Shape-selective alkylation of biphenyl over mordenites: effects of dealumination on shape-selectivity and coke deposition

To understand the relationships between shape-selectivity and coke deposition in the alkylation of biphenyl over H-mordenite (HM), thermogravimetric analyses were examined for the catalyst after the reaction. The coke deposition during the catalysis was very severe over HM with low SiO/Al₂O₃ ratio, however, dealumination enhanced the decrease of coke deposition. Over highly dealuminated HM, volatile organic compounds, mainly biphenyl derivatives, were observed in addition to carbonaceous deposits. The deposits are produced from biphenyl derivatives on acid sites in the HM pore, and the ease of their formation is governed by acid site density and acid strength. The decrease of carbonaceous deposits and the increase of encapsulated biphenyl derivatives are related with the increase of both selectivity and yield of 4,4-diisopropylbiphenyl (4,4-DIPB). The increase of reaction temperature up to 250°C enhanced the catalysis over highly dealuminated HM, however, further increase of the temperature resulted in extensive decrease of the selectivity of 4,4-DIPB. Coke deposition also increased with the temperature although its level was low. The composition of 4,4-DIPB in encapsulated DIPB isomers remained as high as 80% in spite of a change of the distribution of bulk products.     

Effects of SiO2/Al2O3 ratio of H-mordenite on encapsulated products inside the pores in shape-selective isopropylation of biphenyl

The effects of SiO2/Al2O3 ratio of H-mordenite on the selectivity of encapsulated products in the pores and of bulk products were investigated in the isopropylation of biphenyl. The selectivity of 4,40 -diisopropylbiphenyl (4,40 -DIPB) of bulk products was varied with SiO2/Al2O3 ratio. Highly dealuminated H-mordenite gave a selectivity higher than 80%, whereas the selectivity was low for H-mordenite with SiO2/Al2O3 ratio of 10-20. On the other hand, the selectivity of 4,40 -DIPB in encapsulated DIPB isomers was higher than 85% for all H-mordenites regardless of SiO2/Al2O3 ratio. These results show that all H-mordenites catalyze the isopropylation of biphenyl with high shape-selectivity inside the pore. The low selectivity of 4,40 -DIPB in bulk products for H-mordenites with low SiO2/Al2O3 ratio was not due to a lack of shape-selectivity of the H-mordenites, but to non-regioselective isopropylation at the external acid sites. Non-regioselective catalysis over H-mordenite with low SiO2/Al2O3 ratio could be induced by choking pores by coke deposition. This revised version was published online in July 2006 with corrections to the Cover Date.     

The conversions of 1,3,5-trimethylbenzene over beta zeolite: Effect of SiO2/Al2O3 ratio

A series of beta zeolites with various SiO₂/Al₂O₃ ratios has been synthesized. These samples were characterized with respect to crystallinity, particle size, acidity and sorption capacities of water, n-hexane and cyclohexane. The conversion of 1,3,5-trimethylbenzene (TrMB) was conducted in a fixed bed reactor at 493–743 K and atmospheric pressure. The conversion of 1,3,5-TrMB decreased with an increase in the SiO₂/Al₂O₃ ratio of the zeolite. The zeolites with low SiO₂/Al₂O₃ ratio favored the disproportionation and the zeolites with high SiO₂/Al₂O₃ ratio favored the isomerization. These can be interpreted by the acid concentration of zeolite. In the isomerization, all zeolites produced more 1,2,4-TrMB than 1,2,3-TrMB. In the disproportionation, the selectivity of tetramethylbenzene (TeMB) was in the order of 1,2,3,5->1,2,4,5->1,2,3,4-TeMB. The concentration of 1,2,4,5-TeMB is greater than that at equilibrium. The results show that shape selectivity comes into effect. The reaction temperature and the reaction time on stream also affect the selectivity significantly due to coke formation in the zeolites. © 1998 SCI     

