NO removal performance of CO in carbonation stage of calcium looping for CO_(2) capture

Calcium looping realizes CO_(2)capture via the cyclic calcination/carbonation of CaO.The combustion of fuel supplies energy for the calciner.It is unavoidable that some unburned char in the calciner flows into the carbonator,generating CO due to the hypoxic atmosphere in the carbonator.CO can reduce NO in the flue gases from coal-fired power plants.In this work,NO removal performance of CO in the carbonation stage of calcium looping for CO_(2)capture was investigated in a bubbling fluidized bed reactor.The effects of carbonation temperature,CO concentration,CO_(2)capture,type of CaO,number of CO_(2)capture cycles and presence of char on NO removal by CO in carbonation stage of calcium looping were discussed.CaO possesses an efficient catalytic effect on NO removal by CO.High temperature and high CO concentration lead to high NO removal efficiency of CO in the presence of CaO.Taking account of better NO removal and CO_(2)capture,the optimal carbonation temperature is 650℃.The carbonation of CaO reduces the catalytic activity of CaO for NO removal by CO due to the formation of CaCO_(3).Besides,the catalytic performance of CaO on NO removal by CO gradually decreases with the number of CO_(2)capture cycles.This is because the sintering of CaO leads to the fusion of CaO grains and blockage of pores in CaO,hindering the diffusion of NO and CO.The high CaO content and porous structure of calcium-based sorbents are beneficial for NO removal by CO.The presence of char promotes NO removal by CO in the carbonator.CO_(2)/NO removal efficiencies can reach above 90%.The efficient simultaneous NO and CO_(2)removal by CO and CaO in the carbonation step of the calcium looping seems promising.

Earth-Abundant CaCO_(3)-Based Photocatalyst for Enhanced ROS Production,Toxic By-Product Suppression,and Efficient NO Removal

Photoinduced reactive oxygen species(ROS)-based pollutant removal is one of the ideal solutions to achieve the conversion of solar energy into chemical energy and thus to address environmental pollution.Here,earthabundant CaCO_(3)-decorated g-C_(3)N_(4)(g-C_(3)N_(4)labeled as CN,CaCO_(3)-decorated g-C_(3)N_(4)sample labeled as CN-CCO)has been constructed by a facile thermal polymerization method for safe and efficient photocatalytic NO removal.The decorated CaCO_(3)as“transit hub”extends theπbonds of CN to deviate from the planes and steers the random charge carriers,which thus provides extra active sites and expedites spatial charge separation to facilitate adsorption/activation of reactants and promote formation of ROS participating in the removal of pollutant.Furthermore,boosted generation of ROS regulates the photocatalytic NO oxidation pathway and thus increases the selectivity of products.NO prefers to be directly oxidized into final product(nitrate)rather than toxic intermediates(NO_(2)),which is well demonstrated by theoretically simulated ROS-based reaction pathways and experimental characterization.The present work promotes the degradation of pollutant and simultaneously suppresses the formation of toxic by-product,which paves the way for ROS-based pollutant removal.

Prediction and interpretation of photocatalytic NO removal on g-C_(3)N_(4)-based catalysts using machine learning

Predictive modeling of photocatalytic NO removal is highly desirable for efficient air pollution abatement.However,great challenges remain in precisely predicting photocatalytic performance and understanding interactions of diverse features in the catalytic systems.Herein,a dataset of g-C_(3) N_(4)-based catalysts with 255 data points was collected from peer-reviewed publications and machine learning(ML)model was proposed to predict the NO removal rate.The result shows that the Gradient Boosting Decision Tree(GBDT)demonstrated the greatest prediction accuracy with R 2 of 0.999 and 0.907 on the training and test data,respectively.The SHAP value and feature importance analysis revealed that the empirical categories for NO removal rate,in the order of importance,were catalyst characteristics>reaction process>preparation conditions.Moreover,the partial dependence plots broke the ML black box to further quantify the marginal contributions of the input features(e.g.,doping ratio,flow rate,and pore volume)to the model output outcomes.This ML approach presents a pure data-driven,interpretable framework,which provides new insights into the influence of catalyst characteristics,reaction process,and preparation conditions on NO removal.

