Morphology and valence state evolution of Cu:Unraveling the impact on nitric oxide electroreduction

Ammonia(NH3)serves as a critical component in the fertilizer industry and fume gas denitrification.However,the conventional NH3production process,namely the Haber-Bosch process,leads to considerable energy consumption and waste gas emissions.To address this,electrocatalytic nitric oxide reduction reaction(NORR)has emerged as a promising strategy to bridge NH3consumption to NH3production,harnessing renewable electricity for a sustainable future.Copper(Cu)stands out as a prominent electrocatalyst for NO reduction,given its exceptional NH3yield and selectivity.However,a crucial aspect that remains insufficiently explored is the effects of morphology and valence states of Cu on the NORR performance.In this investigation,we synthesized CuO nanowires(CuO-NF)and Cu nanocubes(Cu-NF)as cathodes through an in situ growth method.Remarkably,CuO-NF exhibited an impressive NH3yield of 0.50±0.02 mg cm^(-2)h^(-1)at-0.6 V vs.reversible hydrogen electrode(RHE)with faradaic efficiency of29,68%±1,35%,surpassing that of Cu-NF(0.17±0.01 mg cm^(-2)h^(-1),16.18%±1.40%).Throughout the electroreduction process,secondary cubes were generated on the CuO-NF surface,preserving their nanosheet cluster morphology,sustained by an abundant supply of subsurface oxygen(s-O)even after an extended duration of 10 h,until s-O depletion ensued.Conversely,Cu-NF exhibited inadequate s-O content,leading to rapid crystal collapse within the same timeframe.The distinctive current-potential relationship,akin to a volcano-type curve,was attributed to distinct NO hydrogenation mechanisms.Further Tafel analysis revealed the exchange current density(i0)and standard heterogeneous rate constant(k0)for CuO-NF,yielding 3.44×10^(-6)A cm^(-2)and 3.77×10^(-6)cm^(-2)s^(-1)when NORR was driven by overpotentials.These findings revealed the potential of CuO-NF for NO reduction and provided insights into the intricate interplay between crystal morphology,valence states,and electrochemical performance.

Cu-based materials for electrocatalytic CO_(2) to alcohols:Reaction mechanism,catalyst categories,and regulation strategies

Electrocatalytic CO_(2) reduction reaction(CO_(2)RR)technology,which enables carbon capture storage and resource utilization by reducing CO_(2) to valuable chemicals or fuels,has become a global research hotspot in recent decades.Among the many products of CO_(2)RR(carbon monoxide,acids,aldehydes and alcohols,olefins,etc.),alcohols(methanol,ethanol,propanol,etc.)have a higher market value and energy density,but it is also more difficult to produce.Copper is known to be effective in catalyzing CO_(2) to high valueadded alcohols,but with poor selectivity.The progress of Cu-based catalysts for the selective generation of alcohols,including copper oxides,bimetals,single atoms and composites is reviewed.Meanwhile,to improve Cu-based catalyst activity and modulate product selectivity,the modulation strategies are straighten out,including morphological regulation,crystalline surface,oxidation state,as well as elemental doping and defect engineering.Based on the research progress of electrocatalytic CO_(2) reduction for alcohol production on Cu-based materials,the reaction pathways and the key intermediates of the electrocatalytic CO_(2)RR to methanol,ethanol and propanol are summarized.Finally,the problems of traditional electrocatalytic CO_(2)RR are introduced,and the future applications of machine learning and theoretical calculations are prospected.An in-depth discussion and a comprehensive review of the reaction mechanism,catalyst types and regulation strategies were carried out with a view to promoting the development of electrocatalytic CO_(2)RR to alcohols.

Simultaneous catalytic hydrolysis of carbonyl sulfide and carbon disulfide over Al_2O_3-K/CAC catalyst at low temperature

In this work, a series of coal-based active carbon （CAC） catalysts loaded by A1203 were prepared by sol-gel method and used for the simulta- neous catalytic hydrolysis of carbonyl sulfide （COS） and carbon disulfide （CS2） at relatively low temperatures of 30-70 ℃. The influences of calcinations temperatures and operation conditions such as： reaction temperature, 02 concentration, gas hourly space velocity （GHSV） and relative humidity （RH） were also discussed respectively. The results showed that catalysts with 5.0 wt% A1203 calcined at 300 ℃ had supe- rior activity for the simultaneous catalytic hydrolysis of COS and CS2. When the reaction temperature was above 50 ℃, catalytic hydrolysis activity of COS could be enhanced but that of CS2 was inhibited. Too high RH could make the catalytic hydrolysis activities of COS and CS2 decrease. A small amount of 02 introduction could enhance the simultaneous catalytic hydrolysis activities of COS and CS2.

