High N2 Selectivity Research Articles

Study on the effect and mechanism of support structure and characteristic on Ag-based catalysts for low-temperature selective catalytic oxidation of ammonia

Herein, the influence of support type and properties on the catalytic activity and selectivity of Ag-based NH3-SCO catalyst was studied through the evaluation of NH3-SCO performance, the physicochemical characterization of H2-TPR, NH3-TPD, N2 isothermal adsorption–desorption, XPR and XPS, and the mechanism study of 1H MAS NMR, In-situ DRIFTS and DFT calculations. Ag/nano-TiO2, Ag/Al2O3, and Ag/MnO2 all showed better NH3-SCO activity because of more abundant Brønsted and Lewis acid sites of Al2O3 and TiO2 and more actual Ag loading amount due to the larger specific surface area and suitable surface chemistry. The N2 selectivity of Ag/nano-TiO2 is significantly better, which may be due to the highly dispersed Ag species and the abundant Brønsted acid sites with higher N2 selectivity. The mechanism study showed that the terminal hydroxyl was the preferred consumption target of Ag species, and this consumption promoted the effective dispersion and stable anchoring of Ag on the TiO2 surface.

Precisely controlled bimetallic nanocatalysts on mesoporous silica nanoparticle supports for highly efficient and selective nitrate reduction

Monodisperse, bimetallic nanocatalysts, homogeneously supported on mesoporous silica nanoparticles, are demonstrated as highly active, reducing catalysts for rapid and selective nitrate transformation. For this, we finely controlled catalyst size and composition based on new synthesis strategies. Specifically, atomic clusters of Mreducing/Cu nanocatalysts (Mreducing = Pd, Pt) were optimized for nitrate reduction via subsequent Mreducing impregnation (Mreducing/Cu/Mreducing combinations). Reaction kinetics were observed to be affected by the ratio of Mreducing to Cu, for which Pd−rich Pd/Cu/Pd nanocatalysts showed better performance than Cu−rich analogs. Product selectivity (ammonium vs. nitrogen) was highly correlated with nanocatalyst morphology, with nitrogen gas (dominant) selectivity observed for relatively larger Pd particles. Lastly, MSN−Pd/Cu/Pd catalyst are highly stable in water, with no catalyst deterioration over multiple reactions (10 cycles), while maintaining consistently high reaction rates and N2 selectivity. Taken together, this study demonstrates the critical importnace of precise catalyst control and stability towards optimizing nitrate reduction processes.

High N2-selectivity of nitrite reduction by palladium-laden nanocomposite with self-sufficient electron donators

Selectively reducing nitrite to gaseous nitrogen (N2) with an effective and recyclable fashion stands as an attractive alternative for treating the relevant wastewater. Herein, a Pd-based nanocomposite (Pd@EDA-CMPS) was subtly assembled by encapsulating Pd(0) nanoparticles into a porous polystyrene carrier, which was aforehand functionalized with ethylenediamine (EDA) as the endogenous electron donator. Systematical macroscopic experiments confirm that the pre-grafted EDA groups can substantially stimulate the catalytic activity of the laden Pd(0) nanoparticles with high removal efficiency and N2 selectivity of Pd@EDA-CMPS toward nitrite; specifically, high N2 selectivity (86%) was achieved by Pd@EDA-CMPS with an excellent anti-interference ability against competing anion and a broad pH-range applicability (4–11), whereas no N2 production was detected for its counterparts (CMPS, EDA-CMPS, and Pd@CMPS). Spectroscopic analyses reveal that the grafted EDA groups played a decisive role in the formation of H-loaded Pd(0) nanoparticles inside the porous substrate, which joint with the unique pH-buffering ability of EDA drove the reaction to the production of nitrogen (N2) rather than ammonia (NH3). The exhausted Pd@EDA-CMPS can be promisingly regenerated by NaOH (eluting) and NaBH4 (restoring) solution without obvious loss in treatment capacity and N2 selectivity. This work provides a feasible strategy for catalytically reducing nitrite into N2 without the provision of exogenous reductor such as hydrogen.