Sb_(2)WO_(6)/BiOBr 2D nanocomposite S-scheme photocatalyst for NO removal

Photocatalysis technology is an efficient method for removing nitrogen oxides at low concentrations.Herein,dimension-matched Sb_(2)WO_(6)/BiOBr photocatalysts were synthesized at room temperature via precipitation-deposition way.Under visible light irradiation,the as-obtained Sb_(2)WO_(6)/Bi OBr photocatalysts showed enhanced photocatalytic performance compare with the pure Sb_(2)WO_(6) and BiOBr for removal of NO.The optimal ratio for photocatalytic performance of Sb_(2)WO_(6)/BiOBr composite was found to be 30 wt.%of Sb_(2)WO_(6),which showed excellent recycling property even after 5 runs.Moreover,in situ DRIFT was carried out to reveal the time-dependent evolution of reaction intermediates during photocatalytic NO oxidation.The probable photocatalytic mechanism was considered based on the active species capture experiments.The enhanced photocatalytic performance for the Sb_(2)WO_(6)/BiOBr composite photocatalyst perhaps is attributed to the interaction between BiOBr and Sb2WO6 and S-scheme charge transfer path.

Highly efficient photocatalytic NO removal and in situ DRIFTS investigation on SrSn(OH)_(6)

A novel SrSn(OH)_(6) photocatalyst with large plate and particle size were synthesized via a facile chemical precipitation method. The photocatalytic activity of the SrSn(OH)_(6) was evaluated by the removal of NO at ppb level under UV light irradiation. Based on the ESR measurements, SrSn(OH)_(6) photocatalyst was found to have the ability to generate the main active species of O_(2)^(·-), ^(·)OH and ^(1)O_(2) during the photocatalytic process. Moreover, SrSn(OH)_(6) photocatalyst not only exhibits high photocatalytic activity for NO removal (79.6%), but also has good stability after five cycles. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to investigate the NO_(x) transfer pathway and the intermediate products distribution during the adsorption and photocatalytic NO oxidation process. The present work not only provides an efficient material for air pollutants purification at room temperature but also in-depth understanding of the mechanism involved in the photocatalytic NO removal process.

Synthesis of crystalline carbon nitride with enhanced photocatalytic NO removal performance:An experimental and DFT theoretical study

The pristine carbon nitride derived from the thermally-induced polymerization of nitrogen-containing precursors(e.g.cyanamide,dicyanamide,melamine and urea)displays low crystallinity because of the predominantly kinetic hindrance.Herein,we reported a modified molten-salts method to fabricate the crystalline carbon nitride under ambient pressure,which is expected to the large-scale production of crystalline carbon nitride.The obtained crystalline carbon nitride displayed about 3.0 times higher photocatalytic NO removal performance than that of pristine carbon nitride under visible light irradiation(λ<400 nm).Detailed experimental characterization and theoretical calculation revealed the crucial roles of crystallinity in crystalline carbon nitride for the enhanced photocatalytic NO removal performance.This research provided deep insights into the crystallinity of carbon nitride for the enhanced photocatalytic performance.

Modulation of photocatalytic activity of SrBi_(2)Ta_(2)O_(9)nanosheets in NO removal by tuning facets exposure

Photocatalysts with exposure of different crystal facets often show great differences in their photocatalytic activities due to differences in surface atomic arrangement and coordination.Thus,the actual photoreaction mechanism of a specific crystal facet in photocatalysis deserves to be explored.In this paper,as a case study,Sr Bi_(2)Ta_(2)O_(9)photocatalyst with preferential facet exposure was explored for the photocatalytic removal of NO at a ppb level.The efficiency of NO removal was remarkably improved by tuning the crystal exposure facet with high(200)facet exposure ratio.Optimized exposure of(200)crystal facet in Sr Bi_(2)Ta_(2)O_(9)(SBT)by thermal calcination at 800℃(SBT-800)leads to the highest NO removal activity of51%under a 300 W Xe lamp for 20 min;under visible light,SBT 800 achieves a 5-fold enhancement in NO removal efficiency compared to its counterpart,SBT-900.Active species capture experiments prove that the superoxide radical·O_(2)-is the main active species for the photocatalytic removal of NO,and surface selective deposition experiments conclude that(200)is the main electron-rich crystal plane,based on which the results of density functional theory(DFT)computation reveal the Bi O terminated nature of(001)crystal plane,where the models with both Bi O and Ta O terminated(001)planes were created and computated.Mechanistic study reveals that Sr Bi_(2)Ta_(2)O_(9)with a larger exposure of(200)facet provides more active reduction sites,thereby reducing more O_(2)to·O_(2)-,which further oxidizes the adsorbed NO to NO_(2)-/NO_(3)-.The present work underlines the role of facet tuning in the photoactivity modulation for NO removal photocatalytically.