球形表面富锰Mn_(x)Co_(3-x)O_(4-η)尖晶石型催化剂选择性催化还原NO_(x)研究

采用共沉淀法制备了高比表面积的Mn_(x)Co_(3-x)O_(4)球形催化剂,研究了NH3选择性催化还原NOx性能。Mn-Co金属氧化物具有尖晶石结构,随着Co含量的增加,晶体结构由四方相转变为立方相。高浓度的表面活性氧物种和变价元素的强有效电子转移(Co^(3+)+Mn^(3+)↔Co^(2+)+Mn^(4+))有利于提高Mn_(x)Co_(3-x)O_(4)(x=1.0、1.5、2.0)尖晶型石催化剂的氧化还原能力,催化剂表面的Mn富集作用形成了氧缺陷结构和丰富的表面活性位点,进一步促进SCR脱硝反应,呈现出优异的催化性能。COtet(CoMn)octO_(4)晶体结构中,Mn离子(Mn^(3+)和Mn^(4+),以三价锰为主)和部分Co离子被配置到八面体中心,这些物种作为活性位点存在着较强的电子转移交互作用,该构型对促进低温脱硝活性和保护活性位点耐受SO_(2)毒害具有重要的意义。Mn-Co尖晶石表面的NH_(3)-SCR脱硝反应过程主要遵循Eley-Rideal反应机理,即吸附态NH_(3)与气态NO(或NO_(2))的反应路径。随着反应温度的增加,反应生成的NH_(4)NO_(3)中间体很可能转化为NH_(4)NO_(2)物种,进而分解为N_(2),提高了催化剂的氮气选择性。

Behaviors and kinetics of toluene adsorption-desorption on activated carbons with varying pore structure

This work was undertaken to investigate the behaviors and kinetics of toluene adsorption and desorption on activated carbons with varying pore structure. Five kinds of activated carbon from different raw materials were selected. Adsorption isotherms and breakthrough curves for toluene were measured. Langmuir and Freundlich equations were fitted to the equilibrium data, and the Freundlich equation was more suitable for simulating toluene adsorption. The process consisted of monolayer, multilayer and partial active site adsorption types. The effect of the pore structure of the activated carbons on toluene adsorption capacity was investigated. The quasi-first-order model was more suitable for describing the process than the quasi-second-order model. The adsorption data was also modeled by the internal particle diffusion model and it was found that the adsorption process could be divided into three stages. In the external surface adsorption process, the rate depended on the specific surface area. During the particle diffusion stage, pore structure and volume were the main factors affecting adsorption rate. In the final equilibrium stage, the rate was determined by the ratio of meso-and macro-pores to total pore volume. The rate over the whole adsorption process was dominated by the toluene concentration. The desorption behavior of toluene on activated carbons was investigated,and the process was divided into heat and mass transfer parts corresponding to emission and diffusion mechanisms, respectively. Physical adsorption played the main role during the adsorption process.

Remarkable N_(2)-selectivity enhancement of NH_(3)-SCR over HPMo modified MnCo-BTC@SiO_(2) catalyst

In this work,the phosphomolybdate(HPMo)modification strategy was applied to improve the N_(2) selectivity of Mn Co-BTC@SiO_(2)catalyst for the selective catalytic reduction of NO_(x),and further,the mechanism of HPMo modification on enhanced catalytic performance was explored.Among Mn Co-BTC@SiO_(2-x) catalysts with different HPMo concentrations,Mn CoBTC@SiO_(2)-0.75 catalyst exhibited not only the highest NH_(3)-SCR performance(95% at 200-300℃)but also the best N_(2)selectivity(exceed 80% at 100-300℃)due to the appropriate redox capacity,greater surface acidity.X-ray photoelectron spectrometer(XPS)and temperature programmed reduction of H_(2)(H_(2)-TPR)results showed that the modification with HPMo reduced the oxidation-reduction performance of the catalyst due to electron transfer from Mo^(5+)to Mn^(4+)/Mn^(3+)and prevent the excessive oxidation of ammonia adsorption species.NH_(3)temperature-programmed desorption of(NH_(3)-TPD)results showed that the modification with HPMo could significantly improve the surface acidity and NH_(3)adsorption,which enhance the catalytic activity and N_(2)selectivity.In-situ diffused reflectance infrared Fourier transform spectroscopy(in-situ DRIFTS)revealed that modification with HPMo increased significantly the amount of adsorbed NH_(3)species on the Bronsted acid site and C_(B)/C_(L),it suppressed the production of N_(2)O by inhibiting the production of NH species,the deep dehydrogenation of ammonia adsorption species.This study provided a simple design strategy for the catalyst to improve the low-temperature catalytic performance and N_(2)selectivity.

