Selective Catalytic Reduction Of Nitrogen Oxides Research Articles

Recent Progress on Low-Temperature Selective Catalytic Reduction of NOx with Ammonia.

Selective catalytic reduction of nitrogen oxides (NOx) with ammonia (NH3-SCR) has been implemented in response to the regulation of NOx emissions from stationary and mobile sources above 300 °C. However, the development of NH3-SCR catalysts active at low temperatures below 200 °C is still needed to improve the energy efficiency and to cope with various fuels. In this review article, recent reports on low-temperature NH3-SCR catalysts are systematically summarized. The redox property as well as the surface acidity are two main factors that affect the catalytic activity. The strong redox property is beneficial for the low-temperature NH3-SCR activity but is responsible for N2O formation. The multiple electron transfer system is more plausible for controlling redox properties. H2O and SOx, which are often found with NOx in flue gas, have a detrimental effect on NH3-SCR activity, especially at low temperatures. The competitive adsorption of H2O can be minimized by enhancing the hydrophobic property of the catalyst. Various strategies to improve the resistance to SOx poisoning are also discussed.

Synergistic Catalytic Removal of NOx and n-Butylamine via Spatially Separated Cooperative Sites.

Synergistic control of nitrogen oxides (NOx) and nitrogen-containing volatile organic compounds (NVOCs) from industrial furnaces is necessary. Generally, the elimination of n-butylamine (n-B), a typical pollutant of NVOCs, requires a catalyst with sufficient redox ability. This process induces the production of nitrogen-containing byproducts (NO, NO2, N2O), leading to lower N2 selectivity of NH3 selective catalytic reduction of NOx (NH3-SCR). Here, synergistic catalytic removal of NOx and n-B via spatially separated cooperative sites was originally demonstrated. Specifically, titania nanotubes supported CuOx-CeO2 (CuCe-TiO2 NTs) catalysts with spatially separated cooperative sites were creatively developed, which showed a broader active temperature window from 180 to 340 °C, with over 90% NOx conversion, 85% n-B conversion, and 90% N2 selectivity. A synergistic effect of the Cu and Ce sites was found. The catalytic oxidation of n-B mainly occurred at the Cu sites inside the tube, which ensured the regular occurrence of the NH3-SCR reaction on the outer Ce sites under the matching temperature window. In addition, the n-B oxidation would produce abundant intermediate NH2*, which could act as an extra reductant to promote NH3-SCR. Meanwhile, NH3-SCR could simultaneously remove the possible NOx byproducts of n-B decomposition. This novel strategy of constructing cooperative sites provides a distinct pathway for promoting the synergistic removal of n-B and NOx.

Facile one-pot synthesis of Cu-SSZ-39 catalysts with excellent catalytic performance in NH3-SCR reaction

Nitrogen oxide (NOx) emission from diesel vehicles has caused severe pollution to the atmospheric environment. Selective catalytic reduction of NOx with NH3 (NH3-SCR) technology has been widely used to remove NOx from diesel vehicle exhaust. Cu-SSZ-39 zeolites have exhibited excellent NH3-SCR catalytic activity and hydrothermal stability, giving them promise for practical application. A facile one-pot synthesis method to prepare Cu-SSZ-39 zeolites was developed, with complete crystallization achieved in 24 h. Moreover, the Cu content could be controlled by adjusting the amount of Cu-TEPA added without the need for complex post-treatment processes. Cu-SSZ-39 catalysts synthesized through the one-pot synthesis method exhibited excellent NH3-SCR activity and hydrothermal stability. The one-pot-synthesized Cu-SSZ-39 catalysts contained in situ generated CuO species, which can act as sacrificial sites to protect Cu2+ under sulfidation conditions. Considering their efficient synthesis process, excellent NH3-SCR activity, hydrothermal stability and sulfur resistance, one-pot-synthesized Cu-SSZ-39 catalysts hold great promise for future applications.