Theoretical investigation on NO reduction electro-catalyzed by transition-metal-anchored SnOSe nanotubes

Electrochemical NO reduction reaction(NORR)to NH3 emerges as a fascinating approach to achieve both the migration of NO pollutant and the green synthesis of NH3.In this contribution,within the framework of computational hydrogen model and constant-potential implicit solvent model,the NORR electrocatalyzed by a novel transition-metal-anchored SnOSe armchair nanotube(TM@SnOSe_ANT)was investigated using density functional theory calculations.Through the checking in terms of stability,activity,and selectivity,Sc-and Y@SnOSe_ANTs were screened out from the twenty-five candidates.Considering the effects of pH,solvent environment,as well as applied potential,only Sc@SnOSe_ANT is found to be most promising.The predicted surface area normalized capacitance is 11.4μF/cm^(2),and the highest NORR performance can be achieved at the U_(RHE) of-0.58 V in the acid environment.The high activity originates from the mediate adsorption strength of OH.These findings add a new perspective that the nanotube can be served as a highly promising electrocatalyst towards NORR.

Removal of nitric oxide from simulated flue gas using aqueous persulfate with activation of ferrous ethylenediaminetetraacetate in the rotating packed bed

Nitric oxide being a major gas pollutant has attracted much attention and various technologies have been developed to reduce NO emission to preserve the environment.Advanced persulfate oxidation technology is a workable and effective choice for wet flue gas denitrification due to its high efficiency and green advantages.However,NO absorption rate is limited and affected by mass transfer limitation of NO and aqueous persulfate in traditional reactors.In this study,a rotating packed bed(RPB)was employed as a gas-liquid absorption device to elevate the NO removal efficiency(η_(NO))by aqueous persulfate((NH_(4))_(2)S_(2)O_(8))activated by ferrous ethylenediaminetetraacetate(Fe^(^(2+))-EDTA).The experimental results regarding the NO absorption were obtained by investigating the effect of various operating parameters on the removal efficiency of NO in RPB.Increasing the concentration of(NH_(4))_(2)S_(2)O_(8) and liquid-gas ratio could promoted the oxidation and absorption of NO while theη_(NO) decreased with the increase of the gas flow and NO concentration.In addition,improving the high gravity factor increased theη_(NO) and the total volumetric mass transfer coefficient(K_(G)α )which raise theη_(NO) up to more than 75%under the investigated system.These observations proved that the RPB can enhance the gas-liquid mass transfer process in NO absorption.The correlation formula between K_(G)α and the influencing factors was determined by regression calculation,which is used to guide the industrial scale-up application of the system in NO removal.The presence of O_(2) also had a negative effect on the NO removal process and through electron spin resonance spectrometer detection and product analysis,it was revealed that Fe^(2+)-EDTA activated(NH_(4))2S_(2)O_(8) to produce•SO_(4)^(-),•OH and•O_(2)^(-),played a leading role in the oxidation of NO,to produce NO_(3)^(-)as the final product.The obtained results demonstrated a good applicable potential of RPB/PS/Fe^(2+)-EDTA in the removal of NO from flue gases.

Effect of different acid anions on highly efficient Ce-based catalysts for selective catalytic reduction of NO with NH_(3)

Three kinds of Ce-based catalysts(CePO_(4),CeVO_(4),Ce_(2)(SO_(4))_(3))were synthesized and used for the selective catalytic reduction(SCR)of NO by NH_(3).NH_(3)-SCR performances were conducted in the temperature range of 80 to 400°C.The catalytic efficiencies of the three catalysts are as follow:CePO_(4)>CeVO_(4)>Ce_(2)(SO_(4))_(3),which is in agreement with their abilities of NH_(3)adsorption capacities.The highest NO conversion rate of CePO_(4)could reach about 95%,and the catalyst had more than 90%NO conversion rate between 260 and 320°C.The effect of PO_(4)^(3–),VO_(4)^(3–)and SO_(4)^(2–)on NH_(3)-SCR performances of Ce-based catalysts was systematically investigated by the X-ray photoelectron spectroscopy analysis,NH_(3)temperature programmed desorption,H2 temperature programmed reduction and field emission scanning electron microscopy tests.The key factors that can enhance the SCR are the existence of Ce4+,large NH_(3)adsorption capacity,high and early H2 consumptions,and suitable microstructures for gas adsorption.Finally,CePO_(4)and CeVO_(4)catalysts also exhibited relatively strong tolerance of SO2,and the upward trend about 8%was detected due to the sulfation enhancement by SO2 for Ce_(2)(SO_(4))3.

