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Fig. 1. NO conversion versus temperature over: (a) WO3(9)/TiO3; (b) V205(0.78)/TiO2; (c) V205(1.4)/TiO2; (d) V205(0.78)-WO3(9)/TiO2; (e) V205(1.4)-WO3(9)/TiO>. Experimental conditions: catalyst weight, 160 mg (60-100 mesh); P=1 atm; flow rate=60 Ncc/min; feed: He+800 ppm NH3+800 ppm NO +1% O32. Reprinted with permission from [14].

Figure 1 NO conversion versus temperature over: (a) WO3(9)/TiO3; (b) V205(0.78)/TiO2; (c) V205(1.4)/TiO2; (d) V205(0.78)-WO3(9)/TiO2; (e) V205(1.4)-WO3(9)/TiO>. Experimental conditions: catalyst weight, 160 mg (60-100 mesh); P=1 atm; flow rate=60 Ncc/min; feed: He+800 ppm NH3+800 ppm NO +1% O32. Reprinted with permission from [14].

Related Figures (18)

Scheme 1. Proposed structures for monomeric vanadyl species [46-49] and polymeric metavanadate species [51] in their dehydrated forms on the surface of VO5-TiO> catalysts.
Scheme 1. Proposed structures for monomeric vanadyl species [46-49] and polymeric metavanadate species [51] in their dehydrated forms on the surface of VO5-TiO> catalysts.
Fig. 2. (A) Concentration profiles of NO, NH3, N2 and N2O over the V20s;-WO3-TiO; catalyst at a space velocity of 7.41 g! h—!. The inlet concentration of NO and NH; are 500 Vppm; balance He with 2% O>. (B) Concentration profiles of NO, NH3, Nz and NO over the Fe,03— SiO, catalyst at a space velocity of 1601 g~' h”!. The inlet concentration of NO and NH; are 500 Vppm; balance He with 2% O5. Reprinted with permission from [91]. tract the reactant NH; (the case of reactions (7) and
Fig. 2. (A) Concentration profiles of NO, NH3, N2 and N2O over the V20s;-WO3-TiO; catalyst at a space velocity of 7.41 g! h—!. The inlet concentration of NO and NH; are 500 Vppm; balance He with 2% O>. (B) Concentration profiles of NO, NH3, Nz and NO over the Fe,03— SiO, catalyst at a space velocity of 1601 g~' h”!. The inlet concentration of NO and NH; are 500 Vppm; balance He with 2% O5. Reprinted with permission from [91]. tract the reactant NH; (the case of reactions (7) and
Fig. 3. Comparison of the conversion of NO in copper samples (%%wt CuO) on various oxide supports. Reprinted with permission from [95]. Several kinetic studies, mostly obtained under “real’’ conditions, have been reported for the SCR reaction. These are based on both merely empirical expressions (e.g. power-law kinetics) and/or mechan- istic approaches (e.g. Langmuir—Hinshelwood or The same features have been reported on catalysts with different active cations [12] like, e.g. on Mn- based catalysts (MnO,—AlO3, MnO,-WO3-AlLO3 [26,96] and MnO,-TiO>, [79]), on a number of Cu- expressions (e.g. power-law kinetics) and/or mechan- Parallel behaviors, with a temperature range with maximum NO conversion upon SCR and the competi- tion of SCR and ammonia oxidation reactions, have been found on any vanadia-based catalyst, like for V,05-ZrO, catalysts [93]. However, very similar behavior has also been reported for catalysts with very different formulations. In Fig. 2, a comparison is shown between the behavior of a V30;-WO3-TiO, catalyst and a Fe.O3—SiO, catalyst [91]. Again, this behavior can be found for supported CuO-based catalysts [12,21,94,95], as shown in Fig. 3.
Fig. 3. Comparison of the conversion of NO in copper samples (%%wt CuO) on various oxide supports. Reprinted with permission from [95]. Several kinetic studies, mostly obtained under “real’’ conditions, have been reported for the SCR reaction. These are based on both merely empirical expressions (e.g. power-law kinetics) and/or mechan- istic approaches (e.g. Langmuir—Hinshelwood or The same features have been reported on catalysts with different active cations [12] like, e.g. on Mn- based catalysts (MnO,—AlO3, MnO,-WO3-AlLO3 [26,96] and MnO,-TiO>, [79]), on a number of Cu- expressions (e.g. power-law kinetics) and/or mechan- Parallel behaviors, with a temperature range with maximum NO conversion upon SCR and the competi- tion of SCR and ammonia oxidation reactions, have been found on any vanadia-based catalyst, like for V,05-ZrO, catalysts [93]. However, very similar behavior has also been reported for catalysts with very different formulations. In Fig. 2, a comparison is shown between the behavior of a V30;-WO3-TiO, catalyst and a Fe.O3—SiO, catalyst [91]. Again, this behavior can be found for supported CuO-based catalysts [12,21,94,95], as shown in Fig. 3.
