Molecular engineering binuclear copper catalysts for selective CO_(2) reduction to C_(2) products

Molecular copper catalysts serve as exemplary models for correlating the structure-reaction-mechanism relationship in the electrochemical CO_(2) reduction(eCO_(2)R),owing to their adaptable environments surrounding the copper metal centres.This investigation,employing density functional theory calculations,focuses on a novel family of binuclear Cu molecular catalysts.The modulation of their coordination configuration through the introduction of organic groups aims to assess their efficacy in converting CO_(2) to C_(2)products.Our findings highlight the crucial role of chemical valence state in shaping the characteristics of binuclear Cu catalysts,consequently influencing the eCO_(2)R behaviour,Notably,the Cu(Ⅱ)Cu(Ⅱ)macrocycle catalyst exhibits enhanced suppression of the hydrogen evolution reaction(HER),facilitating proton trans fer and the eCO_(2)R process.Fu rthermore,we explo re the impact of diverse electro n-withdrawing and electron-donating groups coordinated to the macrocycle(R=-F,-H,and-OCH_3)on the electron distribution in the molecular catalysts.Strategic placement of-OCH_3 groups in the macrocycles leads to a favourable oxidation state of the Cu centres and subsequent C-C coupling to form C_(2) products.This research provides fundamental insights into the design and optimization of binuclear Cu molecular catalysts for the electrochemical conversion of CO_(2) to value-added C_(2) products.

Cerium-tungsten oxides supported on activated red mud for the selective catalytic reduction of NO_(x)

Activated red mud(RM)has been proved to be a promising base material for the selective catalysis reduction(SCR)of NOx.The inherent low reducibility and acidity limited its low-temperature activity.In this work,molybdenum oxide,tungsten oxide,and cerium oxide were used to reconfigure the redox sites and acid sites of red mud based catalyst.When activated red mud was reconfigured by cerium-tungsten oxide(Ce-W@RM),the NOx conversion kept above 90%at 219-480℃.The existence of Ce^(3+)/Ce^(4+) redox electron pairs provided more surface adsorbed oxygen(O_(α)) and served as a redox cycle.Positive interactions between Ce,W species and Fe oxide in red mud occurred,which led to the formation of unsaturated chemical bond and promoted the activation of adsorbed NH_(3) species.WO_(3) and Ce_(2)(WO_(4))_(3)(formed by solid-state reaction between Ce and W species)could provide more Brønsted acid sites(W-O modes of WO_(3),W=O or W-O-W modes of Ce_(2)(WO_(4))_(3)).CeO_(2) species could provide more Lewis acid sites.The Langmuir-Hinshelwood(L-H)routes and Eley-Rideal(E-R)routes occurred in the low-temperature SCR reaction on the Ce-W@RM surface.NH_(4)^(+) species on Brønsted acid sites,NH_(3) species on Lewis acid sites,bidentate nitrate and bridging nitrate species were key active intermediates species.

Superior resistance to alkali metal potassium of vanadium-based NH_(3)-SCR catalyst promoted by the solid superacid SO_(4)^(2-)-TiO_(2)

The significant decrease of acid sites caused by alkali metal poisoning is the major factor in the deactivation of commercial V_(2)O_(5)-WO_(3)/TiO_(2)NH_(3)-SCR catalysts.In this work,the solid superacid SO_(4)^(2-)-TiO_(2) modified by sulfate radicals,was selected as the catalyst support,which showed superior potassium resistance.The physicochemical properties and K-poisoning resistance of the V_(2)O_(5)-WO_(3)/SO_(4)^(2-)-TiO_(2)(VWSTi) catalyst were carried out by XRD,BET,H2-TPR,NH3-TPD,XPS,in situ DRIFTS and TG.The results pointed out that the introduction of SO_(4)^(2-)significantly increased the NH3-SCR catalytic activity at high temperatures,with an exceptionally high NO_(x) conversion over 90% between 275℃ and 500℃.When 0.5%(mass) K_(2)O was doped on the catalysts,the catalytic performance of the traditional V_(2)O_(5)-WO_(3)/TiO_(2)(VWTi) catalyst decreased significantly,while the VWSTi catalyst could still maintain a NOxconversion over 90%in the range of 300–500℃.The characterizations suggested that the support of SO_(4)^(2-)-TiO_(2) greatly increased the number of acidic sites,thereby enhancing the adsorption capacity of the reactant NH_(3).The results above demonstrated a potential approach to achieve superior potassium resistance for NH3-SCR catalysts using solid superacid.