InP quantum dots on g-C_(3)N_(4) nanosheets to promote molecular oxygen activation under visible light

Largely limited by the high dissociation energy of the O—O bond,the photocatalytic molecular oxygen activation is highly challenged,which re strains the application of photocatalytic oxidation technology for atmospheric pollutants removal.Herein,we design and fabricate the InP QDs/g-C_(3)N_(4) compounds.The introduction of InP QDs promotes the charge transfer within the interface resulting in the effective separation of photo-generated carriers.Furthermore,InP QDs greatly facilitates the activation of molecular oxygen and promote the formation of O_(2)·under visible-light illuminatio n.These conclusions are identified by experimental and calculation results.Hence,NO can be combined with the O_(2)·to form O—O—N—O intermediate to direct conversion into NO_(3).As a result,the NO removal ratio of g-C_(3)N_(4) has a one fold increase after InP QDs loaded and the generation of NO_(2) is effectively inhibited.This wo rk may provide a strategy to design highly efficient materials for molecular oxygen activation.

Influence of CePO_(4)with different crystalline phase on selective catalytic reduction of NO_(x)with ammonia

A series of cerium phosphate catalysts with different crystal phases were synthesized by hydrothermal method and co-precipitation method.Hexagonal cerium phosphate(CePO_(4)-H)shows better NH_(3)-SCR denitration activity than monoclinic cerium phosphate(CePO_(4)-M)and mixed phases of CePO_(4)-H and CePO_(4)-M.Moreover,CePO_(4)-H also exhibits excellent activity stability with stream time and cycling stability.Various characterizations were carried out to explain the effects of different crystal phases of CePO_(4)on the activity.Among these catalysts,CePO_(4)-H has much stronger surface acidity that is conducive to the adsorption and activation of NH_(3),and more surface adsorbed oxygen species that can effectively improve SCR activity.In situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)were performed to investigate the adsorption and reaction of NH_(3)and NO_(x)on CePO_(4)-H and CePO_(4)-M,and the results suggest that the better activity over CePO_(4)-H follows mainly the Eley-Rideal mechanism in the activity temperature window(300-500℃)with 100%NO conversion.

Combining SnO_(2-x)and g-C_(3)N_(4)nanosheets toward S-scheme heterojunction for high selectivity into green products of NO degradation reaction under visible light

NOx emissions cause many negative impacts on the living environment.The photocatalysis of semiconductors is superior for nitric oxide(NO)degradation due to their low redox potential.In this report,we combine SnO_(2-x)/g-C_(3)N_(4)heterojunction photocatalyst toward the high selectivity into green products under visible light illumination.Results show that SnO_(2-x)/g-C_(3)N_(4)heterojunction degraded 40.8%of NO,which is 1.6 times higher than that of g-C_(3)N_(4).In addition,the selectivity coefficient of SnO_(2-x)/g-C_(3)N_(4)is higher 3 times than both pure SnO_(2-x)and g-C_(3)N_(4).Furthermore,SnO_(2-x)/g-C_(3)N_(4)expresses a superior stability for NO photocatalytic-degradation after five cycles.The scavenger trapping test results,and electron spin resonance(ESR)analysis also provide more understanding of the charge transfer mechanism of materials.SnO_(2-x)/g-C_(3)N_(4)heterojunction shows a high removal efficiency of NO gas,making it an up-and-coming environmental treatment candidate.

