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Ind. Eng. Chem. Res. 1996, 35, 2516-2521
An Experimental and Theoretical Investigation of the Behavior of a Monolithic Ti-V-W-Sepiolite Catalyst in the Reduction of NOx with NH3 Ana Bahamonde,† Alessandra Beretta,‡ Pedro Avila,† and Enrico Tronconi*,‡ Instituto de Cata´ lisis y Petroleoquı´mica, CSIC, Campus U. Auto´ noma, 28049 Madrid, Spain, and Dipartimento di Chimica Industriale e Ingegneria Chimica “Giulio Natta”, Politecnico di Milano, 20133 Milano, Italy
A novel Ti-V-W-sepiolite catalyst for the selective catalytic reduction (SCR) of NOx with NH3 was characterized by surface area and pore size distribution measurements, SEM, EDX, XRD, and FT-IR and FT-LR spectroscopy: the catalyst consists of TiO2 particles impregnated with vanadia and tungsta and dispersed among the sepiolite fibers. Intrinsic kinetics of NOx reduction were determined over the catalyst in powder form. The behavior of the catalyst in the shape of a honeycomb was investigated with respect to the influence of area velocity, reaction temperature, and NH3/NO feed ratio on the NO reduction efficiency. Based on the intrinsic kinetics and on the measured catalyst morphology, a previous mathematical model of SCR monolith reactors provided predictions of NO conversion closely in line with the data. The model was used also to investigate how the catalyst efficiency could be improved by changing its pore structure. Introduction The SCR (selective catalytic reduction) process is generally recognized as the most effective technology available for control of NOx emissions from thermal power plants and is being widely applied all over the world (Kuroda et al., 1989; Chichanowicz et al., 1988). In fact, the problem of NOx removal is becoming more and more acute because of stricter regulations: e.g., the limits on NOx emissions for furnaces operated on liquid and gaseous fuels have been reduced to 75 and 60 ppm, respectively, for 1994 in Germany (Cybulski and Moulijn, 1994). In the SCR system, the catalytic reactor is an assembly of catalyst baskets, each consisting of square elements made of homogeneous ceramic honeycombs (Cho, 1994). Many authors have studied the use of ceramic honeycombs for removal of nitrogen oxides (Williams et al., 1986). Also, several different methods for manufacturing monolithic catalysts have been reported (DeLuca and Campbell, 1977), extrusion being currently one of the most widely used techniques. In the manufacturing process, the composition of the ceramic paste (e. g., concentration of water, organic additives, binders, and pore-creating materials) strongly affects the physical properties of the extrudates like microstructure, morphology-porosity, and crushing strength, which must be carefully controlled in order to produce suitable honeycombs. The major components of commercial SCR monolithic catalysts are titanium dioxide (TiO2), tungsten trioxide (WO3), vanadium pentoxide (V2O5), and molybdenum trioxide (MoO3) (Bosch and Janssen, 1984; Blanco et al., 1996). Because of the abrasive action of the dust particles, which can be present in the effluent gases from coal-fired power plants, incorporated-type monoliths are used. Incorporation of the catalytic components into the monolith is performed by adding them to the ingredient mixture, from which the monolith is subsequently formed, dried, and calcined. † ‡
CSIC. Fax: +34-1-5854760. Politecnico di Milano. Fax: +39-2-70638173.