Low-temperature NH_(3)-SCR performance of a novel Chlorella@Mn composite denitrification catalyst

The synthesis process of conventional Mn-based denitrification catalysts is relatively complex and expensive.In this paper,a resource application of chlorella was proposed,and a Chlorella@Mn composite denitrification catalyst was innovatively synthesized by electrostatic interaction.The Chlorella@Mn composite denitrification catalyst prepared under the optimal conditions(0.54 g/L Mn^(2+)concentration,20 million chlorellas/mL concentration,450℃ calcination temperature)exhibited a well-developed pore structure and large specific surface area(122 m^(2)/g).Compared with MnOx alone,the Chlorella@Mn composite catalyst achieved superior performance,with~100%NH_(3)selective catalytic reduction(NH_(3)-SCR)denitrification activity at 100-225℃.The results of NH_(3)temperature-programmed desorption(NH_(3)-TPD)and H_(2)temperature-programmed reduction(H_(2)-TPR)showed that the catalyst had strong acid sites and good redox properties.Zeta potential testing showed that the electronegativity of the chlorella cell surface could be used to enrich with Mn^(2+).X-ray photoelectron spectroscopy(XPS)confirmed that Chlorella@Mn had a high content of Mn^(3+)and surface chemisorbed oxygen.In-situ diffuse refectance infrared Fourier transform spectroscopy(in-situ DRIFTS)experimental results showed that both Langmuir-Hinshelwood(L-H)and Eley-Rideal(E-R)mechanisms play a role in the denitrification process on the surface of the Chlorella@Mn catalyst,where the main intermediate nitrate species is monodentate nitrite.The presence of SO_(2)promoted the generation and strengthening of Bronsted acid sites,but also generated more sulfate species on the surface,thereby reducing the denitrification activity of the Chlorella@Mn catalyst.The Chlorella@Mn composite catalyst had the characteristics of short preparation time,simple process and low cost,making it promising for industrial application.

Research progress on metal-organic framework compounds(MOFs)in electrocatalysis

Metal-organic frameworks(MOFs)have favorable characteristics such as large specific surface area,high porosity,structural diversity,and pore surface modification,giving them great potential for development and attractive prospects in the research area of modern materials electrocatalysis.However,unsatisfactory catalytic activity and poor electronic conductivity are the main challenges facing MOFs.This review focuses on MOF-based materials used in electrocatalysis,based on the types of catalytic reactions that have used MOF-based materials in recent years along with their applications,and also looks at some new electrocatalytic materials and their future development prospects.

The poisoning and regeneration effect of alkali metals deposed over commercial V_2O_5-WO_3/TiO_2 catalysts on SCR of NO by NH_3

In this study,commercial V2O5-WO3/TiO2catalysts were deactivated by loading with alkali metals(K and Na).These catalysts were then regenerated by washing with either deionized water or 0.5 mol/L H2SO4(through the ultrasonic-assisted method).The samples used in this research were characterized by NH3-temperature programmed desorption(TPD),and X-ray photoelectron spectroscopy(XPS).Results showed that Na2O and K2O doping can poison the V2O5-WO3/TiO2catalyst and that the poisoning effect of Na2O was stronger than that of K2O.However,the Na2O-loaded sample was easier to regenerate than the K2O-loaded sample.The surfaces of catalysts can be sulfated by washing with dilute sulfuric acid because strong acid sites adhere to the catalyst surface.SO42-could also promote catalyst activity.As indicated by the NH3-TPD findings,the deposition of Na2O and K2O could also reduce the amount of desorbed ammonia and destabilize the acid sites,especially strong chemisorption sites.XPS results revealed that catalysts were deactivated by the decrease in the concentration of chemisorbed oxygen[the Oa/(Oα+Oβ)ratio].In the Na2O-doped catalyst,much chemisorbed oxygen was lost(from 28.8%to10.6%).However,the decrease in the Oa/(Oα+Oβ)ratio was less significant in the K2O-doped catalyst(from28.8%to 23.5%).Nonetheless,the binding energies of O1s broadened with respect to both high and low energy.In particular,the binding energy of chemisorbed oxygen increased from 531.5 to 531.8 eV.

