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.     

Selective catalytic reduction of NO by C2H2 over Ce-Al2O3 catalyst with rate-determining step of NO oxidation

Ce-Al2O3 catalysts prepared by co-precipitation are investigated both in NO oxidation by O2 and in selective catalytic reduction of NO by C2H2(C 2 H 2-SCR).It is found that C2H2-SCR is initiated and controlled by NO oxidation to NO 2 over Al2O3.Ce loading on Al2O3 is almost inactive for NO oxidation below 350 C,since NO2 strongly adsorbs on cerium oxide,leading to the active sites being blocked,which was characterized by temperature-programmed desorption of NO and NO 2 and Fourier transform infrared spectroscopy after NO+O 2 coadsorption over the samples.However,in the case of C2H2-SCR,Ce loading on Al 2 O 3 significantly improves the reaction by accelerating the NO oxidation step in the temperature range of 250-450 C,since the nitrate species produced by NO 2 adsorption is an active intermediate required by C2H 2-SCR.     

DRIFT Study on Cr2O3-SO42-/TiO2 Catalyst for Low Temperature Selective Catalytic Reduction of NO with NH3

Chromium oxides supported on TiO2 showed good activity for the selective catalytic reduction of NO by NH3.The catalytic activity of Cr2O3-SO42-/TiO2 catalyst was greatly enhanced by the addition of SO42-into TiO2 support.The catalyst surface properties were characterized with NH3-TPD（temperature programmed desorption） and H2-TPR（temperature programmed reduction）.The sulphate on the catalyst surface could enhance the acidity and redox of the catalyst obviously.The reaction mechanism on this catalyst was researched in detail by in situ diffuse reflectance Fourier transform infrared（FTIR） spectroscope.Eley-Rideal and Langmuir-Hinshelwood mechanism existed simultaneously for selective catalytic reduction（SCR） reaction of NO over Cr2O3-SO42-/TiO2 catalyst.     

Facile preparation of Fe-Y catalyst under water-free conditions for selective catalytic reduction of NO x by ammonia

A series of Fe-Y zeolite catalysts with different Fe loading were prepared by ferrocene sublimation under solvent and water-free conditions.The dispersion,structure and morphology of the iron species on the Fe-Y catalysts were characterized by XRD,TEM and UV-Vis.The catalytic activities of Fe-Y samples were measured in selective catalytic reduction of NO with ammonia(NH3-SCR).The results showed that the iron species on the HY zeolite support were mainly made up of isolated Fe3+ions,Fex Oy oligomers and a little amount of<3 nm spherical Fe2O3particles.Isolated Fe3+ions are predominating among all the Fe-Y catalysts.The sum of isolated Fe3+ions and Fex Oy oligomers took up more than 90%percent of total iron species on the Fe-Y till 10.0 wt%loading of Fe.     

Hydrogenolysis of glycerol over HY zeolite supported Ru catalysts

An enhanced active and selective catalyst consisting of ruthenium supported on dealuminated HY zeolite has been prepared by a wet impregnation method. It was found that BET surface area of Ru/HY catalysts significantly increases after HCl treatment. This treatment also increases the concentration of strong acid sites in the catalyst. The hydrogenolysis of glycerol over 5 wt% Ru/HY catalyst was investigated at 190-220 ℃, an initial H2pressure of 3-6 MPa, and in 20 wt% glycerol aqueous solution. The results indicate that HCl treated Ru/HY catalyst shows higher activity compared with the untreated Ru/HY catalyst, and that the glycerol hydrogenolysis efficiency is influenced by the porosity and acidity of the support. A selectivity to 1,2-PDO of 81.3% at a glycerol conversion of 60.1% under 3 MPa H2pressure and 220 ℃ for 10 h was achieved over the modified Ru/HY catalyst with a 1.0 mol/L HCl treatment. It has also been shown that a longer reaction time, a higher temperature and a higher H2pressure have the positive effects on the glycerol hydrogenolysis efficiency of the enhanced Ru/HY.     

NaA分子筛膜催化剂上CO和C2H4混合气的选择性氧化反应

Defect-free zeolite NaA membranes were coated onto the surface of spherical Pt/Al2O3 particles using a two-step hydrothermal method. The structure and morphology of the synthesized composite catalysts were characterized using XRD and SEM techniques, respectively. The results indicated a layer of compact and uniform NaA molecular sieve membrane with a thickness of about 20 滋m was coated on the spherical Pt/Al2O3 particles after the two-step hydrothermal synthesis. The prepared NaA membrane coated catalysts were used in the oxidation of a mixture of CO and C2H4 to study the reactant selectivity over the coated zeolite NaA membranes. Under the optimized conditions, the oxidation selectivity for CO over C2H4 on the composite catalyst was as high as 96%. The feasible application of this composite membrane coated catalyst to the selective removal of CO in the presence of C2H4 was anticipated.     