This paper presents the preparation and characterization of a low-dust SCR monolithic Ti-V-W-sepiolite catalyst, as well as a systematic study of the effects of the operating conditions (NH3/NO feed ratio, area velocity, and reaction temperature) on NO reduction with ammonia in the presence of excess oxygen. For the same reaction, intrinsic kinetics are also derived over the catalytic system in powder form and included in an existing mathematical model of the monolith SCR reactor (Tronconi and Forzatti, 1992; Tronconi et al., 1992), which fully accounts for both external and intraporous transport phenomena. The model is shown to predict successfully the experimental effects of the operating variables under representative SCR conditions over the Ti-V-W-sepiolite monolithic catalyst. The mathematical treatment is also applied to analyze the influence of the catalyst pore structure, an aspect which is relevant to the rational design of SCR catalysts. Experimental Part Catalyst Preparation and Characterization. A monolithic catalyst made of titania-vanadia-tungsta and Sepiolite was manufactured by extrusion of a paste with atomic composition Ti-V-W ) 92-7.8-0.2% w/w (Blanco et al., 1988) homogeneously mixed with 50% w/w of R-sepiolite (essentially a Mg silicate). The resulting chemical composition as determined by XRF was: 43.2% w/w TiO2, 4.2% V2O5, and 0.2% WO3 + sepiolite. Square-cell honeycombs were prepared with a pitch of 3.54 mm, 0.89 mm wall thickness, and lengths ranging from 6 to 24 cm. Other characteristics are given in Table 1. BET surface areas were measured by nitrogen adsorption-desorption in a Micromeritics 2100 D instrument; the pore-size distribution was determined by mercury intrusion in a Micromeritics 9300 porosimeter. The overall appearance of the surface, as well as the average size of the particles, was determined in a scanning electronic microscope (SEM) JEOL JSM 6400. The composition of the catalyst surface, both at the bulk (I) and external surface (E) of the monolith, was
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Ind. Eng. Chem. Res., Vol. 35, No. 8, 1996 2517 Table 2. Morphological Characteristics of the Honeycomb Catalyst bulk density surface area (BET) total pore volume (MIP) pore-size distribution micropores mesopores
Figure 1. Schematic diagram of the experimental system for activity runs of monolithic SCR catalysts. Table 1. Geometrical Characteristics of the Honeycomb Catalyst cell shape cell density open section
square 8 cells/cm2 0.070 cm2
open frontal area geometric surface area
0.56 846 m2/m3
determined by EDX using a LINK EXL detector for energy-dispersive X-ray analysis (EDX). The nature of phases of the catalysts was determined by means of a FT-Raman spectrometer Brucker Model RFS 100, with an excitation Laser NdYAG. Kinetic Study. For the purposes of the present work, part of the kinetic data already reported by Odenbrand et al. (1994) were used. The data were collected by performing DeNOx reaction runs in a steady-state flow microreactor operating in a differential regime. The absence of internal diffusional resistances was secured by using the catalyst in the form of fine particles (0.1-0.2 mm), which were obtained by crushing the extruded honeycomb matrix. The influence of temperature and of the concentration of reactants (NO, NH3, O2) was examined. The effect of NO2 was not considered due to its very limited content in flue gases from thermal power plants, where typical NO/NO2 molar ratios are in excess of 10/1 (Yaverbaum, 1979). On the other hand, the effect of water vapor was not addressed in this work since it has been reported by several authors that the rate of NO reduction over V/Ti/ O-based catalysts is only weakly influenced by the addition of water (e.g., Lintz and Turek, 1992; Svachula et al., 1993). Additional details on experimental setup and procedures are given by Odenbrand et al. (1994). Activity Tests over the Monolithic Catalyst. SCR activity tests over the catalyst in the shape of monolith were carried out in an integral reactor. A schematic of the experimental apparatus is shown in Figure 1. The reactor consisted of a crystal Pyrex tube electrically heated with three thermoresistances to grant isothermal conditions. Three 0.5 mm thermocoax 9676 (Philips) thermocouples type K, inserted at different locations along the catalytic reactor, allowed the control of the axial temperature profile. Free space between the honeycomb catalyst and the reactor wall was filled with inert material to prevent bypass. Reactant gases were supplied from cylinders (NO/N2 ) 10/90 v/v, NH3/N2 ) 5/95 v/v, O2, N2), via highprecision pressure regulators and mass-flow controllers. Ammonia was injected directly at the top of the reactor. The other reactant gases were premixed and preheated before being admitted into the reactor.