Superior room-temperature efficacy of selective catalytic reduction of NOx by CO utilizing metal-modified Fe2O3 catalysts

Fe2O3-based catalysts demonstrate significant potential for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) by CO. However, their effectiveness is limited at lower temperatures, impeding widespread industrial adoption. To overcome this, we optimize the Fe2O3-based catalyst component through 3 wt% cobalt (Co) loading, which improves the synergistic removal of CO and NOx pollutants. Our developed catalyst, Co-Fe2O3 on an amorphous SiO2 substrate, exhibits superior room-temperature activity in CO-SCR, achieving CO and NOx conversion ratios as well as N2 selectivity above 80 % at 25 °C, and over 93 % at 100–500 °C. The enhancement in catalyst performance is elucidated through density functional theory calculations and experimental investigations, revealing the creation of heteronuclear active sites via metal modification, and consequent improvements in redox characteristics and acidity. Our findings offer a robust pathway towards the industrial implementation of ammonia-free-SCR technology with synergistic removal of CO and NOx and provide insights for designing superior heterogeneous catalysts.

Time-resolved in situ/operando infrared spectroscopy of Cu-supported zeolite X catalyst during NH3–SCR of NO: A modulated excitation study

Zeolite X was used as support of copper catalyst (Cu/X) for selective catalytic reduction (SCR) of nitrogen oxide (NO) with ammonia (NH3). Modulated excitation in situ/operando infrared (IR) spectroscopy and phase-sensitive detection (PSD) were applied to study the reaction intermediates that formed on the Cu/X during transient experiments. Changing the gas concentration to periodically create unsteady conditions enabled the selective extraction of the dynamic species that were directly involved in the reaction. The IR results showed that only Lewis acid sites (LX) existed on zeolite X,and Brønsted acid sites (B) and extra Lewis acid sites (LCu) were generated after Cu loading. The transient experiment results indicated that the SCR reactions on Cu/X obeys the Eley − Rideal (E − R) mechanism, in which NH3 is first adsorbed on the LX and LCu sites (LX–NH3, LCu–NH3) and then moved to the B sites (B–NH3), where it reacted with gas-phase NO to form NH2NO intermediate, which finally decomposed into N2 and H2O. Moreover, it is found that the NH3 adsorbed on LCu and B sites exhibits stronger reactivity than that on the LX sites.

Promoted NH3-SCR activity and hydrothermal stability of Cu-SSZ-50 catalyst synthesized by one-pot method

Nitrogen oxide (NOx) is one of the most critical contaminants in the air, and the control of NOx emission from diesel vehicles is very important. Cu-based small-pore zeolites have already been applied for NOx abatement on diesel vehicles. Among the small-pore zeolites, Cu-SSZ-50 catalysts with good NH3-SCR catalytic activity were believed to have potential for application. In this study, a one-pot synthesis method for Cu-SSZ-50 catalysts was developed for the first time, using the co-templates of Cu-TEPA and 2,6-dimethyl-N-methylpyridinium hydroxide. In this synthesis method, Cu-SSZ-50 with various Cu contents can be obtained by adjusting the amount of Cu-TEPA without the need for a further after-treatment process. The addition of Cu-TEPA affected the framework atoms and Cu species, and a lower Si/Al ratio and more SCR active Cu species were obtained. The synthesized catalyst with a Cu/Al ratio of 0.40 exhibited over 90% NOx conversion between 200 °C and 450 °C for the selective catalytic reduction of NOx with NH3 (NH3-SCR). Meanwhile, over 80% NOx conversion could be obtained from 250 °C to 450 °C after hydrothermal aging at 750 °C for 16 h. In addition, both L-H and E-R mechanisms were proven to exist for the one-pot-synthesized Cu-SSZ-50 by in situ DRIFTS experiments. The simple synthesis procedure, excellent catalytic activity and hydrothermal stability brighten the prospects for the application of Cu-SSZ-50.

Advancements in low-temperature NH3-SCR of NOx using Ba-based catalysts: a critical review of preparation, mechanisms, and challenges.

Presently, selective catalytic reduction (SCR), with either carbon monoxide, urea, hydrocarbons, hydrogen, or ammonia as a reductant, has become a nitrogen oxide (NOx) removal technology (NOx conversion) of many catalytic companies and diesel engine exhaust gas. Although, there exists a serious threat of low-temperature limitations. So far, certain scientists have shown that barium-based (Ba-based) catalysts have the potential to be highly effective at SCR of NOx at low temperatures when ammonia is used as the reducing agent. The process of NOx storage and reduction which alternate SCR is known as the Lean NOx trap. Herein, we give the condensed advancements and production of the catalysts that involve BaO in low-temperature NH3-SCR of NOx, the advantages of BaO catalysts compared to the recently hot electrocatalysis, the stability of BaO catalyst materials, and the condensed advancements and production of the catalysts that involve BaO in low-temperature NH3-SCR of NOx. These catalysts are viewed in the light of their preparation method, particulate, and posture in mixed oxides. Also, the characteristic features of Ba-based catalysts are carefully considered and briefed under the following areas: preparation method and precursor, crystallinity, calcination temperature, morphology, acid sites, the specific surface area for reaction, redox property, and activation energy of catalysts. More to these are the discussions on Eley-Rideal [E-R] and Langmuir-Hinshelwood [L-H] mechanisms, the H2O/SO2 and O2 permissiveness, and the NH3-SCR reaction mechanism over Ba-based catalysts highlighting their possible effects. Finally, we proposed the prospect and the likely future research plan for the low-temperature NH3-SCR of NOx.