Direct catalytic nitrogen oxide removal using thermal, electrical or solar energy

Considering the significant importance in both ecological and environmental fields, converting nitrogen oxide(NO_(x), especially NO) into value-added NH3or harmless N2lies in the core of research over the past decades. Exploring catalyst for related gas molecular activation and highly efficient reaction systems operated under low temperature or even mild conditions are the key issues. Enormous efforts have been devoted to NO removal by utilizing various driving forces, such as thermal, electrical or solar energy,which shine light on the way to achieve satisfying conversion efficiency. Herein, we will review the stateof-the-art catalysts for NO removal driven by the above-mentioned energies, including a comprehensive introduction and discussion on the pathway and mechanism of each reaction, and the recent achievements of catalysts on each aspect. Particularly, the progress of NO removal by environmentally friendly photocatalysis and electrocatalysis methods will be highlighted. The challenges and opportunities in the future research on the current topic will be discussed as well.

Self-doped Br in Bi_(5)O_(7)Br ultrathin nanotubes:Efficient photocatalytic NO purification and mechanism investigation

Bismuth-rich Bi_(5)O_(7)Br is a promising photocatalyst for pollutant removal owing to its stability and appropriate band structure in comparison with bismuth oxybromide.However,bulk-phase Bi_(5)O_(7)Br suffers from poor light absorption and high charge recombination rates resulting in poor activity.Elemental doping is a powerful strategy to enhance photocatalytic activity.In this study,we prepared a series of Br autodoped ultrathin Bi_(5)O_(7)Br nanotubes and explored the effect of Br doping on photocatalytic NO removal.The optimal doping content was determined via a photocatalytic NO removal experiment,which revealed the optimal ratio of Bi and Br was approximately 3:1.In situ diffuse reflectance infrared Fourier transform spectroscopy(In situ DRIFT)and density functional theory(DFT)studies revealed that NO removal mechanism catalyzed by Br doped Bi_(5)O_(7)Br.Our work presents a new strategy for the enhancement of photocatalytic pollutant degradation by bismuth oxyhalide photocatalysts.

Ultralow specific surface area vermiculite supporting Mn-Ce-Fe mixed oxides as“curling catalysts”for selective catalytic reduction of NO with NH_(3)

In this study,the ultralow specific surface area clay vermiculite(VMT)was selected to be a catalyst support for the NH_(3)-SCR process,and the active components MnCeFeO_(x)loaded on vermiculite was just like curling on ice from the TEM results.The de-NO_(x)performance of Mn-Ce-Fe/VMT exhibited almost complete NO conversion with a gas hourly space velocity(GHSV)of 15,300 h^(-1)at 150℃,which was 25%and 10%higher than that of Mn/VMT and Mn-Ce/VMT,respectively.Ce and Fe co-doping improved the BET surface area,the quantities of active Mn^(4+),the acid sites and NH_(3)adsorption energy of Mn/VMT,all of which contributed to the increase in low-temperature SCR activity.In situ DRIFT measurements suggested that NO_(x)removal over Mn-Ce-Fe/VMT followed both Eley-Rideal(E-R)and Langmuir-Hinshelwood(L-H)mechanisms at 150℃,but the E-R mechanism played a dominant role.Corresponding Mn-Ce-Fe/VMT monolithic catalysts reached 90%NO conversion with a GHSV of 4000 h^(-1).

Enhancing low-temperature NH_(3)-SCR performance of Fe-Mn/CeO_(2)catalyst by Al_(2)O_(3)modification

In the work,supported catalysts of FeO_(x) and MnO_(x) co-supported on aluminum-modified CeO_(2)was synthesized for low-temperature NH_(3)-selective catalytic reduction(NH_(3)-SCR)of NO.Impressively,the SCR activity of the obtained catalyst is markedly influenced by the adding amount of Al and the appropriate Ce/Al molar ratio is 1/2.The activity tests demonstrate that Fe-Mn/Ce1 Al2 catalyst shows over 90%NO conversion at 75-250℃and exhibits better SO_(2)resistance compared to Fe-Mn/CeO_(2).Fe-Mn/Ce1 Al2 shows the expected physicochemical characters of the ideal catalyst including the larger surface and increased active reaction active sites by controlling the amount of Al doping.Also,the better catalytic activity is well correlated with the present advantaged surface adsorption oxygen species,Mn^(4+)species,Ce^(3+)species and the enhanced reducibility of Fe-Mn/Ce1 Al2,which is superior to the Fe-Mn/CeO_(2)catalyst.More importantly,we further demonstrate that the amount and strength of surface acid sites are improved by Al-doping and more active intermediates(monodentate nitrate)is generated during NH_(3)-SCR reaction.This work provides certain insight into the rational creation of simple and practical denitration catalyst environmental purification.