0.64 cm3/g 93 m2/g 0.56 cm3/g bimodal rm ) 125 Å, m ) 0.285 cm3/cm3 rM ) 260 Å, M ) 0.275 cm3/cm3
The analysis of the outlet stream was carried out using two distinct sampling lines. A heated Teflon line equipped with filters, flow regulators, and micrometer valves carried the gas stream to a Luminox (BOC) chemiluminescence NOx analyzer for determination of both NO and total NOx concentrations. NO2 concentration was calculated by difference and was found lower than 15 ppm in all the experiments. The same line was used to measure NOx concentrations in the feed stream. A NH3 scrubber was inserted at the inlet to the NOxmeter in order to avoid erroneous measurements due to the presence of ammonia in the gas mixture. The other sampling line, equipped with a particulate filter, was connected to an IR spectrophotometer ADC 13609, Model 8V/35, for analysis of NH3 and N2O. Negligible formation of N2O was always detected in the experiments herein presented. The influence of the following operating conditions was studied: area velocity (AV ) volumetric flow rate/ geometric area of monolith catalyst), R ()inlet NH3/NO molar ratio), and reaction temperature. Consistent with the kinetic study over the powder catalyst, the feed composition was selected as follows: [NO] ) 1000 ppm, [NH3] ) 500-1100 ppm, [O2] ) 3% v/v, [N2] as balance. Mathematical Model of the SCR Monolith Reactor. A previous mathematical description of the honeycomb SCR reactor (Tronconi et al., 1992; Tronconi et al., 1994) has been herein applied. It is based on the following simplifying assumptions: (i) identical conditions within the monolith channels; (ii) isothermal conditions; (iii) negligible axial mass diffusion as compared to convective contributions; (iv) developing laminar flow in the monolith channels; (v) negligible kinetic dependence on O2 and H2O. The gas-solid transport of NO and NH3 is evaluated according to the analogy with the thermal Graetz-Nusselt problem with constant wall temperature (Tronconi and Forzatti, 1992), and intraporous diffusion of the reactants is described according to the Wakao-Smith random pore model (Wakao and Smith, 1962), which is suitable for bimodal pore size distributions (Beekman and Hegedus, 1991). Thus, the resulting one-dimensional single-channel mathematical model of the monolith reactor is based on (i) the differential gas-phase mass balances of NO and NH3, combining axial convective and transverse diffusional fluxes and (ii) the algebraic continuity equations for NO and NH3 across the gas-solid interface. The model was successfully validated on a predictive basis by comparing calculated values of NO conversion with experimental data of test runs over a commercial SCR honeycomb catalyst covering the effects of R, reaction temperature, feed flow rate, and monolith length (Tronconi et al., 1992). Results and Discussion Characterization of the Monolithic Catalyst. Morphological Study. The results of BET and of mercury intrusion measurements on the present monolithic catalyst are summarized in Table 2. It is noted that the catalyst exhibits a bimodal pore-size distribu-
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Figure 2. Scanning electron micrograph of the V-W-Tisepiolite monolithic catalyst.
Figure 4. EDX spectra of the monolithic catalyst: Ext ) external part of the monolithic wall; Int ) internal part.
Figure 3. Ti-V-Si line profiles inside the wall of the catalyst.
