New CeO2–TiO2, WO3–TiO2 and WO3–CeO2–TiO2 mesoporous aerogel catalysts for the low temperature selective catalytic reduction of NO by NH3

Abstract

New mesoporous and well-structured aerogel catalysts (CeO 2 -TiO 2 , WO 3 -TiO 2 and WO 3 -CeO 2 -TiO 2 ) were elaborated via the sol gel method, characterized by means of various techniques (XRD; N 2 -Physisorption at 77 K; NH 3 -TPD; H 2 -TPR; DRUV-Vis spectroscopy) and evaluated in the selective catalytic reduction (SCR) of NO by NH 3 . The results reveal that all the aerogel catalysts develop essentially the diffraction peaks of TiO 2 anatase phase and are classified as mesoporous materials with a high surface area (70 < S BET < 106 m 2 /g), large porosity (0.27 < V PT < 0.46 cm 3 /g) and nanometer size of crystallites (8-15 nmm). The addition of Ce and/or W influences differently the structure, texture, crystallites size, surface oxygen concentration, total acidity and redox ability of aerogel samples and clearly affects their NO-SCR activity which follows this order: TiO 2 < WO 3 -TiO 2 < CeO 2 -TiO 2 < WO 3 -CeO 2 -TiO 2 . It was also found that cerium species are more active in the low temperature NO-SCR reaction than tungsten ones (NO conversions obtained at 300 °C using CeO 2 -TiO 2 and WO 3 -TiO 2 were 75 % and 0 %, respectively). On the other hand, it was suggested that the interactions between Ce and W species play a key role in improving the reactivity of WO 3 -CeO 2 -TiO 2 catalyst in the SCR of NO by NH 3 . Interestingly, the NO conversion into N 2 reaches 85 % at 300 °C and exceeds 90 % between 320 and 400 °C over this novel meso-structured aerogel catalyst.

Effect of acidic components (SO42- and WO3) on the surface acidity, redox ability and NH3-SCR activity of new CeO2-TiO2 nanoporous aerogel catalysts: A comparative study

“…Yu et al [29], investigated a series of sulfated catalysts (CuSO 4 /TiO 2 , Fe 2 (SO 4 ) 3 /TiO 2 , MnSO 4 /TiO 2 , Ce(SO 4 ) 2 /TiO 2 and CoSO 4 /TiO 2 ) in the NH 3 -SCR reaction and demonstrated that the amount of acid sites was the main factor which affects the catalytic activity of metal sulfate catalysts. Furthermore, in our previous work [26], we showed that WO 3 -CeO 2 -TiO 2 exhibits higher SCR activity than WO 3 -TiO 2 and CeO 2 -TiO 2 aerogel catalysts due to the synergetic effect between W and Ce which influences the acidity and reducibility of catalyst. Li et al [30] reported that a novel CeO 2 /TiO 2 -MoO 3 catalyst exhibits100% NO conversion at 200-350 °C.…”

“…The powder aerogels (TiO 2 , CeO 2 -TiO 2, CeO 2 -TiO 2 -SO 4 2and WO 3 -CeO 2 -TiO 2 ) were prepared via the one step sol gel protocol, then dried under the supercritical drying conditions of solvent (ethanol). The detailed method adopted for the elaboration of samples was described in our previous works [20,26]. Ammonium metatungstate hydrate ((NH 4 ) 6 H 2 W 12 O 24 .xH 2 O, Sigma Aldrich, > 99.9%) and cerium nitrate (Ce(NO 3 ) 3 .6H 2 O, Aldrich) were used as W and Ce precursors, respectively.…”

“…In this framework, Gao et al [22,23] reported that CeO 2 -TiO 2 xerogel catalyst, elaborated via sol-gel method, exhibits much better NH 3 -SCR performance than the same catalysts prepared by impregnation and co-precipitation methods, owing to its high surface area, better redox ability, strong interaction between CeO 2 and TiO 2 and well dispersed CeO 2 species. On the other hand, many literature reports have proved that adding acidic components (sulfuric acid [24], phosphoric acid [25]; oxides of: W [26], Mo [27] or Nb [28]) into Ce based catalysts enhances its acidic functions and thereby improves significantly its NO-NO-SCR activity. Yu et al [29], investigated a series of sulfated catalysts (CuSO 4 /TiO 2 , Fe 2 (SO 4 ) 3 /TiO 2 , MnSO 4 /TiO 2 , Ce(SO 4 ) 2 /TiO 2 and CoSO 4 /TiO 2 ) in the NH 3 -SCR reaction and demonstrated that the amount of acid sites was the main factor which affects the catalytic activity of metal sulfate catalysts.…”

“…This method presents several advantages including a simple and low cost technology, low process-temperatures and flexible control of the structure and size of final products using many operating parameters [31]. In addition, it can give aerogel mixed oxides with interesting properties, such as: high purity, nanometer size and developed mesoporous texture…, which make them useful for many applications, especially for catalysis [20,26,32].…”

Tungsten Oxide Modified V2O5-Sb2O3/TiO2 Monolithic Catalyst: NH3-SCR Activity and Sulfur Resistance

“…Ma et al [29] studied the effect of CeO 2 modification on the low-temperature NH 3 -SCR activity of the V 2 O 5 -WO 3 /TiO 2 catalyst. They demonstrated that V-O-Ce bridging bonds were formed in the catalyst, and the reducibility of the catalyst was enhanced due to the synergistic effect between Ce and V. The introduction of WO 3 can improve the NH 3 -SCR activity of the catalyst by increasing the redox property and Brönsted acidity [30]. Indeed, Lietti et al [31] observed that the V 2 O 5 -WO 3 /TiO 2 catalyst has both higher transient and steady-state reactivity in SCR than the binary V 2 O 5 /TiO 2 counterpart.…”