Regulating active oxygen species and acidity of Ca doped LaMnO3 perovskite catalysts toward efficient n-butylamine oxidation

It is of great significance to design catalysts with high activity, N2 selectivity and stability for nitrogen-containing volatile organic compound (NVOC) catalytic purification. Meanwhile, the role of oxygen species in NVOC catalytic oxidation is still ambiguous. Herein, the oxygen species of La-Mn perovskite catalysts were engineered by doping Ca in La site to elucidate their role in catalytic n-butylamine oxidation. Results demonstrate that La0.9Ca0.1MnO3 exhibits the highest activity owing to its abundant adsorbed oxygen species and high surface area, achieving 100 % n-butylamine conversion (500 ppm; GHSV=60,000 mL g−1h−1) at 200 °C with N2 selectivity of ca. 95 %. More adsorbed oxygen species generated due to Ca doping accelerates the oxidation rate and C-C cleavage of alcohol and acetate intermediates, resulting in higher CO2 yield. Meanwhile, Ca-doping also modifies the acidity of catalysts, which affects the adsorption/desorption process of alkaline substances and yield of nitrogen-containing products. In addition, La0.9Ca0.1MnO3 shows superior stability, high water and SO2 resistance, and acceptable activity for other common NVOCs, demonstrating a promising catalyst for NVOC oxidation even under harsh operation conditions. Furthermore, the toxic effect of pollutant or products during n-butylamine catalytic oxidation on the growth of Chlorella Vulgaris was investigated and results suggest that catalytic oxidation is an environmentally friendly method for NVOC purification. This work sheds light on the relationships among oxygen species, catalyst acidity, and n-butylamine catalytic oxidation, which expand the understanding of rational design of efficient catalyst for NVOC oxidation.

Eley−Rideal path enhanced NH3-SCR: Central Fe atoms activation for electron transfer promotion

Manganese modified Fe2O3 catalyst is a promising candidate to replace the commercial NH3-SCR catalyst for controlling NOx emission due to its superior performance and N2 selectivity at low temperature. In order to elucidate the effects of different modification methods of Mn on physicochemical properties and reaction mechanism in Fe-Mn binary catalysts, two kinds of Mn modified Fe2O3 are prepared by co-precipitation and impregnation method, respectively. Compared with MnO2 loaded Fe2O3, Mn doped Fe2O3 achieves above 85 % of NOx conversion with 20 % increase in N2 selectivity within 100–200°C. Transient reaction experiments and DFT calculation results prove that doping Mn effectively increases the reaction rate of the main reaction and reduces the formation of N2O through Eley−Rideal path. The formation of multiple Fe-O-Mn structures after Mn doping facilities the formation of coordination bond between the central Fe atoms and NH3 via modulating local charge density of Fe atoms, effectively improving the adsorption of NH3 and preventing its excessive oxidation, which leads to high activity and N2 selectivity at low temperature. This mechanism provides theoretical support for increasing the activity and N2 selectivity of NH3-SCR catalysts at low temperature and gains clear insight on the interaction between binary metal oxides.

A High-Performance Mn/TiO2 Catalyst with a High Solid Content for Selective Catalytic Reduction of NO at Low-Temperatures.

Mn/TiO2 catalysts with varying solid contents were innovatively prepared by the sol-gel method and were used for selective catalytic reduction of NO at low temperatures using NH3 (NH3-SCR) as the reducing agent. Surprisingly, it was found that as the solid content of the sol increased, the catalytic activity of the developed Mn/TiO2 catalyst gradually increased, showing excellent catalytic performance. Notably, the Mn/TiO2 (50%) catalyst demonstrates outstanding denitration performance, achieving a 96% NO conversion rate at 100 °C under a volume hourly space velocity (VHSV) of 24,000 h-1, while maintaining high N2 selectivity and stability. It was discovered that as the solid content increased, the catalyst's specific surface area (SSA), surface Mn4+ concentration, chemisorbed oxygen, chemisorption of NH3, and catalytic reducibility all improved, thereby enhancing the catalytic efficiency of NH3-SCR in degrading NO. Moreover, NH3 at the Lewis acidic sites and NH4+ at the Bronsted acidic sites of the catalyst were capable of reacting with NO. Conversely, NO and NO2 adsorbed on the catalyst, along with bidentate and monodentate nitrates, were unable to react with NH3 at low temperatures. Consequently, the developed catalyst's low-temperature catalytic reaction mechanism aligns with the E-R mechanism.