tion in the range of micro- and mesopores. A detailed study of the morphological properties of titania-vanadia-tungsta-sepiolite catalysts in pellet form is given elsewhere (Avila et al., 1993). SEM Study. A micrograph of the catalyst surface is shown in Figure 2. The right half of this picture, corresponding to the small rectangle in the left half, is magnified by a factor of 5. The microscopy results showed that this catalyst consists of two types of particles. The first ones have sizes ranging from 100 to 250 µm; they are composed of bundles of fibers ranging from 0.2 to 1 µm in length and 100-1000 Å in width. These observations are in agreement with the fibrous structure of sepiolite described by Alvarez (1984). The second type of particles are pseudospherical, with sizes ranging from 0.05 to 0.1 µm; they are grouped together to form units of varying sizes (0.3 to 1 µm), in which the original particles maintain their identity. These results can be interpreted by assuming that the TiO2 particles, impregnated with the vanadium and wolframiun salts, are dispersed among the sepiolite fibers. EDX Study. The association of vanadia with titania has been investigated by EDX. In Figure 3 the line profiles of Ti, V, and Si are shown. It appears that Ti and V concentrations are parallel; on the other hand, Si is abundant where Ti and V are lacking. These features imply that the vanadium salt has been impregnated on the TiO2 particles but not on the sepiolite fibers. The EDX spectra of the catalyst surface were obtained both at the bulk (Int) and at the external surface (Ext) of the monolith wall. The results are shown in Figure
4. The spectra were similar in both parts, indicating that the catalyst composition is uniform along the wall thickness. The main components of the catalyst were Ti, V, Si, and Mg; traces of Ca, Fe, and K were also detected. These elements form part of the natural silicate introduced in the preparation of the catalyst, which is essentially a magnesium silicate. Tungsten was not detected because it is below the detection limit. An important content of sulfur was measuredsprobably as sulphateswhich proceeds from the original titania paste. FT-LR Study. Figure 5 shows the laser-Raman spectra of the studied catalyst and of anatase titania as a reference. It is known from the literature that V2O5 species are characterized by three signals at 288, 701, and 994 cm-1 (Cai and Ozkan, 1991). In the present catalytic system, such signals were not detected, while only the typical peaks belonging to the anatase phase (Deo et al., 1991) were apparent. These results seem to suggest that vanadium remains dispersed on the surface of titania. XRD and FT-IR spectroscopy results (Bahamonde, 1992) also support that this catalyst can be considered as a mixture of the natural silicate essentially as magnesium silicate, and titania; in fact, no additional phase was detected. Thus, according to the bulk of the characterization results, the present monolithic catalyst could be envisioned as consisting of titanium dioxide particles (where the vanadium and wolframium are dispersed) homogeneously allocated among the fibers of a siliceous material which provides the basis of the monolithic structure (Avila et al., 1993). Kinetic Study over Powdered Catalytic Material. In Figures 6and 7 the measured rates of nitric oxide reduction over the V-W-Ti-sepiolite catalyst in powder form have been plotted as a function of nitric oxide and ammonia concentrations, respectively, at different operating temperatures. A linear dependence on the nitric oxide concentration was observed. On the contrary, a strong influence of saturation phenomena for the ammonia reactant was evident; the region corresponding to a kinetic dependence on ammonia was limited to very low concentrations at low reaction
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Figure 5. FT-LR spectra of the monolithic catalyst and of TiO2 anatase. Table 3. Optimal Parameter Estimates for the DeNOx Rate Expression (Equation 1), with 95% Confidence Limits ln k° ) 13.90 ( 9.47 Ea/R ) 8660 ( 5150 K
ln K°NH3 ) 2.260 ( 1.49 ∆H°NH3/R ) -6105 ( 3552 K
All of these observations are apparently in agreement with the rate expression for the DeNOx reaction already used by several authors, including Beekman and Hegedus (1991), Lefers et al. (1991), and Tronconi and Forzatti (1992):
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Figure 6. Kinetic runs over the catalyst in powder form: influence of the NO concentration on the NO reduction rate at different temperatures.