Formation of active oxygen species on single-atom Pt catalyst and promoted catalytic oxidation of toluene

Catalytic oxidation of toluene over noble metal catalysts is a representative reaction for elimination of volatile organic compounds(VOCs).However,to fully understand the activation of molecular oxygen and the role of active oxygen species generated in this reaction is still a challenging target.Herein,MgO nanosheets and single-atom Pt loaded MgO(Pt SA/MgO)nanosheets were synthesized and used as catalysts in toluene oxidation.The activation process of molecular oxygen and oxidation performance on the two catalysts were contrastively investigated.The Pt SA/MgO exhibited significantly enhanced catalytic activity compared to MgO.The oxygen vacancies can be easily generated on the Pt SA/MgO surface,which facilitate the activation of molecular oxygen and the formation of active oxygen species.Based on the experimental data and theoretical calculations,an active oxygen species promoted oxidation mechanism for toluene was proposed.In the presence of H2O,the molecular oxygen is more favorable to be dissociated to generate•OH on the oxygen vacancies of the Pt SA/MgO surface,which is the dominant active oxygen species.We anticipate that this work may shed light on further investigation of t10.1007/s12274-020-2765-1he oxidation mechanism of toluene and other VOCs over noble metal catalysts.

Mn2NiO4 spinel catalyst for high-efficiency selective catalytic reduction of nitrogen oxides with good resistance to H2O and SO2 at low temperature

Mn-Ni oxides with different compositions were prepared using standard co-precipitation(CP) and urea hydrolysis-precipitation(UH) methods and optimized for the selective catalytic reduction of nitrogen oxides(NOx) by NH3 at low temperature.Mn((2))Ni(1)Ox-CP and Mn(2)Ni(1)Ox-UH(with Mn:Ni molar ratio of 2:1) catalysts showed almost identical selective catalytic reduction(SCR) catalytic activity,with about 96% NOx conversion at 750 C and-99%in the temperature range from 100 to 250℃.X-ray diffraction(XRD) results showed that Mn(2)Ni(1)Ox-CP and Mn(2)Ni(1)Ox-UH catalysts crystallized in the form of Mn2NiO4 and MnO2-Mn2NiO4 spinel,respectively.The latter gave relatively good selectivity to N2,which might be due to the presence of the MnO2 phase and high metal-O binding energy,resulting in low dehydrogenation ability.According to the results of various characterization methods,it was found that a high density of surface chemisorbed oxygen species and efficient electron transfer between Mn and Ni in the crystal structure of Mn2NiO4 spinel played important roles in the high-efficiency SCR activity of these catalysts.Mn(2)Ni(1)Ox catalysts presented good resistance to H2O or/and SO2 with stable activity,which benefited from the Mn2NiO4 spinel structure and Eley-Rideal mechanism,with only slight effects from SO2.

Mesoporous molecular sieve-based materials for catalytic oxidation of VOC: A review

As the main contributor of the formation of particulate matter as well as ozone, volatile organic compounds(VOCs) greatly affect human health and the environmental quality. Catalytic combustion/oxidation has been viewed as an efficient, economically feasible and environmentally friendly way for the elimination of VOCs. Supported metal catalyst is the preferred type of catalysts applied for VOCs catalytic combustion because of the synergy between active components and support as well as its flexibility in the composition. The presence of support not only plays the role of keeping the catalyst with good stability and mechanical strength, but also provides a large specific surface for the good dispersion of active components, which could effectively improve the performance of catalyst as well as decrease the usage of active components, especially the noble metal amount. Mesoporous molecular sieves, owing to their large surface area, unique porous structures, large pore size as well as uniform pore-size distribution, were viewed as superior support for dispersing active components. This review focuses on the recent development of mesoporous molecular sieve supported metal catalysts and their application in catalytic oxidation of VOCs. The effect of active component types, support structure, preparation method, precursors, etc. on the valence state, dispersion as well as the loading of active species were also discussed and summarized. Moreover, the corresponding conversion route of VOCs was also addressed.This review aims to provide some enlightment for designing the supported metal catalysts with superior activity and stability for VOCs removal.