不同硅铝比ZSM-22分子筛的合成

采用静态水热合成法,以氢氧化钾为碱源,硅溶胶为硅源,1,6-己二胺为模板剂,考察了晶化温度[(423～443)K]、晶化时间[(12～72)h]和原料配比对合成ZSM-22分子筛的影响,优化了合成条件。结果表明,最佳合成条件为:晶化温度433 K、晶化时间48 h、n(Al2O3)∶n(SiO2)∶n(K2O)∶n(DAH)∶n(H2O)=0.11∶10∶1.3∶3.0∶400。在此基础上,通过碱度的调变,合成了较纯n(Al2O3)∶n(SiO2)=40～130的ZSM-22分子筛。     

Carbon monoxide hydrogenation over Fe/HZSM-5 catalysts. Effect of SiO2/Al2O3 zeolite ratio

Iron catalysts supported on ZSM-5 zeolites of a wide range of silica-to-alumina ratios (29-) have been prepared and tested in carbon monoxide hydrogenation. The crystalline phases of the catalysts were characterized by X-ray diffraction and their acidity by infrared spectroscopy of adsorbed pyridine. The catalytic tests were conducted at 533 K, an overall pressure of 21 bar and a feed ratio CO/H₂ close to 1. It was found that the selectivity to light olefins (C₂–C₄) increases in parallel with the increase of the Si/Al ratio of the zeolite. This was explained in terms of the decrease in Brønsted acidity of the catalysts. As a consequence, very high olefin selectivities can be achieved by decreasing the number of strong acid sites in the zeolite structure, but at the expense of high oxygenate formation.     

纳米ZSM-5在高硅铝比料液中的再生长机制及其甲醇制芳烃性能

芳烃选择性低是ZSM-5催化甲醇制芳烃反应的难点问题,调变ZSM-5酸性质是提升选择性的重要方法。本研究将SiO₂/Al₂O₃为50的纳米ZSM-5分别置于硅铝比为50、110、220、440和660的料液中继续水热生长,优化其表面酸性,以提高轻质芳烃选择性。采用X射线衍射（XRD）、透射电子显微镜（TEM）、X射线荧光光谱（XRF）、吡啶红外（Py-IR）、氨气程序升温脱附（NH₃-TPD）等手段分析所得ZSM-5形貌、织构和酸性质,研究其水热再生长规律。发现生长过程中原粉部分溶解,包围在其表面的料液先形成小晶粒,经逐步堆积完成对原粉的包覆,最终形成孔道贯通性良好的单晶。在较低硅铝比料液中样品粒径分布不均匀,然而随着料液硅铝比的增加,包覆趋向均匀且表面呈现凸起结构。二次生长显著改变了表面酸性质及芳构化性能,在硅铝比为220的料液中生长后总酸量增加到194.9μmol/g,高于原粉的169.7μmol/g。值得注意的是,催化剂表面的强酸占比由原粉的37%显著增加至53%,B/L值也由原粉的0.56增加至3.19。该酸性的变化在促进甲醇芳构化的同时,还能强化芳烃的脱烷基化而提高BTX选择性,使总芳烃选择性和BTX选择性分别由16.1%和8.2%提高到23.8%和13.5%。     

超稳Y型分子筛的骨架硅铝比对甘油气相脱水反应的影响

以铵交换和高温水热处理法制备了不同硅铝比的超稳Y型分子筛（USY）,利用X射线衍射、扫描电镜、氮气吸附脱附和吡啶红外等技术对USY进行了表征。以USY为催化剂,考察了USY的骨架硅铝比对气相甘油脱水制丙烯醛的影响。X射线衍射和扫描电镜结果表明,铵交换和高温水热处理只是提高USY的硅铝比,相对结晶度略有降低,而对Y型分子筛的结构和形貌没有影响。氮气吸附-脱附和吡啶红外结果表明,随USY骨架SiO₂/Al₂O₃比提高,总酸量和B酸酸量逐渐降低,L酸酸量有所增多,介孔孔体积和平均孔径有所增大。气相甘油脱水反应结果表明,催化剂织构性质对甘油转化率和丙烯醛选择性的影响大于酸性的影响,因而SiO₂/Al₂O₃比为29的USY催化剂的反应性能最好,甘油转化率和丙烯醛收率分别达到了84.5%和51.8%。     

Ethenolysis of esters of vegetable oils: Effect of B2O3 addition to Re2O7/SiO2.Al2O3-SnBu4 and CH3ReO3/SiO2.Al2O3 metathesis catalysts

Impregnation of SiO₂.Al₂O₃ (24.3% Al₂O₃ with 6% B₂O₃ increases the activity of supported Re₂O₇ in the ethenolysis of methyl oleate, but reduces the activity of CH₃ReO₃ on the same support. Re₂O₇/SiO₂.Al₂O₃/B₂O₃-SnBu₄ is shown to be an effective catalyst for the ethenolysis of methyl linoleate and of the methyl esters of olive oil, and can be recycled after calcination at least five times without loss of activity.     