Figure 7. Kinetic runs over the catalyst in powder form: influence of the NH3 concentration on the NO reduction rate at different temperatures.
temperatures, but it expanded significantly with increasing T. Oxygen (3% v/v) was in large excess in all runs; as reported by Odenbrand et al. (1994), at such concentration levels the influence of O2 on the reaction kinetics over the present catalysts is negligible.
kcCNOKNH3CNH3 dCNO ) kcCNOθNH3 ) dt 1 + KNH3CNH3
(1)
Equation 1 is consistent with a Rideal mechanism where NO in the gas phase reacts with NH3 strongly adsorbed on the catalyst active sites (Ramis et al., 1990). A nonlinear multiple regression code based on Marquardt’s minimization procedure (Marquardt, 1963) was used to fit the proposed kinetic model (eq 1) to the experimental data. Model calculations are also displayed as solid lines in Figures 6 and 7, corresponding to the optimal parameter estimates given in Table 3. The match appears satisfactory as the model deviations from the data are fully comparable with the experimental uncertainty. Also, all of the parameter estimates are statistically significant and are associated with narrow confidence limits (also reported in Table 3). Finally, it is worth noting that the estimated temperature dependences of the kinetic parameters are physically consistent (Ea ) 72.0 kJ mol-1, ∆HNH3 ) -50.8 kJ mol-1) and in agreement with the values reported by Inomata et al. (1980) and by Odenbrand et al. (1994) for similar V-TiO2-based catalytic systems. SCR Runs over the Monolithic Catalyst: Influence of the Operating Variables and Comparison with Model Predictions. The experimental effect of the feed ratio R for a constant nitric oxide concentration at 300 and 350 °C is shown at different area velocities in Figures 8 and 9, respectively. It can be observed that the reduction of NO was limited by the ammonia concentration for substoichiometric feed ratios (R < 1). In correspondence with excess of ammonia, on the contrary, the NO conversion
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Figure 8. Activity tests over the monolithic catalyst: influence of the NH3/NO feed ratio on NO conversion at 300 °C at different area velocities.
Figure 9. Activity tests over the monolithic catalyst: influence of the NH3/NO feed ratio on NO conversion at 350 °C at different area velocities.
was controlled by space velocity and by the reaction temperature, while it tended to become independent of the feed ratio R. Such a behavior is well-known in SCR operations; it is also in line with the proposed rate expression (eq 1), which explains the data in Figures 8 and 9 by a continuous change from first-order kinetics in ammonia at low NH3 concentrations to zero-order kinetics at high NH3 concentrations. As expected, the measured NO conversion increased with decreasing area velocity and with increasing reaction temperature. However, the comparison of the data in Figures 8 and 9 corresponding to AV ) 6.75 N m/h indicates that the observed temperature dependence was minor in the range of conditions investigated. This points out that mass-transfer limitations definitely play a controlling role on the overall DeNOx process over the catalyst in the shape of monolith. Indeed, evidence of the high catalyst activity is provided by the limiting NO conversion (80%) attained already at 300 °C under conditions representative of industrial SCR operation (R ) 0.8, AV ) 6.75 N m/h). The solid lines in Figures 8 and 9 interpolate values of NO conversion calculated by the mathematical model of the SCR reactor described above. It is to be emphasized that the model was applied in a purely predictive mode, after inclusion of both the morphological data and the reaction kinetics which were determined independently. Thus, intraporous diffusivities of NO and NH3 were evaluated using the Wakao-Smith model from the catalyst pore-size distribution given in Table 2; the rate constants were estimated according to the Arrhenius
Figure 10. Calculated influence of the area velocity and the reaction temperature on NO conversion at R ) 0.8 for the experimental and an improved catalyst morphology.