Application of AERMOD on near future air quality simulation under the latest national emission control policy of China: A case study on an industrial city

Air quality model can be an adequate tool for future air quality prediction, also atmospheric observations supporting and emission control strategies responders. The influence of emission control policy （emission reduction targets in the national ＂China＇s 12th Five-Year Plan （2011-2015）＂） on the air quality in the near future over an important industrial city of China, Xuanwei in Yunnan Province, was studied by applying the AERMOD modeling system. First, our analysis demonstrated that the AERMOD modeling system could be used in the air quality simulation in the near future for SO2 and NOx under average meteorology but not for PM10. Second, after evaluating the simulation results in 2008 and 2015, ambient concentration of SO2, NOx and PM10 （only 2008） were all centered in the middle of simulation area where the emission sources concentrated, and it is probably because the air pollutions were source oriented. Last but not least, a better air quality condition will happen under the hypothesis that the average meteorological data can be used in near future simulation. However, there are still heavy polluted areas where ambient concentrations will exceed the air quality standard in near future. In spatial allocation, reduction effect of SO2 is more significant than NOx in 2015 as the contribution of SO2 from industry is more than NOx. These results inspired the regulatory applications of AERMOD modeling system in evaluating environmental pollutant control policy

Co-or Ni-modified Sn-MnO_(x) low-dimensional multi-oxides for high-efficient NH_(3)-SCR De-NO_(x):Performance optimization and reaction mechanism

NH_(3)-SCR performances were explored to the relationship between structure morphology and physio-chemical properties over low-dimensional ternary Mn-based catalysts prepared by one-step synthesis method.Due to its strong oxidation performance,Sn-MnO_(x) was prone to side reactions between NO,NH_(3)and O_(2),resulting in the generation of more NO_(2)and N_(2)O,here most of N_(2)O was driven from the non-selective oxidation of NH_(3),while a small part generated from the side reaction between NH_(3)and NO_(2).Co or Ni doping into Sn-MnO_(x) as solid solution components obviously stronged the electronic interaction for actively mobilization and weakened the oxidation performance for signally reducing the selective tendency of side reactions to N_(2)O.The optimal modification resulted in improving the surface area and enhancing the strong interaction between polyvalent cations in Co/Ni-Mn-SnO_(2)to provide more surface adsorbed oxygen,active sites of Mn^(3+) and Mn^(4+),high-content Sn^(4+) and plentiful Lewis-acidity for more active intermediates,which significantly broadened the activity window of Sn-MnOx,improved the N^(2) selectivity by inhibiting N_(2)O formation,and also contributed to an acceptable resistances to water and sulfur.At low reaction temperatures,the SCR reactions over three catalysts mainly obeyed the typical Elye-rideal(E-R)routs via the reactions of adsorbed L-NH_(x)(x=3,2,1)and B-NH_(4)^(+) with the gaseous NO to generate N_(2) but also N_(2)O by-products.Except for the above basic E-R reactions,as increasing the reaction temperature,the main adsorbed NO_(x)-species were bidentate nitrates that were also active in the Langmuir-Hinshelwood reactions with adsorbed L-NH_(x) species over Co/Ni modified Mn-SnO_(2) catalyst.

Novel Mn-Ce bi-oxides loaded on 3D monolithic nickel foam for low-temperature NH_(3)-SCR de-NO_(x):Preparation optimization and reaction mechanism

This study explored the superior citrate method(CM)to synthesize Mn-Ce bi-oxides on 3 D monolithic Ni-foam(NF)catalysts for the selective catalytic reduction of NO by NH_(3)(NH_(3)-SCR).The 17 wt%Mn(7)Ce(3)O_(x)/NF(CM-17)catalyst shows the NO_(x)conversion of 98.7%at 175℃and 90%in the presence of 10 vol%H2 O.It is revealed that the combination of surface-active oxygen(formed by high-level oxygen vacancies)and strongly oxidized Mn4+species promots the Fast-SCR reactions,in which Mn4+species play a leading role in NH_(3)-SCR reaction,and the unsaturated Ni atoms and also Ce3+species promote electron exchange and thus improve the redox performance.The coexistence mechanisms of Fast-SCR reactions and E-R pathways are observed over Mn-CeO_(x)/NF catalyst,which may be promoted by the Br?nsted sites at low temperature.In addition,the heat resistance,stability,3 D monolithic porous structure and excellent physical properties of foam nickel provide a unique growth substrates for catalysts preparation and reaction sites for NO_(x)purification.Therefore,industrial application of Mn-Ce bioxides loaded on 3 D monolithic is proposed to be achieved through reasonable preparation methods.

