Highly dispersed Cu supported on mesoporous Al-KIT-6 for oxidative carbonylation of methanol to dimethyl carbonate

Microporous NaY zeolite is a common support of Cu catalysts for oxidative carbonylation of methanol, but the dispersion of Cu species on NaY is usually subjected to its micropore size. Here, ordered mesoporous KIT-6 was employed as the support for Cu catalyst and Al was incorporated into its framework to increase the surface acidity, which eventually improves the surface exchange capacity and Cu dispersion. The evolution of the state of Cu species on KIT-6 was analyzed combined with control of Cu loading. The physicochemical properties of the supports and corresponding catalysts were characterized by N₂ adsorption–desorption, X-ray diffraction, ammonia temperature programmed desorption, Fourier transform infrared spectra, transmission electron microscopy, hydrogen temperature programmed reduction, and X-ray photoelectron spectroscopy. It was found that mesoporous KIT-6 showed better Cu dispersion than microporous NaY zeolite. Agglomerated CuO, dispersed CuO, and Cu²⁺ are the major Cu species observed on the catalyst surface. The increased surface acidic sites of KIT-6 by Al incorporation promoted the formation of Cu²⁺ and dispersion of CuO. With the increase in Cu loading, the Cu²⁺ content in the catalyst was decreased gradually along with increase in the bulk CuO. It was speculated that some exchanged Cu²⁺ could be transformed into highly dispersed CuO and even bulk CuO after calcination at a high Cu loading. Combined with the catalyst evaluation results, it was deduced that highly dispersed Cu²⁺ and CuO particles play significant roles in catalytic activity. The catalyst Cu/Al-K-10 achieved the highest space time yield of dimethyl carbonate of 135.4 mg/(g·h), which is 2.7 times the Cu/K-10 owing to its more dispersed Cu species. This laid the basis for preparing highly dispersed Cu species on mesoporous silica supports.     

红外光谱法研究表面溢出效应

采用红外光谱法, 利用重氢交换反应证明在Pt-NaY/HY体系有氢溢出(spillover)效应发生, 测量了100 ℃和50 ℃时的交换速率。发现在50 ℃时高频羟基的交换速率大于低频羟基。并对溢出机构进行了初步的讨论。     

以催化裂化废催化剂为原料合成NaY分子筛的研究

针对催化裂化(FCC)废催化剂的回收利用问题,提出了一种废催化剂再利用的方法,即以FCC废催化剂为铝源,合成时只补充部分硅源,采用自制的高效NaY沸石导向剂,水热合成NaY分子筛。同时,以普通的化工原料合成了对比试样Y型分子筛。讨论了不同的FCC废催化剂预处理方式对合成产物性能的影响,发现以经过碱熔活化处理的废催化剂为原料合成的Y分子筛拥有更高的结晶度和纯度。采用X射线衍射、热分析、程序升温脱附法(NH3-TPD)和N₂静态容量吸附法对结晶产物和对比样品的晶体结构,热稳定性、酸性质、比表面积以及孔分布进行了表征。结果显示,以FCC废催化剂为原料完全可以合成出与普通原料性能接近的NaY分子筛。其BET比表面积可以达到615 m²·g^-1,孔体积可达0.38 cm³·g^-1,孔径集中在0.51 nm左右。     

Highly active and reusable heterogeneous catalysts for acylation of anisole

In the present study, non-conventional solid acid catalysts such as NaY, metal ion exchanged zeolite NaY (Zn²⁺, Fe³⁺, Ce³⁺, La³⁺ and Nd³⁺), H-mordenite, H-β and HZSM-5 were used in order to overcome the disadvantages of conventional Friedel-Crafts catalysts for the acylation of anisole with acetic anhydride. Among the various zeolites studied, the HY zeolite shows an intermediate activity. Zeolite containing transition metal ions (Zn²⁺ and Fe³⁺) are less active and zeolite NaY is nearly inactive. The catalysts exhibit the activity in the order H-β>transition metal ions (Zn²⁺ and Fe³⁺)>HY>NaY zeolite. The highest catalytic activity of H-β could be due to its larger pore size. The type of acidity and the acid strength in zeolite Y were determined by FTIR and differential scanning calorimetric (DSC) studies on the pyridine adsorbed catalysts. The correlation of catalytic activity with acidity reveals that Brönsted acid sites in zeolite promote the acylation of anisole.     