Unraveling the Mechanistic Origin of High N2 Selectivity in Ammonia Selective Catalytic Oxidation on CuO-Based Catalyst.

NH3 emissions from industrial sources and possibly future energy production constitute a threat to human health because of their toxicity and participation in PM2.5 formation. Ammonia selective catalytic oxidation to N2 (NH3-SCO) is a promising route for NH3 emission control, but the mechanistic origin of achieving high N2 selectivity remains elusive. Here we constructed a highly N2-selective CuO/TiO2 catalyst and proposed a CuOx dimer active site based on the observation of a quadratic dependence of NH3-SCO reaction rate on CuOx loading, ac-STEM, and ab initio thermodynamic analysis. Combining this with the identification of a critical N2H4 intermediate by in situ DRIFTS characterization, a comprehensive N2H4-mediated reaction pathway was proposed by DFT calculations. The high N2 selectivity originated from the preference for NH2 coupling to generate N2H4 over NH2 dehydrogenation on the CuOx dimer active site. This work could pave the way for the rational design of efficient NH3-SCO catalysts.

Surface B-site exsolving double perovskite supported copper use for control the catalytic performance for high-temperature CO-SCR

There is little research on the use of double perovskites (AA'BB'O6) in the CO reduction NO. Therefore, a series of CuX/LCM catalysts which supported CuO on double perovskite were prepared by sol-gel method and initial wet impregnation method. The best activity while preserving the double perovskite structure is found in Cu5/LCM with 5 % Cu. The Cu5/R-LCM catalyst was made by performing a high-temperature exsolution treatment with LCM and loading R-LCM with CuO in order to address the issue of unstable high-temperature activity and low N2 conversion of Cu5/LCM. The findings demonstrate that Cu5/R-LCM has a high N2 selectivity and an excellent conversion rate of NO at high-temperatures. The interaction between Co and Cu (Cu2++Co2+↔Cu++Co3+) on the Cu5/R-LCM catalyst inhibits CuO from being reduced at high-temperatures and exhibits good high-temperature stability. The surface synergistic oxygen vacancies (SSOVs) created by Co and Cu can encourage the dissociation of NO and produce [N] and [O] free radicals. [N] radicals are more likely to form on the surface of Cu5/R-LCM than on Cu5/LCM, and after migrating, they will combine to form N2, improving N2 selectivity. These factors cause Cu5/R-LCM to have superior N2 selectivity and high-temperature catalytic activity than Cu5/LCM.

Selective catalytic oxidation of DMF over Cu-Ce/H-MOR by modulating the surface active sites

Selective catalytic oxidation of the hazardous DMF exhaust gas presents a significant challenge in balancing oxidation activity and products selectivity (CO, NOx, N2, etc.). It is found that Cu/H-MOR demonstrates superior performance for DMF oxidation compared to CuO on other supports (γ-Al2O3, HY, ZSM-5) in terms of product selectivity and stability. The geometric and electronic structures of CuO active sites in Cu/H-MOR have been regulated by CeO2 promoter, leading to an increase in the ratio of active CuO (highly dispersed CuO and Cu+ specie). As a result, the oxidation activity and stability of the Cu/H-MOR catalyst were enhanced for DMF selective catalytic oxidation. However, excessive CuO or CeO2 content led to decreased N2 selectivity due to over-high oxidation activity. It is also revealed that Ce3+ species, active CuO species, and surface acid sites play a critical role in internal selective catalytic reduction reaction during DMF oxidation. The 10Cu-Ce/H-MOR (1/4) catalyst exhibited both high oxidation activity and internal selective catalytic reduction activity due to its abundance of active CuO specie as well as Ce3+ species and surface acid sites. Consequently, the 10Cu-Ce/H-MOR (1/4) catalyst demonstrated the widest temperature window for DMF oxidation with high N2 selectivity. These findings emphasize the importance of surface active sites modification for DMF selective catalytic oxidation.