Influence of NO on the Reduction of NO2 with CO over Pt/SiO2 in the Presence of O2

Reduction of NO2 with CO in the presence of NO and excess oxygen, a model mixture for flue gas, over a 0.1% Pt/SiO2 catalyst was studied. The related reaction mechanisms, such as oxidation of CO and NO, were discussed. It was found that there was a narrow temperature window （180-190 ℃） for the reduction of NO2 by CO. When the temperature was lower than the lower limit of the window, the reduction hardly occurred, while when the temperature was higher than the upper limit of the window, the direct oxidation of CO by O2 occurred and thereby NO2 could not be effectively reduced by CO. The presence of NO shifted the window to higher temperatures owing to the inhibition effect of NO on the activation of O2 on Pt, which made it possible to reduce NO2 by CO in flue gas.     

Performance and Kinetics Studies on Selective Catalytic Reduction of NOx with NH3 over MnOx-WO3/TiO2 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.     

Catalytic Synthesis of Hexyl-naphthalene over H-type Zeolites

H-type zeolites（ HY, Hβ, and HM） were synthesized and characterized by XRD, NH3-TPD, and Py-IR. Selectively catalytic alkylation of naphthalene with n-hexanol to hexyl-naphthalene over the zeolites was carried out. The experimental results show that the catalytic activities of the zeolites are mainly determined by their acid properties and pore structures. The larger the pore diameter is, the higher the catalytic activity is. NH3-TPD profiles show that Hβ and HM have lower acid strengths than HY. HY has both the highest activity and highest selectivity for the hexylnaphthalene. Higher reaction temperatures and longer reaction time are beneficial to the production of β-hexyl-naphthalene over the HY zeolite.     

Effect of Mn（Ⅱ） and Ce（Ⅳ） Ions on the Oxidation of Lactic Acid by Chromic Acid

The kinetics and mechanism of lactic acid oxidation in the presence of Mn（Ⅱ） and Ce（Ⅳ） ions by chromic acid were studied spectrophotometrically. The oxidation of lactic acid by Cr（Ⅵ） was found to proceed in two measurable steps, both of which gave pyruvic acid as the primary product in the absence of Mn（Ⅱ）.2Cr（Ⅵ）＋2CH3CHOHCOOH→2CH3COCOOH＋Cr（Ⅴ）＋C（Ⅲ） Cr（V）＋CH3CHOHCOOH→Cr（Ⅲ）＋CH3COCOOHThe observed kinetics was explained due to the catalytic and inhibitory effects of Mn（Ⅱ） and Ce（Ⅳ） on the lactic acid oxidation by Cr（Ⅵ）. The reactivity of lactic acid depends upon the experimental conditions. It acts as a two- or three- equivalent reducing agent in the absence or presence of Mn（Ⅱ）. It was examined that Cr（Ⅲ） products resulting from the direct reduction of Cr（Ⅵ） by three-equivalent reducing agents. The oxidation of lactic acid follows the complex order kinetics with respect to [lactic acid]. The activation parameters Eo, △H^#, and AS^# were calculated and discussed.     

Effect of conversion of NO2 into no on the catalytic reduction of NO2 with C3H6 in excess O2

During the reduction of NO₂ by C₃H₆ in O₂ over alumina-supported Au, Rh and Pt it was found that three parallel reactions take place,i.e., reduction of NO₂ to N₂ and N₂O, partial decomposition of NO₂ to NO and oxidation of C₃H₆ to CO and CO₂. In the absence of C₃H₆, the NO₂→NO+O₂ reaction reaches a fast equilibrium on Rh and Pt but not on Au and γ-Al₂O₃. Addition of C₃H₆ to the NO₂+O₂ mixture leads to the formation of NO above equilibrium conversion levels.     

Catalytic reduction of nitrogen monoxide with propene over Nb/TiO2 mixed mechanically with Mn2O3

Selective catalytic reduction of nitrogen monoxide (NO) over a catalyst of mechanically mixed Nb/TiO₂ and Mn₂O₃ (Mn₂O₃+Nb/TiO₂) in an oxidizing atmosphere with propene (C₃H₆) was studied. The Mn₂O₃+Nb/TiO₂ catalyst showed high activity for the reduction of NO to N₂. The maximum conversion of NO to N₂ was observed at 200∼300°C, with about 80% reduction of NO to N₂. Mn₂O₃ enhanced the formation of NO₂ from NO and the activation of propene to react with NO₂ for reduction to N₂.     

