Preparation of Modified UiO-66 Catalyst and Its Catalytic Performance for NH_(3)-SCR Denitration

Zirconium-based metal-organic framework UiO-66 was successfully prepared by solvothermal method,and UiO-66 was modified by adding regulators such as formic acid,acetic acid,and hydrochloric acid.The NH_(3)-SCR reactivity of the samples was evaluated by the denitration activity evaluation system,and the UiO-66 and the regulator-modified UiO-66 were characterized by XRD,SEM,BET,FTIR,TG,NH_(3)-TPD,etc.,the effects of regulator types on the structure and properties of UiO-66 were investigated.The experimental results show that,after adding the modifier,the morphology of UiO-66 changes from irregular quadrilateral with serious agglomeration to particles with regular crystal shape and good dispersibility,and the crystal morphology of the catalyst is improved.In addition,after adding the modifier,UiO-66 has a larger specific surface area and stronger surface acidity,which optimizes the catalytic performance of UiO-66.The catalytic performance test results of NH_(3)-SCR show that the low-temperature activity of UiO-66 is poor,and it only shows a certain catalytic activity at higher temperatures.The catalytic activity of UiO-66 was significantly improved after adding the regulator.Among them,the UiO-66-HCl modified with hydrochloric acid had the best catalytic activity,and the denitration rate reached 70%when the denitration temperature was 380℃.

One-step green method to prepare progressive burning gun propellant through gradient denitration strategy

Gradiently denitrated gun propellant(GDGP)prepared by a“gradient denitration”strategy is obviously superior in progressive burning performance to the traditional deterred gun propellant.Currently,the preparation of GDGP employed a tedious two-step method involving organic solvents,which hinders the large-scale preparation of GDGP.In this paper,GDGP was successfully prepared via a novelty and environmentally friendly one-step method.The obtained samples were characterized by FT-IR,Raman,SEM and XPS.The results showed that the content of nitrate groups gradiently increased from the surface to the core in the surface layer of GDGP and the surface layer of GDGP exhibited a higher compaction than that of raw gun propellant,with a well-preserved nitrocellulose structure.The denitration process enabled the propellant surface with regressive energy density and good progressive burning performance,as confirmed by oxygen bomb and closed bomb test.At the same time,the effects of different solvents on the component loss of propellant were compared.The result showed that water caused the least component loss.Finally,the stability of GDGP was confirmed by methyl-violet test.This work not only provided environmentally friendly,simple and economic preparation of GDGP,but also confirmed the stability of GDGP prepared by this method.

Robust photo-assisted removal of NO at room temperature:Experimental and density functional theory calculation with optical carrier

Photo-assisted SCR(PSCR) offers a potential solution for removal of NO at room temperature. MnTiO_(x)as PSCR catalyst exhibits superior performance with NO removal of 100% at the room temperature. Electron paramagnetic resonance(EPR) analysis revealed the presence of numerous oxygen vacancies on MnTiO_(x). Optical carrier density functional theory(DFT) calculations showed that the threedimensional orbital hybridization of Mn and Ti is significantly enhanced under light irradiation. The MnTiO_(x)catalyst exhibited excellent electron–hole separation ability, which can adsorbe NH_(3)and dissociate to form NH_(2)fragments and H atoms. In-situ diffuse reflectance infrared fourier-transform spectroscopy(DRIFTS) indicated that the optical carrier enhanced NH_(3)adsorption on MnTiO_(x), which makes it possess excellent PSCR activity. This work provided an additional strategy to NO removal with PSCR catalysts and showed potential for use in photocatalysis.