Recent progress of Rh‐based three‐way catalysts

AbstractThree‐way catalysts are widely used to control criterion pollutant emissions from the increasing gasoline engines. With the stringent requirements of automotive pollutant emission standards in various countries, Rh has become an irreplaceable component of three‐way catalysts due to its superior NOx elimination, high N2 selectivity, and simultaneous elimination of CO and hydrocarbons. In this review, we systematically review the recent development of Rh‐based three‐way catalysts in terms of potential supports and effective active center construction strategies. We further summarize the key role of Rh metal in the three‐way catalytic mechanism and reaction kinetics. Finally, we conclude the current challenges and future opportunities facing Rh‐based catalysts. It is believed that based on the deep understanding of Rh‐based three‐way catalysts, the design of Rh‐based catalysts with good low‐temperature catalytic performance and low cost is expected to be realized in the future.

Utilizing the immanent chloride ions in wastewater for reactive chlorine species photogeneration towards effective ammonia nitrogen removal

Utilizing the immanent salt (Cl–) in wastewater to generate reactive chlorine species (RCS) satisfies the future needs for sustainable, on-demand, and decentralized ammonia nitrogen (NH4+-N) removal. The microstructural evolution of bismuth oxychloride (BiOCl) photocatalyst under irradiation benefits for overcoming the competition between Cl– and H2O oxidation and achieving high N2 selectivity. Herein, internal electric field (IEF) engineering by carbon doping is applied to promote photocatalytic RCS generation rate over BiOCl. The carbon dopant not only enhances the IEF intensity of BiOCl by a factor of 2.1 times for carrier dynamics promotion, but also improves Cl– oxidation against H2O oxidation. An RCS production rate of 0.23 mg/L min−1 is realized over carbon-doped BiOCl (C-BiOCl) through the accelerated interaction between lattice and environmental Cl–, which is twice that of the undoped BiOCl (0.11 mg/L min−1). The relation between IEF intensity and RCS generation rate over C-BiOCl manifests a correlation coefficient of 0.96. Effective NH4+-N degradation with N2 selectivity of >99% is validated. The system is competent in dealing with saline NH4+-N wastewater with a wide range of NH4+-N (20∼200 mg N/L) and NaCl (6∼10 g/L) concentrations. In the treatment of realistic landfill leachate (884 mg N/L NH4+-N), C-BiOCl displays a photocatalytic NH4+-N removal efficiency of up to 95.6% while maintaining the NO2−-N (∼2 mg N/L) and NO3−-N (∼40 mg N/L) levels. This system provided an interesting and innovative idea for wastewater self-purification.

Performance of ammonia catalytic combustion over Cu-CeOx catalyst and the impact of oxygen concentration

Ammonia has long been regarded as a high-quality zero-carbon fuel; however, limitations in its combustion characteristics have restricted its practical applications. Catalytic combustion is considered an effective solution to overcome the challenges associated with ammonia combustion. In this study, we successfully synthesized a copper-cerium binary catalyst (Cu-CeOx) using the sol-gel method, demonstrating outstanding performance for NH3 catalytic combustion. Through in-situ DRIFTS results, we observed that the 15Cu-CeOx catalyst exhibits both i-SCR and -NH mechanisms. The oxygen concentration affects the N2 selectivity by modulating the overoxidation of NH3. Under high oxygen concentrations, high temperatures promote the excessive oxidation of NH3, and ammonia combustion through the i-SCR mechanism. Conversely, the oxygen concentration was equal to NH3 reaction stoichiometry, the overoxidation of NH3 is limited, and ammonia combustion proceeds through the NH mechanism, resulting in higher N2 selectivity.