Modified cold-rolled sludge as catalyst for selective catalytic reduction of NOx with NH3 at low temperatures

Iron-based mixed oxides are considered commercially promising environmentally friendly catalysts for selective catalytic reduction with NH3 (NH3-SCR) for removing nitrogen oxides (NOx) because of their high catalytic activity. In this work, cold-rolled sludge with high content of iron species was used as the iron precursor for preparing catalysts by supported MnOx and/or sulfuric acid modifications. The prepared catalyst showed 100 % of NOx conversion in the temperature range of 60–180 ℃ and exhibited good resistance to SO2 and H2O. This is mainly attributed to the synergy between MnOx and iron sulfate, which improved the denitration performance at super low-temperature by improving the textural properties, redox capacity, surface acidity, and surface chemical states of the catalyst. Furthermore, the presence of Fe3+ and SO42- protected the active ingredient from the poisoning of SO2 and improved its sulfur resistance. The super low-temperature reaction mechanism of the catalyst was unraveled by transient reaction experiments and In situ DRIFTS. The results show that both Brønsted and Lewis acid sites are present in 10 %Mn/CRS-S-400, and that the reaction is dominated by the Langmuir–Hinshelwood (L–H) mechanism. This study provides an innovative and cost-effective strategy for the design of NH3-SCR catalysts by sulfation iron-based mixed oxides.

Promoting mechanism of CuO on catalytic performance of CeFe catalyst for simultaneous removal of NOx and CO

Nitrogen oxides (NOx) and carbon monoxide (CO) coexisted in numerous industrial waste gases. And selective catalytic reduction of NOx with ammonia (NH3-SCR) and CO catalytic oxidation were considered as the effective technologies for simultaneous elimination of NOx and CO, respectively. However, an efficient bifunctional catalyst was crucial for achieving simultaneous removal of NOx and CO. Herein, we developed a series of Cu-modified CeFe catalysts for simultaneous removal of NOx and CO. The results demonstrated that 5Cu-CeFe catalyst presented the best catalytic performance, achieving approximately 81% NOx removal efficiency and nearly 99% CO conversion rate at 200 °C under a gas houely space velocity of 90,000 h−1. The XPS analysis demonstrated that copper oxides played a critical role in promoting the formation of Ce3+ and Oβ, thereby facilitating the NH3-SCR catalytic performance and CO catalytic oxidation. Moreover, the copper oxide modification of CeFe catalyst attained a trade-off between the surface acidity and redox ability, resulting in improving adsorption and activition capacity of the reactant gases. In situ DRIFTS experiments revealed that the NH3-SCR process primarily obeyed the Eley-Rideal (E-R) pathway over both CeFe and 5Cu-CeFe catalysts, while Langmuir-Hinshelwood (L-H) pathway hardly participated in NH3-SCR process. The presence of Cu+–CO species and surface lattice oxygen was crucial for CO oxidation, and both Mars-van Krevelen (M−K) and L-H pathways might be involved in the CO catalytic oxidation process over 5Cu-CeFe catalyst.

Insight into blast furnace dust for selective catalytic reduction of NOx: An experimental and DFT study

Blast furnace dust (BFD), a solid waste generated from the ironmaking process, causes the environmental problems of soil and water pollution. In this work, we develop the selective catalytic reduction (SCR) catalyst for the nitric oxides (NO) reduction using BFD as the raw material by the co-precipitation method. To guarantee the strongest catalytic capability, different calcined temperatures are tested to activate the catalysts, where the prepared catalysts are labeled as BFD-T with the capital letter T to represent the calcination temperature. α-Fe2O3 is the main crystal phase in BFD-T catalyst and the mesoporous structure is mainly concentrated in 2–15 nm. The BFD-400 catalyst presents the best SCR performances and further increasing of the calcination temperature for the catalyst preparation reduces the reducibility, specific surface area and surface adsorbed oxygen of the catalyst. In the temperature range of 225 ℃ to 350 ℃, the BFD-400 catalyst presents the nitrogen oxides (NOx) conversion of more than 90%, which is attributed to the increase of ferric ion on the catalyst surface. Meanwhile, density functional theory (DFT) is applied to study the adsorption states of the reactant molecules on the catalyst surface and reaction mechanism. During the SCR process, this catalyst shows the excellent resistance to sulfur and water in the coal-fired flue gas due to the weak adsorption energy calculation.