Enhanced selective catalytic reduction of NO with NH3 via porous micro-spherical aggregates of Mn–Ce–Fe–Ti mixed oxide nanoparticles

We rationally designed a high performance denitration(De-NOx) catalyst based on a micrometer-sized spherical Mn–Ce–Fe–Ti(CP-SD)catalyst for selective catalytic reduction(SCR). This was prepared by a co-precipitation and spray drying(CP-SD) method. The catalyst was systematically characterized, and its morphological structure and surface properties were identified. Compare with conventional Mn–Ce–Fe–Ti(CP) catalysts, the Mn–Ce–Fe–Ti(CP-SD) catalyst had superior surface-adsorbed oxygen leading to enhanced 'fast NH3-SCR' reaction. The asobtained Mn–Ce–Fe–Ti(CP-SD) catalyst offered excellent NO conversion and N2 selectivity of 100.0% and 84.8% at 250℃, respectively, with a gas hourly space velocity(GHSV) of 40,000 h-1. The porous micro-spherical structure provides a larger surface area and more active sites to adsorb and activate the reaction gases. In addition, the uniform distribution and strong interaction of manganese, iron, cerium, and titanium oxide species improved H2O and SO2 resistance. The results showed that the Mn–Ce–Fe–Ti(CP-SD) catalyst could be used prospectively as a denitration(De-NOx) catalyst.

Sustainable recycling of titanium from TiO_(2) in spent SCR denitration catalyst via molten salt electrolysis

Spent catalyst used for denitration by selective catalytic reduction(spent SCR denitration catalysts) is one of the important urban mines due to the high content of TiO_(2)(~85 wt%) and the massive accumulation amount(over 100,000 tons),therefore,value-added reutilization of titanium in spent SCR catalysts is considerably meaningful.In this paper,a novel method is proposed for converting the titanium oxide in spent SCR denitration catalysts to metallic titanium.Specifically,titanium dioxide(TiO_(2)) was firstly obtained from spent SCR denitration catalysts after removing the impurities by hydrometallurgy process.Then,TiO_(2) is converted to Ti_(2)CO by carbothermic reduction method,and Ti_(2)CO was further purified by oleic acid capture.Finally,by utilizing the as-prepared Ti_(2)CO as the consumable anode in the NaCl-KCl molten salt,high-purity metallic titanium was deposited at cathode,all confirming the feasibility for the conversion of low-grade TiO_(2) in the spent catalysts,from 60 wt% to high-purity metallic Ti(99.5 wt%), furthermore,the energy consumption of this process is 3950 kWh tonne-1 Ti,which is lower than that of most traditional titanium metallurgy methods.The method herein can provide new insights for the value-added recycling of titanium resources in urban mines.

A Review on the Mechanism of NO Selective Catalytic Oxidation

In this paper,the research status and catalytic mechanism of activated carbon catalysts,molecular sieve catalysts,noble metal catalysts and transition metal oxide catalysts used for NO catalytic oxidation were studied to provide reference for future research.

Introduction of the DeNO_x Project in Huaneng Yuhuan Power Plant

The Selective Catalytic Reduction (SCR) system for flue gas denitration applied in Yuhuan Power Plant with 4×1 000 MW units is introduced in this paper. The technology system structure, process features, basic design data and equipment layout of the SCR flue gas denitration system of original units in the plant are briefly introduced and the retrofi t method of equipments is described, which provide valuable experience for flue gas denitrification retrofit of large-size coal-fired boilers in China.

An Integrated Process for Recycling of ThO₂Based Mixed Oxide Rejected Nuclear Fuel Pellets

This paper presents a study on the process engineering aspects of relevance to the industrial implementation of ThO2 and (Th, U)O2 mixed oxide (MOX) pellet type fuel manufacturing. The paper in particular focuses on the recycling of thoria based fuel production scrap which is an economically important component in the fuel manufacturing process. The thoria based fuels are envisaged for Advanced Heavy Water Reactor (AHWR) and other reactors important to the Indian Nuclear Power Programme. A process was developed for recycling the chemically clean, off-specification and defective sintered ThO2 and (Th, U)O2 MOX nuclear fuel pellets. ThO2 doesn’t undergo oxidation or reduction and thus, more traditional methods of recycling are impractical. The integrated process was developed by combining three basic approaches of recycling namely mechanical micronisation, air oxidation (for MOX) and microwave dissolution-denitration. A thorough investigation of the influence of several variables as heating method, UO2 content, fluoride and polyvinyl alcohol (PVA) addition during microwave dissolution-denitration was recorded on the product characteristics. The suitability evaluation of the recycled powder for re-fabrication of the fuel was carried out by analyzing the particle size, BET specific surface area, phase using XRD, bulk density and impurities. The physical and chemical properties of recycled powder obtained from the sintered (Th1-y, Uy)O2 (y;0 - 30 wt%) pellets advocate 100% utilisation for fuel re-fabrication. Recycled ThO2 by integrated process showed distinctly high sinterability compared to standard powder evaluated in terms of surface area and particle size.

