不同硫源水热合成的MoS2催化剂的形貌和加氢脱氧活性比较研究

分别采用硫脲、L-胱氨酸和硫磺为硫源水热合成了三种MoS₂催化剂,对其结构和形貌特征进行了表征,并以对甲酚为探针化合物,比较研究了三种MoS₂的加氢脱氧（HDO）催化活性。结果表明,硫源对MoS₂晶体结构的影响不大,但对其形貌和比表面积影响较大。与商业MoS₂相比,所制备的MoS₂催化剂都表现出更高的HDO活性;其中,以硫脲为原料合成的MoS₂具有较高的比表面积和花状结构,其催化活性最高,在300℃下进行对甲酚的HDO反应,脱氧度可达99.3%。     

Studies on Electronic Effects in O‐, N‐ and S‐Chelated Ruthenium Olefin‐Metathesis Catalysts

A short overview on the structural design of the Hoveyda–Grubbs‐type ruthenium initiators chelated through oxygen, nitrogen or sulfur atoms is presented. Our aim was to compare and contrast O‐, N‐ and S‐chelated ruthenium complexes to better understand the impact of electron‐withdrawing and ‐donating substituents on the geometry and activity of the ruthenium complexes and to gain further insight into the trans–cis isomerisation process of the S‐chelated complexes. To evaluate the different effects of chelating heteroatoms and to probe electronic effects on sulfur‐ and nitrogen‐chelated latent catalysts, we synthesised a series of novel complexes. These catalysts were compared against two well‐known oxygen‐chelated initiators and a sulfoxide‐chelated complex. The structures of the new complexes have been determined by single‐crystal X‐ray diffraction and analysed to search for correlations between the structural features and activity. The replacement of the oxygen‐chelating atom by a sulfur or nitrogen atom resulted in catalysts that were inert at room temperature for typical ring‐closing metathesis (RCM) and cross‐metathesis reactions and showed catalytic activity only at higher temperatures. Furthermore, one nitrogen‐chelated initiator demonstrated thermo‐switchable behaviour in RCM reactions, similar to its sulfur‐chelated counterparts.     

Effect of the Sulfate Sulfur Content and the Preparation Procedure on the Catalytic Properties of Sulfated Zirconium Oxide

The effects of the composition and the procedure of preparing sulfated zirconium oxides on their catalytic properties in the reactions of 1-butene isomerization to 2-butenes and isobutanol dehydration were studied. The activity was found to depend on the nature of parent zirconium oxide, the sulfate sulfur content, and the temperature of calcination. Catalysts prepared from a crystalline oxide exhibited the highest activity. Their activity depends on the sulfate sulfur content. The calcination of catalysts at temperatures higher than 400°C resulted in a detectable loss of sulfate. The activity of sulfated oxides prepared from an amorphous oxide was noticeably lower; it depended only slightly on the temperature of calcination and sulfate sulfur content. The catalytic behavior of the sulfated oxide in both of the reactions is indicative of the absence of superstrong proton sites. Based on the results, assumptions on the nature of formed surface compounds were made.     

Kinetics and Mechanism of low-Temperature Oxidation of H2S with Oxygen in the gas Phase

The possibility of the formation of polysulfides during oxidation of H₂ S with oxygen on oxide catalysts has been checked, and the sequence of the reaction stages at temperatures below the sulfur dew point determined. The amount of polysulfides formed during H₂ S oxidation has been found to exceed significantly that obtained in the reaction of sulfur with H₂ S. Polysulfides are concluded to be intermediates in H₂ S oxidation to sulfur. The rate of formation of SO₂ from sulfur vapor is shown to be negligibly low at 100-200°C. A reaction scheme involving the formation of sulfur from polysulfides and the formation of sulfur dioxide by direct oxidation of H₂ S is suggested.     

Neopentylphosphines as effective ligands in palladium-catalyzed cross-couplings of aryl bromides and chlorides

The use of neopentylphosphine ligands in the palladium-catalyzed Suzuki, Sonogashira, Heck, and Hartwig-Buchwald couplings of aryl bromides and chlorides are reported. Di-tert-butylneopentylphosphine (DTBNpP) provided highly active catalysts for the coupling of aryl bromides at mild temperatures. Trineopentylphosphine, an air-stable trialkylphosphine, gave inactive catalysts at room temperature, but showed good activity in the H-B amination of aryl chlorides at elevated temperatures.     