Designing ammonia oxidation catalysts via physical mixing of Pt/SiO2 and Cu/ZSM-5

Ammonia (NH3) is emerging as a carbon-neutral fuel alternative; however, its use poses environmental and health risks due to NH3 slip. The NH3-selective catalytic oxidation (NH3-SCO) process, which converts NH3 into N2 and H2O, offers a solution. However, it faces challenges with respect to the formation of byproducts, particularly N2O and NOx. This study focuses on designing NH3-SCO catalysts to enhance low temperature NH3 conversion efficiency while minimizing undesired byproducts. Pt/SiO2 catalysts were synthesized with adjusted Pt particle sizes to improve the NH3-SCO activity and were physically mixed with Cu/ZSM-5 to overcome the low N2 selectivity of Pt-based catalysts by utilizing the selective catalytic reduction (SCR) ability of Cu/ZSM-5. Pt1Cu3 catalyst, a physical mixture of Pt/SiO2 and Cu/ZSM-5 in a 1:3 mass ratio, was found to be the most effective, achieving complete NH3 oxidation at 250 ℃ while maintaining a high N2 selectivity of approximately 80%. Further investigation revealed that the performance of the Pt1Cu3 catalyst was significantly influenced by the arrangement and physical proximity of the Pt/SiO2 and Cu/ZSM-5 catalysts, with a closely contacted mixture showing synergistic effects that enhanced activity and selectivity. These results suggest that the Pt1Cu3 catalyst offers a promising solution for NH3 emission control by utilizing a balanced approach that combines SCO and SCR reactions.

The Development of the Regenerable Catalytic System in Selective Catalytic Oxidation of Ammonia with High N2 Selectivity.

Supported particulate noble-metal catalysts are widely used in industrial catalytic reactions. However, these metal species, whether in the form of nanoparticles or highly dispersed entities, tend to aggregate during reactions, leading to a reduced activity or selectivity. Addressing the frequent necessity for the replacement of industrial catalysts remains a significant challenge. Herein, we demonstrate the feasibility of the 'regenerable catalytic system' exemplified by selective catalytic oxidation of ammonia (NH3-SCO) employing Ag/Al2O3 catalysts. Results demonstrate that our highly dispersed Ag catalyst (Ag HD) maintains >90% N2 selectivity at 80% NH3 conversion and >80% N2 selectivity at 100% NH3 conversion after enduring 5 cycles of reducible aggregation and oxidative dispersion. Moreover, it consistently upholds over 98% N2 selectivity at 100% NH3 conversion after 10 cycles of Ar treatment. During the aggregation-dispersion process, the Ag HD catalyst intentionally aggregated into Ag nanoparticles (Ag NP) after H2 reduction and exhibited remarkable regenerable capabilities, returning to the Ag HD state after calcination in the air. This structural evolution was characterized through in situ transmission electron microscopy, atomically resolved high-angle annular dark-field scanning transmission electron microscopy, and X-ray absorption spectroscopy, revealing the on-site oxidative dispersion of Ag NP. Additionally, in situ diffuse reflectance infrared Fourier transform spectroscopy provided insights into the exceptional N2 selectivity on Ag HD catalysts, elucidating the critical role of NO+ intermediates. Our findings suggest a sustainable and cost-effective solution for various industry applications.