Polymerization of ethylene over metallocenes confined inside the supercage of a NaY zeolite

Metallocene catalysts entrapped inside the supercages of NaY zeolite were prepared by reacting NaY with methylaluminoxane (MAO) or trimethylaluminium (TMA) and then with Cp₂ZrCl₂ (Cp: cyclopentadienyl) or Cp₂TiCl₂. NaY/MAO/Cp₂ZrCl₂ and NaY/MAO/Cp₂TiCl₂ catalysts could polymerize ethylene. The amount of additional MAO for the polymerization was lowered to a mole ratio of Al/Zr of 186. Molecular weights and melting points of polyethylene polymerized with NaY-supported catalysts were higher than those of polyethylene obtained with homogeneous metallocene catalysts. It could be confirmed by extraction experiments that the metallocene catalyst was confined securely inside the supercage of the NaY zeolite.     

Synthesis of NaX and NaY Zeolites from Tunisian Kaolinite as Base Catalysts: An Investigation of Knoevenagel Condensation

The synthesis of Faujasite‐type zeolites with high purity has been successfully performed from Tunisian kaolinite and the effects of different crystallization parameters on the final products were widely investigated. The alkaline fusion of kaolinite followed by hydrothermal treatment lead to zeolite NaX synthesis whereas the classic hydrothermal transformation of metakaolinite produces NaY zeolite. The results show that an increase in the synthesis temperature and time has improved the crystallization process of the zeolite NaX whereas the SiO₂/Al₂O₃ and the Na₂O/SiO₂ molar ratios were the key parameters to obtain a pure zeolite NaY. The highest specific surface areas obtained with the optimal crystallization conditions were 554 m2 g^?1 and 592 m2 g^?1 for respectively NaX and NaY zeolites. The basic properties of NaX and NaY zeolites were explored in the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate at 140 °C as a test reaction in the absence of solvent. The influence of ion exchange with cesium cation on the catalytic activity of prepared catalysts was also investigated. It was found that the NaX provided higher activity than that of NaY catalyst due to its lower Si/Al ratio whereas a cesium exchange conferred higher basicity to the prepared Na‐faujasite.     

Generation of active site confined inside supercage of NaY zeolite on a nano-scale and its ethylene polymerization

To generate an active site that consisted of one Cp₂ZrCl₂ molecule and 1-2 MAO molecules inside supercage of NaY zeolite, two preparation ways for supported catalyst were estimated. First, higher concentration of MAO and Cp₂ZrCl₂, and long reaction time were introduced during the preparation of supported catalyst. It showed activity in ethylene polymerization without any additional MAO. It indicates that Cp₂ZrCl₂ coordinated with only 1-2 MAO molecules could be an active site due to the fact that supercage has nano-scaled diameter of supercage, 1.2 nm, and it could contain only 1-2 MAO molecules inside it theoretically. In situ generation of active site between NaY/MAO and homogeneous Cp₂ZrCl₂ also showed experimental evidence that an active site was generated inside the supercage of NaY zeolite. It showed low activity with long activation time, suggesting the presence of a diffusion effect of Cp₂ZrCl₂ in the pore of NaY. However, NaY/Cp₂ZrCl₂ and homogeneous MAO system showed the characteristic PE polymerization with homogeneous catalyst, indicating that active site was not generated inside the supercage of NaY.     

Schwermetallausgetauschte Zeolithe als Katalysatoren für die Selektivoxidation

Transition Metal Zeolites as Catalysts for the Partial Oxidation of Methanol Zeolites containing cations of the 4th period of the periodical system from Ti to Cu have been prepared by ion exchange of a NaY zeolite in aqueous solutions. Structural and surface chemical properties of the zeolites were characterized by adsorption, DTA, thermogastitrimetry, x-ray, ESR, IR, and UV-V is spectroscopy. It could be shown that both localization and coordination state of transition metal ions is fairly different and depends on the thermal treatment of the zeolites. By exchanging sodium ions the acidic properties as well as the ability of the zeolites to interact with H₂O or CO₂ is changed and depends on the kind of transition metal ion. VO and Cr exchanged zeolites proved to be selective catalysts for the oxidative dehydrogenation of methanol to formaldehyde with a maximum selectivity of 70%. It is concluded that in contrast to oxides where a redox mechanism is assumed the reaction on zeolites occurs via an associative mechanism.     

