Ag-modified H-Beta, H-MCM-41 and SiO2: Influence of support, acidity and Ag content in ozone decomposition at ambient temperature

Silver-modified H-MCM-41-50, H-Beta-11 and SiO₂ catalysts were synthesized by incipient wet impregnation method using aqueous solution of silver nitrate. The catalysts were characterized using X-ray powder diffraction, scanning electron microscope, X-ray fluorescence, nitrogen physisorption and FTIR spectroscopy. The catalysts were tested in the heterogeneous catalytic decomposition of ozone at ambient temperature. The highest degree of ozone decomposition was observed over the mild acidic 5 wt.% Ag-H-MCM-41-50 (98%) mesoporous molecular sieve catalyst followed by 5 wt.% Ag-SiO₂ (90%). It was found that the most acidic catalyst 5 wt.% Ag-H-Beta-11 showed the lowest ozone decomposition. The content of Ag was also observed to influence the ozone decomposition. The 5 wt.% Ag-H-MCM-41-50 mesoporous molecular sieve catalyst exhibited higher catalytic activity than 2 wt.% Ag-H-MCM-41-50. The acidic properties, structure of catalyst supports and the metal content were found to be important for the ozone decomposition reaction.     

Synthesis of Novel Ag Modified MCM-41 Mesoporous Molecular Sieve and Beta Zeolite Catalysts for Ozone Decomposition at Ambient Temperature

Mesoporous molecular sieve Na-MCM-41 with Si/Al ratio 20 and 50 and Na-beta zeolite with Si/Al ratio 11 were synthesized and characterized using X-ray powder diffraction, scanning electron microscope and nitrogen adsorption. The Ag (5 and 2 wt%) modifications of H-MCM-41-20, H-MCM-41-50 and H-beta-11 catalysts were carried out using impregnation method. The catalysts were tested in the decomposition of ozone at ambient temperature. The 5 wt% Ag-H-MCM-41 catalyst showed a very high decomposition of ozone (~98%). The 5 wt% Ag-H-MCM-41-50 catalyst exhibited higher decomposition rate than 2 wt% Ag-H-MCM-41-50. The Ag modified H-MCM-41 catalyst with higher Si/Al ratio showed higher reaction rate than the catalyst with lower Si/Al ratio. The H-MCM-41 catalyst without Ag exhibited the lowest decomposition of ozone indicating an important role of Ag in the reaction.     

Cu-MCM-41催化剂对偏三甲苯的催化氧化性能

通过水热晶化法合成不同Cu含量的Cu-MCM-41催化剂,考察在偏三甲苯/H₂O₂ 体系中制备2,3,5-三甲基苯醌的催化氧化性能,研究了反应时间、反应温度、催化剂铜含量、反应物物质的量比和催化剂用量对反应活性的影响。结果表明,催化剂在偏三甲苯的催化氧化反应中具有良好的催化活性。最佳反应条件:偏三甲苯用量1.0 g,550 ℃焙烧的Cu-MCM-41催化剂［n(Cu)∶n(Si)＝1∶50］用量0.05 g,n(H₂O₂ )∶n(偏三甲苯)=3.5∶1,反应温度70 ℃,反应时间6 h,此条件下,偏三甲苯转化率78.86%,2,3,5-三甲基苯醌收率66.13%。     

Room temperature oxidation of acetone by ozone over alumina-supported manganese and cobalt mixed oxides

Volatile organic compounds (VOCs) are among the major sources of air pollution. Catalytic ozonation is an efficient process for removing VOCs at lower reaction temperature compared to catalytic oxidation. In this study, a series of alumina supported single and mixed manganese and cobalt oxides catalysts were used for ozonation of acetone at room temperature. The influence of augmenting the single Mn and Co catalysts were investigated on the performance and structure of the catalyst. The manganese and cobalt single and mixed oxides catalysts of the formula Mn10%-CoX and Co10%-MnX (where X= 0, 2.5%, 5%, or 10%) were prepared. It was found that addition of Mn and Co at lower loading levels (2.5% or 5%) to single metal oxide catalysts enhanced the catalytic activity. The mixed oxides catalysts of (Mn10%-Co2.5%) and (Mn10%-Co5%) led to acetone conversion of about 84%. It is concluded that lower oxidation state of the secondary metal improves ozone decomposition and oxidation of acetone.     