Nanoscale Precursor Distribution by Microfluidization for Scalable Production of Highly Efficient Thermocatalysts

AbstractThe preparation of two‐dimensional (2D) materials often requires complicated exfoliation procedures having low yields. The exfoliated nanosheets are prone to thermal aggregation and unsuitable for thermocatalysis. Herein, a scalable approach produces 2D catalyst precursors well‐distributed and mixed at the nanoscale. Using continuous microfluidization and single‐layer layered double hydroxide (LDH) synthesis, the prepared suspension contained exfoliated hexagonal boron nitride (h‐BN) nanosheets and single‐layer LDHs. The increased contact area between h‐BN and LDHs enables the formation of highly dispersed MnCoAl mixed metal oxide nanoparticles anchored on h‐BN nanosheets after calcination. In the selective catalytic reduction of NOx with NH3 (NH3‐SCR, a representative thermocatalytic application), this nanocomposite demonstrates a record turnover frequency of 0.772 h−1 among reported Mn‐based NH3‐SCR catalysts, with high NOx conversion and high N2 selectivity at low temperatures. By creating 2D precursors mixed at the nanoscale, this new synthetic approach can realize the scalable production of highly efficient thermocatalysts.

Selective oxidation of ammonia nitrogen to nitrogen gas by Fe2+/PMS/Cl−: The role of reactive chlorine species

Ammonia nitrogen (NH4+-N) can pose a threat to ecosystems and human health. Many methods have been used for the removal of NH4+-N. In particular, reactive chlorine species (RCS, including Cl·, Cl2·−, and ClO·) show superior performance for the selective oxidation of NH4+-N to nitrogen gas (N2). Herein, Fe2+/peroxymonosulfate (PMS)/Cl− process was proposed to generate RCS for the conversion of NH4+-N to N2, in which Fe2+ was used as the activator of PMS in the presence of Cl−. Fe2+, PMS, and Cl− concentrations could affect the removal of NH4+-N in Fe2+/PMS/Cl− process. Fe2+/PMS/Cl− exhibited good performance in removing NH4+-N at pH 3.5–8.0. At all investigated conditions, NH4+-N was mainly converted to N2, and N2 selectivity was more than 90 %. Under optimal conditions, 50 % of NH4+-N was removed in 5 min, and the removal efficiency reached the maximum of 96 % within 120 min with the high N2 selectivity of 100 %. The electron spin resonance tests, scavenging experiments, and probe experiments demonstrated the generation of RCS in Fe2+/PMS/Cl− reaction system. Experimental results and model analysis consistently proved that ClO· and Cl· were crucial radicals during the selective oxidation of NH4+-N, especially ClO·. Fe2+/PMS/Cl− system could remove NH4+-N and COD simultaneously in real wastewater. This study can provide an efficient strategy for the removal of NH4+-N.

Disclosing the enhanced NH3-SCR-DeNOx activity of Cu-containing zeolite Y prepared with 15-Crown-5

The phase-pure zeolite Y with a high n(Si)/n(Al) ratio is obtained with the cyclic polyether 15-Crown-5 as a structure-directing agent. In copper-exchanged for this new zeolite outperformed other Cu-containing zeolite Y counterparts during NH3-SCR-DeNOx with more than 80% NO conversion and more than 85% N2 selectivity in the temperature range of 100 – 500 °C. The presence of Cu+ species located in sodalite cages with elevated redox cyclability guarantees high activity and N2 selectivity up to 400 °C over CuY-Crown. Above 400 °C, a high activity and N2 selectivity are related to the accessibility of chemisorbed NH3 to the gaseous NO during the NH3-SCR-DeNOx.

Highly active and stable VOx/TiO2 nanosheets for low-temperature NH3-SCR of NO: Structure-directing role of support

Low-temperature NH3-SCR over conventional catalysts based on V2O5/TiO2 is significantly limited by the narrow range of operating temperatures and poor activity at low temperatures. Herein, a novel catalyst consisting of defective TiO2 nanosheets supported vanadia (V/TNS) is successfully developed for the low-temperature NH3-SCR of NO. The V/TNS catalyst demonstrated excellent SCR performance, achieving over 95 % conversion with high N2 selectivity (>90 %) over a wide temperature range of 140–380 °C. Importantly, V/TNS was highly resistant to H2O and SO2 poisoning during 30 h of continuous operation, maintaining an NO conversion efficiency that exceeded 92 % at 180 °C. In contrast, a high-surface-area anatase TiO2 particle-supported catalyst (V/TiO2(A)) suffered from catalytic deactivation. Detailed characterization revealed that the TNS support, with its abundant surface defects and high surface area, improved vanadia dispersion and facilitated the formation of surface V4+ species and oxygen vacancies. These factors synergistically enhanced the adsorption and activation of NH3 and NOx, boosting catalytic performance. Moreover, the presence of SO2 had a notable inhibitory effect on the adsorption and activation of NH3 and NOx and their reactions on V/TiO2(A), while these detrimental effects were considerably mitigated on V/TNS.