Isolation of the Copper Redox Steps in the Standard Selective Catalytic Reduction on Cu‐SSZ‐13

Operando X‐ray absorption experiments and density functional theory (DFT) calculations are reported that elucidate the role of copper redox chemistry in the selective catalytic reduction (SCR) of NO over Cu‐exchanged SSZ‐13. Catalysts prepared to contain only isolated, exchanged Cu^II ions evidence both Cu^II and Cu^I ions under standard SCR conditions at 473 K. Reactant cutoff experiments show that NO and NH₃ together are necessary for Cu^II reduction to Cu^I. DFT calculations show that NO‐assisted NH₃ dissociation is both energetically favorable and accounts for the observed Cu^II reduction. The calculations predict in situ generation of Brønsted sites proximal to Cu^I upon reduction, which we quantify in separate titration experiments. Both NO and O₂ are necessary for oxidation of Cu^I to Cu^II, which DFT suggests to occur by a NO₂ intermediate. Reaction of Cu‐bound NO₂ with proximal NH₄⁺ completes the catalytic cycle. N₂ is produced in both reduction and oxidation half‐cycles.     

Conversion of NO in NO/N2, NO/O2/N2, NO/C2H4/N2 and NO/C2H4/O2/N2 Systems by Dielectric Barrier Discharge Plasmas

An experimental study on the conversion of NO in the NO/N₂, NO/O₂/N₂, NO/C₂H₄/N₂ and NO/C₂H₄/O₂/N₂ systems has been carried out using dielectric barrier discharge (DBD) plasmas at atmospheric pressure. In the NO/N₂ system, NO decomposition to N₂ and O₂ is the dominating reaction; NO conversion to NO₂ is less significant. O₂ produced from NO decomposition was detected by an on-line mass spectrometer. With the increase of NO initial concentration, the concentration of O₂ produced decreases at 298 K, but slightly increases at 523 K. In the NO/O₂/N₂ system, NO is mainly oxidized to NO₂, but NO conversion becomes very low at 523 K and over 1.6% of O₂. In the NO/C₂H₄/N₂ system, NO is reduced to N₂ with about the same NO conversion as that in the NO/N₂ system but without NO₂ formation. In the NO/C₂H₄/O₂/N₂ system, the oxidation of NO to NO₂ is dramatically promoted. At 523 K, with the increase of the energy density, NO conversion increases rapidly first, and then almost stabilizes at 93–91% of NO conversion with 61–55% of NO₂ selectivity in the energy density range of 317–550 J L⁻¹. It finally decreases gradually at high energy density. A negligible amount of N₂O is formed in the above four systems. Of the four systems studied, NO conversion and NO₂ selectivity of the NO/C₂H₄/O₂/N₂ system are the highest, and NO/O₂/C₂H₄/N₂ system has the lowest electrical energy consumption per NO molecule converted.     

Hydrocarbon radicals and nitroxy complexes on the surface of HZSM-5 and CuZSM-5 zeolites: An ESR study

The conditions favorable for the formation of oligomer and benzene cation radicals upon C₂H₄, C₆H₆, and C₃H₆ adsorption on thermally activated HZSM-5 and CuZSM-5 zeolites were studied. In the case of isolated copper ions, the radicals were shown to be formed from C₃H₆ but not from C₂H₄ and C₆H₆. Paramagnetic nitroxy complexes, which were formed as a result of the interaction of adsorbed hydrocarbons C₂H₄, C₆H₆, and C₃H₆ with NO and NO₂, were revealed on HZSM-5 zeolite and Al₂O₃. Hydrocarbon radicals and nitroxy complexes are localized on different zeolite sites. Nitroxy complexes are formed on aluminum cations. The role of radicals and nitroxy complexes in the process of NO _x selective catalytic reduction by hydrocarbons on the zeolites was discussed on the basis of the temperature dependences of the concentrations of these species.     

Praseodymium Oxide Modified CeO2/Al2O3 Catalyst for Selective Catalytic Reduction of NO by NH3

A series of CeO₂/Al₂O₃ catalysts was modified with praseodymium oxide using an extrusion method. The catalytic activities of the obtained catalysts were measured for the selective catalytic reduction of NO with NH₃ to screen suitable addition of praseodymium oxide. These samples were characterized by XRD, N₂‐BET, NH₃‐TPD, NO‐TPD, Py‐IR, H₂‐TPR, Raman spectra and XPS, respectively. Results showed the optimal catalyst with the Pr/Ce molar ratio of 0.10 exhibited more than 90% NO conversion in a wide temperature range of 290–425°C under GHSV of 5000 h^?1. The number of Lewis acid sites and the chemisorbed oxygen concentration of the catalysts would increase with the Pr incorporation, which was favorable for the excellent catalytic performance. In addition, the Pr incorporation inhibited growth of the Al₂O₃ crystal particles and led to the lattice expansion of CeO₂, which increased catalytic activity. The results implied that the higher chemisorbed oxygen concentrations and the more Lewis acid sites were conductive to obtain the excellent SCR activity.     

