Metal oxides nanoparticles on SBA-15: Efficient catalyst for methane combustion

Catalysts based on crystalline nanoparticles of Mn and Co metal oxides supported on mesoporous silica SBA-15 have been developed. These materials were characterized by XRD, BET and transmission electron microscopy (TEM) techniques. SBA-15 mesoporous silica was synthesized by a conventional sol–gel method using a tri-block copolymer as surfactant. Supported Mn₃O₄ and Co₃O₄ nanoparticles were obtained after calcination of as-impregnated SBA-15 by a metal salt precursor. The catalytic activity was evaluated in the combustion of methane at low concentration.Co₃O₄/SBA-15 (7 wt.%) exhibits the highest performance among the different oxides. Furthermore, this novel generation of catalysts appeared as active as conventional LaCoO₃ perovskite, usually taken as reference for this reaction. Thanks to its organized meso-structures, SBA-15 material creates peculiar diffusion conditions for reactants and/or products.     

Oxidative coupling of methane on Ce/Na/CaO catalysts

Oxidative coupling of methane was investigated on Na/CaO and Ce/Na/CaO catalysts with different sodium and cerium contents. The reaction was carried out in a micro fixed-bed flow reactor operating at atmospheric pressure, at 700 and 750°C and molar ratio feed of CH₄ : O₂ : N₂ = 50 : 10 : 40. Catalysts were compared at isoconversion and were characterized by BET, XRD and XPS. The addition of cerium to Na/CaO catalyst increased the specific activity by a factor of eight. These catalytic and characterization results were related to the presence not only of Na₊O^- active sites, formed by the introduction of Na₊ in the CaO lattice, but also to peroxide active sites. A mechanism is proposed to explain the role of cerium in increasing the rate of the regeneration step of the O_s^– and Na₂O₂ sites.     

Oxidative coupling of methane over Ce4+-doped Ba3 WO6 catalysts: investigation on oxygen species responsible for catalytic performance

Ce⁴⁺ doped Ba₃ WO₆ complex oxides were used as catalysts for methane oxidative coupling (MOC), and characterized by XPS and O₂-TPD-MS techniques. The results indicate that the ratio of electrophilic oxygen species O^– and O ₂ ^– to lattice oxygen on the surface is crucial for C₂ selectivity. By adjusting the relative amount of cations in Ba-W-Ce complex oxides with perovskite superstructure interstitial oxygen species can be created which benefits C₂ selectivity by raising the relative amount of (O^– + O ₂ ^– ) on the surface.     

Oxidative coupling of methane by carbon dioxide: a highly C2 selective La2O3/ZnO catalyst

In the oxidative coupling of methane by carbon dioxide, La₂O₃/ZnO catalysts were found to have high C₂ selectivity and good stability. The coupling selectivity on La₂O₃/ZnO is about 90%, which is much higher than that on pure La₂O₃ or ZnO. The consumption ratio of carbon dioxide to methane is approximately one. X-ray diffraction analysis reveals that the structural forms of the oxides are unchanged during the reaction. The reaction mechanism for C₂ formation is discussed.     

Oxidative coupling of methane over Na+-ZrO2-C1-/Al2O3 catalysts

Oxidative coupling of methane (OCM) was carried out over Na⁺-ZrO₂-Cl /A1[₂O₃ catalysts in a temperature range from 1023 to 1123 K. The catalysts were prepared by impregnating the α- or γ-Al₂O₃ supports with sodium carbonate and/or zirconyl chloride. The OCM activity was examined using the catalysts prepared by three different preparation procedures. The best catalyst was the one prepared by subsequent impregnation of sodium carbonate-preimpregnated γ-Al₂O₃ with a mixed solution of sodium carbonate and zirconyl chloride. It was found that preimpregnated sodium played an important role in reducing the combustion activity of the γ-Al₂O₃. The catalyst with an optimal composition showed the highest C₂ selectivity and yield of 40.8% and 15.1%, respectively. From the X-ray diffraction analysis it was found that tetragonal ZrO₂ was formed and that NaCl existed in the catalysts with relatively high sodium contents.     

Oxidative coupling of methane using Li/MgO catalyst: Re-appraisal of the optimum loading of Li

The effect of the level of lithium carbonate doping on MgO, prepared by thermal decomposition of the basic carbonate, is re-examined. A low, sub monolayer, loading, ie. 0.2% Li₂CO₃-MgO is shown to significantly enhance both the specific activity for methane activation and the total C₂ hydrocarbon selectivity. The study indicates that the optimal loading of alkali promoters on MgO prepared in this way is considerably lower than indicated in previous studies.     

Oxidative coupling of methane to C2-hydrocarbons over La-promoted CaO catalysts

La₂O₃ promoted CaO [La/Ca (mol/mol) = 0.05] catalyst shows very high activity and selectivity (methane conversion: 25%, C₂-selectivity: 66% and C₂-space-time-yield: 864 mmol ·g^–1 (cat.)·h^–1) with no catalyst deactivation in oxidative coupling of methane to C₂-hydrocarbons at 800 ° C.     

