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.

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.

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.

Study on Simultaneous Catalytic Reduction of Sulfur Dioxide and Nitric Oxide on Rare Earth Mixed Compounds

CeO2/γ-Al2O3, La203/γ-Al2O3, CeO2-La203/γ-Al2O3 and CeO2-La2O3, which were prepared by impregnating in certain ratio, were used as the catalysts for the reduction of SO2 and NO by CO. Separate and simultaneous removal of SO2 and NO over LaEO3/γ-Al2O3, CeOE/γ-Al2O3, CeOE-LaEO3/γ-Al2O3 were investigated. The phase characteristics of catalysts were also analyzed by X-ray diffraction. The result shows that the conversions of SO2 and NO are above 98 % over CeOE/γ-Al2O3 and CeOE-LaEO3/γ-Al2O3. After SO2 is added in the NO-CO-N2 system （NO ：SO2 = 1：2 - 1 ： 3）, the conversions of SO2 and NO are both above 98%. Furthermore, it is found that CeO2-La2O3 with various ratios has different activity for the simultaneous reduction of SO2 and NO.

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.

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.

Catalytic reduction of nitric oxide with carbon monoxide on copper-cobalt oxides supported on nano-titanium dioxide

A series of copper-cobalt oxides supported on nano-titanium dioxide were prepared for the reduction of nitric oxide with carbon monoxide and characterized using techniques such as XRD, BET and TPR. Catalyst CuCoOx/TiO2 with Cu/Co molar ratio of 1/2, CuCo total loading of 30% at the calcination temperature of 350℃ formed CuCo204 spinel and had the highest activity. NO conversion reached 98.9% at 200℃. Mechanism of the reduction was also investigated, N20 was mainly yielded below 100℃, while N2 was produced instead at higher temperature. O2 was supposed to accelerate the reaction between NOx and CO for its oxidation of NO to give more easily reduced NO2, but the oxidation of CO by O2 to CO2 decreased the speed of the reaction greatly. Either SO2 or H20 had no adverse impact on the activity of NO reduction; however, in the presence of both SO2 and H20, the catalyst deactivated quickly.

Direct and Indirect Applications of Dielectric Barrier Discharge Plasma to Catalytic Reduction of Nitrogen Oxides from Exhaust Gas

Dielectric barrier discharge （DBD） plasma was utilized to oxidize NO contained in the exhaust gas to NO2, ultimately improve the selective catalytic reduction of nitrogen oxides （NOx）. In the one case, DBD was created directly in the exhaust gas （direct application）, and in the an other case, ozone produced by DBD was injected into the exhaust gas （indirect application）. A comparative study between such direct and indirect applications of DBD plasma was made in terms of the NOx removal efficiency and the energy consumption. The NO2 content in the exhaust gas was changed by the voltage applied to the DBD device （for direct application） or by the amount of ozone added to the exhaust gas （for indirect application）. In both cases, NO was easily oxidized to NO2, and the change in NO2 content largely affected the NOx removal performance of the catalytic reactor placed downstream, where both NO and NO2 were reduced to N2 in the presence of ammonia as the reducing agent. The experiments were primarily concerned with the effect of reaction temperature on the catalytic NOx reduction at various NO2 contents. The direct and indirect applications of DBD were found to remarkably improve the catalytic NOx reduction, especially at low temperatures.

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.

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.

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.

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.

Low-Temperature Selective Catalytic Reduction of NO with NH_3 over Fe–Ce–O_x Catalysts

In this study,we used a simple impregnation method to prepare Fe-Ce-O_x catalysts and tested them regarding their low-temperature(200-300 ℃) selective catalytic reduction(SCR) of NO using NH_3.We investigated the effects of Fe/Ce molar ratio,the gas hourly space velocity(GHSV),the stability and SO_2/H_2O resistance of the catalysts.The results showed that the FeCe(1:6)O_x(Ce/Fe molar ratio is 1:6) catalyst,which has some ordered parallel channels,exhibited good SCR performance.The FeCe(1:6)O_x catalyst had the highest NO conversion with an activity of 94-99%at temperatures between 200 and300 ℃ at a space velocity of 28,800 h^(-1).The NO conversion for the FeCe(1:6)O_x catalyst also reached 80-98%between 200 and 300 ℃ at a space velocity of204,000h^(-1).In addition,the FeCe(1:6)O_x catalyst demonstrated good stability in a 10-h SCR reaction at200-300 ℃.Even in the presence of SO_2 and H_2O,the FeCe(1:6)O_x catalyst exhibited good SCR performance.