Effect of samarium on the N_(2) selectivity of Sm_(x)Mn_(0.3-x)Ti catalysts during selective catalytic reduction of NO_(x) with NH_(3)

This work aims to study the improvement effect of Sm on Mn-based catalysts for selective catalytic reduction (SCR) of NO with NH3.A series of Sm_(x)Mn_(0.3-x)-xTi catalysts (x=0,0.1,0.15,0.2,and 0.3) were prepared by co-precipitation.Activity tests indicated that the Sm_(0.15)Mn_(0.15)Ti catalyst showed superior performances,with a NO conversion of 100%and N_(2)selectivity above 87%at 180–300℃.The characterizations showed that Sm doping suppressed the crystallization of TiO_(2)and Mn2O3phases and increased the specific surface area and acidity.In particular,the surface area increased from 152.2 m^(2)·g^(-1)for Mn0.3Ti to 241.7 m^(2)·g^(-1)for Sm_(0.15)Mn_(0.15)Ti.These effects contributed to the high catalytic activity.The X-ray photoelectron spectroscopy (XPS) results indicated that the relative atomic ratios of Sm^(3+)/Sm and Oβ/O of Sm_(0.15)Mn_(0.15)Ti were 76.77at%and 44.11at%,respectively.The presence of Sm contributed to an increase in surface-absorbed oxygen (Oβ) and a decrease in Mn^(4+)surface concentration,which improved the catalytic activity.In the results of hydrogen temperature-programmed reduction(H_(2)-TPR),the presence of Sm induced a higher reduction temperature and lower H_(2)consumption (0.3 mmol·g^(-1)) for the Sm_(0.15)Mn_(0.15)Ti catalyst compared to the Mn0.3Ti catalyst.The decrease in Mn^(4+)weakened the redox property of the catalysts and increased the N_(2)selectivity by suppressing N_(2)O formation from NH3oxidation and the nonselective catalytic reduction reaction.The in situ diffuse reflectance infrared Fourier transform spectra (DRIFTs) revealed that NH3-SCR of NO over the Sm_(0.15)Mn_(0.15)Ti catalyst mainly followed the Eley–Rideal mechanism.Sm doping increased surface-absorbed oxygen and weakened the redox property to improve the NO conversion and N_(2)selectivity of the Sm_(0.15)Mn_(0.15)Ti catalyst.

A Multi-Attribute Decision-Making Method Using Belief-Based Probabilistic Linguistic Term Sets and Its Application in Emergency Decision-Making

Probabilistic linguistic term sets(PLTSs)are an effective tool for expressing subjective human cognition that offer advantages in the field ofmulti-attribute decision-making(MADM).However,studies have found that PLTSs have lost their ability to accurately capture the views of decision-makers(DMs)in certain circumstances,such as when the DM hesitates between multiple linguistic terms or the decision information is incomplete,thus affecting their role in the decision-making process.Belief function theory is a leading streamof thought in uncertainty processing that is suitable for dealing with the limitations of PLTS.Therefore,the purpose of this study is to extend PLTS to incorporate belief function theory.First,we provide the basic concepts of the extended PLTS(i.e.,belief-based PLTS)through case analyses.Second,the aggregation operator of belief-based PLTS is defined with the ordered weighted average(OWA)-based soft likelihood function,which is improved by considering the reliability of the information source.Third,to measure the magnitude of different belief-based PLTSs,the belief interval of singleton is calculated,and the comparison method of belief-based PLTS is constructed based on probabilities.On the basis of the preceding discussion,we further develop an emergency decision framework that includes several novel techniques,such as attribute weight determination and decision information aggregation.Finally,the usefulness of the framework is demonstrated through a case study,and its effectiveness is illustrated through a series of comparisons.

