Selective catalytic reduction of NO with NH3 over titanium modified Fe Mg O catalysts: Performance and characterization

Overview of mechanisms of Fe-based catalysts for the selective catalytic reduction of NOx with NH3 at low temperature

With the increasingly stringent control of NOx emissions, NH3-SCR, one of the most effective de-NOx technologies for removing NOx, has been widely employed to eliminate NOx from automobile exhaust and industrial production. Researchers have favored iron-based catalysts for their low cost, high activity, and excellent de-NOx performance. This paper takes a new perspective to review the research progress of iron-based catalysts. The influence of the chemical form of single iron-based catalysts on their performance was investigated. In the section on composite iron-based catalysts, detailed reviews were conducted on the effects of synergistic interactions between iron and other elements on catalytic performance. Regarding loaded iron-based catalysts, the catalytic performance of iron-based catalysts on different carriers was systematically examined. In the section on iron-based catalysts with novel structures, the effects of the morphology and crystallinity of nanomaterials on catalytic performance were analyzed. Additionally, the reaction mechanism and poisoning mechanism of iron-based catalysts were elucidated. In conclusion, the paper delved into the prospects and future directions of iron-based catalysts, aiming to provide ideas for the development of iron-based catalysts with better application prospects. The comprehensive review underscores the significance of iron-based catalysts in the realm of de-NOx technologies, shedding light on their diverse forms and applications. The hope is that this paper will serve as a valuable resource, guiding future endeavors in the development of advanced iron-based catalysts.

Investigation of Mg-doping effect on the activity and P tolerance of V2O5-MoO3 /TiO2 catalysts for NH3-SCR

V₂O₅-MoO₃/TiO₂ catalyst modified by Mg was studied to obtain higher NOx SCR activity and higher P, SO₂, and H₂O resistance than the V₂O₅-MoO₃/TiO₂. The results show that Mg modification can promote the denitration activity of V₂O₅-MoO₃/TiO₂ catalyst, and the maximum NOx removal efficiency of Mg₁-SCR catalyst was 97.5%; the optimum reaction temperature and flow rate were 350℃ and 1200 mL/min, respectively. Mg doping can broaden the reaction temperature window of the catalyst, and the denitration efficiency can reach more than 87% at 300℃. P₂O₅ solution was prepared as poisoning precursor and mixed with catalyst to simulate the process of catalyst P-poisoning. The step-wise study showed that Mg_0.5-SCR and Mg₁-SCR catalyst displays higher durable resistance to P, SO₂, and H₂O than original catalyst. The degree of denitrification efficiency reduction of Mg₁-SCR is 4% smaller than that of Mg₀-SCR after passing SO₂. Mg_0.5-SCR catalyst achieves 88% denitrification efficiency at 350 °C after simulating phosphorus poisoning. The catalysts have been characterized by X-ray diffraction, Brunner - Emmet - Teller, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscop, programmed temperature desorption, and programmed temperature reduction. The obtained results suggested that the Mg doping made the active components more dispersed on the surface of the supports, improved the thermal stability of the catalyst, promoted the transition of VOx from monomeric state to polymerized state, inhibited the interaction between P and V, and protected the acid site.

Modified red mud catalyst for the selective catalytic reduction of nitrogen oxides: Impact mechanism of cerium precursors on surface physicochemical properties

Red mud, as industrial solid waste, causes severe environmental problems such as soil alkalization and groundwater pollution. In this work, we researched and developed the red mud as a selective catalytic reduction catalyst for NO_x removal with NH₃ (NH₃-SCR). After selective dissolution and specific heat treatment, different Ce precursors were used to modifying its physical and chemical properties. The results showed that Ce(NO₃)₃ and Ce(NH₄)₂(NO₃)₆ modified red mud (RMcn and RMcan) had excellent SCR performance below 300 °C. Ce(SO₄)₂ modified red mud (RMcs) showed relatively low NO_x conversions at 200-300 °C. The redox property was improved with the Ce(NO₃)₃ and Ce(NH₄)₂(NO₃)₆, while depressed with the Ce(SO₄)₂. Agglomerates generated on the RMcs and blocked the accumulated pores due to the formation of Ce₂(SO₄)₃. The surface acidity of RMcs enhanced with increased adsorption for ammonia. However, these new adsorbed ammonia species, highly related to the sulfate from the Ce₂(SO₄)₃, were inert and did not react with the adsorbed or gaseous NO species at 200-300 °C. The abundant surface lattice oxygen from CeO₂ microcrystals improved the catalytic oxidation capacity of the RMcn and RMcan.

Insights over Titanium Modified FeMgOx Catalysts for Selective Catalytic Reduction of NOx with NH3: Influence of Precursors and Crystalline Structures

Titanium modified FeMgOx catalysts with different precursors were prepared by coprecipitation method with microwave thermal treatment. The iron precursor is a key factor affecting the surface active component. The catalyst using FeSO4 and Mg(NO3)2 as precursors exhibited enhanced catalytic activity from 225 to 400 °C, with a maximum NOx conversion of 100%. Iron oxides existed as γ-Fe2O3 in this catalyst. They exhibited highly enriched surface active oxygen and surface acidity, which were favorable for low-temperature selective catalytic reduction (SCR) reaction. Besides, it showed advantage in surface area, spherical particle distribution and pores connectivity. Amorphous iron-magnesium-titanium mixed oxides were the main phase of the catalysts using Fe(NO3)3 as a precursor. This catalyst exhibited a narrow T90 of 200/250–350 °C. Side reactions occurred after 300 °C producing NOx, which reduced the NOx conversion. The strong acid sites inhibited the side reactions, and thus improved the catalytic performance above 300 °C. The weak acid sites appeared below 200 °C, and had a great impact on the low-temperature catalytic performance. Nevertheless, amorphous iron-magnesium-titanium mixed oxides blocked the absorption and activation between NH3 and the surface strong acid sites, which was strengthened on the γ-Fe2O3 surface.