parameters given in Table 3. Under this respect, the match between calculations and experiments shown in the figures is remarkably good. In particular, the following remarks apply. (a) The dedicated study of the kinetic dependence on ammonia concentration (Figure 7) allowed a correct prediction of the monolith performances when affected by the feed ratio R; this is particularly evident at high temperatures and AV values (Figure 9), where both the adsorption and the conversion of ammonia are limited. (b) The match between data and model predictions supports the absence of dependences on H2O and NO2 in the rate expression: indeed, only traces of NO2 were formed in our runs, whereas it is known that no significant kinetic influence is associated with water at the concentration levels which correspond to its formation as a reaction product (Lintz and Turek, 1992); at the greater H2O contents prevailing in SCR applications to actual flue gases, eq 1 can still be satisfactory once the water effect is incorporated in the estimates of the kinetic constants kc and KNH3 (Lefers et al., 1991; Tronconi and Forzatti, 1992). (c) The model is able to reproduce the very small apparent activation energy of the process by properly combining the intrinsic reaction kinetics with the external and internal diffusional resistances which prevail in the operation of the monolithic catalyst. (d) Based on the adequate description of the kinetics and of the mass-transfer phenomena, the PFR model simulates successfully the influence of residence time on NO reduction. Once assessed its adequacy, the model can be applied as a diagnostic tool to evaluate the relative significance of the factors involved in the overall catalyst performances. It has been estimated that, in the range of operating conditions herein explored, the utilization of the catalyst was severely limited by strong intraporous resistances. In fact, effectiveness factors as low as 0.08-0.03 were calculated in correspondence to R ) 0.8, AV ) 6-10 N m/h, and temperatures between 300 and 400 °C. Space to improvements of the DeNOx-ing activity of the present catalyst seems, consequently, offered by a proper modification of the catalyst morphology. For instance, the model calculates that a hypothetical pore size distribution corresponding to a small micropore radius (40 Å) and to a large macropore radius (2000 Å) (being the volume fraction of micropores m ) 0.21 and the volume fraction of macropores M ) 0.35) would result in a nearly 3-fold increase of the monolith
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effectiveness factor, due to enhancements of both the catalyst specific surface area and the intraporous diffusivities of the reactants. As an example, by comparing calculated NO removal efficiencies for the experimental and the improved catalyst morphologies, Figure 10 shows that substantial savings of catalyst could be attained, in principle, for a set NO conversion. Literature Cited Alvarez, A. Sepiolite. Properties and uses. Developments in Sedimentology; Elsevier: Admsterdam, The Netherlands, 1984; Vol. 37, pp 253-287. Avila, P.; Blanco, J.; Bahamonde, A.; Palacios, J. M. Influence of the binder on the properties of catalysts based on titaniumvanadium oxides. J. Mater. Sci. 1993, 28, 4113-4118. Bahamonde, A. Development of monolithic catalysts for NOx. Ph.D. Thesis, Complutense University, Madrid, Spain, 1992. Beekman, J. W.; Hegedus, L. L. Design of Monolith Catalysts for Power Plant NOx Emission Control. Ind. Eng. Chem. Res. 1991, 30, 969. Binder-Begsteiger, I.; Herzog, G. W.; Megla, E.; Tomann-Rosos, M. Kinetics of the DeNOx reaction over TiO2-WO3 honeycomb catalyst. Chem. Ing. Tech. 1990, 62, 