One-pot synthesis of bimetallic CeCu-SAPO-34 for high-efficiency selective catalytic reduction of nitrogen oxides with NH_(3) at low temperature

NH_(3) selective catalytic reduction(SCR) has been widely recognized as a promising technique for reducing nitrogen oxides from diesel vehicle exhausts. High-efficiency SCR catalysts that could perform at low temperatures are essential to denitration. In this work, a series of bimetallic CeCu-SAPO-34 molecular sieves were synthesized by one-step hydrothermal method. The Ce Cu-SAPO-34 maintained good crystallinity and a regular hexahedron appearance of Cu-SAPO-34 after introducing Ce species, while exhibiting a higher specific surface area and pore volume. The as-prepared CeCu-SAPO-34 with 0.02%(mass) Ce constituent exhibited the best catalytic activity below 300℃ and a maximum NO_(x) conversion of 99% was attained;the NO_(x) removal rates of more than 68% and 94% were achieved at 150℃ and 200℃, respectively. And the introduction of cerium species in Cu-SAPO-34 improves the low-temperature hydrothermal stability of the catalyst towards NH_(3)-SCR reaction. Additionally, the introduced Ce species could enhance the formation of abundant weak Br?nsted acid centers and promote the synergistic effect between CuO grains and isolated Cu^(2+) to enhance the redox cycle, which benefit the NH_(3)-SCR reaction.This work provides a facile synthesis method of high-efficiency SCR denitration catalysts towards diesel vehicles exhaust treatment under low temperature.

Transformation of mercury speciation through the SCR system in power plants

Coal-fired utility boilers are now identified as the largest source of mercury in the United States. There is speculation that the installation of selective catalytic reduction （SCR） system for reduction of NOx can also prompt the oxidation and removal of mercury. In this paper, tests at six full-scale power plants with similar type of the SCR systems are conducted to investigate the effect of the SCR on the transformation of mercury speciation. The results show that the SCR system can achieve more than 70%-80% oxidation of elemental mercury and enhance the mercury removal ability in these units. The oxidation of elemental mercury in the SCR system strongly depends on the coal properties and the operation conditions of the SCR systems. The content of chloride in the coal is the key factor for the oxidization process and the maximum oxidation of elemental mercury is found when chloride content changes from 400 to 600 ppm. The sulfur content is no significant impact on oxidation of elemental mercury.

Influence of chromium modification on the properties of MnO_x-FeO_x catalysts for the low-temperature selective catalytic reduction of NO by NH_3

Catalytic properties of MnOx-FeOx complex oxide （hereafter denoted as Mn-Fe） catalysts modified with different loadings of chromium oxide were investigated by using the combination of physico-cbemical techniques, such as N2 physisorption, X-ray diffraction （XRD）, high-resolution transmission electron microscope （HRTEM）, in situ Fourier transform infrared spectroscopy （in situ FT-IR） and temperature-programmed reduction （TPR） and their catalytic activities were evaluated with the selective catalytic reduction （SCR） of NOx by NH3. It was found that with the addition of Cr, more NO could be removed in the low-temperature window （below 120 ℃）. Among the tested catalysts, Mn-Fe- Cr （2 ： 2 ： 1） catalyst exhibited the best catalytic performance at 80 ℃ with the NO conversion higher than 90%. The combination of the reaction and characterization results indicated that （1） the strong interaction among tertiary metal oxides existed in the catalysts when Cr was appropriately added, which made the active components better dispersed with less agglomeration and sintering and the largest BET specific surface area could be obtained; （2） Cr improved the low-temperature reducibility of the catalyst and promoted the formation of the active intermediate （-NH3＋）, which favored the low-temperature SCR reaction.