镍盐和氧化镍在NaY沸石中存在状态研究

用ＸＲＤ、ＥＸＡＦＳ和ＴＰＲ方法研究了Ｎｉ（ＮＯ３）２／ＮａＹ和ＮｉＯ／ＮａＹ分散体系。在沸石上，Ｎｉ（ＮＯ３）２的分散比ＮｉＯ容易得多。ＸＲＤ相定量方法测定的ＮｉＯ在ＮａＹ沸石上的分散阈值很低，仅为密置单层容量的２％左右。在分散阈值关ＮｉＯ在沸石上处于分散相和笼外小晶粒两种状态。分散相ＮｉＯ比笼外ＮｉＯ小晶粒难还原。样品中ＮｉＯ含量超过阈值时，笼外小晶粒长大成ＸＲＤ可检测的较大晶粒。     

NaY Zeolite Functionalized by Sulfamic Acid/Cu(OAc)2 as a Novel and Reusable Heterogeneous Hybrid Catalyst in Efficient Synthesis of Bis,Tris, and Tetrakis(indolyl)methanes, 3,4‐Dihydropyrimidin‐2(1H)‐ones,and 2‐Aryl‐1H‐benzothiazoles

An efficient acid‐catalyzed synthesis of some bis, tris, and tetrakis(indolyl)methanes, 3,4‐dihydropyrimidin‐2(1H )‐ones, and 2‐aryl‐1H ‐benzothiazoles is reported using NaY zeolite functionalized by sulfamic acid/Cu(OAc )₂ (NaY zeolite‐NHSO₃H /Cu(OAc )₂) in excellent yield. The heterogeneous catalyst has a simple work‐up procedure and could be recycled and reused for six reaction cycles.     

微波固相法制备ZnCl2/NaY催化剂ZnCl2/NaY在月桂烯Diels-Alder反应中的催化性能

比较了微波固相法、普通加热法和简单混合法制备的ZnCl2/NaY及溶液离子交换法制备的ZnNaY在月桂烯与丙烯醛Diels-Alder反应中的催化性能,发现微波固相法制备的催化剂表现出最高的环加成选择性和区域选择性.通过对微波固相法制备的催化剂中ZnCl2负载量的考察,揭示了微波诱导ZnCl2在NaY分子筛表面形成了不同催化活性中心的特点,分散在分子筛表面的ZnCl2具有更高的催化活性和区域选择性.微波辐射可成功地将ZnCl2固载于NaY分子筛中,当ZnCl2负载量为6.3%时,ZnCl2与NaY分子筛主要发生固态离子交换反应;当ZnCl2负载量达25%时,催化活性提高了3倍,区域选择性提高了1倍以上.而且,以微波固相法制备的ZnCl2/NaY催化剂,其环加成选择性和区域选择性随反应温度的升高而下降.     

Formation of Frustrated Lewis Pairs in Ptx‐Loaded Zeolite NaY

The formation of a frustrated Lewis pair consisting of sodium hydride (Na⁺H^?) and a framework‐bound hydroxy proton O(H⁺) is reported upon H₂ treatment of zeolite NaY loaded with Pt nanoparticles (Pt_x/NaY). Frustrated Lewis pair formation was confirmed using in situ neutron diffraction and spectroscopic measurements. The activity of the intrazeolite NaH as a size‐selective catalyst was verified by the efficient esterification of acetaldehyde (a small aldehyde) to form the corresponding ester ethyl acetate, whereas esterification of the larger molecule benzaldehyde was unsuccessful. The frustrated Lewis pair (consisting of Na⁺H^? and O(H⁺)) generated within zeolite NaY may be a useful catalyst for various catalytic reactions which require both H^? and H⁺ ions, such as catalytic hydrogenation or dehydrogenation of organic compounds and activation of small molecules.     