Oxidative coupling of methane: An inherent limit to selectivity?

Mechanistic considerations show that pressure must be taken into account in evaluating oxidative coupling catalyst performance, and predict an upper limit of around 30% yield of higher hydrocarbons at one atmosphere.     

Au-Promoted Pt nanoparticles supported on MgO/SBA-15 as an efficient catalyst for selective oxidation of glycerol

A systematic study of Au-promoted and unpromoted Pt/MgO/SBA-15 catalyst is developed to separate the promoter effect from electron transfer effect between Au and Pt. Multi-characterizations revealed that Au and Pt metals in these bimetallic catalysts mainly exist in the form of alloy, and the main role of Au is to reduce the size of AuPt alloy nanoparticles, thus enhancing the adsorption and activation of intermediate products. Through the optimization of various factors (including MgO content, Au/Pt molar ratio, reaction temperature and time), the Au₁Pt₂/MgO/SBA-15 (0.05) catalyst exhibits excellent catalytic activity and glyceric acid selectivity for the selective oxidation of glycerol. Density functional theory calculation confirmed that the synergistic effect between Pt and Au active sites could facilitate the oxidation of primary hydroxyl group by promoting the activation of C H bond and the oxidation of aldehyde group. The results may give insights on designing effective Pt based bimetallic catalyst for selective oxidation of glycerol.     

Influence of SBA-15 support on CeO2–ZrO2 catalyst for the dehydrogenation of ethylbenzene to styrene with CO2

Pure oxides of ceria (CeO₂) and zirconia (ZrO₂) were prepared by precipitation method and a catalyst comprising of 25 mol% of CeO₂ and 75 mol% of ZrO₂ (25CZ) mixed metal oxide was prepared by co-precipitation method and also a catalyst with 25 wt% of 25CZ (25 mol% of CeO₂ and 75 mol% of ZrO₂) and 75 wt% SBA-15(25/25CZS) was prepared by precipitation–deposition method. Aqueous NH₃ solution was used as a hydrolyzing agent for all the precipitation reactions. These catalysts were characterized by X-ray diffraction and nitrogen adsorption–desorption techniques for the confirmation of SBA-15 structural intactness. All these catalysts were found to be effective for the oxidative dehydrogenation of ethylbenzene (ODHEB) to styrene in the presence of CO₂ and also it was observed that there was a sequential enhancement in the catalytic activity from individual oxides to mixed oxides followed by supported mixed oxide catalysts. Of the catalysts studied in this work, the supported 25/25CZS catalyst exhibited the superior activity, which was about 10–20 times higher than the activity of bulk single oxides in terms of turn over frequency.     

Oxidative coupling of methane: maximizing the yield of coupling products under cofeed operating conditions

Considerable disagreement often exists regarding the conversion and activity of many oxidative coupling catalysts. The wide discrepancy in results, obtained on a given catalyst, is essentially due to differences in temperature and space velocity as well as the use of inert gas diluents. We have thus used three dimensional graphics in order to locate the region of maximum C₂+ yield as a function of catalyst bed hot spot temperature and linear space velocity. The conclusion of our study, involving pure La₂O₃, is that much of the research in this field is being carried out in the wrong region of catalyst activity.     

以微晶纤维素为助剂制备Ni/SBA-15加氢脱芳催化剂

以微晶纤维素(MCC)为辅助模板剂,制备了SBA-15介孔分子筛,并以该材料为载体制备了Ni/SBA-15-MCC加氢脱芳催化剂。通过XRD、N₂吸附-脱附、FTIR、XPS、H₂-TPR和SEM等手段对催化剂进行了表征。以萘的十二烷溶液为模拟油,在微型固定床反应器上评价了其催化性能。结果表明,与未添加MCC的Ni/SBA-15催化剂相比,Ni/SBA-15-MCC催化剂的孔径增大,介孔有序度更高,Ni/SBA-15-MCC表面残留的含碳基团使NiO与载体的相互作用力减弱。这些变化有利于减小反应的扩散阻力,有利于NiO分散及还原,缓解萘和四氢萘的竞争吸附,从而提高催化剂的活性及选择性。在反应压力3MPa,温度280℃,氢油体积比360,质量空速2.5 h–1的条件下,Ni/SBA-15-MCC萘转化率接近100%,十氢萘选择性约为98%,与Ni/SBA-15相比,分别提高了6%和10%。     

Preparation of phosphate promoted Na2WO4/Al2O3 catalyst and its application for oxidative desulfurization

Phosphate promoted Na₂WO₄/Al₂O₃ catalyst with 10 wt.% tungsten was prepared by simple impregnation method. Analytical characterization results showed that tungstate and phosphate were uniformly dispersed in alumina matrix and its structural properties were preserved. The effect of phosphate as promoter in catalyst activity was studied using dibenzothiophine (DBT) as model oil and the results reveal that it plays an important role in oxidation activity of Na₂WO₄/Al₂O₃ catalyst, in addition, the catalytic activity of Na₂WO₄/Al₂O₃ was increased gradually with increasing phosphorus contents up to 2.5 wt.%. The catalyst was recycled and the results show that no significant decrease in catalyst activity was observed even after five recycled runs. We also applied our catalyst in oxidative desulfurization (ODS) of FCC diesel oil (with sulfur contents 4100 ppm), and more than 92% of sulfur was removed from diesel oil under mild reaction conditions.     