Kinetics of selective catalytic reduction of NO by NH_3 on Fe-Mo/ZSM-5 catalyst

The catalyst of Fe-Mo/ZSM-5 has been found to be more active than Fe-ZSM-5 and Mo/ZSM-5 separately for selective catalytic reduction （SCR） of nitric oxide （NO） with NH3. The kinetics of the SCR reaction in the presence of O2 was studied in this work. The results showed that the observed reaction orders were 0.74-0.99, 0.01-0.13, and 0 for NO, O2 and NH3 at 350-450℃, respectively. And the apparent activation energy of the SCR was 65 kJ/mol on the Fe-Mo/ZSM-5 catalyst. The SCR mechanism was also deduced. Adsorbed NO species can react directly with adsorbed ammonia species on the active sites to form N2 and H2O. Gaseous O2 might serve as a reoxidizing agent for the active sites that have undergone reduction in the SCR process. It is also important to note that a certain amount of NO was decomposed directly over the Fe-Mo/ZSM-5 catalyst in the absence of NH3.

TiO_2-Supported Binary Metal Oxide Catalysts for Low-temperature Selective Catalytic Reduction of NO_x with NH_3

Binary metal oxide（MnOx-A/TiO2）catalysts were prepared by adding the second metal to manganese oxides supported on titanium dioxide（TiO2）,where,A indicates Fe2O3,WO3,MoO3,and Cr2O3.Their catalytic activity,N2 selectivity,and SO2 poisonous tolerance were investigated.The catalytic performance at low temperatures decreased in the following order：Mn-W/TiO2〉Mn-Fe/TiO2〉Mn-Cr/TiO2〉Mn-Mo/TiO2,whereas the N2 selectivity decreased in the order：Mn-Fe/TiO2〉Mn-W/TiO2〉Mn-Mo/TiO2〉Mn-Cr/TiO2.In the presence of 0.01%SO2 and 6%H2O,the NOx conversions in the presence of Mn-W/TiO2,Mn-Fe/TiO2,or Mn-Mo/TiO2 maintain 98.5%,95.8%and 94.2%, respectively,after 8 h at 120°C at GHSV 12600 h？ 1 .As effective promoters,WO3 and Fe2O3 can increase N2 selectivity and the resistance to SO2 of MnOx/TiO2 significantly.The Fourier transform infrared（FTIR）spectra of NH3 over WO3 show the presence of Lewis acid sites.The results suggest that WO3 is the best promoter of MnOx/TiO2,and Mn-W/TiO2 is one of the most active catalysts for the low temperature selective catalytic reduction of NO with NH3.

Combination of biodiesel-ethanol-diesel fuel blend and SCR catalyst assembly to reduce emissions from a heavy-duty diesel engine

In this study, the efforts to reduce NOx and particulate matter （PM） emissions from a diesel engine using both ethanol-selective catalytic reduction （SCR） of NOx over an Ag/Al2O3 catalyst and a biodiesel-ethanol-diesel fuel blend （BE-diesel） on an engine bench test are discussed. Compared with diesel fuel, use of BE-diesel increased PM emissions by 14% due to the increase in the soluble organic fraction （SOF） of PM, but it greatly reduced the Bosch smoke number by 60%-80% according to the results from 13-mode test of European Stationary Cycle （ESC） test. The SCR catalyst was effective in NOx reduction by ethanol, and the NOx conversion was approximately 73%. Total hydrocarbons （THC） and CO emissions increased significantly during the SCR of NOx process. Two diesel oxidation catalyst （DOC） assemblies were used after Ag/Al2O3 converter to remove CO and HC. Different oxidation catalyst showed opposite effect on PM emission. The PM composition analysis revealed that the net effect of oxidation catalyst on total PM was an integrative effect on SOF reduction and sulfate formation of PM. The engine bench test results indicated that the combination of BE-diesel and a SCR catalyst assembly could provide benefits for NOx and PM emissions control even without using diesel particle filters （DPFs）.

Low-Temperature SCR of NO with NH_3 on Mn-Based Catalysts Modified with Cerium

A series of Mn-based catalysts, MnOx, MnOx-CeO, Pd-Mn-Ce, MnOx/AC were prepared. And their performances for NO low-temperature SCR were investigated in this study. The NO conversion is about 90% at 100 ℃ on MnOx-CeOand almost all NO can be converted at 120 ℃. Similar results are also observed in the tests on MnOx-CeO/AC. The excellent low-temperature catalytic activity of modified Mn-based catalysts, which may be mainly due to the oxygen storage function of CeO, can improve the oxygen flow on the catalysts surface. Then the oxidation of NO to NO2 is accelerated, which is the key step of NO SCR.

