MnOx-CuOx cordierite catalyst for selective catalytic oxidation of the NO at low temperature

Experimental investigation on sucrose/alumina catalyst coated converter in gasoline engine exhaust gas

In this study, a modified catalytic converter was employed to treat the harmful exhaust gas pollutants of a twin-cylinder, four-stroke spark-ignition engine. This research mainly focuses on the emission reduction of unburnt hydrocarbons, carbon monoxide, and nitrogen oxides at low light-off temperatures. A sucrolite catalyst (sucrolite) was coated over the metallic substrate present inside the catalytic converter, and exhaust gas was allowed to pass through it. A scanning electron microscope, X-ray diffraction, and Fourier transform infrared spectroscopy were used to investigate the changes in morphology, chemical compounds, and functional group elements caused by the reactions. Catalytic reactions were studied by varying the engine loads and bed temperatures, and the results were compared with those of the commercial catalytic converter. The results show that sucrose present in the catalyst was suitable at low temperatures while alumina was suitable for a wide range of temperatures. In the case of the modified catalytic converter, the maximum catalytic conversion efficiencies achieved for oxidizing CO and HC were 70.73% and 85.14%, respectively, and for reduction reaction at NO_x was 60.22% which is around 42% higher than in commercial catalytic converter. As a result, this study claims that sucrolite catalyst is effective for low-temperature exhaust gas.

Experimental and theoretical studies on NO selective catalytic oxidation over α-MnO2

Based on the experimental and theoretical methods, the NO selective catalytic oxidation process was proposed. The experimental results indicated that lattice oxygen was the active site for NO oxide over the α-MnO₂(110) surface. In the theoretical study, DFT (density functional theory) and periodic slab modeling were performed on an α-MnO₂(110) surface, and two possible NO oxidation mechanisms over the surface were proposed. The non-defect α-MnO₂(110) surface showed the highest stability, and the surface O_s (the second layer oxygen atoms) position was the most active and stable site. O₂ molecule enhanced the joint adsorption process of two NO molecules. The reaction process, including O₂ dissociation and O=N-O-O-N=O formation, was calculated to carry out the NO catalytic oxidation mechanism over α-MnO₂(110). The results showed that NO oxidation over the α-MnO₂(110) surface exhibited the greatest possibility following the route of O=N-O-O-N=O formation. Meanwhile, the formation of O=N-O-O-N=O was the rate-determining step.

Carbon-based zero valent iron catalyst for NOX removal at low temperatures: performance and kinetic study

In order to solve the problem of nitrous oxide (NO_X) removal at low temperatures, the carbon-based zero valent iron (C-ZFe) catalyst was prepared and studied. According to the kinetic study and the obtained kinetic parameters, the De-NO_X reactor was designed to provide information for industrial applications. The box-behnken experimental design (BBD) was used to study the performance of C-ZFe, and the optimized operating parameters were obtained as the temperature was 408.15 K, the catalyst bed height was 140 cm (the space velocity was 459 h^-1), the concentration of NO was 550 ppm, under which the NO_X conversion was 72.7%. A kinetic model based on Langmuir-Hinshelwood (L-H) and Mars Van Krevelen mechanism was used to describe the kinetics for the reduction of NO by C-ZFe at low temperatures. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), surface area and pore size distribution measurements, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) results supported the validity of the model proposed. The gas-solid catalytic kinetic process of NO removal by C-ZFe was a quasi-first-order kinetic reaction, the apparent activation energy was 41.57 kJ/mol, and the pre-exponential factor was 2980 min^-1.

Bimetallic modified halloysite particle electrode enhanced electrocatalytic oxidation for the degradation of sulfanilamide

The treatment of antibiotics wastewater by electrocatalytic oxidation has attracted much attention. In the paper, a novel halloysite bimetallic (HLS-Cu-Mn) particle electrode material was prepared and a bench-scale electrocatalytic reaction tank was designed. A three-dimensional electrocatalytic oxidation reactor composed of HLS-Cu-Mn and a bench-scale electrocatalytic reaction tank was used to degrade Sulfanilamide (SA) wastewater. Characterization of the synthesized material was conducted with Scanning electron microscopy (SEM), X-ray polycrystalline powder diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET). The electron spin resonance spectroscopy test results confirmed that HLS-Cu-Mn produced a large number of •OH. The electrochemical workstation confirmed that HLS-Cu-Mn had strong electrocatalytic activity and repolarization ability. Under the optimum preparation conditions and degradation process parameters, the removal efficiency of SA and TOC was 99.84% and 88.95% respectively. The method also has good degradation efficiency for aniline, phenol, herbicides, antibiotics, and dyeing wastewater. It was found that 4 main intermediates appeared in the degradation process by Ultra-high performance liquid chromatography/triple tandem quadrupole mass spectrometry (LC-MS). In sum, it was believed that this work provides a new vision and idea for water treatment.