Simultaneous removal of gaseous CO and elemental mercury over Cu-Co modified activated coke at low temperature

Cu-Co multiple-oxides modified on HNO_3-pretreated activated coke(AC_(N))were optimized for the simultaneous removal of gaseous CO and elemental mercury(Hg^(0))at low temperature(<200℃).It was found that 2%CuOx-10%CoOx/AC_(N)catalyst calcined at 400℃resulted in the coexistence of complex oxides including CuO,Cu_2 O,Co_(3)O_(4,Co_(2)O_(3)and CoO phases,which might be good for the simultaneous catalytic oxidation of CO by Co-species and removal of Hg^(0)by Cu-species,benefiting from the synergistic catalysis during the electrointeraction between Go and Cu cations(CoO■Co_(3)O_(4)and Cu_(2)O■CuO).The catalysis removal of CO oxidation was obviously depended on the reaction temperature obtaining94.7%at 200℃,while no obvious promoting effect on the Hg^(0)removal(68.3%-78.7%).These materials were very substitute for the removal of CO and Hg^(0)from the flue gas with the conditions of 8-20 vol.%O_(2)and flue-gas temperature below 200℃.The removal of Hg^(0)followed the combination processes of adsorption and catalytic oxidation reaction via LangmuirHinshelwood mechanism,while the catalysis of CO abided by the Mars-van Krevelen mechanism with lattice oxygen species.

Study on mechanism of low-temperature oxidation of n-hexanal catalysed by 2D ultrathin Co_(3)O_(4) nanosheets

Achieving high catalytic performance with lower possible cost and higher energetic efficiency is critical for catalytic oxidation of volatile organic compounds(VOCs).However,traditional thermocatalysts generally undergo low catalytic activity and fewer active sites.Herein,this paper synthesizes nearly all-surface-atomic,ultrathin two-dimensional(2D)Co_(3)O_(4) nanosheets to address these problems through offering a numerous active sites and high electron mobility.The 2D Co_(3)O_(4) nanosheets(1.70 nm)exhibit catalyzation to the total oxidation of n-hexanal at the lower temperature of r90%=202℃,and at the space velocity of 5.0×10^(4) h^(-1).It is over 1.2 and 6 times higher catalytic activity than that of 2D CoO nanosheets(1.71 nm)and bulk Co_(3)O_(4) counterpart,respectively.Transient absorption spectroscopy analysis shows that the oxygen vacancy defect traps electrons,thereby preventing the recombination with holes,increasing the lifetime of electrons,and making electron-holes reach a nondynamic equilibrium.The longer the electron lifetime is,the easier the oxygen vacancy defects capture electrons.Furthermore,the defects combine with oxygen to form active oxygen components.Compared with the lattice oxygen involved in the reaction of bulk Co_(3)O_(4),the nanosheets change the catalytic reaction path,which effectively reduces the activation energy barrier from 34.07 to 27.15 kJ/mol.The changed surface disorder,the numerous coordinatively-unsaturated Co atoms and the high ratio of O_(ads)/O_(lat) on the surface of 2D Co_(3)O_(4) nanosheets are responsible for the catalytic performance.

Development of Mn-Si-MEL as a bi-functional adsorption-catalytic oxidation material for VOCs elimination

Mn-Si-MEL zeolite was developed as a bi-functional adsorption-catalytic oxidation material for volatile organic compounds(VOCs)elimination due to its good hydrophobicity&good organophileproperty brought by the substitution of Mn for Al in zeolite and the superior catalytic oxidation property endowed by the existence of Mn species.Various Mn-Si-MEL samples were obtained by introducing Mn to MEL crystallization system via different ways.It was found the incorporated Mn ways have a significant effect on the behavior of Mn being involved in the crystallization of MEL and finally influenced the distribution of Mn in zeolite as well the physicochemical properties of product zeolite.The seeding method(MnS2(Seed))is favorable for the good incorporation and uniform distribution of Mn in zeolite while both recrystallization method(Mn-S2(RC))and direct synthesis method(Mn-S2(DH))are favorable for obtaining more reducible Mn species and surface adsorbed oxygen species.The Mn amount incorporated into zeolite follows Mn-S2(RC)(1.96 wt%)>Mn-S2(Seed)(1.07 wt%)≈Mn-S2(DH)(0.97 wt%),the adsorption capacity of various samples follows Mn-S2(Seed)(83.3μmol/g)≈Mn-S2(RC)(82.1μmol/g)>Mn-S2(DH)(76.1μmol/g),while the catalytic oxidation ability of three samples follows Mn-S2(RC)≈Mn-S2(DH)>Mn-S2(Seed).Furthermore,Mn-S2(RC)which exhibits both superior adsorption capacity and catalytic oxidation ability shows good hydrophobicity and superior recyclability,demonstrating its great potential to be applied in the VOCs elimination by an enrichment-degradation route.