Study on methane selective catalytic reduction of NO on Pt/Ce_(0.67)Zr_(0.33)O_2 and its application

Monolithic catalysts of Pt/La-Al2O3 and Pt/Ce0.67Zr0.3302 were prepared to investigate methane selective catalytic reduction （SCR） of NO. The results indicate that Pt/Ce0.67Zr0.33O2 shows high activity and both NO and CH4 can be converted completely at 450℃. Meanwhile, NO and CH4 can be converted completely when there exists excess oxygen. The Pt/Ce0.67Zr0.33O2 catalyst were further investigated by using methane as reducing agent to SCR NO in a novel equipment which combined the CH4 selective catalytic reduction of NO with methane combustion. The result shows that the catalyst is high active and the novel equipment is very effective. The conversion of NO is above 92% under the conditions used in this work. The prepared burner and catalysts have great potential for application.

Study on SCR De NO_x mechanism through in situ electrical conductivity measurements on V_2O_5-WO_3/TiO_2 catalysts

V2O5-WO3/TiO2 catalysts were prepared by impregnation method and in situ electrical conductivity measurements were carried out to investigate the reaction mechanism for ammonia SCR (selective catalytic reduction) of NOx. The electrical conductivity change with ammonia supply and the increase of electrical conductivity were mainly caused by reduction of the labile surface oxygen. The electrical conductivity change of catalysts shows close relationship with the conversion rate of NOx. Variation of conversion rate in atmosphere without gaseous oxygen also supports that the labile lattice oxygen is indispensable in the initial stage of the de NOx reaction. These results suggest that the liable lattice oxygen acts decisive role in the de NOx mechanism. They also support that De NOx reaction occurs through the Eley-Rideal type mechanism. The amount of labile oxygen can be estimated from the measurement of electrical conductivity change for catalysts with ammonia supply.

Unregulated emissions from a diesel engine equipped with vanadium-based urea-SCR catalyst

The present work is aimed at the study of number-size distribution of particles, volatile organic compounds （VOCs）, and carbonyl compounds （CC） or carbonyls emitted from a 4-cylinder turbocharged diesel engine equipped with a vanadium-based urea selective catalytic reduction catalyst. The engine was run on an electric dynamometer in accordance with the European steady-state cycle. Pollutants were analyzed using an electric low pressure impactor, a gas chromatograph/mass spectrometer, and a high performance liquid chromatography system for the number-size distribution of particles, VOCs, and CC emissions, respectively. Experimental results revealed that total number of particles were decreased, and their number-size distributions were moved from smaller sizes to larger sizes in the presence of the catalyst. The VOCs were greatly reduced downstream of the catalyst. There was a strong correlation between the conversion of styrene and ethyl benzene. The conversion rate of benzene increased with increase of catalyst temperature. Formaldehyde, acetaldehyde, acrolein and acetone were significantly reduced, resulting in a remarkable abatement in carbonyls with the use of the vanadium-based urea-SCR system.

Redistributing Cu species in Cu-SSZ-13 zeolite as NH3-SCR catalyst via a simple ion-exchange

The nature and distribution of Cu species in Cu-SSZ-13 play a vital role in selective catalytic reduction of NO by NH3(NH3-SCR),but existing methods for adjusting the Cu distribution are complex and difficult to control.Herein,we report a simple and effective ion-exchange approach to regulate the Cu distribution in the one-pot synthesized Cu-SSZ-13 that possesses sufficient initial Cu species and thus provides a“natural environment”for adjusting Cu distribution precisely.By using this proposed strategy,a series of Cu-SSZ-13x zeolites with different Cu contents and distributions were obtained.It is shown that the dealumination of the as-synthesized Cu-SSZ-13 during the ion-exchange generates abundant vacant sites in the double six-membered-rings of the SSZ-13 zeolite for relocating Cu2+species and thus allows the redistribution of the Cu species.The catalytic results showed that the ion-exchanged Cu-SSZ-13 zeolites exhibit quite different catalytic performance in NH3-SCR reaction but superior to the parent counterpart.The structure–activity relationship analysis indicates that the redistribution of Cu species rather than other factors(e.g.,crystallinity,chemical composition,and porous structure)is responsible for the improved NH3-SCR performance and SO_(2) and H_(2)O resistance.Our work offers an effective method to precisely adjust the Cu distribution in preparing the industrial SCR catalysts.