Selective methane chlorination to methyl chloride by zeolite Y-based catalysts

The CH₄ chlorination over Y zeolites was investigated to produce CH₃Cl in a high yield. Three different catalytic systems based on Y zeolite were tested for enhancement of CH₄ conversion and CH₃Cl selectivity: (i) HY zeolites in H⁺-form having various Si/Al ratios, (ii) Pt/HY zeolites supporting Pt metal nanoparticles, (iii) Pt/NaY zeolites in Na⁺-form supporting Pt metal nanoparticles. The reaction was carried out using the gas mixture of CH₄ and Cl₂ with the respective flow rates of 15 and 10 mL min⁻¹ at 300–350 °C using a fixed-bed reactor under a continuous gas flow condition (gas hourly space velocity = 3000 mL g⁻¹ h⁻¹). Above the reaction temperature of 300 °C, the CH₄ chlorination is spontaneous even in the absence of catalyst, achieving 23.6% of CH₄ conversion with 73.4% of CH₃Cl selectivity. Under sufficient supplement of thermal energy, Cl₂ molecules can be dissociated to two chlorine radicals, which triggered the C-H bond activation of CH₄ molecule and thereby various chlorinated methane products (i.e., CH₃Cl, CH₂Cl₂, CHCl₃, CCl₄) could be produced. When the catalysts were used under the same reaction condition, enhancement in the CH₄ conversion was observed. The Pt-free HY zeolite series with varied Si/Al ratios gave around 27% of CH₄ conversion, but there was a slight decrease in CH₃Cl selectivity with about 64%. Despite the difference in acidity of HY zeolites having different Si/Al ratios, no prominent effect of the Si/Al ratios on the catalytic performance was observed. This suggests that the catalytic contribution of HY zeolites under the present reaction condition is not strong enough to overcome the spontaneous CH₄ chlorination. When the Pt/HY zeolite catalysts were used, the CH₄ conversion reached further up to 30% but the CH₃Cl selectivity decreased to 60%. Such an enhancement of CH₄ conversion could be attributed to the strong catalytic activity of HY and Pt/HY zeolite catalysts. However, both catalysts induced the radical cleavage of Cl₂ more favorably, which ultimately decreased the CH₃Cl selectivity. Such trade-off relationship between CH₄ conversion and CH₃Cl selectivity can be slightly broken by using Pt/NaY zeolite catalyst that is known to possess Frustrated Lewis Pairs (FLP) that are very useful for ionic cleavage of H₂ to H⁺ and H⁻. Similarly, in the present work, Pt/NaY(FLP) catalysts enhanced the CH₄ conversion while keeping the CH₃Cl selectivity as compared to the Pt/HY zeolite catalysts.     

Experimental and theoretical studies of carbon monoxide oxidation over W/Cu/Ce trimetallic oxides: the effect of W addition

It is a significant method to prepare highly dispersed polymetallic oxides using in-situ doping metal organic frameworks as precursors. Herein, a series of straw-like W/Cu/Ce trimetallic oxides were prepared by using phosphotungstic ionic liquid@Ce-based metal organic framework adsorbing with copper acetylacetonate as precursors. The effect of W content on catalytic activity of W/Cu/Ce trimetallic oxides for carbon monoxide (CO) oxidation was well-investigated. Comprehensive characterization methods and density functional theory calculations were adopted to reveal the property changes of Cu/CeO₂ catalyst by the addition of W. The results demonstrated that W, Cu, and Ce are highly dispersed in the prepared W/Cu/Ce trimetallic oxides, and adding proper amount of W can improve the activity of the catalyst. H₂ temperature-program reduction profiles, X-ray photoelectron spectroscopy, in-situ diffuse reflectance infrared Fourier transform spectroscopy, and density functional theory calculations clearly revealed that after the addition of W, the strength of Ce-O bond is weakened, the oxygen vacancy is increased, and the adsorption of CO is enhanced, respectively, which are vital reasons for its high catalytic activity. In addition, the CO oxidation reaction pathway over prepared W/Cu/Ce trimetallic oxides based on the Mars-van Krevelen mechanism was studied, and the results exhibited that CO can wrest the lattice oxygen of W/Cu/Ce trimetallic oxides to form CO₂, which is also proved to be the rate-determining step in reaction process.     

α-Fe2O3在Y沸石上的分散

用草酸高铁铵浸渍NaY沸石, 并在高温下焙烧, 得到α-Fe_2O_3/NaY沸石体系。经XRD相定量外推法测定, α-Fe_2O_3在NaY沸石上的最大分散量为0.060 gα-Fe_2O_3/gNaY, 仅占α-Fe_2O_3在沸石表面密置单层量的5.5%。首次尝试用正电子寿命谱方法测定α-Fe_2O_3在沸石表面的最大分散量, 所得结果与XRD方法完全吻合。由程序升温还原方法发现沸石上α-Fe_2O_3的还原分两步进行, α-Fe_2O_3先还原成Fe_3O_4, 然后再还原成金属。α-Fe_2O_3分散相与沸石之间的强相互作用, 使这两个还原反应受到阻抑。     