以微晶纤维素为助剂制备Ni/SBA-15加氢脱芳催化剂

以微晶纤维素（MCC）为辅助模板剂,制备了SBA-15介孔分子筛,并以该材料为载体制备了Ni/SBA-15-MCC加氢脱芳催化剂。通过XRD、N2吸附-脱附、FTIR、XPS、H2-TPR和SEM等手段对催化剂进行了表征,以萘的十二烷溶液为模拟油,在微型固定床反应器上评价了其催化性能。结果表明：与未添加MCC的Ni/SBA-15催化剂相比,Ni/SBA-15-MCC催化剂的孔径增大,介孔有序度更高,Ni/SBA-15-MCC表面残留的含碳基团使NiO与载体的相互作用力减弱。这些变化有利于减小反应的扩散阻力,有利于NiO分散及还原,缓解萘和四氢萘的竞争吸附,从而提高催化剂的活性及选择性。在反应压力3 MPa,温度280 ℃,氢油体积比360,质量空速2.5 h-1的条件下,Ni/SBA-15-MCC萘转化率接近100%,十氢萘选择性为98%,与Ni/SBA-15相比,分别提高了6%和10%。     

微波辅助ZrO2-SO2-4/SBA-15催化合成棕榈酸甲酯

以三嵌段醚共聚物P123作为模板剂、正硅酸乙酯为硅源,合成介孔分子筛SBA-15。以SBA-15为载体,利用尿素水解法制备ZrO₂-SO^2-₄改性的固体酸催化剂,对其进行表征。实验结果表明,合成的固体酸催化剂具有典型的介孔结构特征。将催化剂应用于微波法催化合成棕榈酸甲酯,考察反应时间、反应温度、辐射功率、酸醇物质的量比和催化剂用量对酯化率的影响,结果表明,在n（十六酸）∶n（甲醇）=1∶15、SZ/SBA-15催化剂用量0.8 g、反应时间20 min、反应温度40 ℃和微波辐射功率400 W条件下,酯化率可达87.70%,微波反应时间较传统合成方法大大缩短。     

Co改性Na_2WO_4/Mn/SiO_2甲烷催化氧化催化剂结构及性能研究

本文制备了一系列不同Co含量的Na_2WO_4/Co-Mn/SiO_2双功效催化剂,用于甲烷催化转化制备氢甲酰化合成丙醛的原料气。当气体空速GHSV=24 000 h~(-1)、CH_4/O_2=2.5,Co负载量为6%(质量分数)的催化剂上可得到C_2H_4/CO/H_2=1/1/1,且(C_2H_4+CO)总收率达23%。XRD和XPS结果表明,在Na_2WO_4/Co-Mn/SiO_2催化剂上Co只以+2价形式存在,并分散到α-方晶石和/或Na_2WO_4晶相结构中。Mn则以两种化学态共存,即Mn~(3+)和Mn~(4+),且随着Co负载量的增加,更多的Mn~(3+)转化为Mn~(4+)。结果表明,C_2H_4选择性随Co的增加而降低,CO和H_2的选择性及收率则与催化剂表面的Co/W比值近似呈线形关系。     

Ce-Doped La2O3 based catalyst for the oxidative coupling of methane

The effect of ceria was studied on the oxidative coupling of methane (OCM) with Ce-doped La₂O₃ in a La:Ce molar ratio of 75:25 using two preparation methods. The characterisation techniques used were XRD and XPS. The results revealed high concentration of oxygen vacancies. Different types of ions (Ce^3 + + Ce^4 +) were detected. More surface Ce^3 + and higher ratio [(O₂^2― + O^—)/ O^2―] were obtained in the oxide synthesised by the solvothermal method, affecting the OCM reaction in terms of higher C₂ hydrocarbons selectivity. This was ascribed to the higher relative amount of O^― species on the catalyst surface.     

Short communication: acidity of Ni-W catalyst supported on zirconium doped mesoporous SBA-15

Ordered hexagonal mesoporous x-ZrSi SBA-15 (where x is the Zr/Si ratio) with 0 < x < 0.12 was successfully synthesized, pelletized and impregnated with a Ni-W bifunctional metal to fabricate a series of novel ring-opening catalysts suitable for the conversion of excess aromatics in petroleum refining. Results obtained from N₂ isotherm techniques and TEM analysis indicate that these x-ZrSi supports have high surface areas and narrow pore size distributions with well-ordered hexagonal pore structures. NH₃-TPD revealed an increase in acidity with Zirconium content for the x-ZrSi support, with a plateau expected as x approaches 0.16. While deposition of Ni-W onto the x-ZrSi support resulted in a significant increase in acidity for low values of x, the impact was reduced as the Zirconium content increased. When normalized with the catalyst surface area, the acidity of both the support and impregnated catalyst was equivalent for a given total metal content to silica ratio.