硫酸化对CeO2-ZrO2催化剂上NH3选择催化还原NO反应的影响

由发电厂等固定源和柴油机等移动源排放的一氧化氮(NO)造成的环境污染问题日益严重.随着严苛的排放法规出台,NO排放控制技术受到越来越多关注.NH3选择性催化还原(SCR)技术是目前去除NO应用最为广泛的方法之一.商业催化剂V2O5-WO3/TiO2在300–400℃温度窗口内显示出优越的NO去除效率,但仍存在一些问题,如钒氧化物的毒性以及在高温时形成N2O和SO3.因此,开发出低钒或无钒的新型催化剂是解决上述问题的关键.CeO2和含铈材料是重要的催化剂载体,具有良好的还原能力和氧存储功能,因而广泛应用于催化领域.CeO2添加到商用催化剂中不仅可以降低钒用量,而且可以提高催化剂抗碱金属中毒能力.CeO2-WO3催化剂在200℃以上时比商用催化剂具有更宽的温度窗口,并展现出较高的抗SO2和碱金属中毒能力.CeO2-ZrO2催化剂通过添加过渡金属元素可以提升其SCR活性,在较宽的温度窗口内具有较高的催化活性.废气中SO2可导致催化剂失活,在实际应用中催化剂硫中毒是较为常见的催化剂失效原因.通常情况下,锰基和铁基催化剂最容易硫中毒.然而CeO2催化剂在硫酸化处理后却展现出良好的SCR活性.催化剂硫酸化主要包括气相、液相和前驱体硫化三种方法.三种方法各有异同,但在催化剂表面形成的硫物种都是SO42–.硫酸化可以增强Ce基催化剂的SCR活性,但是对于硫化引起的催化剂表面酸性、氧化还原性以及NO吸附脱附性质的详细研究报道较少.本文通过液相法对CeO2-ZrO2(CeZr)催化剂进行了硫酸化.XRD结果表明,硫酸化并未对催化剂结晶结构产生影响.TPD和TPR结果表明,硫酸化后催化剂(S-CeZr)表面酸性增强,但抑制了其氧化性.通过原位红外光谱技术系统研究了催化剂在SCR反应过程中表面物种的变化,结果发现,CeZr和S-CeZr的催化机理相同,不同的SCR活性主要是由表面酸性和氧化性引起的.CeO2基催化剂在不同温度窗口遵循不同反应机理.CeZr催化剂具有较强的氧化还原性,使其对NO和NH3具有很强的氧化能力,所以其在低于200℃时具有较好的SCR活性.而S-CeZr催化剂具有更多的Br?nsted酸性位,导致NO不易吸附在催化剂表面,所以其在低温时SCR活性较差,但在高温时(>200℃)具有优良的SCR活性.通过SCR活性和反应机理研究,发现在高温时(>200℃),表面酸性尤其是强酸Br?nsted酸性位在SCR反应中起到决定性作用;而在低温时(<200℃),酸性位对NH3分子较强的键合作用导致NH3难以被氧化,所以较强的酸性位对SCR活性具有抑制作用,而氧化还原性在低温时对SCR反应起到主要作用.同时,在高温时,较高的氧化性可使NH3被O2直接氧化,导致N2选择性降低.     

过渡金属氧化物催化剂上NH3 分解Claus反应机理研究

运用浸渍法制备了七种过渡金属氧化物催化剂.对于NH3 分解反应均可获得很高的NH3转化率;对于NH3分解Claus反应则可以获得较高的SO2转化率和单质硫选择性.通过比较发现Co3O4-TiO2和Fe2O3-TiO2催化剂的低温活性比较高.经过XRD表征发现,在NH3分解Claus反应中,催化剂的活性相可能是过渡金属硫化物.结合活性评价和XRD表征结果提出了NH3分解Claus反应的机理.     