分子筛表面酸性对微波固相法制备ZnCl2/Y催化剂的影响

 采用XRD和原子吸收光谱法研究了微波作用下分子筛表面酸性对ZnCl2与Y分子筛固态相互作用的影响．结果表明，微波辐射可显著促进ZnCl2在分子筛表面分散，其分散阈值与分子筛表面酸性有关．随着分子筛表面酸量和酸强度增加，ZnCl2在分子筛表面的最大分散量减少，分散的ZnCl2与Y分子筛的固态离子交换量也减少；NaY型分子筛比HY分子筛更容易发生固态离子交换反应．考察了微波固相法制备的ZnCl2／HY催化剂在苯甲醚与乙酰氯酰化反应中的催化性能．结果表明，在分子筛表面分散的ZnCl2具有更高的催化活性及对甲氧基苯乙酮选择性．     

载体H+含量对CuY甲醇氧化羰基化反应性能影响

通过过量浸渍Cu(NO_3)_2溶液于Y分子筛载体上,制备出Cu负载量为6.4%的CuY催化剂,考察了甲醇氧化羰基化反应的催化性能,并采用X射线衍射(XRD)、H2程序升温还原(H2-TPR)、透射电子显微镜(TEM)和NH3程序升温脱附(NH3-TPD)等手段对催化剂表面微观结构进行了表征。研究表明,随Y分子筛载体H+含量的增加,可使更多Cu物种落位于分子筛微孔笼结构中,且高度分散,而笼内未交换的Na+能进一步促进铜物种更多落位于载体超笼结构中,形成更多甲醇氧化羰基化反应的Cu+活性中心。同时随铜物种引入,催化剂中产生了明显的中强酸,酸量随落位于载体笼结构中的Cu物种的增加而增加,催化剂总酸量随之增加,导致甲醇氧化羰基化产物分布发生改变,碳酸二甲酯(DMC)选择性明显降低。对比等体积浸渍法制备的92.3%的高DMC选择性CuY催化剂,以不含H+的NaY分子筛为载体,过量浸渍法制备的CuY催化剂酸量少、Cu物种活性中心多,在保持82.4%的高DMC选择性时,其DMC的时空收率(STY)也高达109.1mg·g~(-1)·h-1。     

过渡金属氧化物掺杂对铜锰氧化物催化CO氧化性能的影响

以乙酸铜和乙酸锰为铜锰前驱体,以NH₄HCO₃为沉淀剂,相应金属硝酸盐为掺杂剂,采用共沉淀法制备了不同过渡金属氧化物掺杂的铜锰氧化物催化剂.?采用N₂物理吸附、X射线衍射,氢气-程序升温还原和原位红外漫反射光谱等方法对催化剂进行了表征,考察了系列催化剂上CO反应性能.?结果表明,掺杂过渡金属氧化物可以调变催化剂对CO的吸附能力,进而影响催化剂性能.     

Zeolite NaY-mediated oxidation of dyes with H2O2: unique heterogeneous non-transition metal center cleavage of H2O2 under visible light irradiation

This study investigated the visible-light catalysis mediated by zeolite NaY on the oxidation of dyes with H₂O₂. The results demonstrated that zeolite NaY acts as a sink for the electron from the photo-excited dye in the heterogeneous catalysis. Furthermore, the electron can effectively activate H₂O₂ to produce ^·OH radical that is a powerful oxidant for the oxidation of dye at room temperature. The effects of the framework topology, Si/Al ratio, and exchangeable cation of the zeolite on the oxidation of various dyes were also shown.     

微波辐射促进ZnCl2与Y分子筛固相反应的研究

ZnCl2/Y catalysts prepared by solid-state reaction of anhydrous ZnCl2 and Y zeolites under microwave irradiation were characterized by XRD, IR and AAS. ZnCl2 was intercalated in Y zeolites and dispersed on the surface of Y zeolite, part of ZnCl2 dispersed could result in solid-state ion exchange with Y. The amount of dispersion and solid-state ion exchange were related to ZnCl2 loading and the surface acid property of the zeolite. When ZnCl2 loading was 37.5% (mass fraction) in NaY zeolite, ZnCl2 was still completely dispersed on the surf are of zeolite and the degree of solid- state ion exchang was 84%. The appearance of new band at 890 cm-l in the framework IR spectra of ZnCl2/NaY sample was due to the dispersed ZnCl2 coordinating strongly with oxygen of NaY surface. With the increasing of the number of arid centers and the acid strength of the surface of Y zeolite the amount of solid-state ion exchange decreased.