High efficiency removal of NO using waste calcium carbide slag by facile KOH modification

Waste calcium carbide slags(CS),which are widely applied to desulfurisation,are not typically used in denitration.Herein,to well achieve waste control by waste,a facile and highefficiency denitration strategy is developed using KOH to modify the calcium carbide slags(KCS).Various KCS samples were investigated using a series of physical and chemical characterisations.The performance test results showed that the KOH concentration and reaction temperature are the main factors affecting the denitration efficiency of KCS,and CS modified with 1.5 mol/L KOH(KCS-1.5)can achieve 100% denitration efficiency at 300℃.Such excellent removal efficiency is due to the catalytic oxidation of the oxygen-containing functional groups derived from the KCS.Further studies showed that KOH treatment significantly increased the concentration of oxygen vacancies,nitro compounds,and basic sites of CS.This study provides a novel strategy for the resource utilisation of waste CS in the future.

Effect of different doping elements on performance of Ce-Mn/TiO_(2)catalyst for low temperature denitration

Sm and Ho were doped in Ce-Mn/TiO_(2)catalyst respectively to enhance its denitration performance at low temperature.X-ray diffraction(XRD),N2adsorption-desorption,X-ray photoelectron spectroscopy(XPS),NH3-temperature programmed desorption(NH3-TPD),H2-temperature programmed reduction(H2-TPR)and in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)techniques were used to analyze the structure and performance of catalysts.The results demonstrate that Ho doping increases the amount of acid sites and improves low temperature redox property of Ce-Mn/TiO_(2),which lead to excellent DeNOxperformance of Ho-Ce-Mn/TiO_(2)in the whole reaction temperature range.Sm doping results in decline of redox property,but it is beneficial to increasing the acid sites of Ce-Mn/TiO_(2).The increased surface acid sites and moderate oxidative ability impart Sm-Ce-Mn/TiO_(2)higher denitration activity and N2selectivity at temperature above 150℃.Lewis acid sites and redox property are the main factors affecting the activity of catalysts.Doping of Ho and Sm both improves sulfur resistance performance of Ce-Mn/TiO_(2)by inhibiting the adsorption of SO_(2)and formation of sulfate.Ce-Mn/TiO_(2)modified by Ho shows better sulfur resistance than that doped with Sm because of its more surface acid sites.

Promotion effect of bulk sulfates over CeO_(2)for selective catalytic reduction of NO by NH_(3)at high temperatures

Understanding the influence of sulfates over catalysts for selective catalytic reduction of NO with NH_(3)(NH_(3)-SCR)is crucial due to the universal presence of SO_(2)in exhaust gas.Depending on the degree of sulfation,there mainly exist surface and bulk sulfates and NH_(3)-SCR activity is generally considered to suffer more from bulk sulfates.Herein,the unique function of bulk sulfates over Ce O_(2)in promoting hightemperature SCR reaction is revealed.Notably,compared with CeO_(2)dominated with surface sulfates(S-CeO_(2)-4h)and commercial V_2O_5-WO_(3)/TiO_(2),CeO_(2)with bulk sulfates(S-Ce O_(2)-72h)exhibits admirable NO conversion at the temperature range of 400-550℃.Bulk sulfates provide more Br?nsted acid sites with stronger strength for NH_(3)adsorption.Moreover,the oxidation ability of Ce O_(2)is significantly inhibited due to electron-withdrawing effect from bulk sulfates,which alleviates NH_(3)oxidation at high temperatures.More NH_(3)adsorption with high stability and limited NH_(3)oxidation capacity ensure the excellent catalytic performance for S-CeO_(2)-72h in high-temperature denitration.This work provides new insight of bulk sulfates in promoting SCR activity and open a new avenue to design de NO_xcatalysts employed at high temperatures.