SiO2/Al2O3 ratio dependence of microstructures and dielectric properties in barium strontium titanate glass ceramics

(Ba, Sr)TiO₃-Al₂O₃-SiO₂ glass ceramic system with various SiO₂/Al₂O₃ ratios was investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM), dielectric spectroscopy and impedance spectroscopy. The XRD results demonstrated that the proper SiO₂/Al₂O₃ ratio could promote the crystallization of the major crystalline phase from the glass matrix. The dielectric property investigations showed that the dielectric constant passes through a maximum value while the dielectric breakdown strength has a minimum value with increasing SiO₂/Al₂O₃ ratio. Meanwhile, the complex impedance analyses suggest the resistance of the glass-crystal interface rapidly decreases and the capacitance of the crystal slightly decreases with the increase of SiO₂/Al₂O₃ ratio. The relaxation mechanisms of the (Ba, Sr)TiO₃ glass ceramics changed from localized relaxation to long range conductivity as the SiO₂/Al₂O₃ ratio was increased from 1.43 to 1.83. The variations in the dielectric response and the activation energy of the glass-crystal interface in the (Ba, Sr)TiO₃ glass ceramics with the ratio of 2.40 could be attributed to the crystallization of fresnoite phase.     

Enhanced dielectric characteristics of Ba0.94Bi0.04(Fe0.5Nb0.5)O3 coated with SiO2 and SiO2/Al2O3 over a broad frequency and temperature range

Pure phase of Ba_0.94Bi_0.04(Fe_0.5Nb_0.5)O₃ (BBFN) nano-particles were obtained by chemical co-precipitation method. The core-shell structure of BBFN@SiO₂ and BBFN@SiO₂/Al₂O₃ particles and the target ceramics were successfully prepared by aqueous chemical coating approach. The microstructures and dielectric properties of BBFN@SiO₂ and BBFN@SiO₂/Al₂O₃ were studied. Both the BBFN@SiO₂ and BBFN@SiO₂/Al₂O₃ samples show significantly decreased dielectric loss and good frequency and temperature stability on relative permittivity. Compared to the rapid decline of relative permittivity of BBFN@SiO₂, the synergistic effect of SiO₂ and Al₂O₃ in BBFN@SiO₂/Al₂O₃ ceramics made the relative permittivity of which remains a relatively high level with very low dielectric loss, making it more suitable in colossal permittivity applications. Based on the impedance analysis, the grain boundary effect and IBLC models play the important role for the improvement of dielectric properties of BBFN@SiO₂/Al₂O₃ samples.     

Formation of carbon nanotubes from the carbon monoxide disproportionation reaction over Co/Al2O3 and Co/SiO2 catalysts

The ammonia method has been successfully used for preparing thermostable and well dispersed alumina‐supported catalysts with a surface average size of cobalt particle D _{s= 5.7} nm. The disproportionation reaction of CO over this Co/Al₂O₃ catalyst and a similar Co/SiO₂ catalyst leads to the formation of carbon nanotubes demonstrating the same morphology. The amount of nanotubes over Co/Al₂O₃, however, is much larger than that obtained over Co/SiO₂, because of a faster ageing in the latter solid. Similar support effects have already been reported for other catalytic reactions involving carbon oxides. This revised version was published online in July 2006 with corrections to the Cover Date.     

