Currently, selective catalytic reduction (SCR) of NO x with NH3 in the presence of SO2 by using vanadium-free catalysts is still an important issue for the removal of NO x for stationary sources. Developing high-performance catalysts for NO x reduction in the presence of SO2 is a significant challenge. In this work, a series of Fe2O3-promoted halloysite-supported CeO2-WO3 catalysts were synthesized by a molten salt treatment followed by the impregnation method and demonstrated improved NO x reduction in the presence of SO2. The obtained catalyst exhibits superior catalytic activity, high N2 selectivity over a wide temperature range from 270 to 420 °C, and excellent sulfur-poisoning resistance. It has been demonstrated that the Fe2O3-promoted halloysite-supported CeO2-WO3 catalyst increased the ratio of Ce3+ and the amount of surface oxygen vacancies and enhanced the interaction between active components. Moreover, the SCR reaction mechanism of the obtained catalyst was studied using in situ diffuse reflectance infrared Fourier transform spectroscopy. It can be inferred that the number of Bronsted acid sites is significantly increased, and more active species could be produced by Fe2O3 promotion. Furthermore, in the presence of SO2, the Fe2O3-promoted halloysite-supported CeO2-WO3 catalyst can effectively prevent the irreversible bonding of SO2 with the active components, making the catalyst exhibit desirable sulfur resistance. The work paves the way for the development of high-performance SCR catalysts with improved NO x reduction in the presence of SO2.

Improved NO x Reduction in the Presence of SO 2 by Using Fe 2 O 3 -Promoted Halloysite-Supported CeO 2 -WO 3 Catalysts

Mechanistic aspects of NH3-SCR reaction over CeO2/TiO2-ZrO2-SO42− catalyst: In situ DRIFTS investigation

A series of tungsten-modified Cu0.02Fe0.2TiOx catalysts (Cu0.02Fe0.2WaTiOx; a = 0.01, 0.02, and 0.03) was synthesized by sol-gel method. Their catalytic activities were investigated for the selective catalytic reduction (SCR) of NO with NH3, in the presence/absence of 5 vol.% H2O. The characterization techniques of XRD, BET, Raman, H2-TPR, NH3-TPD, XPS, in situ DRIFTS, and kinetic studies were used to reveal the effect of tungsten modification on the redox and acidity of the Cu0.02Fe0.2WaTiOx catalysts. The relationship among the species composition, acid property, and oxidation-reduction behavior of the Cu0.02Fe0.2WaTiOx catalysts was established. Results demonstrated that a moderate amount of tungsten doping can markedly enhance the specific surface area, improve the abundant Bronsted and Lewis acid sites, and tune the surface species composition, which all benefited high-performance catalysis. Water/sulfur resistance also improved because of the excellent acidity levels. Among the Cu0.02Fe0.2WaTiOx catalysts, Cu0.02Fe0.2W0.02TiOx showed the highest NO conversion, a wide reaction-temperature window (235–520 °C) with >90% NO conversion, high N2 selectivity, and high water/sulfur resistance even in the presence of 5 vol.% H2O. Moreover, Cu0.02Fe0.2W0.02TiOx retained its outstanding catalytic activity under a rather high gas hourly space velocity (GHSV) of 100,000 h−1. In conclusion, the combined effects of redox and sufficient acidities on catalytic activity played key roles in superior SCR performance and water/sulfur durability. Furthermore, the NH3-SCR reaction over Cu0.02Fe0.2W0.02TiOx may follow the Eley–Rideal reaction pathway according to the in situ DRIFTS and kinetic studies results.

Effect of W on the acidity and redox performance of the Cu0.02Fe0.2WaTiOx (a = 0.01, 0.02, 0.03) catalysts for NH3-SCR of NO

Low temperature high activity of M (M = Ce, Fe, Co, Ni) doped M-Mn/TiO2 catalysts for NH3-SCR and in situ DRIFTS for investigating the reaction mechanism

Structure, synthesis, and catalytic properties of nanosize cerium-zirconium-based solid solutions in environmental catalysis

Anatase (A) TiO2 is widely used as a support of the supported vanadium-based and non-vanadium-based catalysts for NH3-SCR reaction. However, there is lack of enough attention for brookite (B) and rutile (R) TiO2. Therefore, in the present work, we synthesize a series of TiO2-A, TiO2-B, and TiO2-R, and then used as supports to prepare CeO2/TiO2-A, CeO2/TiO2-B, and CeO2/TiO2-R catalysts with the purpose of clarifying the crystal form effect of TiO2 supports on the physicochemical properties and catalytic performance of these supported ceria-based catalysts for NH3-SCR reaction. Characterization results exhibit that H2 consumption (responding to reduction property), acid amounts, surface Ce3+ content, surface adsorbed oxygen species, and catalytic performance of these supported ceria-based catalysts give the order of CeO2/TiO2-R > CeO2/TiO2-B > CeO2/TiO2-A, which is related to the interaction (i.e., Ce3+ + Ti4+ ↔ Ce4+ + Ti3+) between CeO2 and TiO2 (anatase, brookite, and rutile). Especially, CeO2/TiO2-R catalyst exhibits the optimal catalytic performance for NH3-SCR reaction among these supported ceria-based catalysts owing to the most excellent reduction property as well as the largest amounts of acid sites, surface Ce3+ content, and surface adsorbed oxygen species.

Jun Du

Papers

Selective catalytic reduction of NOx by NH3 over CeO2 supported on TiO2: Comparison of anatase, brookite, and rutile