A pilot scale study on co-capture of SO_2 and NOx in O_2/CO_2 recycled coal combustion and techno-economic evaluation

This paper presents the study on co-capture of SO2 and NOx in O2/CO2 recycled coal combustion in a pilot scale facility with the heat input of 0.3 MW by using high-sulphur lean coal.Detailed comparison of SO2 and NOx emission indexes and desulphurization and denitration rates have been made among three working conditions of O2/CO2,O2/CO2 with limestone injection(O2/CO2+Ca) and O2/RFG(recycled flue gas) with limestone injection(O2/RFG+Ca).Combustion in air was performed as a base case.Results showed that in the O2/RFG with limestone injection,desulphurization and denitration rates could reach up to 96% and 89%,respectively.Limestone injection under the high-CO2 atmosphere caused a significant reduction on SO2 emission and NOx emission as well.This indicated O2/CO2 recycled coal combustion could reduce the investment on the flue gas purification.The techno-economic evaluation indicated that Oxy-combustion technique is not only feasible for CO2 emission control based on existing power plants but is also cost-effective.

Effects of different introduction methods of Ce^4+and Zr^4+on denitration performance and anti-K poisoning performance of V2O5-WO3/TiO2 catalyst

The purpose of this work is to explore the effects of the introduction methods of Ce^4+and Zr^4+on the physicochemical properties,activity,and K tolerance of V2 O5-WO3/TiO2 catalyst for the selective catalytic reduction of NOx by NH3.Four different methods,namely pre-impregnation,post-impregnation,coimpregnation,and co-precipitation,were used to synthesize a series of V2 O5-WO3-TiO2-CeO2-ZrO2 catalysts.The catalysts were characterized by XRD,BET,NH3-TPD,XPS,and H2-TPR techniques.Moreover,the activity and anti-K poisoning performance were tested by an NH3-SCR model reaction.The results show that the introduction of Ce^4+and Zr^4+can improve the catalytic performance of V2O5-WO3/TiO2 catalyst,but the impregnation method cannot enhance the anti-K poisoning performance.Ce^4+and Zr^4+introduced by co-precipitation method can effectively improve the tolerance of K,which is mainly due to the incorporation of Ce^4+and Zr^4+into TiO2 lattice to form a uniform TiO2-CeO2-ZrO2 solid solution,resulting in the optimal surface acidity and redox performance,and reducing the decreases caused by Kpoisoning.Furthermore,based on the best introduction method,we further optimized the molar ratio of Ce^4+/Zr^4+,It is found that the catalyst exhibits the best anti-K poisoning performance when the molar ratio of Ce^4+/Zr^4+is 2:1.

Enhanced simultaneous absorption of NO_(x) and SO_(2) in oxidation-reduction-absorption process with a compounded system based on Na_(2)SO_(3)

Oxidation of sulfite and competitive absorption existed in Na_(2)SO_(3) solution for simultaneous removal of NO_(x) and SO_(2),inhibited the long-term high-efficiency when used for practical applications.A matching strategy was developed to solve these problems.Antioxidants combination was used to retard the oxidation of antioxidant and enhance inhibition of S(IV)(tetravalent sulfur)oxidation.Hydroquinone(HQ)and sodium thiosulfate(ST)showed a positive synergistic effect on inhibition of S(IV)oxidation.When SO_(2) concentration was 500 and 2000 ppmV,the addition of 0.1 wt.%HQ and 1 wt.%ST decreased the percentage of S(IV)oxidized by oxygen by over 30%and 40%,respectively.Alkali(Na_(2)CO_(3))alleviated the competitive absorption between NO_(x) and SO_(2).Moreover,Na_(2)CO_(3) exhibited an enhancement effect on the absorption of NO_(x) and SO_(2) when coupled with anti-oxidants.While the increase of oxygen pressure accelerated the oxidation of S(IV),the anti-oxidants can retard the oxidation.The measurement of pH suggested the removal efficiency of NO_(x) highly depended on SO_(3)^(2-) concentration rather than pH.The further investigation of the mechanism suggested the match effect was related to the interaction between ST and the intermediate product of HQ.The match strategy holds a potential for application of SO_(3)^(2-) to denitration.