Manganese-based catalysts supported on carbon xerogels for the selective catalytic reduction of NOx using a hollow fibre-based reactor

As a more compact, affordable and efficient alternative to traditional catalytic converters, catalytic hollow fibre-based reactors have significant potential in addressing the high nitrogen oxides (NOx) emission associated with the combustion of green ammonia. In this work, the performance of a series of manganese (Mn)-based catalysts supported on three different carbon xerogels during the ammonia-selective catalytic reduction (NH3-SCR) reaction was investigated in a packed bed reactor configuration under typical vehicle exhaust gas conditions. The best catalyst candidate Mn-CX, which was associated with the highest NO conversion (i.e. 24% at 225 °C) and highest nitrogen selectivity (i.e. 85% at 225 °C), was deposited in a 7-channelled hollow fibre substrate via a combined sol-gel and incipient wetness impregnation method. At 225 °C and 1 atm, the performance of the hollow fibre-based reactor was enhanced by a factor of four compared to the packed bed reactor (i.e. rO2= 3300 molO2∙m−3∙h−1∙gcat−1 and rO2= 810 molO2∙m−3∙h−1∙gcat−1). The superior performance of the hollow fibre-based reactor is attributable to the unique morphology of the hollow fibre substrate, which lends itself to minimised mass transfer limitations. The markedly improved performance of the hollow fibre-based reactor underlines its potential as a technically and economically feasible solution to mitigate the high NOx emissions associated with ammonia combustion. The identification of the catalytic hollow fibre-based reactor as a viable exhaust gas after-treatment technology for green ammonia-fuelled engines, addresses a significant barrier facing the adoption of green ammonia as a carbon-free, future fuel, thereby facilitating the transition to a decarbonised transport sector.

Improvement of SO2 resistance of Cu-SSZ-13 with polyoxometalates in selective catalytic reduction of NOx

Nitrogen oxides (NOx) are harmful to the environment and human health. Cu-SSZ-13 catalyst plays a crucial role in selective catalytic reduction of NOx with NH3 benefiting from its good activity and structure stability. However, the sulfur resistance of Cu-SSZ-13 needs to be improved. Therefore, polyoxometalates (POMs) with strong acidity and strong oxidizing are chosen to enhance the catalytic performance of Cu-SSZ-13. Among them, Cu–CePW sample has better structural stability and the best NOx conversion rate over 95% between 250 and 450 °C and the best resistance to water vapor and SO2 up to about 90%. Besides, Ce and W species increases the amount of acid sites on the surface of sample especially at low temperature, and Ce species activates the Cu species in the catalyst and protects the active sites in the presence of SO2. Furthermore, Cu–CePW possesses both Lewis acid sites and Brønsted acid sites at the same time, and the reaction mechanism of Cu–CePW in NH3-SCR reaction involved both L-H mechanism and E-R mechanism.

Economical and Sustainable Synthesis of Small-Pore Chabazite Catalysts for NOx Abatement by Recycling Organic Structure-Directing Agents.