载体改性对Cu/B/Al2O3结构及其催化醋酸仲丁酯加氢性能的影响

以γ-Al₂O₃为载体采用分步浸渍法制备了不同金属氧化物进行载体改性的Cu/B/M/Al₂O₃(M=Mg,Ca,Ni)催化剂,并测试了其催化醋酸仲丁酯加氢反应的性能。结果表明,以NiO进行载体改性的催化剂导致酯加氢反应中大量酸催化产物及烃类出现;以MgO进行载体改性不利于金属Cu的分散且催化剂的结构稳定性较差;以CaO对γ-Al₂O₃载体进行改性不仅能够促进金属Cu的分散,提高催化剂的酯加氢活性和产物选择性,而且可以有效减少反应中非活性碳物种在催化剂表面的沉积。     

Influence of Al2O3/SiO2 ratio in multicomponent LNAS glasses and glass-ceramics on the crystallization behavior,microstructure and mechanical performance

Transparent glass-ceramics containing eucryptite and nepheline crystalline phases were prepared from alkali (Li, Na) aluminosilicate glasses with various mole substitutions of Al₂O₃ for SiO₂. The relationships between glass network structure and crystallization behavior of Li₂O–Na₂O–Al₂O₃–SiO₂ (LNAS) glasses were investigated. It was found that the crystallization of the eucryptite and nepheline in LNAS glasses significantly depended on the concentration of Al₂O₃. LNAS glasses with the addition of Al₂O₃ from 16 to 18 mol% exhibited increasing Q⁴ (mAl) structural units confirmed by NMR and Raman spectroscopy, which promoted the formation of eucryptite and nepheline crystalline phases. With the Al₂O₃ content increasing to 19–20 mol%, the formation of highly disordered (Li, Na)₃PO₄ phase which can serve as nucleation sites was inhibited and the crystallization mechanism of glass became surface crystallization. Glass-ceramics containing 18 mol% Al₂O₃ showed high transparency ～84% at 550 nm. Moreover, the microhardness, elastic modulus and fracture toughness are 8.56 GPa, 95.7 GPa and 0.78 MPa m^1/2 respectively. The transparent glass-ceramics with good mechanical properties show high potential in the applications of protective cover of displays.     

高硅铝比小晶粒NaY分子筛/高岭土复合物的合成及其催化裂化性能

以两种不同粒径的高岭土为原料,采用水热法合成了高硅铝比小晶粒NaY分子筛/高岭土复合物,通过XRD、SEM、晶粒度分析和N₂物理吸附等表征手段对复合物进行了结构和形貌表征。结果表明,与商品NaY相比,高岭土合成样品的结构稳定性和水热稳定性显著提高,以细化高岭土为原料合成样品的晶粒尺寸达310 nm,比表面积达807 m²·g^-1。以改性NaY分子筛/高岭土复合物为活性组分制备了催化裂化催化剂,采用NH₃程序升温脱附(NH₃-TPD)技术对其酸性特征进行了分析,并在小型微反装置上对其重油催化裂化性能进行了评价。研究结果发现,随着骨架硅铝比增大,催化剂表面酸中心强度增加,而酸量下降。采用细化高岭土合成的NaY分子筛/高岭土复合物的分子筛晶粒更小,催化剂酸中心数量以及催化裂化性能均大幅度提升。随着高温焙烧高岭土/偏高岭土质量比的增加,合成产物中的高岭土基质含量增加,催化剂表面酸中心强度下降。以原料高温焙烧高岭土/偏高岭土质量比为0.5,骨架硅铝比为6.1(摩尔比)的样品制备的催化剂,去柴重油转化率高达85.4%,同时有高达64.2%的汽油收率,表现出优异的重油催化裂化性能。     

Understanding the solidification and leaching behavior of synthesized Cr-containing stainless steel slags with varying Al2O3/SiO2 mass ratios