60. Blanco, J.; Avila, P.; Bahamonde, A.; Barthelemy, C.; Chaco´n, C.; Ramos, J. M. Spanish Patent No. 8803453, 1988. Blanco, J.; Avila, P.; Bahamonde, A.; Yates, M. Application of Catalysts in the control of Nitrogen Oxides emissions from stationary sources. Lat. Am. Res. 1996, in press. Bosch, H.; Janssen, F. Catalytic Reduction of Nitrogen Oxides. A Review on the Fundamentals and Technology. Catal. Today 1988, 2, 1-531. Buzanowski, M. A.; Yang, R. T. Simple design of monolith reactor for Selective Catalytic Reduction of NO for Power Plant Emission Control. Ind. Eng. Chem. Res. 1990, 29, 2074-2078. Cai, Y.; Ozkam, U. S. Vanadia/Titania catalysts in Selective Catalytic Reduction of nitric oxide with ammonia. Appl. Catal. 1991, 78, 241-255. Chichanowicz, J. E. Selective Catalytic Reduction controls NOX in Europe. Power Eng. 1988, 8, 36-38. Cho, S. M. Properly Apply Selective Catalytic Reduction for NOx removal. Air Pollut. Control, Chem. Eng. Prog. 1994, 90, 3945. Cybulski, A.; Moulijn, J. A. Monoliths in heterogeneous catalysis. Catal. Rev.-Sci. Eng. 1994, 36, 179-270. DeLuca, J. P.; Campbell, L. E. Monolithic Catalyst Supports. Adv. Mater. Catal. 1977, 293-324. Deo, G.; Turek, A. M.; Wachs, I. E.; Machej, T.; Haber, J.; Das, N.; Eckert, H.; Hirt, A. M. Physical and chemical characterization of surface vanadium oxide supported on titania: influence
of the titania phase (anatase, rutile, broolite and B). Appl. Catal. A 1992, 91, 37-42. Inomata, M.; Miyamoto, Y.; Murakami, Y. Mechanism of the reaction of NO and NH3 on Vanadium Oxide catalyst in the presence of oxygen under the dilute gas condition. J. Catal. 1980, 62, 140-148. Kuroda, H.; Morita, Y.; Murataka, T. Recent developments in the SCR systems and its operational experiences. Proceedings of the Joint Symposium on Stationary Combustion NOx Control, 1989, EPA-600/9-89-062b. Lefers, J. B; Lodder, P.; Enoch, G. D. Modelling of Selective Catalytic DeNOx ReactorssStrategy for Replacing Deactivated Catalysts Elements. Chem. Eng. Technol. 1991, 15, 192-200. Lintz, H.-G.; Turek, T. Intrinsic kinetics of nitric oxide reduction by ammonia on a vanadia-titania catalyst. Appl. Catal. A 1992, 85, 13-25. Marquardt, F. W. An algorithm for least-square estimation of nonlinear parameters, J. Soc. Ind. Appl. Math. 1963, 11, 431441. Odenbrand, C. U. I.; Bahamonde, A.; Avila, P.; Blanco, J. Kinetic Study of the Selective Reduction of Nitric Oxide over VanadiaTungsta-Titania/Sepiolite catalyst. Appl. Catal. B 1994, 5, 117-131. Ramis, G.; Busca, G.; Bregani, F.; Forzatti, P. Fourier TransformInfrared study of adsorption and coadsorption of nitric oxide, nitrogen dioxide and ammonia on vanadia-titania and mechanism of Selective Catalytic Reduction. Appl. Catal. 1990, 64, 259-278. Svachula, J.; Ferlazzo, N.; Forzatti, P.; Tronconi, E. Selective Reduction of NOx by NH3 over Honeycomb DeNOxing Catalysts. Ind. Eng. Chem. Res. 1993, 32, 1053-1060. Tronconi, E.; Forzatti, P. Adequacy of Lumped Parameter Models for SCR Reactors with Monolith Structure. AIChE J. 1992, 38, 201-210. Tronconi, E., Forzatti, P., Gomez Martin, J. P., Malloggi, S. Selective Catalytic Removal of NOx: a Mathematical Model for Design of Catalyst and Reactor. Chem. Eng. Sci. 1992, 47, 2401. Wakao, N.; Smith, J. M. Diffusion in Catalyst Pellets. Chem. Eng. Sci. 1962, 17, 825-836. Williams, J.; Lachman, Y.; Rosenbusch, T. Extruded honeycombs as catalystic substrates for stationary emissions control of NOx. Proceedings of 80th Annual Meeting of APCA, New York, 1987, 87-52.1-10. Yaverbaum, L. H. Nitrogen Oxides Control and Removal; Noyes Data Corp.: New Jersey, 1979.
Received for review December 1, 1995 Accepted April 23, 1996X IE9507179 X Abstract published in Advance ACS Abstracts, June 1, 1996.