Cu的负载方法对CuSAPO-34脱除柴油车尾气中NOx的影响

采用X射线衍射、扫描电镜、原子吸收、程序升温还原、X射线吸收近边吸收谱、X射线光电子能谱、氮吸附等手段对水热合成(HS)、等体积浸渍(PVI)与离子交换(IE)法制备的CuSAPO-34样品进行了表征,并评价了老化前后催化剂上C₃H₆-SCR与NH₃-SCR脱除模拟柴油车尾气中NO_x的反应活性.结果表明,IE法制得的催化剂活性最高,尤其在C₃H₆-SCR低温阶段;PVI法制得的催化剂活性最差.制备方法影响CuSAPO-34催化剂的比表面积、孔径分布和活性组分价态从而改变其催化活性.各催化剂均存在Cu⁺和Cu²⁺,但比例明显不同.HS样品以Cu²⁺为主,另两种样品则含较多的Cu⁺.老化不仅部分破坏了分子筛的形貌、降低了分子筛的比表面积,尤其是表面Cu含量,而且有部分Cu生成了CuSO₄,使得老化后催化剂的脱硝活性降低.PVI法制得的催化剂老化后活性下降幅度最小,表明该分子筛抗老化能力较强.     

Ni-Ti-O混合氧化物的制备、表征及其富氧选择性催化还原NO

采用均匀共沉淀法制备了不同Ni/Ti摩尔比的Ni-Ti-O混合氧化物,考察了它们在富氧条件下丙烯选择性催化还原NO反应中的催化性能,并运用X射线衍射,N₂吸附-脱附、吡啶吸附、程序升温脱附和原位红外光谱对催化剂进行了表征.结果表明,Ni/Ti摩尔比为1的催化剂表现出最佳催化活性,430℃时NO_x转化率达68%.该催化剂具有锐钛矿结构,比表面积较高(149m²/g),有利于提高催化活性;其表面Lewis酸性位有利于硝酸盐物种的吸附,而硝酸盐物种是该反应的重要中间体.     

酸性金属氧化物对锰铈氧化物催化剂脱硝温度窗口的调控作用

利用溶胶-凝胶法,采用三种酸性金属氧化物（氧化铌、氧化钨和氧化钼）对锰铈复合氧化物催化剂进行了改性. 测试了催化剂的氮氧化物选择性催化还原（SCR）活性,以筛选对应不同温度窗口的合适酸性氧化物改性剂. 同时评价了催化剂的NO氧化和NH₃氧化活性. 利用X射线衍射、BET比表面积测试、H₂程序升温还原、NH₃/NO_x程序升温脱附和NH₃/NO_x吸附红外光谱等手段对催化剂进行了表征. MnO_x-CeO₂催化剂表现出良好的低温（100-150 ℃）活性. 酸性金属氧化物的添加削弱了催化剂的氧化还原特性,从而抑制了NH₃的活化和NO₂辅助的快速SCR反应. 与此同时,相对高温（250-350 ℃）区NH₃的氧化也受到了抑制,B酸和L酸上的NH₃吸附得以增强. 因此,催化剂的SCR脱硝温度窗口向高温移动,改性效果Nb₂O₅ < WO₃ < MoO₃.     

Promotion of Non-thermal Plasma on Catalytic Reduction of NOx by C3H8 Over Co/BEA Catalyst at Low Temperature

The effects of non-thermal plasma on selective catalytic reduction of NO_x by C₃H₈ (C₃H₈-SCR) over Co/BEA catalyst were investigated over a wide range of reaction temperatures (473–773 K). The significant synergistic effect between non-thermal plasma and catalytic reduction by C₃H₈ was exhibited at low temperatures from 473 to 673 K. The synergetic effect diminished with increasing temperature. The NO_x removal efficiency of non-thermal plasma facilitated C₃H₈-SCR hybrid system increased significantly with the increase in NO₂/NO ratio from 0.13 to 1.06 when the specific input energy increased from 0 to 136 J L^?1. The oxidation performance of NO to NO₂ was significantly enhanced by C₃H₈ in the plasma reactor. Results of CO₂/CO ratio and CO₂ selectivity suggested that adding non-thermal plasma improved CO₂ selectivity of C₃H₈-SCR. 200 ppm SO₂ slightly inhibited NO_x conversion of the non-thermal plasma facilitated C₃H₈-SCR hybrid system at below 673 K, whereas it exhibited no obvious effect at over 673 K. Non-thermal plasma was more selective toward NO oxidation than SO₂ oxidation in the presence of C₃H₈. The non-thermal plasma facilitated C₃H₈-SCR hybrid system could be used stably in durability tests with several hundreds ppm of SO₂.