This study investigated the effect of Al₂O₃/SiO₂ mass ratios on the equilibrium crystallization behavior of synthesized CaO–SiO₂–MgO–Al₂O₃–Cr₂O₃ stainless steel slags to understand the selective concentration behavior of Cr into a primary Mg(Cr,Al)₂O₄ spinel phase during slag solidification and to determine the leaching stability of Cr-containing slags. The spinel solid solution was precipitated within the temperature range of 1600-1400 °C, where the Cr/(Cr+Al) mole ratio in the Mg(Cr,Al)₂O₄ spinel phase gradually decreased for slags with higher Al₂O₃/SiO₂ mass ratios. When the Al₂O₃/SiO₂ mass ratio increased from 0.125 to 0.5, the Cr content in the amorphous glass phase gradually decreased, with a subsequent increase in the Cr content in the crystalline phase. For slags with a unit Al₂O₃/SiO₂ mass ratio and MgO mole percent comprising less than the combined sum of the Cr₂O₃ and Al₂O₃ mole percents, the Cr content in the amorphous glass phase increased, which was correlated with the enhanced substitution of Cr³⁺ with Al³⁺ in the spinel. The trend of the amount of Cr-related ions in the leachate was consistent with the trend of Cr in the amorphous glass phase: the amount decreased for slags with Al₂O₃/SiO₂ mass ratios from 0.125 to 5 and then increased for slags with an Al₂O₃/SiO₂ mass ratio of 1. The results suggest that the addition of appropriate amounts of Al₂O₃ to stainless steel slags could be conducive to stabilizing Cr into the primary spinel phase to minimize Cr leaching into the environment.     

用CuO/A12O3/堇青石催化剂选择性催化还原脱硝的实验和动力学研究

The CuO/γ-Al2O3/cordierite catalyst, after being sulfated by sulfur dioxide (SO2) at 673 K, exhibits high activities for selective catalytic reduction (SCR) of nitrogen oxide (NO) with ammonia (NH3) at 573-723 K. The intrinsic kinetics of SCR of NO with NH3 over CuO/γ-Al2O3/cordierite catalyst has been measured in a fixed-bed reactor in the absence of internal and external diffusions. The experimental results show that the reaction rate can be quantified by a first-order expression with activation energy of 94.01 kJ•mol1 and the corresponding pre-exponential factor of 3.39×108 cm3•g1•s1 when NH3 is excessive. However, when NH3 is not enough, an Eley-Rideal kinetic model based on experimental data is derived with Ea of 105.79 kJ•mol1, the corresponding A of 2.94×109 cm3•g1•s1, heat of adsorption ΔHads of 87.90 kJ•mol1 and the corresponding Aads of 9.24 cm3•mol1. The intrinsic kinetic model obtained was incorporated in a 3D mathematical model of monolithic reactor, and the agreement of the prediction with experimental data indicates that the present kinetic model is adequate for the reactor design and engineering scale-up.     

Ultra-low core loss FeSiAl soft magnetic composites with in-situ double oxidation layers of outer Fe3O4 layer and inner super-thin Al2O3/SiO2 hybrid layer

How to synchronously reduce eddy current loss and hysteresis loss still remains a challenge for achieving low core loss of soft magnetic composite (SMC). In-situ surface oxide effectively combines the formation of insulating layer and the release of internal stress during the molding process. In this study, FeSiAl SMC has been fabricated by powder metallurgy method with in-situ oxidated FeSiAl powder, in which FeSiAl powder are covered by outer Fe₃O₄ insulating layer and inter super-thin Al₂O₃/SiO₂ hybrid layer. Fe₃O₄ layer alleviates dilution magnetic effect, ensuring high saturated magnetization and effective permeability. The super-thin Al₂O₃/SiO₂ hybrid layer enhances electrical resistance, reducing eddy loss. Effects of the in-situ oxidation time on insulating layer and soft magnetic performances of SMC are investigated in detail. Synchronous reduction of eddy current loss and hysteresis loss is achieved through high resistance accompanied with proper insulating layer thickness and low coercive force provided by the special microstructure. For powder with 90 min oxidation at 500 °C, core loss of SMC is low up to 64 mW/cm³ at 50 mT and 100 kHz and 363 mW/cm³ at 100 mT and 100 kHz, while the permeability is kept at 50 until 1100 kHz and is stable until 140 °C. Meanwhile, DC bias performance reaches 51.2% at 100 Oe applied field and Q value is 104.8 at 400 kHz.     