Highly active CoMo HDS catalyst for the production of clean diesel fuels

HY–Al₂O₃-supported CoMo catalysts with a chelating agent and phosphorus for the hydrodesulfurization (HDS) of diesel fractions were prepared. The activity measurements with the prepared catalysts were carried out with straight-run light gas oil feedstocks in a pilot plant under industrial hydrotreating conditions. As a result, Cosmo Oil Co., Ltd. developed a new CoMoP/HY–Al₂O₃ catalyst, C-606A, which had three times higher HDS activity than the conventional CoMoP/Al₂O₃ catalyst. Commercial operations to produce ultra-low sulfur diesel (ULSD) with C-606A have successfully demonstrated its high performance and high stability. This catalyst has an extremely high activity, which enables to achieve <10-ppm sulfur in products in diesel hydrotreater designed to produce 500-ppm sulfur diesel fuels. Mo K-edge EXAFS, TEM and FT-IR of adsorbed NO were performed to investigate the nature of the active sites on the developed catalysts. The results showed that the new catalyst has multiple layers of MoS₂ slabs and the edges of MoS₂ are mainly occupied by Co–Mo–S phases. XPS and FT-IR were used to investigate the sulfiding behavior of Co and Mo in the formation process of the active sites during sulfidation. The results showed that addition of carboxylic acid to the impregnation solution postponed the sulfidation of Co at low temperatures, thereby increasing formation of the Co–Mo–S phase.     

Selective performance of sol-gel synthesised titanium dioxide photocatalysts in aqueous oxidation of various-type organic pollutants

Photocatalysts synthesized by sol-gel method inevitably incorporate carbon together with dopants. The objective of the research consists in the synthesis and testing of photocatalytic activity of carbon-containing titanium dioxide photocatalysts calcinated at various temperatures. The optical and structural properties of the catalysts were also studied. The activity was tested in visible light in aqueous photocatalytic oxidation of three various-type pollutants, methyl-tert-butyl ether, p-toluidine and phenol, where the divergent character of the C-TiO₂ catalysts was distinctively observed: methyl-tert-butyl ether and p-toluidine were oxidized with the efficiency close to or even surpassing that of UV-irradiated P25 (Evonik), whereas phenol was oxidized poorly. The observed photocatalytic activity, where quantum efficiency varied from 0.6 to 2.3 and from 0.1 to 1.2% for p-toluidine and phenol degradation respectively, may be explained by the different electrostatic properties of the catalysts’ surface and the tested substances, i.e. their interaction. This compromises the widespread usage of phenol as a reference substance for comparison of catalytic activities of catalysts.     

Conversion of ethanol on HZSM-5 modified zeolite, according to data from in situ spectrokinetic studies

The conversion of ethanol on zeolite catalysts is studied spectrokinetically in situ. Ethoxy groups and polyene structures (compaction products) are found to be key intermediates on the studied catalysts under reaction conditions. Ethoxy groups are shown to convert into diethyl ether by a bimolecular mechanism at relatively low temperatures in the presence of ethanol in the gas phase. The character of the conversion of ethoxy groups is found to change at temperatures above 200°C: they become a source for the formation of surface polyene structures, which in turn are converted into a complex combination of hydrocarbons.     

Hydrodeoxygenation of benzofuran over sulfided and reduced Ni–Mo/γ-Al2O3 catalysts: Effect of H2S

Effect of H₂S on the catalytic performance of the reduced and sulfided Ni–Mo/Al₂O₃ catalysts in hydrodeoxygenation of benzofuran is studied. The steady-state reaction experiments showed a decrease in activity for both reduced and sulfided catalysts when H₂S was introduced into the feed. The reaction conversion of benzofuran over the reduced catalyst still remained superior to that of the sulfided catalyst in the presence of H₂S, however, at high reaction temperatures, the product distribution over the pre-reduced catalyst is similar to the sulfided catalyst. The studies with temperature-programmed desorption (TPD), temperature-programmed reaction (TPRxn) and X-ray photoelectron spectroscopy (XPS) techniques showed a partial sulfidation of the reduced catalysts when exposed to H₂S under reaction conditions, however, the catalyst does not go through a complete conversion to a molybdenum sulfide phase. Instead oxygen–sulfur exchange on the surface leaves behind oxisulfide species, with catalytic activity closely resembling that of the reduced catalysts. The effect of H₂S on the reaction performance is mainly coming from the competitive adsorption between H₂S and benzofuran and the formation of SH groups with decomposition of H₂S at high temperatures.     