Promotional catalytic activity and reaction mechanism of Ag-modified Ce_(0.6)Zr_(0.4)O_(2) catalyst for catalytic oxidation of ammonia

Ce1-xZrxO_(2) composite oxides(molar,x=0-1.0,interval of 0.2)were prepared by a cetyltrimethylammonium bromide-assisted precipitation method.The enhancement of silver-species modification and catalytic mechanism of adsorption-transformationdesorption process were investigated over the Ag-impregnated catalysts for lowtemperature selective catalytic oxidation of ammonia(NH_(3)-SCO).The optimal 5 wt.%Ag/Ce_(0.6)Zr_(0.4)O_(2) catalyst presented good NH_(3)-SCO performancewith>90% NH_(3) conversion at temperature(T)≥250°C and 89% N_(2) selectivity.Despite the irregular block shape and underdeveloped specific surface area(∼60m2/g),the naked and Ag-modified Ce_(0.6)Zr_(0.4)O_(2) solid solution still obtained highly dispersed distribution of surface elements analyzed by scanning electron microscope-energy dispersive spectrometer(SEM-EDS)(mapping),N_(2) adsorptiondesorption test and X-ray diffraction(XRD).H2 temperature programmed reduction(H2-TPR)and X-ray photoelectron spectroscopy(XPS)results indicated that Ag-modification enhanced the mobility and activation of oxygen-species leading to a promotion on CeO_(2) reducibility and synergistic Ag0/Ag+and Ce^(4+)/Ce^(3+)redox cycles.Besides,Ag+/Ag_(2)O clusters could facilitate the formation of surface oxygen vacancies that was beneficial to the adsorption and activation of ammonia.NH3-temperature programmed desorption(NH_(3)-TPD)showed more adsorption-desorption capacity to ammoniawere provided by physical,weakandmedium-strong acid sites.Diffused reflectance infrared Fourier transform spectroscopy(DRIFTS)experiments revealed the activation of ammonia might be the control step of NH3-SCO procedure,during which NH3 dehydrogenation derived from NHx-species and also internal selective catalytic reduction(i-SCR)reactions were proposed.

δ-MnO_(2) decorated layered double oxides in-situ grown on nickel foam towards electrothermal catalysis of n-heptane

Energy-saving and efficient monolithic catalysts are hotspots of catalytic purification of industrial gaseous pollutants.Here,we have developed an electrothermal catalytic mode,in which the ignition temperature required for the reaction is provided by Joule heat generated when the current flows through the catalyst.In this paper,Mn/NiAl/NF,Mn/NiFe/NF and Mn/NF metal-based monolithic catalysts were prepared using nickel foam (NF) as the carrier for thermal and electrothermal catalysis of n-heptane.The results indicated that Mn-based monolithic catalysts exhibit high activity in thermal and electrothermal catalysis.Mn/NiFe/NF achieve conversion of n-heptane more than 99%in electrothermal catalysis under a direct-current (DC) power of 6 W,and energy-saving is 54% compared with thermal catalysis.In addition,the results indicated that the introduction of NiAl (or NiFe) greatly enhanced the catalytic activity of Mn/NF,which attributed to the higher specific surface area,Mn3+/Mn4+,Ni3+/Ni^(2+),adsorbed oxygen species (Oads)/lattice oxygen species (Olatt),redox performance of the catalyst.Electrothermal catalytic activity was significantly higher than thermal catalytic activity before complete conversion,which may be related to electronic effects.Besides,Mn/NiFe/NF has good cyclic and long-term stability in electrothermal catalysis.This paper provided a theoretical basis for applying electrothermal catalysis in the field of VOCs elimination.