Plasma-assisted catalysis total oxidation of trichloroethylene over gold nano-particles embedded in SBA-15 catalysts

The oxidative decomposition of trichloroethylene (TCE) in dry air was investigated in non-thermal plasma at atmospheric pressure and room temperature, both in the absence and in the presence of gold containing mesoporous silica (GMS) catalysts. In the absence of catalyst, TCE removal reached 100% for average powers dissipated in the plasma above 3 W, for a TCE concentration of 430 ppmv. Carbon monoxide and carbon dioxide were the major reaction products with CO₂ selectivity up to 25% and CO selectivity up to 70%. In the presence of gold containing mesoporous catalysts, the concentrations of CO and CO₂ increased as compared to those obtained with plasma alone. The GMS catalysts can dissociate ozone produced in plasma to oxygen radicals that decompose TCE. Among these catalysts, the one containing the least amount of Au (0.5% GMS) showed the best catalytic performance. In the presence of ozone generated in the plasma, isolated gold cations might play a critical role for the catalytic behavior.     

MOx/Y催化剂常温催化臭氧氧化甲苯的性能

以Y分子筛为载体,采用等体积浸渍法制备了MO_x/Y催化剂,并用于常温催化臭氧氧化甲苯反应。采用XRD、BET、H_2-TPR、甲苯吸附对催化剂进行表征,以甲苯转化率维持95%以上的时间(t_(95))为指标对催化性能进行评价。结果表明:10%MnO_2/Y催化剂〔m(MnO_2)/m(Y)=0.1〕具有较大的比表面积(538.6m~2/g)和孔容积(0.440 cm~3/g),较好的催化臭氧氧化甲苯活性(t95=210 min);CuO的加入提高了催化活性,5%MnO_2-5%CuO/Y〔m(MnO_2)/m(Y)=0.05且m(CuO)/m(Y)=0.05〕催化剂上t95=240min,CO_x选择性为80.6%,CO_2与CO摩尔比为4.970。由表征结果可知,较大的比表面积和孔容积有利于甲苯吸附,CuO与Mn O_2之间的相互作用促进了氧化还原性能的提高,进而有利于催化活性的提高。GC-MS结果表明:反应副产物堵塞催化剂孔道,占据催化剂表面活性位,导致催化剂失活。5%MnO_2-5%CuO/Y催化剂失活-再生4次后t_(95)可达220 min。     

Higher Oxidation State Responsible for Ozone Decomposition at Room Temperature over Manganese and Cobalt Oxides: Effect of Calcination Temperature

The heterogeneous catalytic decomposition of ozone was investigated over unsupported manganese and cobalt oxide at room temperature. All catalysts were characterized by X-ray diffraction (XRD), N₂ adsorption–desorption (Brunauer–Emmet–Teller method), H₂-temperature programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS). The catalytic activity test indicated that these oxides had a good activity on ozone conversion meanwhile the catalysts remained highly active over time under reaction conditions. The treated temperature of the catalyst had a significant impact on the performance of ozone abatement and the samples treated at lower temperature showed higher activity. The surface area decreased obviously when developing the calcination temperature and H₂-TPR results demonstrated that much higher oxidation state of metal ions and active oxygen species were maintained on the surface under low treated temperature. XPS analysis showed that there were higher oxidation states of metal ions (Mn⁴⁺ and Co³⁺) and adsorbed oxygen species on the surface of catalysts treated at lower temperature, both of which play a significant role in ozone decomposition. However, the activity of manganese oxide was higher than that of cobalt oxide and the possible reason for this phenomenon was discussed.     

Catalytic Oxidation of Oleic Acid in Supercritical Carbon Dioxide Media with Molecular Oxygen

Oxidation of oleic acid was performed over various ordered porous catalysts containing transition metal in supercritical carbon dioxide (scCO₂) media with molecular oxygen. Oleic acid was completely decomposed into mono- and dicarboxylic acids over porous catalysts, viz., mesoporous molecular sieves (CrMCM-41, MnMCM-41, CoMCM-41) and microporous molecular sieves (CrAPO-5, CoMFI, MnMFI) using scCO₂ at 353 K for 8 h. Among the different catalysts studied, microporous and mesoporous catalysts containing chromium, in presence of scCO₂ showed high distribution of azelaic and pelargonic acids as compared to their analogs containing cobalt or manganese. The presence of scCO₂ medium with the catalysts increased the distribution of azelaic and pelargonic acids. The effect of CO₂ pressure, reaction temperature and reaction time on oxidation of oleic acid over CrMCM-41 was also investigated. Additionally it is noticed that the catalyst can be recycled with negligible loss of catalytic activity.     