Overwhelming low ammonia escape and low temperature denitration efficiency via MnOx-decorated two-dimensional MgAl layered double oxides

Low temperature catalysts are attracting increasing attention in the selective catalytic reduction(SCR)of NO with NH3.Mn Ox-decorated Mg Al layered double oxide(Mn/Mg Al-LDO)was synthesized via a facile fast pour assisted co-precipitation(FP-CP)process.Compared to the Mn/Mg Al-LDO obtained via slow drop assisted coprecipitation(SD-CP)method,the Mn/Mg Al-LDO(FP-CP)has excellent activity.The Mn/Mg Al-LDO(FP-CP)catalyst was shown to possess a high NO conversion rate of 76%-100%from 25 to 150℃,which is much better than the control Mn/Mg Al-LDO(SD-CP)(29.4%-75.8%).In addition,the Mn/Mg Al-LDO(FP-CP)offered an enhanced NO conversion rate of 97%and a N2selectivity of 97.3%at 100℃;the NO conversion rate was 100%and the N2selectivity was 90%at 150℃with a GHSV of 60,000 h^-1.The Mn/Mg Al-LDO(FP-CP)catalyst exhibited a smaller fragment nano-sheet structure(sheet thickness of 7.23 nm).An apparent lattice disorder was observed in the HRTEM image confirming the presence of many defects.The H2-TPR curves show that the Mn/Mg Al-LDO(FP-CP)catalyst has abundant reducing substances.Furthermore,the enhanced surface acidity makes the NH3concentration of the Mn/Mg Al-LDO(FP-CP)catalyst lower than 100 ml·m^-3after the reaction from 25 to 400℃.This can effectively reduce the ammonia escape rate in the SCR reaction.Thus,the Mn/Mg Al-LDO(FP-CP)catalyst has potential applications in stationary industrial installations for environmentally friendly ultra-low temperature SCR.

Selective catalytic NO_x reduction on Antimony promoted V_2O_5-Sb/TiO_2 catalyst

Quantum chemical calculation was carried out to choose a promoter which can reduce the poisoning of V2O5/TiO2 catalysts by SO2. Several atoms were chosen as candidates and new catalysts were synthesized by impregnation method. The NOx conversion rate was measured at temperatures between 100 and 400 ℃ and poisoning effect was investigated. The most promising candidate promoter, Se, was excluded because of its high vapor pressure. On the other hand, Sb shows best promoting properties. Sb promoted catalyst reaches the maximum NOx conversion rate at 250 ℃. It also shows considerably enhanced resistance to poisoning of V2O5/TiO2 catalysts by SO2.

Catalytic Performance of MnO_x-WO_3/TiO_2 Catalyst for Selective Catalytic Reduction of NO_x with NH_3 and Its Tolerance Towards SO_2

The performance of Mn-W/TiO2 for selective catalytic reduction（SCR） of NOx with NH3 and its resistance to different concentrations of SO2 at various temperatures were investigated. The results show that WO3 increased the active sites and enhanced the strength of acid, so it was an effective promoter of MnOJTiO2. The NOx conversion on Mn-W/TiO2 ranges from 80.3% to 99.6% between 100 ℃to 350℃ at GHSV=18900 h 1, while N2 product selectivity changes from 100% to 98.7%. In the presence of 0.01% SO2 and 6% H20, NOx conversion maintained 98.5% at 120℃. The influence of more than 0.01% SO2 on the activity of MnOx-WO3/TiO2 will disappear if the temperature rises above 250℃. By means of heating and sweeping with He, the activity of the catalysts can be recovered. At 300℃, NOx conversion yielded 99% with 0.07% SO2 and reached the level of commercial V-W/TiO2 catalysts. The Mn-W/TiO2 catalyst showed excellent performance for SCR of NOx with NH3 in a wider range of temperature with strong tolerance to SO2.