Remarkable enhancement in the N2 selectivity of NH3-SCR over the CeNb3Fe0.3/TiO2 catalyst in the presence of chlorobenzene

The simultaneous removal of NO_x and dioxins is the frontier of environmental catalysis, which is still in the initial stage and poses several challenges. In this study, a series of CeNb₃Fe_x/TiO₂ (x = 0, 0.3, 0.6, and 1.0) catalysts were prepared by the sol-gel method and examined for the synergistic removal of NO_x and CB. The CeNb₃Fe_0.3/TiO₂ catalyst exhibits an optimum catalytic performance, with an NO_x conversion greater than 95% at 260-380 °C. It also exhibits an optimal CB oxidation activity, in which CB promoted both the NO_x conversion and N₂ selectivity below 250 °C. Moreover, the more favorable ratios of Ce⁴⁺ to Ce³⁺ and plentiful surface-adsorbed oxygen species are the reasons why CeNb₃Fe_0.3/TiO₂ catalyst has better catalytic activity than other catalysts at the lower temperature. Simultaneously, owing to the modulation of Fe to the redox properties of Ce and Nb, the large number of oxygen vacancies and acid sites was generated, and the CeNb₃Fe_0.3/TiO₂ catalyst is beneficial to NO_x reduction and CB oxidation. Furthermore, the results of in situ DRIFTS study reveal the NH₃-SCR reactions over CeNb₃Fe_0.3/TiO₂ catalysts are mainly conformed to by the L-H mechanism (< 350 °C) and E-R mechanism (> 350 °C), respectively, and the multi-pollutant conversion mechanism in the synergistic reaction was systematically studied.

Study on denitration and sulfur removal performance of Mn-Ce supported fly ash catalyst

Nitrogen oxides (NOx) are the main pollutants of air, which mainly come from the combustion of coal and fossil fuels. In this paper, with fly ash used as the catalyst carrier, the effects on the denitration and sulfur resistance of Mn-Ce loading sequence and molar ratio were studied. The catalyst was characterized and analyzed by XRD, XPS, SEM. The results show that when Mn-Ce bimetal is loaded at the same time, Mn ions enter the CeO₂ lattice to form a solid solution of Mn-O-Ce fluorite structure, which makes the catalyst has the best denitration and sulfur resistance. The catalyst denitration performance increases first and then decreases with the increase of Mn-Ce molar ratio. When Mn-Ce is 1:1, the denitration efficiency is higher, the total conversion rate of NO is the highest and the deactivation time is the longest, the catalyst is resistant to sulfur performance is also the best.

A review of Mn-based catalysts for low-temperature NH3-SCR: NOx removal and H2O/SO2 resistance

The development of high-efficiency catalysts is the key to the low-temperature NH₃-SCR technology. The introduction of SO₂ and H₂O will lead to poisoning and deactivation of the catalysts, which severely limits the development and application of NH₃-SCR technology. This review introduces the necessity of NO_x removal, explains the mechanisms of H₂O and SO₂ poisoning on NH₃-SCR catalysts, highlights the Mn-based catalysts of different active metals and supports and their resistance to H₂O and SO₂, and analyses the relationship between metal modification, selection of support and preparation method, morphology and structure design and SO₂/H₂O resistance. Given the current problems, this review points out the future research focus of Mn-based catalysts and also puts forward corresponding countermeasures to solve the existing problems.

NO oxidation performance and kinetics analysis of BaMO3 (M=Mn, Co) perovskite catalysts

Perovskite is an efficient and emerging catalyst for NO oxidation. In this study, BaMnO₃ and BaCoO₃ perovskite catalysts were synthesized by the sol-gel method, and their catalytic oxidation performances of NO were studied. The catalytic performances indicated that BaMnO₃ and BaCoO₃ perovskites had the highest NO oxidation activities with the NO conversions of 78.2% at 350 °C and 84.3% at 310 °C, respectively. The high activities of BaMnO₃ and BaCoO₃ perovskite catalysts were related to the abundant surface adsorption oxygen (O_A = 76.21% and 78.57%, respectively) and the high concentration of Mn⁴⁺ (Mn⁴⁺/Mn = 66.95%) and Co³⁺ (Co³⁺/Co = 63.8%). Moreover, the results of FT-IR and kinetics revealed that NO and O₂ adsorbed on the surface of samples and combined with the B-O band to form bidentate nitrate and bridging nitrate, which eventually was converted into NO₂. The kinetics analysis revealed that the NO oxidation reaction followed the Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms. In addition, the activation energies were 36.453 kJ/mol for BaMnO₃ and 30.081 kJ/mol for BaCoO₃, implying that BaMnO₃ and BaCoO₃ provide low-cost and efficient catalysts, which can be comparable to Pt noble metal catalysts.

