Iron-Based Composite Oxide Catalysts Tuned by CTAB Exhibit Superior NH3–SCR Performance

Abstract

Iron-based oxide catalysts for the NH3–SCR (selective catalytic reduction of NOx by NH3) reaction have gained attention due to their high catalytic activity and structural adjustability. In this work, iron–niobium, iron–titanate and iron–molybdenum composite oxides were synthesized by a co-precipitation method with or without the assistance of hexadecyl trimethyl ammonium bromide (CTAB). The catalysts synthesized with the assistance of CTAB (FeM0.3Ox-C, M = Nb, Ti, Mo) showed superior SCR performance in an operating temperature range from 150 °C to 400 °C compared to those without CTAB addition (FeM0.3Ox, M = Nb, Ti, Mo). To reveal such enhancement, the catalysts were characterized by N2-physisorption, XRD (Powder X-ray diffraction), NH3-TPD (temperature-programmed desorption of ammonia), DRIFTS (Diffuse Reflectance Infrared Fourier Transform Spectroscopy), XPS (X-ray Photoelectron Spectroscopy), and H2-TPR (H2-Total Physical Response). It was found that the crystalline phase of Fe2O3 formed was influenced by the presence of CTAB in the preparation process, which favored the formation of crystalline γ-Fe2O3. Owing to the changed structure, the redox-acid properties of FeM0.3Ox-C catalysts were modified, with higher exposure of acid sites and improved ability of NO oxidation to NO2 at low-temperature, both of which also contributed to the improvement of NOx conversion. In addition, the weakened redox ability of Fe prevented the over-oxidation of NH3, thus accounting for the greatly improved high-temperature activity as well as N2 selectivity.

Design of High-Performance Iron–Niobium Composite Oxide Catalysts for NH3-SCR: Insights into the Interaction between Fe and Nb

“…As it is recognized that oxides in the amorphous state exhibited high NH 3 -SCR performance, the highly dispersed or amorphous state of FeNb 0.4 O x was possibly correlated to its low activation energy. With the assistance of CTAB, diffraction peaks of maghemite-phase Fe 2 O 3 (γ-Fe 2 O 3 ) appeared for the FeNb 0.4 O x -C catalyst, which was favorable for the SCR reaction and agreed well with our previous research . Such formation of the new phase agreed well with the results of kinetic studies that more active sites were available over FeNb 0.4 O x -C compared with those over FeNb 0.4 O x .…”

“…20 In our previous research, we added hexadecyl trimethyl ammonium bromide (CTAB) in the preparation process of Fe−M catalysts (M = Nb, Ti, Mo) to improve the SCR performance effectively, of which Fe−Nb catalysts exhibited high NO x conversion and N 2 selectivity. 21 Herein, a series of iron−niobium composite oxide catalysts was prepared with the assistance of CTAB in the preparation process, of which the FeNb 0.4 O x -C catalyst exhibited the highest NO x conversion. Further characterization including N 2 -physisorption analysis, XRD, Raman, TG/DTA, NH 3 -TPD, H 2 -TPR, and XPS was carried out to reveal the effect of Nb and CTAB addition and further understand the activity− structure relationship.…”

“…More recently, doping with Nb was found to improve the catalytic activity and SO 2 resistance of an FeTi catalyst, which adjusted the structure of Fe 2 O 3 and led to the adsorption of more NH 3 as well as NO . In our previous research, we added hexadecyl trimethyl ammonium bromide (CTAB) in the preparation process of Fe–M catalysts (M = Nb, Ti, Mo) to improve the SCR performance effectively, of which Fe–Nb catalysts exhibited high NO x conversion and N 2 selectivity . Herein, a series of iron–niobium composite oxide catalysts was prepared with the assistance of CTAB in the preparation process, of which the FeNb 0.4 O x -C catalyst exhibited the highest NO x conversion.…”

Ni–Fe Cocatalysts on Magnesium Silicate Supports for the Depolymerization of Kraft Lignin

“…Meanwhile, Fe has been used as an efficient catalyst in the reaction because Fe metal can weaken lignin’s C–O binding ability. Another reason was that increasing the metal ratio resulted in increased productivity caused by the Fe metal acting as an acidic site. , Figure b shows the highest selectivity of guaiacol over other products. This could arise from the cleavage of the C–C bond in the 4-ethylguaiacol intermediate during guaiacol formation.…”

Carbon Nanosphere-Encapsulated Fe Core–Shell Structures for Catalytic CO2 Hydrogenation

“…600 °C for supported catalysts. 61,62 The observed 50 °C shift was probably due to the restricted diffusion of H 2 through the carbon shell, which caused the reduction to occur at higher temperatures. The small H 2 consumption peaks before 400 °C may be attributed to the hydrogenation of functional groups on the surface of the carbon shell, such as hydroxyl and C�O groups.…”