Selective Catalytic Reduction of NO_x with NH₃ on Cu-, Fe-, and Mn-Zeolites Prepared by Impregnation: Comparison of Activity and Hydrothermal Stability

Cu-, Fe-, and Mn-zeolite (SSZ-13, ZSM-5, and BEA) catalysts have been prepared by incipient wetness impregnation and characterized by N2 physisorption, H2-TPR, NH3-TPD, and XPS methods. Both metal and zeolite support influence the deNOx activity and hydrothermal stability. Cu-zeolites and Mn-zeolites showed medium temperature activity, and Fe zeolites showed high temperature activity. Among all the catalysts, Cu-SSZ-13 and Fe-BEA are the most promising hydrothermally resistant catalysts. Fresh and hydrothermally treated catalysts were further examined to investigate the acidic and redox properties and the zeolite surface composition. Increased total acidity after metal impregnation and loss of acidity due to hydrothermal treatment were observed in all the catalysts. Hydrothermal treatment resulted in migration of metal or in strong metal support interations, whereby changes in reduction patterns are observed

Strategies of Coping with Deactivation of NH3-SCR Catalysts Due to Biomass Firing

Firing of biomass can lead to rapid deactivation of the vanadia-based NH3-SCR catalyst, which reduces NOx to harmless N2. The deactivation is mostly due to the high potassium content in biomasses, which results in submicron aerosols containing mostly KCl and K2SO4. The main mode of deactivation is neutralization of the catalyst’s acid sites. Four ways of dealing with high potassium contents were identified: (1) potassium removal by adsorption, (2) tail-end placement of the SCR unit, (3) coating SCR monoliths with a protective layer, and (4) intrinsically potassium tolerant catalysts. Addition of alumino silicates, often in the form of coal fly ash, is an industrially proven method of removing K aerosols from flue gases. Tail-end placement of the SCR unit was also reported to result in acceptable catalyst stability; however, flue-gas reheating after the flue gas desulfurization is, at present, unavoidable due to the lack of sulfur and water tolerant low temperature catalysts. Coating the shaped catalysts with thin layers of, e.g., MgO or sepiolite reduces the K uptake by hindering the diffusion of K+ into the catalyst pore system. Intrinsically potassium tolerant catalysts typically contain a high number of acid sites. This can be achieved by, e.g., using zeolites as support, replacing WO3 with heteropoly acids, and by preparing highly loaded, high surface area, very active V2O5/TiO2 catalyst using a special sol-gel method

Catalytic Transfer Hydrogenation of Bio-Based Furfural with NiO Nanoparticles

A facile, yet highly efficient, catalytic system was developed for the catalytic transfer hydrogenation (CTH) of biomass-derived furfural (FF) to furfuryl alcohol (FAOL) over commercially available NiO nanoparticles using 2-propanol as solvent and H-donor. The catalyst system yielded 94.4% of FAOL after only 30 min of reaction at 170 °C, and a satisfactory FAOL yield of 80.9% was also attained under milder reaction conditions (150 °C, 4 h). Furthermore, the NiO catalyst proved reusable for CTH of FF several times, maintaining its pristine activity after calcination in air. The catalyst effectiveness was further confirmed by performing scaled-up CTH of FF and CTH of various other aldehydes. Compared to other Ni-based catalysts reported for the hydrogenation of FF, the present system absolutely averted using H2 gas as pure NiO nanoparticles with acid–base properties did not require pre-reduction

Selective catalytic reduction of nitric oxide with a novel Mn–Ti–Ce oxide core-shell catalyst having improved low-temperature activity and water tolerance

A novel core-shell-shell Mn–Ti–Ce oxide catalyst (MnOx@TiO2@CeO2) was synthesized by a three-step method and applied for the selective catalytic reduction of NOx with ammonia (NH3-SCR). The catalyst exhibited an excellent low-temperature activity with NOx conversion &gt;80% in a broad temperature range under both dry (120–260 °C) and wet (180–255 °C) conditions with a weight hourly space velocity (WHSV) of 240,000 mL/(g·h). Nitrogen physisorption and X-ray photoelectron spectroscopy (XPS) results showed that the formation of the inner TiO2 shell significantly increased the specific surface area, surface Mn4+/Mn ratio and chemisorbed oxygen, which could provide more active sites and promote the oxidation of NO to NO2. Ammonia temperature-programmed desorption (NH3-TPD) results indicated that the formation of the outer CeO2 shell not only extensively increased the surface acid sites but also enhanced the acid strength, beneficial for the ammonia adsorption and resulting in a good water tolerance.</p