Novel mesoporous solid superacidic catalysts: activity and selectivity in the synthesis of thymol by isopropylation of m-cresol with 2-propanol over UDCaT-4, -5, and -6

The alkylation of m-cresol with isopropyl alcohol in the presence of novel superacidic catalysts named as UDCaT-4, UDCaT-5, and UDCaT-6 was investigated. The catalysts are modified versions of zirconia showing high catalytic activity, stability, and reusability in the presence of water as compared to conventional sulfated zirconia. The objective of the present investigation was to explore the potential of these catalysts in this alkylation of m-cresol with isopropyl alcohol to thymol, which has widescale applications. The reactions were conducted in liquid phase in the temperature range of 433-473 K. Both, O- and C-alkylated products were obtained at lower temperatures, while at higher temperatures, thymol was the main product of the reaction. The catalytic activity increases in the order UDCaT-5 > UDCaT-6 >UDCaT-4 > sulfated zirconia. Thymol could be efficiently obtained with selectivity reaching up to 79% at an isopropyl alcohol conversion of 92% with UDCaT-5. This process can be a replacement for the existing process based on zeolites where high temperature and pressure are required. Synergistic effects of very high sulfur content present (9% S) and preservation of the tetragonal phase in UDCaT-5, in comparison with sulfated zirconia (4% S), were responsible for higher catalytic activity. A systematic investigation of the effects of various operating parameters was accomplished, and a mathematical model is developed to describe the reaction pathway and validated with experimental results. The reaction was carried out without using solvent, and the process subscribes to the principles of green chemistry.     

过渡金属硫化物催化剂上SO2的还原

 对系列过渡金属硫化物催化剂上CO还原SO2的反应进行了研究．结果表明，FeS的催化性能最好，而MnS的催化性能最差，其他几种催化剂的活性顺序依次为CoS＞CuS＞NiS．催化剂的活性与硫化物自身的氧化还原能力、所具有的晶相结构及其同SO2的吸附键合作用力有密切的关系．在硫化物催化剂上，SO2还原的反应机理很可能是贫、富含硫化合物的交替作用机理．     

The Influence of Bridge Type on the Activity of Supported Metallocene Catalysts in Ethylene Polymerization简

Ethylene polymerization was carried out by immobilization of rac-ethylenebis(1-indenyl)zirconium dichloride(Et(Ind)2 ZrCl2) and rac-dimethylsilylbis(1-indenyl)zirconium dichloride(Me2 Si(Ind)2 ZrCl2) preactivated with methylaluminoxane(MAO) on calcinated silica at different temperatures. Polymerizations of ethylene were conducted at different temperatures to find the optimized polymerization temperature for maximum activity of the catalyst. The Me2 Si bridge catalyst showed higher activity at the lower polymerization temperature compared to the Et bridge catalyst. The highest catalytic activities were obtained at temperatures about 50 °C and 70 °C for Me2 Si(Ind)2 ZrCl2 /MAO and Et(Ind)2 ZrCl2 /MAO catalysts systems, respectively. Inductively coupled plasma-atomic emission spectroscopy results and polymerization activity results confirmed that the best temperature for calcinating silica was about 450 °C for both catalysts systems. The melting points of the produced polyethylene were about 130 °C, which could be attributed to the linear structure of HDPE.     

n-hydrocarbons conversions over metal-modified solid acid catalysts

The quality of a straight-run fuel oil can be improved if saturated n-hydrocarbons of low octane number are converted to their branched counterparts. Poor reactivity of traditional catalysts in isomerization reactions imposed the need for the development of new catalysts among which noble metal promoted acid catalysts, liquid and/or solid acid catalysts take a prominent place. Sulfated zirconia and metal promoted sulfated zirconia exhibit high activity for the isomerization of light alkanes at low temperatures. The present paper highlights the original results which indicate that the modification of sulfated zirconia by incorporation of metals (platinum and rhenium) significantly affects catalytic performances in n-hydrocarbon conversion reactions. Favourable activity/selectivity of the promoted sulfated zirconia depends on the crystal phase composition, critical crystallites sizes, platinum dispersion, total acidity and type of acidity. Attention is also paid to the recently developed solid acid catalysts used in other conversion reactions of hydrocarbons.     