Fig. 4. FT-IR spectra of the adsorbed species arising from adsorp- tion of ammonia over a V,0;-WO;/TiO2 sample (WO3=9% (w/w) and V,0; =1.47% (w/w)) and subsequent outgassing at RT (a), 400 K (b), 523 K (c), and 623 K (d). The spectra of the activated catalyst have been subtracted. Reprinted with permission from [133]. The thermal stability of NH3 adsorbed species has also been investigated by FTIR: it has been found that Lewis bonded molecular species are thermally more stable than ammonium ions (Fig. 4) [122]. It has also been reported that water competes with ammonia on
Fig. 4. FT-IR spectra of the adsorbed species arising from adsorp- tion of ammonia over a V,0;-WO;/TiO2 sample (WO3=9% (w/w) and V,0; =1.47% (w/w)) and subsequent outgassing at RT (a), 400 K (b), 523 K (c), and 623 K (d). The spectra of the activated catalyst have been subtracted. Reprinted with permission from [133]. The thermal stability of NH3 adsorbed species has also been investigated by FTIR: it has been found that Lewis bonded molecular species are thermally more stable than ammonium ions (Fig. 4) [122]. It has also been reported that water competes with ammonia on
Scheme 2. Schemes of the generation of the Brgénsted acid sites from surface vanadyl centers.
Scheme 2. Schemes of the generation of the Brgénsted acid sites from surface vanadyl centers.
Scheme 3. Proposed structures for ammonia adsorbed on V,0;—TiO3: (a) Lewis-bonded NH; at Ti sites; (b) H-bonded NH; on oxide sites; (c) Lewis-bonded NH3 at vanadyl sites; (d) ammonium ions bonded at V Br¢gnsted acid sites.
Scheme 3. Proposed structures for ammonia adsorbed on V,0;—TiO3: (a) Lewis-bonded NH; at Ti sites; (b) H-bonded NH; on oxide sites; (c) Lewis-bonded NH3 at vanadyl sites; (d) ammonium ions bonded at V Br¢gnsted acid sites.
Fig. 5. FT-IR spectra of the adsorbed species arising from NH; adsorption (20 torr) over CuO-TiO, at (a) r.t. and subsequent outgassing at (b) 373 K, (c) 423 K, (d) 523 K, and (e) 623 K. Reprinted with permission from [19]. G. Busca et al./Applied Catalysis B: Environmental 18 (1998) 1-36
Fig. 5. FT-IR spectra of the adsorbed species arising from NH; adsorption (20 torr) over CuO-TiO, at (a) r.t. and subsequent outgassing at (b) 373 K, (c) 423 K, (d) 523 K, and (e) 623 K. Reprinted with permission from [19]. G. Busca et al./Applied Catalysis B: Environmental 18 (1998) 1-36
Fig. 6. FT-IR spectra of the adsorbed species arising from the interaction of NO (10 torr) with adsorbed ammonia on a model V205;-WO3-— TiO, catalyst, at different temperatures: (a) 300 K; (b) 373 K; (c) 403 K; (d) 423 K; (e) 453 K; (f) 523 K.
Fig. 6. FT-IR spectra of the adsorbed species arising from the interaction of NO (10 torr) with adsorbed ammonia on a model V205;-WO3-— TiO, catalyst, at different temperatures: (a) 300 K; (b) 373 K; (c) 403 K; (d) 423 K; (e) 453 K; (f) 523 K.
Fig. 7. Results of transient response experiments performed at 493 K over a V20s;-WO;/TiO> sample (WO3=9% (w/w) and V205=1.47% (w/ w)). Section (A): outlet reactor concentration following a step addition of NO (700 ppm) in He+1% Op, (squares) and of NH; (700 ppm) in He+1% Op (triangles). The theoretical inlet step is also reported (dashed line). Section (B): outlet reactor concentrations following a step addition of NH3 (700 ppm) in He+NO (700 ppm)-+O, 1%. The N, and H,O concentrations have not been reported. Section (C): outlet reactor concentrations following a step addition of NO (700 ppm) in He+NHs3 (700 ppm)+O, 1%. The Nz and HO concentrations have not been reported.