Control of the Chemoselectivity in the Oxidation of Geraniol Over Lanthanum, Titanium and Niobium Catalysts Supported on Mesoporous Silica MCM-41

The selective catalytic oxidation of geraniol with hydrogen peroxide over lanthanum, titanium and niobium catalysts supported on mesoporous silica MCM-41 has been investigated. Among the various catalysts studied, Nb-MCM-41 showed an excellent selectivity for allylic epoxide. In contrast, La-MCM-41 and Ti-MCM-41 catalysts exhibited high selectivity to citral. Catalyst??s characterization and activity results clearly demonstrated that the differences in the product distribution were due to the presence of different acid sites and the better coordination of oxidant with the catalyst used. All the catalysts were characterized by nitrogen adsorption?Cdesorption isotherms at 77?K, TPD-pyridine and XRD.     

Preparation of sulfated alumina supported on mesoporous MCM-41 silica and its application in esterification

New types of mesoporous SA/MCM-41 solid acid catalysts were prepared by loading sulfated alumina (SA) on MCM-41. The prepared catalysts were characterized by XRD, IR, N₂ physisorption, elemental analysis, FT-IR of adsorbed pyridine and NH₃-TPD. The esterification of acetic acid with n-butanol and citric acid with n-butanol were used as model reactions to test the catalytic activities and reusability of the SA/MCM-41 solid acid catalysts. Compared with SA catalyst, SA/MCM-41 catalysts exhibited higher catalytic performances, which were attributed to their high BET surface area and large pore volume. Moreover, 20SA/MCM-41 solid acid catalyst showed excellent reusability in both esterifications.     

耐高温焦炉煤气氨分解催化剂的研究

研究了经过改进的MgO载体对NH3分解活性和反应热稳定性的影响。在容易造成催化剂烧结的高温、水蒸气等条件下,对催化剂进行活性评价;通过超高温处理,观察催化剂活性下降情况,配合XRD分析结果以及SEM照片,发现通过ZrO2修饰载体和特定方法制备的催化剂,在高温下能够较好地抑制Ni、Co活性组分的烧结,具有良好的热稳定性。     

催化臭氧氧化有机废气处理技术研究进展

气相催化臭氧氧化是一种能够使有机废气在低温下实现催化氧化的高级氧化技术。气相催化臭氧氧化的催化剂载体主要有氧化铝、二氧化硅、二氧化钛、沸石和分子筛SBA-16等,负载的活性组分主要集中在铜、钴、锰和镍等金属氧化物,研究较多的是MnOx/γ-Al₂O₃。综述国内外催化臭氧氧化技术的研究进展,并对催化臭氧氧化有机废气的研究方向进行展望。催化氧化影响因素研究主要集中在活性组分及负载量、反应温度、运行时间、副产物和湿度等。反应机理研究按反应过程拆分为臭氧分解和有机物氧化两部分,研究认为,实现有机物氧化的关键物为催化分解臭氧产生的活性氧或过氧化物物种O^*₂。今后研究需解决的问题有催化剂载体的吸附性能影响、避免催化剂失活的最佳反应温度和完整的气相催化氧化反应机理。     

Pyrolysis of an LDPE-LLDPE-EVA copolymer mixture over various mesoporous catalysts

The aim of the present work was to study the performance of mesoporous catalysts in the catalytic cracking of an LDPE+LLDPE+EVA copolymer. Mesoporous catalysts, including MCM-41, Nano-MCM-41, Al-Nano-MCM-41, MMZ-ZSM-5 and Meso-MFI, were applied for this reaction. Also, microporous HZSM-5 was used for a comparison. All of the catalysts showed higher decomposition abilities than thermal decomposition. The catalytic conversion of the LDPE+LLDPE+EVA copolymer was highest with the use of Meso-MFI due to its pore size and strong Br?nsted acidity, with high selectivity for lower olefin and gasoline range hydrocarbon. Both MMZ-ZSM-5 and Al-Nano-MCM-41 have an acid site that induced the decomposition reactions, and thus, produced compounds with lower carbon numbers in liquid products. MCM-41, which exhibits no acidity, showed a similar distribution of liquid products to that via thermal cracking, while Nano-MCM-41 showed better catalytic cracking ability due to its high surface area.     