Properties change of activated coke for sintering flue gas purification in cyclic removal of SO_(2) and NO_(x)

The properties of activated coke(AC)for sintering flue gas purification greatly affect the efficiency of desulfurization and denitration,but they gradually change during cycles.The change in properties of coal-based AC during cycles was studied to clarify the change law and AC optimization index.The AC oxygen content rapidly increases 13.49 to 17.87 wt.%in the early cycles to form phenol,which promotes the denitration rate 55.63%to 78.20%.The denitration performance slowly increases in subsequent cycles becaof the generation of quinone AC slow oxidation.However,the oxygen-containing groups are not conducive to adsorption capacity of AC for NO.The adsorbed NO species which can be replaced SO2 is the main NO species on AC,and its amount decreases with the decrease in CC content of AC.The AC chemical loss leads to the opening of closed pores,expansion of original pores and formation of new pores,causing micropore volume to increase 0.085%to 0.152%,compressive strength to decrease 472 to 336 N,and abrasive resistance to decrease 97.87%to 94.16%during cycles.The low oxygen content and high micropore volume are favorable to the initial desulfurization performance,and the former is more decisive.After a while,the desulfurization rate is linearly positively correlated with the micropore volume regardless of the chemistry.4-h desulfurization rate increased 69.03%to 85.91%during 25 cycles due to the increasing micropore volume.The AC properties change in cycles will greatly affect the desulfurization and denitration rate in the height direction of the flue gas purification system.Selecting the coal-based AC with moderate micropore volume,easy oxidation surface and less original oxygen-containing groups facilitates the better purification efficiency at lower cost for sintering plants.

Control of nitrogen oxides emission by selective non-catalytic reduction in preheating section during iron ore pellets production

Reducing the NO_(x) emission from pelletizing process is of great importance to the green development of iron and steel industry.The flue gas temperature of preheating(PH)section during grate-kiln iron ore pelletizing process typically ranges within 850–1050℃,which meets the temperature requirements of selective non-catalytic reduction(SNCR)for NO_(x).The in-bed SNCR behavior of NO_(x) in the PH section was investigated,and the influence of relevant parameters was revealed.Results show that with the flue gas temperature rising,the denitration rate reached a peak value and then declined,where the appropriate temperature range was 950–1000℃.Increasing the NH_(3)/NO ratio(NSR)contributed to improving the denitration rate,and the appropriate NSR was 1.0.Oxygen content in the flue gas also showed an important influence on denitration rate,which reached a peak value and then dropped with the oxygen content rising.Under the condition of 18 vol.%oxygen content,the denitration reaction mainly occurred in the form of 4NO+4NH_(3)+O_(2)=4N_(2)+6H_(2)O.For restricting the competitive reaction of NH_(3) oxidation,the oxygen content in flue gas of PH section should be kept at an appropriate range.In general,the denitration rate reached about 25%in the PH section through spraying ammonia.

Denitration of Nitroarenes Under Ambient Physiological Conditions Catalyzed by Graphdiyne-Supported Palladium

The direct cleavage of C–NO_(2)bonds for reductive denitration of nitroarenes remains a challenging transformation in synthetic organic chemistry.Herein,we report a biocompatible palladium-deposited graphdiyne nanocatalyst(Pd@GDY/DSPE-PEG)that can catalyze reductive denitration of nitroarenes under ambient physiological conditions.Mechanistic studies support this transformation via the oxidative addition of nitroarenes with Pd(0)and subsequent ligand exchange to form arylpalladium hydride.This one-step reductive denitration via Pd@GDY/DSPE-PEG successfully facilitates the repair of the nitrated proteins arising from endogenic ONOO−and restores their physiological function,including blocking the apoptosis pathway in living cells.Moreover,Pd@GDY/DSPE-PEG was further successfully applied for catalytic denitration to reduce the level of 3-nitrotyrosine residues of proteins located in the mouse brain hippocampus in vivo.This study provides an ideal strategy for designing highly active enzymatic mimicking synthetic catalysts for the regulation of the nitrated protein level and the detoxification of nitrative damage of living cells and tissues.