Fig. 7. Results of transient response experiments performed at 493 K over a V20s;-WO;/TiO> sample (WO3=9% (w/w) and V205=1.47% (w/ w)). Section (A): outlet reactor concentration following a step addition of NO (700 ppm) in He+1% Op, (squares) and of NH; (700 ppm) in He+1% Op (triangles). The theoretical inlet step is also reported (dashed line). Section (B): outlet reactor concentrations following a step addition of NH3 (700 ppm) in He+NO (700 ppm)-+O, 1%. The N, and H,O concentrations have not been reported. Section (C): outlet reactor concentrations following a step addition of NO (700 ppm) in He+NHs3 (700 ppm)+O, 1%. The Nz and HO concentrations have not been reported.
Proposed reactant species, intermediates and active sites in different mechanisms and/or kinetic schemes for SCR on vanadia-based catalysts Table |
Proposed reactant species, intermediates and active sites in different mechanisms and/or kinetic schemes for SCR on vanadia-based catalysts Table |
Proposed reactant species, intermediates and active sites in different mechanisms and/or kinetic schemes for SCR on vanadia-based catalysts Table 2
Proposed reactant species, intermediates and active sites in different mechanisms and/or kinetic schemes for SCR on vanadia-based catalysts Table 2
Fig. 8. Mechanism of the NO—NH; reaction on vanadium oxide catalysts proposed by Inomata et al. [68] in the presence of oxygen. Reprinted with permission from [68](c).
Fig. 8. Mechanism of the NO—NH; reaction on vanadium oxide catalysts proposed by Inomata et al. [68] in the presence of oxygen. Reprinted with permission from [68](c).
Fig. 9. Mechanism of the NO-—NH; reaction on supported vanadium oxide catalysts proposed by Janssen et al. [71](b) in the presence of oxygen. Reprinted with permission from [71](b).
Fig. 9. Mechanism of the NO-—NH; reaction on supported vanadium oxide catalysts proposed by Janssen et al. [71](b) in the presence of oxygen. Reprinted with permission from [71](b).
Fig. 10. Mechanism of the NO—NH3 reaction on vanadium oxide catalysts proposed by Ozkan et al. [73](b) in the presence of oxygen.
Fig. 10. Mechanism of the NO—NH3 reaction on vanadium oxide catalysts proposed by Ozkan et al. [73](b) in the presence of oxygen.
Fig. 11. Mechanism of the NO-—NH; reaction on supported vanadium oxide catalysts proposed by Ramis et al. [123] in the presence of oxygen.
Fig. 11. Mechanism of the NO-—NH; reaction on supported vanadium oxide catalysts proposed by Ramis et al. [123] in the presence of oxygen.
Fig. 12. Scheme illustrating the catalytic cycle of the SCR reaction over vanadia/titania catalyst in the presence of oxygen proposed by Topsge et al. [173]. Reprinted with permission from [173](c).
Fig. 12. Scheme illustrating the catalytic cycle of the SCR reaction over vanadia/titania catalyst in the presence of oxygen proposed by Topsge et al. [173]. Reprinted with permission from [173](c).
Fig. 13. Scheme illustrating the catalytic cycle of the SCR reaction over Cu-ZSM5 catalyst in the presence of oxygen proposed by Komatsu et al. [29]. Reprinted with permission from [29].
Fig. 13. Scheme illustrating the catalytic cycle of the SCR reaction over Cu-ZSM5 catalyst in the presence of oxygen proposed by Komatsu et al. [29]. Reprinted with permission from [29].
Fig. 14. Scheme illustrating the mechanism of the NO—NHs3 reaction over Cu-based catalyst in the presence of oxygen proposed by Centi et : [21]. Reprinted with permission from [21]. where NH species are produced by NH; dissociation. This mechanism is, however, only tentative since it is
Fig. 14. Scheme illustrating the mechanism of the NO—NHs3 reaction over Cu-based catalyst in the presence of oxygen proposed by Centi et : [21]. Reprinted with permission from [21]. where NH species are produced by NH; dissociation. This mechanism is, however, only tentative since it is
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