The application of small-pore chabazite-type SSZ-13 zeolites, key materials for the reduction of nitrogen oxides (NOx) in automotive exhausts and the selective conversion of methane, is limited by the use of expensive N,N,N-trimethyl-1-ammonium adamantine hydroxide (TMAdaOH) as an organic structure-directing agent (OSDA) during hydrothermal synthesis. Here, we report an economical and sustainable route for SSZ-13 synthesis by recycling and reusing the OSDA-containing waste liquids. The TMAdaOH concentration in waste liquids, determined by a bromocresol green colorimetric method, was found to be a key factor for SSZ-13 crystallization. The SSZ-13 zeolite synthesized under optimized conditions demonstrates similar physicochemical properties (surface area, porosity, crystallinity, Si/Al ratio, etc.) as that of the conventional synthetic approach. We then used the waste liquid-derived SSZ-13 as the parent zeolite to synthesize Cu ion-exchanged SSZ-13 (i.e., Cu-SSZ-13) for ammonia-mediated selective catalytic reduction of NOx (NH3-SCR) and observed a higher activity as well as better hydrothermal stability than Cu-SSZ-13 by conventional synthesis. In situ infrared and ultraviolet-visible spectroscopy investigations revealed that the superior NH3-SCR performance of waste liquid-derived Cu-SSZ-13 results from a higher density of Cu2+ sites coordinated to paired Al centers on the zeolite framework. The technoeconomic analysis highlights that recycling OSDA-containing waste liquids could reduce the raw material cost of SSZ-13 synthesis by 49.4% (mainly because of the higher utilization efficiency of TMAdaOH) and, meanwhile, the discharging of wastewater by 45.7%.

Graphene aerogel loaded with CeO2 as a catalyst for selective catalytic reduction of NOx with NH3 at low temperature

NH3 selective catalytic reduction (NH3-SCR) has been a common method for eliminating nitrogen oxides (NOx) from the flue gas. The low-temperature denitrification has sparked widespread concern. Here, a CeO2/graphene aerogel (CeO2/GA) catalyst material was synthesized by a one-step hydrothermal method using a three-dimensional (3-D) porous graphene aerogel structure as a carrier for NH3-SCR at low-temperature. The presence of nanoparticle CeO2 inhibited agglomeration between graphene sheets, while the graphene aerogel as a carrier produced a porous structure and improved nanoparticle dispersal. The specific surface area of composite catalyst material was 178.68 m2/g. Catalysts with efficient charge transfer and abundant chemisorbed oxygen promoted redox reactions, more acidic sites were essential to improving catalytic activity. At 270 °C, the NOx conversion (94.9%) of this catalyst was 2.9 times higher than that of pure CeO2 and it demonstrated good N2 selectivity and catalytic stability.

Research Progress on Sulfur Deactivation and Regeneration over Cu-CHA Zeolite Catalyst

Benefiting from the exceptional selective catalytic reduction of NOx with ammonia (NH3-SCR) activity, excellent N2 selectivity, and superior hydrothermal durability, the Cu2+-exchanged zeolite catalyst with a chabazite structure (Cu-CHA) has been considered the predominant SCR catalyst in nitrogen oxide (NOx) abatement. However, sulfur poisoning remains one of the most significant deterrents to the catalyst in real applications. This review summarizes the NH3-SCR reaction mechanism on Cu-CHA, including the active sites and the nature of hydrothermal aging resistance. On the basis of the NH3-SCR reaction mechanism, the review gives a comprehensive summary of sulfate species, sulfate loading, emitted gaseous composition, and the impact of exposure temperature/time on Cu-CHA. The nature of the regeneration of sulfated catalysts is also covered in this review. The review gives a valuable summary of new insights into the matching between the design of NH3-SCR activity and sulfur resistance, highlighting the opportunities and challenges presented by Cu-CHA. Guidance for future sulfur poisoning diagnosis, effective regeneration strategies, and a design for an efficient catalyst for the aftertreatment system (ATS) are proposed to minimize the deterioration of NOx abatement in the future. Finally, we call for more attention to be paid to the effects of PO43- and metal co-cations with sulfur in the ATS.

Advances and perspectives from a decade of collaborative efforts on zeolites for selective catalytic reduction of NOx

Nitrogen oxides (NOx) is a major air pollutant and its release is regulated by increasingly stringent legislation. Selective catalytic reduction using ammonia as a reductant (NH3-SCR) is the most widely applied method to reduce NOx from diesel vehicle exhaust. Significant technological achievements have been developed in the last 10–15 years to minimize NOx by NH3-SCR, particularly using Cu-containing small-pore zeolites as active and stable catalysts. In the present perspective, we highlight some of the most noteworthy advances achieved by industry and academia on the understanding of the unique reaction mechanism of NH3-SCR over Cu-zeolites. With the increased understanding, researchers have been able to rationalize the design and realization of new Cu-zeolite catalysts. Although light-duty diesel vehicles will be electrified in the near future, heavy-duty diesel vehicles will continue to play a large role in future powertrain solutions even beyond 2030. Hence, we highlight some of the challenges and perspectives moving forward.