Catalytic Mechanism of KCl during Carbothermic Reduction of Pre-Oxidized Ilmenite

As alkali additive,KC1 catalyzes effectively the carbothermic reduction of pre-oxidized ilmenite,and the catalytic effect becomes more remarkable as the amount of KC1 increases.During the carbothermic reduction,the gaseous product consists mainly of CO,and the partial pressure of which increases with reaction temperature.The EPMA and XPS of the partially reduced ilmenite ore and that of the used graphite as reductant showed that the potassium ions enter both ilmenite particles and graphite powders during reduction.The above-mentioned phenomena result in the distortion of ilmenite and carbon structure by potassium ions and reaction activity of carbon and ilmenite was enhanced.As a result,the overall carbothermic reduction was catalyzed by KC1.

DFT Study on the Os^+-catalytic Reduction Reaction of N_2O with H_2 in the Gas Phase

The Os＋-catalytic reduction of N2O by H2 in gas phase has been theoretically investigated with B3LYP method.The reaction mechanisms on the sextet and quartet surfaces were found to be similar.The calculated sextet potential energy profiles show that the two reactions involved in the catalytic cycle,Os＋ ＋ N2O → OsO＋ ＋ N2 and OsO＋ ＋ H2 → Os＋ ＋ H2O,have barriers of 28.3 and 123.3 kJ/mol,respectively.In contrast,the reactions on the quartet surfaces are energetically much more favorable.These results rationalize the experimentally observed low catalytic reactivity of sextet（ground-state） Os＋.Further,the crossing between the sextet and quartet surfaces are also suggested and qualitatively discussed.

Performance and Kinetics Studies on Selective Catalytic Reduction of NOx with NH_3 over MnO_x-WO_3/TiO_2 Catalyst

The catalytic activities of MnOx-WO3/TiO2 for selective catalytic reduction（SCR） of NO with NH3 were investigated in a wide range of temperature and reaction condition.It yielded a NOx conversion of 80.3%—99.6% and a N2 product selectivity of 100%—98.7% during 100 °C to 350 °C at gas hourly space velocity（GHSV）=18900 h-1.In the presence of 0.01% SO2 and 6% H2O at 120 °C,the NOx conversion can maintain 98.5%.At 300 °C and with 0.07% SO2 in reactant stream,the NOx conversion stabilized at 99% as high as the commercial V-W/TiO2 catalyst＇s level.The steady-state kinetics study shows that O2 played a promoting role.In the presence of less than 1.5% O2,NOx conversion can increase sharply with the increase of O2 concentration.The reaction order was zero with respect to NH3 and first with respect to NO with excess O2 and H2O.The kinetics active energy（Ea） of Mn-W/TiO2 was calculated to be 6.24 kJ/mol according to the kinetic experiment at various temperatures,much lower than those of other catalysts reported in the literature.Mn-W/TiO2 is an excellent catalyst for SCR of NO with NH3 by now.

A Novel Cu-Mo/ZSM-5 Catalyst for NO_x Catalytic Reduction with Ammonia

The Cu-Mo/ZSM-5 catalysts with different Cu/Mo ratios were prepared by wetimpregnation method, and their catalytic performance for selective catalytic reduction of NO_x wasstudied. The results showed that Cu-Mo/ZSM-5 is a very effective catalyst for NO_x catalyticreduction with ammonia, especially when Cu/Mo molar ratio is about 1.5. It not only exhibited theextremely high catalytic activity, but also showed good stability for O_2. The bulk phase structureof Cu-Mo/ZSM-5 catalysts was determined by XRD technique, and the results indicated that there is amaximum dispersion for Cu species when Cu/Mo molar ratio is 1.5, and an interaction between Cu andMo along with HZSM-5 may be present in Cu-Mo/ZSM-5, which may possibly result in a special structurefavorable for the catalytic reduction of NO_x over Cu-Mo/ZSM-5 catalyst.

Effect of dispersion and distribution of tungsten on W/HZSM-5 for selective catalytic reduction of NO by acetylene

Catalytic performance of W/HZSM-5 in selective catalytic reduction of NO by acetylene was investigated in a reaction system with 1600 ppm of NO, 800 ppm of C2H2, and 9.95% of O2 in He. It was found that promotional effect of tungsten on the reaction is strongly affected by catalyst preparation conditions and Si/Al ratio of the parent zeolite. A better dispersion of tungsten on HZSM-5 and relatively more monomeric tungsten species were found on 8%W/HZSM-5 prepared by impregnation of the zeolite with lower SiO2/A1203 ratio （25） in ammonic ammonium tungstate solution and calcination of the resulting material at higher temperature （550 ℃）. The highest NO conversion to N2 of 86.3% in the reaction system was obtained at 350 ℃ over the catalyst thus prepared. The mechanism of monomeric tungsten species improving the C2H2-SCR can be attributed to accelerating the formation of active nitrate species.