Substitution of WO₃in V₂O₅/WO₃–TiO₂by Fe₂O₃for selective catalytic reduction of NO with NH3

Abstract

To improve N 2 selectivity and lower the cost, WO 3 in V 2 O 5 /WO 3 -TiO 2 was substituted by a low cost composition Fe 2 O 3 for selective catalytic reduction (SCR) of NO with NH 3 . The SCR reaction over V 2 O 5 /Fe 2 O 3 -TiO 2 mainly followed the Eley-Rideal mechanism (i.e. the reaction between activated ammonia species and gaseous NO). There were two active components on V 2 O 5 / WO 3 -TiO 2 for the activation of adsorbed NH 3 (i.e. V 5+ and Fe 3+ ). The acid sites on V 2 O 5 /Fe 2 O 3 -TiO 2 mainly resulted from the support Fe 2 O 3 -TiO 2 , so the adsorbed NH 3 preferred to be activated by Fe 3+ rather than by V 5+ . V 5+ on V 2 O 5 /Fe 2 O 3 -TiO 2 could accelerate the regeneration of Fe 3+ on Fe 2 O 3 -TiO 2 due to the rapid electron transfer between V 5+ and Fe 2+ on the surface, so the activation of adsorbed NH 3 by Fe 3+ was promoted. As some NH 3 adsorbed on V 2 O 5 /Fe 2 O 3 -TiO 2 was not activated by Fe 3+ , the inactivated NH 3 could then be activated by V 5+ on the surface. As a result, 2% V 2 O 5 /Fe 2 O 3 -TiO 2 showed excellent SCR activity, N 2 selectivity and H 2 O/SO 2 durability at 300-450 1C. Furthermore, the emission of 2% V 2 O 5 /Fe 2 O 3 -TiO 2 to the fly ash can be prevented by an external magnetic field due to its inherent magnetization. Therefore, 2% V 2 O 5 /Fe 2 O 3 -TiO 2 could be a promising low-cost catalyst in NO emission control.

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

“…The Fe-ZSM-5-coated V 2 O 5 -WO 3 /TiO 2 catalysts could greatly depress the formation of N 2 O in NH 3 -SCR reaction, depending on the coating content [16], unlike the series configuration systems [17]. Samples of coprecipitated, Fe 2 O 3 -TiO 2 -supported 1% V 2 O 5 , and 1% V 2 O 5 -10% WO 3 /TiO 2 , had similar NO conversions at 150-400 • C but at higher temperatures, lower ones, depending on the temperature, were indicated for the former sample [18]. This showed a better N 2 selectivity at high temperatures ≥400 • C [18]; however, this observation may be apparent because of the difference in NO conversion at the temperature region between the catalysts.…”

“…Samples of coprecipitated, Fe 2 O 3 -TiO 2 -supported 1% V 2 O 5 , and 1% V 2 O 5 -10% WO 3 /TiO 2 , had similar NO conversions at 150-400 • C but at higher temperatures, lower ones, depending on the temperature, were indicated for the former sample [18]. This showed a better N 2 selectivity at high temperatures ≥400 • C [18]; however, this observation may be apparent because of the difference in NO conversion at the temperature region between the catalysts. All 1% V 2 O 5 -10% WO 3 catalysts dispersed on 1-5% Fe 2 O 3 /TiO 2 gave an improvement to N 2 selectivity at temperatures >450 • C, compared to the bare TiO 2 -based catalyst; in addition to that, they showed higher NO conversion below 350 • C but comparable NO conversion at higher temperatures [19].…”

“…An attempt to minimize the formation of N 2 O in NH 3 -SCR processes has been reported: a direct coating of Fe-ZSM-5 onto a commercial V 2 O 5 -WO 3 /TiO 2 catalyst [16], a sequential configuration of V 2 O 5 -WO 3 /TiO 2 and Fe-ZSM-5 [17], and a modification of TiO 2 using Fe 2 O 3 before V 2 O 5 and WO 3 loadings [18,19]. These studies were started from the fact that Fe-exchanged zeolites, representatively Fe-ZSM-5, are a commercially proven catalyst not only for the NH 3 -SCR reaction but also for direct N 2 O decomposition; thereby, the decomposition of N 2 O produced in the SCR reaction into N 2 on Fe ions and/or its reduction by residual NH 3 species [20][21][22][23] is expected, and from that a nanosized iron oxide, γ-Fe 2 O 3 (maghemite), is active for the NH 3 -SCR reaction, although N 2 O production levels were not addressed for this system [24].…”

Upgrading V2O5-WO3/TiO2 deNOx Catalyst with TiO2-SiO2 Support Prepared from Ti-Bearing Blast Furnace Slag

“…Furthermore, the presence of SiO2 in BFS-TiO2 does not allow structural changes except for a slight shift towards higher 2θ values due to shrinkage of the pores, thereby stabilizing the meso-structures [41]. Neither impurities, Al2O3 nor Fe2O3, are detected, probably because of their weakness compared to the strong scattering from anatase, suggesting that impurities well dispersed over the surface of titania or existed as an amorphous phase [13,14]. The difference in crystallinity is not proportional to reflect the enabled NOx conversion because the support also has different acidities and acid sites.…”

“…Commercial titania fail to provide high surface area; however, to be used as a support for deNOx catalyst, titania should be characterized by high surface area and high onset temperature to rutilation. Thus, numerous metal oxides doped with TiO 2 have been studied as mechanical promoters including Al 2 O 3 , SiO 2 , Fe 2 O 3 , and CeO 2 for the improvement of deNO x catalytic activity [12][13][14][15]. Among various mixed oxides, TiO 2 -SiO 2 has drawn special attention owing to its highly active in the SCR reaction and simultaneously, less active in the SO 2 oxidation reaction.…”