Recent advances in selective catalytic oxidation of nitric oxide (NO-SCO) in emissions with excess oxygen: a review on catalysts and mechanisms

Nitric oxides (NO_x, which mainly include more than 90% NO) are one of the major air pollutants leading to a series of environmental problems, such as acid rain, haze, photochemical smog, etc. The selective catalytic oxidation of NO to NO₂ (NO-SCO) is regarded as a key process for the development of selective catalytic reduction of NO_x by ammonia (via fast selective catalytic reduction reaction) and also the simultaneous removal of multipollutant (pre-oxidation and post-absorption). Until now, scholars have developed various types of NO-SCO catalysts, dividing the main groups into noble metals (Pt, Pd, Ru, etc.), metal oxides (Mn-, Co-, Cr-, Ce-based, etc.), perovskite-type oxides (LaMnO₃, LaCoO₃, LaCeCoO₃, etc.), carbon materials (activated carbon, carbon fiber, carbon nanotube, graphene, etc.), and zeolites (ion-exchanged ZSM-5, CHA, SAPO, MCM-41, etc.) in this review. This paper summarizes the recent progress of the above typical catalysts and mostly analyzes the catalytic performance for NO oxidation in terms of the H₂O and/or SO₂ resistances and also the influencing factors, and their reaction mechanisms are described in detail. Finally, this review points out the key problems and possible solutions of the current researches and presents the application prospects and future development directions of NO-SCO technology using the above typical catalysts.

Preparation of the Mn/Co mixed oxide catalysts for low-temperature CO oxidation reaction

The Mn/Co mixed powders with various Mn/Co molar ratios were prepared by the coprecipitation method and used in low-temperature CO oxidation. The physicochemical characteristics of these powders were characterized using the Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), temperature-programmed reduction (TPR), and scanning electron microscopy (SEM) analyses. The results demonstrated that the Mn/Co molar ratio significantly affected both the textural and catalytic properties and the sample with a Mn/Co = 1:1 possessed a BET area of 123.7 m²g^-1 with a small mean pore size of 6.44 nm. The catalytic results revealed that the pure cobalt and manganese catalysts possessed the low catalytic activity and the pure Co catalyst is not active at temperatures lower than 140 °C. The highest catalytic activity was observed for the catalyst with a Mn/Co = 1. The obtained results showed that the incorporation of Pd into the Mn/Co catalyst significantly enhanced the catalytic activity for oxidation of carbon monoxide and the highest CO conversion was observed for the catalyst with 1 wt.% Pd and this catalyst exhibited a CO conversion of 100% at 80 ^°C.

Study on Denitration Performance of Solid Waste Blast Furnace Slag Catalysts under Different Preparation Processes

In this article, blast furnace slag, a high-yield industrial solid waste, was taken as the research object and it was used as the main material. Bentonite was used as the binder, and water was added to shape the blast furnace slag into a small column. The denitration catalyst was prepared using different methods, its denitration performances were compared and analyzed, and the best preparation method and process parameters were screened. Results showed that bentonite will clearly improve denitration performance, and 4:1 blast furnace slag and bentonite was selected as the molding ratio to reduce the effect of bentonite on its performance, combined with the hardness and surface adhesion of the prepared carrier. Separately, the catalysts were prepared using citric acid impregnation, hydrothermal decomposition, and mixing method, and active Mn was loaded. Among them, the hydrothermal decomposition method cannot completely decompose in a closed kettle, resulting in a lower denitration performance. The catalyst prepared using the mixing method is superior to that prepared using the impregnation method because the active component prepared by the former was more uniformly dispersed, and simple and easy to operate, which can meet the needs of the excess denitration catalysts of small enterprises.

Low temperature selective catalytic reduction of nitric oxide with an activated carbon-supported zero-valent iron catalyst

Selective catalytic reduction (SCR) of nitrogen oxides with an activated carbon-supported zero-valent iron catalyst is a method for removing NO under low temperature, which can remove CO and NO simultaneously. In the present study, the thermodynamics of low temperature denitrification was analyzed. By means of X-ray diffraction and Brunner–Emmet–Teller (BET) measurements, the phase and structure of the catalyst were thoroughly investigated. To determine the activity of the catalyst, a series of catalytic performance tests were carried out. The results indicated that the catalyst can act on the chemical reactions during the low-temperature denitrification process. An increase in the iron loading covered the micropores, resulting in a smaller specific surface area, which had little influence on the total pore volume. Moreover, activated carbon provided a carrier structure for iron and reduced NO simultaneously. The reduction of NO with activated carbon to N₂ was the main reaction. By the oxidation of iron and the reduction of activated carbon, the activity of the catalyst decreased.

A novel transition metal-supported catalyst which can be used for denitrification in a low-temperature sintering flue gas.