Feedstock recycling of agriculture plastic film wastes by catalytic cracking

Feedstock recycling by catalytic cracking of a real plastic film waste from Almeria greenhouses (Spain) towards valuable hydrocarbon mixtures has been studied over several acid catalysts. The plastic film waste was mostly made up of ambient degraded low-density polyethylene (LDPE) and ethylene-vinyl acetate (EVA) copolymer, the vinyl acetate content being around 4 wt.%. Nanocrystalline HZSM-5 zeolite (crystal size 60 nm) was the only catalyst capable of degrading completely the refuse at 420 °C despite using a very small amount of catalyst (plastic/catalyst mass ratio of 50). However, mesoporous catalysts (Al-SBA-15 and Al-MCM-41), unlike it occurred with virgin LDPE, showed fairly close conversions to that of thermal cracking. Nanocrystalline HZSM-5 zeolite led to 60 wt.% selectivity towards C₁---C₅ hydrocarbons, mostly valuable C₃---C₅ olefins, what would improve the profitability of a future industrial recycling process. The remarkable performance of nanocrystalline HZSM-5 zeolite was ascribed to its high content of strong external acid sites due to its nanometer dimension, which are very active for the cracking of bulky macromolecules. Hence, nanocrystalline HZSM-5 can be regarded as a promising catalyst for a feasible feedstock recycling process by catalytic cracking.     

用于环戊烯氧化合成戊二醛反应的钨基催化剂的表征

Tungsten-containing hexagonal mesoporous silica （W-HMS） supported tungsten oxide catalysts （WOx/W-HMS） was prepared for the selective oxidation of cyclopentene with aqueous hydrogen peroxide to glutaraldehyde. X-ray diffraction （XRD） results indicated that the crystal form of the active phase （tungsten oxide） of the WOx/W-HMS catalysts was dependent on the W loading and calcination temperature. X-ray photoelectron spec- troscopy （XPS） analysis revealed that the dispersed tungsten oxides on the surface of W-HMS support consisted of a mixture of W（V） and W（VI）. It was found that a high content of amorphous W species in （5＋） oxidation state resuited in the high catalytic activity. When the W loading was up to 12% （by mass） or the catalyst precursor was treated at temperature of 623 K, the catalytic activity decreased due to the presence of WO3 crystallites and the oxidation of W（V） to W（VI） on the catalyst surface. Furthermore, NH3-temperature-programmed-desorption （NH3-TPD） analysis showed that the effects of W loading and calcination temperature on the acidity of the catalysts were related to the catalytic activity. A high selectivity of 80.2% for glutaraldehyde with a complete conversion of cyclopentene was obtained over 8%WOx/W-HMS catalyst calcined at 573 K after 14 h of reaction.     

Well-dispersed Ceria-promoted Sulfated Zirconia Supported on Mesoporous Silica

Ceria-promoted sulfated zirconia (CeSZ) was supported on mesoporous molecular sieve of pure-silica MCM-41 (abbreviated as CeSZ/MCM-41). It was prepared by direct impregnation of metal sulfate onto the as-synthesized MCM-41, followed by solid state dispersion and thermal decomposition. The resultant catalysts were characterized by TG, XRD, nitrogen physisorption and TEM. It was showed that the hollow tubular structure of MCM-41 was retained, even with ZrO₂ loading as high as 60 wt.%. Most of CeSZ was well dispersed on the interior surface of the ordered mesopores, following a slight twist of the channels. The catalytic activity of CeSZ/MCM-41 was studied in the octadecanol oxidation. The improved performance of CeO₂-promoted catalysts was attributed to the high dispersion of sulfated zirconia (SZ) and the introduction of CeO₂ enhancing the oxidation ability of catalysts by retarding the transformation of zirconia from highly catalytic active metastable tetragonal phase to monoclinic phase.     

The effect of mass transfer on the catalytic combustion of benzene and methane over palladium catalysts supported on porous materials

Catalytic combustion of benzene and methane over palladium catalysts supported on FAU and MOR zeolites and MCM-41 and KIT-1 mesoporous materials were studied to illustrate the effect of pore size and shape of supports on their catalytic activities. The palladium catalysts supported on mesoporous materials showed high activity and a steep increase in the conversion of benzene with rising temperature. The low activity of palladium catalysts supported on FAU zeolite was ascribed to mass transfer limitation. However, conversion profiles of methane on palladium catalysts were similar, although their supports were different as zeolites and mesoporous materials. The catalytic behavior of palladium catalysts in the combustion of benzene and methane was explained by the diffusion properties of fuels in the pores of zeolites and mesoporous materials.     