Effect of the preparation conditions on the physicochemical and catalytic properties of Ni<Subscript>2</Subscript>P/SiO<Subscript>2</Subscript> catalysts

The effect of the reduction conditions on the physicochemical and catalytic properties of Ni₂P/SiO₂ catalysts was studied. The catalysts were prepared by impregnating silica with a solution of nickel acetate and diammonium hydrogen phosphate followed by drying, calcination, and temperature-programmed reduction. The Ni₂P/SiO₂ catalysts were reduced prior to hydrodeoxygenation (HDO) of methyl palmitate in the catalytic reactor (in situ) at temperatures of 550, 600, and 650 °С for 3 h and at 600 °С for 1 and 6 h. The reduction temperature and reduction time were shown to affect the conversion of methyl palmitate, and the optimal reduction conditions of the Ni₂P/SiO₂ catalysts were found. The Ni₂P/SiO₂ catalyst synthesized according to a widely used preparation method, including steps of passivation and rereduction at 450 °С in addition to the reduction step, is inferior in activity to the samples prepared in situ.     

2-Pyridylsulfinamides as effective catalysts in the asymmetric alkylation of aldehydes with diethylzinc

Chiral 2-pyridylsulfinamides were shown to be effective catalysts in the alkylation of aryl and alkyl aldehydes with diethylzinc providing the corresponding alcohols in excellent enantioselectivity. Sulfinamide catalysts possessing solitary chirality at the sulfur center produced the product phenethyl alcohol in good enantioselectivity. Diastereomeric sulfinamides possessing chirality at the carbon-bearing nitrogen and at the sulfur of the sulfinamide increased the enantioselectivity of the product alcohols up to >99%. However, there is no effect of the match-mismatch pair of sulfinamide diastereomers on the outcome of the chiral induction of the product phenethyl alcohols. It was conclusively proved that chirality at the sulfur center is mandatory for obtaining good enantioselectivity in the reaction.     

Cationic polymerization and physicochemical properties of a biobased epoxy resin initiated by thermally latent catalysts

The cationic polymerization and physicochemical properties of a biobased epoxy resin, epoxidized castor oil (ECO), initiated by N-benzylpyrazinium hexafluoroantimonate (BPH) and N-benzylquinoxalinium hexafluoroantimonate (BQH) as thermally latent catalysts were studied. As a result, BPH and BQH show an activity at different temperatures in the present systems. The cured ECO/BPH system showed a higher glass transition temperature, a lower coefficient of thermal expansion, and higher thermal stability factors than those of the ECO/BQH system. On the other hand, the mechanical properties of the ECO/BQH system were higher than those of the ECO/BPH system. These have been attributed to the differences in crosslinking level of cured resins, which were induced by the different activity of the latent catalysts.     

Nanostructured perovskite oxides as promising substitutes of noble metals catalysts for catalytic combustion of methane

In this review, we summarize the recent development of nanostructured perovskite oxide catalysts for methane combustion, and shed some light on the rational design of high efficient nanostructured perovskite catalysts via lattice oxygen activation, lattice oxygen mobility and materials morphology engineering.     

Cu-V-O氧化物催化燃烧甲苯的活性和抗硫性

采用溶胶-凝胶法制备一系列不同Cu/V比例的Cu-V-O催化剂,利用XRD、BET、H₂-TPR等手段对催化剂进行了表征,并考察其催化燃烧甲苯的活性和抗硫性。结果表明,适量的Cu掺杂会提高催化剂比表面积,而且Cu-V可以形成Cu₃V₂O₈晶型结构,使V₂O₅晶格氧活动增加,提高催化剂氧化-还原能力。其中,Cu_0.15V_0.85催化剂表现出最佳的活性和抗硫性;通过TiO₂负载可以进一步提高催化剂对甲苯的催化燃烧活性和抗硫性。