH3-SCR deNOx process in an oil-fired power plant: cause of an increase in deNOxing and NH3 oxidation performances at low temperatures

Abstract

The extent of both NO x removal and NH 3 oxidation in the selective reduction of NO x by NH 3 over a sample of a commercial V 2 O 5 -WO 3 /TiO 2 catalyst that had been used for 20,000 h at an NH 3 -SCR deNO x process in a domestic heavy oil-fired power plant has been determined using an on-line IR-based system coupled with a modified White cell and the catalyst has been characterized to ascertain the reason why it possessed visibly different behaviors in the deNO x reaction, compared to a fresh sample. The on-site-used catalyst gave not only much higher deNO x activity at all temperatures less than 400°C than that indicated for a fresh catalyst but also a greatly increased NH 3 oxidation reaction. SEM-EDX measurements with samples of the used and fresh catalysts represented the presence of a huge amount of sulfur in the former sample, very consistent with sulfur amounts determined by a C/S analyzer; however, this did not create the measured enhancement in the lowtemperature deNO x and NH 3 oxidation performances. ICP measurements indicated a significant increase, by 1% as a basis of V 2 O 5 , in an amount of vanadium species after the on-site use and such vanadium species came from heavy oils used to generate electricity at the power plant and were in the form of polycrystalline V 2 O 5 nanoparticles as acquired by XRD measurements. All these results propose that the increased V 2 O 5 content might be associated with the noticeable difference in SCR activity and NH 3 oxidation between both of the samples.

The Role of Fe2O3 Species in Depressing the Formation of N2O in the Selective Reduction of NO by NH3 over V2O5/TiO2-Based Catalysts

“…All the catalysts gave a predominant peak at 2θ = 25.31 • with much smaller diffractions at higher 2θ values, as displayed in Figure 1a-d, and all these peaks were the same as those existing in the pattern for anatase TiO 2 shown in Figure 1e. No diffraction due to the crystalline WO 3 was shown for all the samples, indicating that WO 3 existing in them is amorphous WO x species [27]. There was also no presence of crystalline V 2 O 5 phases, except for c-VWT, in which a weak reflection near 2θ = 21.64 • appeared when the diffraction was magnified, as indicated in Figure 1c, which is assigned to the crystallographic (101) plane of a polycrystalline α-V 2 O 5 (JCPDS card # 41-1426) by comparing it with the pure reference V 2 O 5 with an orthorhombic structure as provided in Figure 1f [27,28].…”

“…A continuous purge of this system was allowed by flowing a compressed air at a rate of 15 L/min that had passed through a train of large volume silica traps to remove H 2 O in the air. The NH 3 -SCR reaction with catalyst samples was conducted in a continuous flow type I-shaped 3/8 OD quartz reactor placed in a three-independent temperature adjustable electric furnace (Lindberg/Blue M Model HTF55347C, Thermo Electron Corp., Asheville, NC, USA) coupled with a Lindberg/Blue M Model CC584343PC PID controller [6,16,27,68]. All gas feed lines were maintained at a temperature near 180 • C to prevent the homogeneous reaction between NO and O 2 , and the condensation of H 2 O produced in the reaction.…”

Effect of Fe-zeolite on formation of N2O in selective reduction of NO by NH3 over V2O5–WO3/TiO2 catalyst

“…All samples prepared here are listed in Table 1. Performance in the NH 3 -SCR deNO x reaction and the resulting N 2 O concentrations were measured directly using a Thermo Electron Nicolet 7600 Fourier-transform [11,13]. The reduction of NO by NH 3 , the decomposition of N 2 O, and the reduction of N 2 O by NH 3 were conducted with the FeZ-promoted V 2 O 5 /TiO 2 -based SCR catalysts using a continuous-flow fixed-bed type I-shaped 3/8 00 OD quartz reactor combined with a Lindberg model HTF55347C split-hinge tube furnace.…”

“…The reduction of NO by NH 3 , the decomposition of N 2 O, and the reduction of N 2 O by NH 3 were conducted with the FeZ-promoted V 2 O 5 /TiO 2 -based SCR catalysts using a continuous-flow fixed-bed type I-shaped 3/8 00 OD quartz reactor combined with a Lindberg model HTF55347C split-hinge tube furnace. Details of this reaction system were provided in our earlier studies [11][12][13]. During the experiments, the temperatures of the catalyst bed in the reactor were controlled using a Lindberg model CC584343PC microprocessor-based proportional-integralderivative (PID) controller.…”

“…Recently, such NH 3 -SCR processes (including urea-SCR) have been considered as anthropogenic emitters of N 2 O, a greenhouse gas with global warming potential of 310 at the 100-year time horizon [3]. Concentrations of N 2 O emissions from SCR systems significantly depend on a variety of factors, including the SCR catalyst formulation and the process operating conditions, e.g., the kind of active constituents and their contents and crystallinity, the kind of promoters, the fraction of NO 2 in the feed gases, reaction temperature, reductant type, the presence of water vapor and its concentration, the oxygen concentration in the feed streams, the space velocity allowed at high temperatures [350°C, the thermal excursion at temperatures below 200°C, fuel types, metal impurities in flue gases, and on-site operation time [1,[4][5][6][7][8][9][10][11][12][13].…”