Synthesis, characterization of high Ti-containing Ti-MCM-41 catalysts and their activity evaluation in oxidation of cyclohexene and epoxidation of higher olefins

A series of titanium rich isomorphous substituted Ti MCM-41 and HMS materials have been synthesized with different Si/Ti ratios. The highest amount of Ti incorporated in synthesis gel is in TiMCM-41 (Si/Ti = 10). Whereas for TiHMS catalysts, Ti is incorporated up to Si/Ti = 50 successfully without forming any extra framework TiO₂. Cyclohexene epoxidation reaction with dry tert-butyl hydroperoxide (TBHP) as an oxidant has been studied to evaluate the catalytic properties of Ti substituted mesoporous catalysts. The effect of molar ratio of substrate:oxidant in this reaction has been studied and high conversion, high selectivity were achieved at 2: 1 molar ratio with TiMCM-41 (Si/Ti =25). Dry TBHP (in dichloromethane) and chloroform were found as good oxidant and solvent system for this reaction. Pure siliceous mesoporous silica and low `Ti' substituted mesoporous silicas were found to be efficient catalysts for oxidation of cyclohexene. An interesting variation of the selectivity from allylic oxidation to epoxidation during oxidation of cyclohexene was observed with an increase in the Ti amount in the mesoporous framework. The allylic oxidation of cyclohexene has been carried out using molecular oxygen as an oxidant and in the presence of a small amount of TBHP as initiator. Siliceous HMS materials gave better conversion compared to MCM-41 type of materials and other conventional silicas like silica gel, fumed silica etc. in allylic oxidation of cyclohexene. Epoxidation of higher cyclic olefins like cyclooctene, cyclododecene, cis-cyclododecene and linear olefins 1-Heptene, cis-2-hexene, 1-undecene was carried out over TiMCM-41 (Si/Ti = 25). Ti substituted mesoporous catalysts were characterized by elemental analysis, XRD, FTIR, UVDRS, ²⁹SiMASNMR, BET surface area and pore size distribution techniques.     

稀土元素对甲硫醇催化分解活性位点的调控作用

采用等体积浸渍法制备La、Ce改性的MCM-41催化剂,考察不同稀土金属元素对甲硫醇催化分解活性位点的调控作用。采用N_2吸附-脱附、XRD、XPS、H_2-TPR和NH_3/CO_2-TPD等对La、Ce改性催化剂进行物理化学性能测试,确定稀土元素La、Ce在催化剂中存在的形态和作用。研究表明,甲硫醇催化分解存在两步反应,低温条件下甲硫醇催化分解生成甲硫醚中间体,高温条件下甲硫醚进一步催化分解生成硫化氢和甲烷等小分子产物。对于10%Ce/MCM-41催化剂,表面活性氧是甲硫醇催化分解的低温活性中心,强酸性位点是甲硫醇催化分解的高温活性中心,二者在反应中起协同催化作用,而对于10%La/MCM-41催化剂,强酸性位点是甲硫醇催化分解的活性中心。     

高铝粉煤灰负载锰基催化剂的催化氧化NO性能研究

氮氧化物催化氧化是烟气脱硝技术的一个重要发展方向。本工作以具有球形镂空结构的预处理后高铝粉煤灰为载体,以硝酸锰为活性组分源,采用溶胶凝胶法制备锰基NO氧化催化剂,采用扫描电镜(SEM)、X射线衍射仪(XRD)、N2物理吸附、H2程序升温还原分析仪(H2-TPR)和X射线光电子能谱(XPS)等分析测试手段对催化剂的NO催化氧化性能进行深入研究。结果表明,载体粒径、锰负载量、硝酸锰凝胶煅烧温度以及NO催化氧化温度对催化剂催化活性均有较大影响。当载体粒径在100~200目(150~75 μm)、锰负载量为8wt%、硝酸锰凝胶煅烧温度为500℃、NO催化氧化温度290℃时,NO催化氧化效果最好,氧化率达到77.8%。SEM结果显示,溶胶凝胶法制备的氧化锰粒子在100~200 nm,且相对均匀负载在载体上。N2-物理吸附表明,催化剂的孔结构主要为介孔,并呈现H3型回滞环。锰基催化剂上化学吸附氧Oβ的占比和Mn4+浓度随着锰负载量的增加先增大后减小,此趋势与NO催化性能变化趋势一致,表明Oβ和Mn4+是影响NO催化氧化效果的决定因素。