PTFE-Modified Mn-Co-Based Catalytic Ceramic Filters with H2O Resistance for Low-Temperature NH3-SCR

Mn-Co-based catalysts were loaded to ceramic filters element by impregnation for the coprocessing of dust and nitrogen oxide (NOx) in flue gas. The influence of the Mn/Co ratio and loading on the catalytic performance was investigated. The Mn-Co-based catalytic ceramic filter with a Mn/Co molar ratio of 2/1 can achieve 99% NO conversion by selective catalytic reduction of NOx with NH3 (NH3-SCR) in the temperature range of 100−180 °C, but its resistance to H2O was relatively poor. The filter element was modified by PTFE to improve the H2O resistance. After modification, the catalytic ceramic filter showed superior resistance to H2O and SO2 at low temperatures (100–180 °C) and satisfactory self-cleaning performance.

Self-assembled biomineralized MnOx for low temperature selective catalytic reduction of NOx

A self-assembled biomineralized MnOx materials was prepared by a simple liquid phase co-precipitation method for selective catalytic reduction (SCR) of nitrogen oxides (NOx). Biomineralized MnOx exhibited great SCR performance (achieve > 99% NOx conversion at 100 °C) and high N2 selectivity (exceed 70% at 75–200 °C). The effects of biomineralized materials on physiochemical properties of catalyst were investigated by various characterization methods. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results showed that the crystal structure and the morphologies of MnOx and biomineralized MnOx are remained the same. In order to eliminate the effect of specific surface area, the rate of specific reaction for biomineralized MnOx was calculated to be about twice than that of MnOx. In-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) analyze intermediates during SCR, and speculated that biomineralized MnOx catalyst may mainly follow the Langmuir-Hinshelwood(L-H) mechanism below 200 ℃. The above excellent N2 selectivity can be attributed to the fast NOx specific reaction rate, form Mn-O-C and Mn-C-N structure, provide abundant oxygen vacancies, and high Mn3+/Mn atomic ratio on the catalyst surface. Moreover, biomineralized MnOx possessed a better catalytic cycle performance due to the synergistic effect between biomass and Mn species. Therefore, a reasonable preparation method is proposed to realize the industrial application of biomineralized manganese oxide.

Recent Advances in MnOx/CeO2-Based Ternary Composites for Selective Catalytic Reduction of NOx by NH3: A Review

Recently, manganese oxides (MnOx)/cerium(IV) oxide (CeO2) composites have attracted widespread attention for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with ammonia (NH3), which exhibit outstanding catalytic performance owing to unique features, such as a large oxygen storage capacity, excellent low-temperature activity, and strong mechanical strength. The intimate contact between the components can effectively accelerate the charge transfer to enhance the electron–hole separation efficiency. Nevertheless, MnOx/CeO2 still reveals some deficiencies in the practical application process because of poor thermal stability, and a low reduction efficiency. Constructing MnOx/CeO2 with other semiconductors is the most effective strategy to further improve catalytic performance. In this article, we discuss progress in the field of MnOx/CeO2-based ternary composites with an emphasis on the SCR of NOx by NH3. Recent progress in their fabrication and application, including suitable examples from the relevant literature, are analyzed and summarized. In addition, the interaction mechanisms between MnOx/CeO2 catalysts and NOx pollutants are comprehensively dissected. Finally, the review provides basic insights into prospects and challenges for the advancement of MnOx/CeO2-based ternary catalysts.

Research on structure-activity relationship dominated by template agents for mesoporous FeTi catalysts in SCR of NO with NH3

Abstract To gain more insight into the effect of the template used for preparing FeTi catalysts for the selective catalytic reduction (SCR) of nitrogen oxide (NOx) on the catalytic structure and performance, a systematic study on FeTi catalysts synthesized using F127, CTAB, and PEG as templates is described. The catalysts exhibited outstanding performance in the SCR of NOx with NH3, exceeding that of a pure FeTi catalyst. Especially, the CTAB-modified FeTi catalyst achieved 100% of NOx conversion at 200 °C. A thorough morphological characterization showed that, compared with F127 and PEG, CTAB induced the formation of smaller catalyst particles with larger surface area, which could provide more acid sites and facilitate the adsorption of NH3, thus contributing to the enhanced activity. In addition, in-situ DRIFTS revealed that the reaction followed the Langmuir–Hinshelwood and Eley–Rideal mechanism, with the coordination of NH3 on Lewis acid sites and the bridged nitrate playing key roles in improving the catalytic performance.