Efficient Cu-Co Dual-Site promotes selective catalytic oxidation of ammonia over cobalt based catalysts

Selective catalytic oxidation of NH3 (NH3-SCO) into N2 and H2O is an efficient method to eliminate excessive NH3 emission from stock farming, agriculture, industrial sectors and NH3 slip in coal-fired power plants and diesel vehicles. However, it is a great challenge to develop the Co3O4 catalyst with high activity and high N2 selectivity at low temperature. Herein, a series of Cu doped Co3O4 catalysts is designed and synthesized, with discovering the role of Co-O bond strength by copper regulation in modulating oxygen vacancies and lattice oxygen to enhance the intrinsic activity and N2 selectivity of NH3-SCO. The Cu1Co2O4 catalyst (93 % NH3 conversion and 80 % N2 selectivity at 160 °C) achieves a higher catalytic performance compared with Co3O4 (78 % NH3 conversion and 50 % N2 selectivity at 160 °C). In addition, the N2 generation rate by normalizing over specific surface area for Cu1Co2O4 (13.1 μmol m-2h−1) is 1.7 times to that of Co3O4 (8.0 μmol m-2h−1), and the apparent activation energy of Cu1Co2O4 (36.7 kJ mol−1) is lower compared to that of Co3O4 (59.8 kJ mol−1). Reactive oxygen species and enhanced electron transfer promote the oxidation of NH3 to nitrate species, which can be further converted to N2 rather than N2O by remaining NH3 on the Cu site. The Cu-Co dual sites significantly contribute to the catalytic activity and N2 selectivity. This doping strategy is beneficial for the development of Co-O bond strength modulation in spinel catalyst and also provides a new idea for improving the NH3-SCO activity and N2 selectivity of Co-based spinel.

Engineering the surface properties of CeVO4 catalysts to improve low temperature De-NOx performance through regulating pH value in synthesis process

The presence of quick electron transfer in metal oxides can well promote selective catalytic reduction (SCR) of NOx with NH3. Here, a series of CeVO4-X (X = 4, 6, 8, 10 and 12) catalysts with engineering the surface properties were successfully synthesized via controlling pH values in the hydrothermal process. The catalysts were evaluated in the NH3-SCR reaction in the temperature range of 90–420 °C. Among them, the CeVO4-8 catalyst with nanorods structure displayed the highest catalytic activity, achieving over 90 % NO conversion between 180 and 390 °C. It also showed high N2 selectivity and good tolerance to H2O and SO2. The effect of different pH values on the catalytic activity and microstructure of CeVO4 catalysts was comprehensively characterized using various techniques such as XRD, Raman, SEM, HR-TEM, N2 adsorption-desorption, H2-TPR, O2/NH3/NO-TPD, XPS, and in-situ DRIFTS. The characterization results revealed that the variation in catalytic activity among these catalysts is attributed to the difference in their surface properties, which were tuned by changing the pH values during synthesis process, despite having the same crystal phase of CeVO4. The superior catalytic performance of the CeVO4-8 catalyst, particularly at low temperature, can be attributed to its higher specific surface area, enhanced acidity, and the electron transfer between cerium and vanadium species (Ce4+ + V4+ ↔ Ce3+ + V5+), consequently resulting in increased redox capacity and facilitating the adsorption and activation of NH3 and NO molecules. This study broadens the applications of CeVO4 in the field of low temperature NOx removal.