Wet oxidation of bleach plant effluent: Effects of pH on the oxidation with or without a Pd/Al2O3 catalyst

Wet oxidation of acidic bleach plant effluent was carried out at 423K and 1.5 MPa in a slurry reactor. The influence of pH of the bleach plant effluent was evaluated for both catalytic and non-catalytic oxidation in the liquid phase. The stability of the heterogeneous catalysts was investigated by measuring the extent of metal leaching into the solution. The pH of wastewater solution was found to influence significantly both the rate of total organic carbon (TOC) removal and the stability of the Pd/Al₂O₃ catalyst. Leaching of palladium and alumina occurred mostly at pH 2 and pH 11 under experimental conditions. With Pd/Al₂O₃, comparable rates of TOC removal were obtained in the pH range of 5 to 9 without significant leaching of both palladium and alumina. No metal leaching was observed using the Pd-Pt/Al₂O₃ catalyst at an initial pH value of 7. Implications of these experimental results for designing a catalytic wet oxidation process are discussed. A novel approach has been proposed for the treatment of effluents from softwood Kraft pulp mills.     

Hydrogen production from steam reforming of methanol over CuO/ZnO/Al2O3 catalysts: Catalytic performance and kinetic modeling

A series of CuO/ZnO/Al_2O_3, CuO/ZnO/ZrO_2/Al_2O_3 and CuO/ZnO/CeO_2/Al_2O_3 catalysts were prepared by coprecipitation and characterized by N_2 adsorption, XRD, TPR, N_2O titration and HRTEM. The catalytic performances of these catalysts for the steam reforming of methanol were evaluated in a laboratory-scale fixed-bed reactor at 0.1 MPa and temperatures between 473 and 543 K. The results showed that the catalytic activity depended greatly on the catalyst reducibility and the specific surface area of Cu. An approximate linear correlation between the catalytic activity and the Cu surface area was found for all catalysts investigated in this study.Compared to CuO/ZnO/Al_2O_3, the ZrO_2-doped CuO/ZnO/Al_2O_3 exhibited higher activity and selectivity to CO,while the CeO_2-doped catalyst displayed lower activity and selectivity. Finally, an intrinsic kinetic study was carried out over a screened CuO/ZnO/CeO_2/Al_2O_3 catalyst in the absence of internal and external mass transfer effects. A good agreement was observed between the model-derived effluent concentrations of CO(CO_2) and the experimental data. The activation energies for the reactions of methanol-steam reforming, water-gas shift and methanol decomposition over CuO/ZnO/CeO_2/Al_2O_3 were 93.1, 85.1 and 116.5 k J·mol~(-1), respectively.     

Dry Reforming of Methane with a Ni/Al2O3‐YSZ Catalyst: The Role of the Catalyst Preparation Protocol

Many studies of Ni based ceramic supporting reforming catalysts are found in the literature. A synthesis of the reported results shows that their efficiency and durability are significantly affected by their fabrication protocol. This research has been aimed at evaluating how the conditions of 1) the ceramic support preparation and 2) the Ni deposition, through an impregnation‐drying‐calcination‐reduction protocol, affect the catalytic activity and the catalyst deactivation over time during methane dry reforming. The catalyst support used in this study was obtained by the mixing and pressing of alumina and YSZ (Yttria Stabilized Zirconia) powders, then calcining the mixtures at high temperature to form pellets of limited porosity (specific surface of 1.5‐10 m²/g), without inducing change to the crystalline phases. The results show that the surface density of the nickel particles, the catalyst activity, and its life span are highly dependent upon the catalyst preparation protocol. The initial nitrate solution concentration, the duration of the impregnation and the specific surface of the ceramic support have, all of them, a considerable influence on the size range of the deposited nickel particles. The surface density, the amount and the size of the latter highly affect the catalytic activity. It has been also shown that an increase in the ratio CH₄/CO₂ is detrimental to the catalytic activity of the tested formulations; a small excess of methane is enough to initiate the deactivation process of the catalyst very quickly for all of the composition tested in this study. A phenomenological deactivation kinetics model has been built and optimized. Although there are differences in deactivation rates among the different formulations tested, the model shows that the deactivation rate is highly dependent upon the reaction rate constant and that zero‐ and first‐order kinetics give statistically the same prediction error; the latter is always lower or equal to the experimental error.