MCM-41 anchored manganese salen complexes as catalysts for limonene oxidation

This work reports the covalent attachment of three different salen-based complexes on MCM-41, using two different methods. In both methods, a diisocyanate is used as a binder. All the prepared catalysts were tested on the liquid phase limonene oxidation reaction, using diluted t-butyl hydroperoxide as oxidant. Limonene oxide, carveol, carvone and a polymer were the main products obtained. The preservation of the MCM-41 channel system was checked by X-ray diffraction, nitrogen adsorption analysis and transmission electron microscopy (TEM). Catalytic activity seems to increase in the following order: Mn(4-OHsalen) < Mn(4-OHsalhd) < Mn(4-OHsalophen).The most active catalysts were used in four consecutive experiments without any activity loss, confirming the success of the anchoring process and the catalysts stability.     

Direct vapor phase oxidation of propylene by molecular oxygen over MCM-41 or MCM-22 based catalysts

Ti and Al containing MCM-41 (Al-c-MCM-41 and Al-Ti-c-MCM-41) have been synthesized and tested for direct oxidation of propylene with molecular oxygen. Al-Ti-c-MCM-41 is more effective than Al-c-MCM-41, while no product was formed for MCM-41 alone. It is also found that MCM-22 with Si/Al₂ ratio of 30 and Na/SiO₂ ratio of 0.18 is active for the reaction and a highest PO yield of 11.3% was obtained at 573 K.     

杂原子MCM-41分子筛对过氧化氢液相氧化环己烷的研究

分别考察了反应温度、过氧化氢用量及加入方式等因素对Cr、Fe和Ce改性后的杂原子MCM-41分子筛催化剂液相催化氧化环己烷制取环己酮反应的影响。研究结果表明，Cr-MCM-41〖JP〗催化剂具有较好的催化活性。选择适当的反应温度、过氧化氢用量和加入方式可以有效提高环己烷转化率和过氧化氢利用率。在70 ℃和n(C₆ H₁₂)∶n(H₂O₂)=1∶2条件下，采用两次加入过氧化氢的方式，环己烷转化率为33.7％，酮醇总选择性97.2％，n(环己酮)∶n(环己醇）＝1.99，过氧化氢利用率37.1%。     

Comparative catalytic studies on the conversion of 1-butene and n-butane to isobutene over MCM-22 and ITQ-2 zeolites

The catalytic properties of H-MCM-22 and Pt-MCM-22 for the skeletal isomerization of 1-butene and the dehydroisomerization of n-butane were compared with those obtained from their delaminated derivatives, H-ITQ-2 and Pt-ITQ-2. The overall results of our study strongly suggests that the desired 1-butene and n-butane conversions to isobutene in steady state occur mainly near the pore mouth inlets of the sinusoidal 10-ring channels retained in both of MCM-22 and ITQ-2 and inside this intralayer void space, respectively, which may be attributed to the unique geometric constraints imposed by the two-dimensionality of the pore system with a suitable degree of ellipticity of 10-ring channels. Whereas coke formation on the sinusoidal channels during the 1-butene skeletal isomerization can occur in such a way as to make most of the intrachannel Brønsted acid sites less available for nonselective dimerization-cracking reactions, it appears that the presence of H₂ in the n-butane dehydroisomerization stream would prevent extensive coke buildup, thereby allowing pore diffusion of reactants and products even in steady state.     

新型MCM-22/MCM-41复合分子筛上FCC汽油降烯烃芳构化反应

采用纳米组装法合成MCM-22/MCM-41微孔/介孔复合分子筛,分别以H-MCM-22和H-MCM-22/MCM-41为催化剂,在固定床微反装置上对FCC汽油进行降烯烃芳构化的对比考察。结果表明,在反应时间2 h内,与MCM-22相比, MCM-22/MCM-41具有高的芳构化性能和持久的初始活性,复合分子筛汽油改质的产物中,芳烃体积分数由28.58%上升至51.1%,烯烃体积分数由34.04％降至5.8％。探讨了新型H-MCM-22/MCM-41复合分子筛用于FCC汽油改质的操作条件以及催化剂失活再生性能。结果表明,最佳反应条件为：反应温度400 ℃,压力2 MPa,空速3 h^-1。失活催化剂经过两次再生,降烯烃芳构化性能基本不变。     

CuO-containing MCM-48 as catalysts for phenol hydroxylation

The CuO–MCM-48 catalysts prepared by wet impregnation technique were originally used as the catalysts, with high phenol conversion and diphenol selectivity, for phenol hydroxylation with hydrogen peroxide. Furthermore, the optimized reaction conditions over these catalysts for phenol hydroxylation were acquired.     

Ti-containing MCM-41 catalysts for liquid phase oxidation of cyclohexene with aqueous H2O2 and tert-butyl hydroperoxide

Framework Ti-substituted and Ti-grafted MCM-41 mesoporous material has been prepared by direct hydrothermal synthesis and a post-synthesis grafting method. The materials have been tested as catalysts for cyclohexene oxidation with aqueous H₂O₂ and tert-butyl hydroperoxide (TBHP). With aqueous H₂O₂ in methanol, the major products were cyclohexene diol and its methyl ethers. No cyclohexene oxide was produced. Titanium leaching was a serious problem, and the catalyst lost its activity irreversibly after only one cycle of reaction. With TBHP, the selectivity for cyclohexene oxide was near 100%, titanium leaching was negligible, and the catalyst could be repeatedly used after regeneration without suffering significant activity loss. However, the reaction rate was lower than when H₂O₂ was used. Framework substituted material and catalysts prepared by Ti-grafting onto a MCM-41 support behaved similar, but the Ti-grafted MCM-41 is somewhat more active. The turnover frequency (TOF) per mole of Ti decreases with an increase of Ti content in the catalyst. This is caused by a reduced Ti dispersion within the silica matrix. This revised version was published online in July 2006 with corrections to the Cover Date.     

Zr (IV)-ninhydrin supported MCM-41 and MCM-48 as novel nanoreactor catalysts for the oxidation of sulfides to sulfoxides and thiols to disulfides

Modification of MCM-41 and MCM-48 mesoporous materials with bonded aminosilane species, Schiff base preparation by ninhydrin and finally complexation with zirconium, has attracted much attention in order to design catalyst with advanced applications in the oxidation of sulfides to sulfoxides and thiols to disulfides in the presence of hydrogen peroxide. In all oxidation of sulfides to sulfoxids 0.4 mL H₂O₂ used as oxidant in the presence of Zr(IV)-ninhydrin supported MCM-41 (0.01 g) or Zr(IV)-ninhydrin supported MCM-48 (0.005 g) at room temperature and solvent-free condition. Also the best conditions for oxidation of thiols to disulfides with 0.4 mL H₂O₂ were 0.005 g Zr(IV)-ninhydrin supported MCM-41 or Zr(IV)-ninhydrin supported MCM-48 at room temperature and in ethanol. These catalysts are characterized by SEM, XRD, TGA, FT-IR, EDS, ICP and BET analysis. Also the Turn over frequency (TOF) and Turn over number (TON) of catalysts are calculated. Obtained results by these heterogeneous catalysts revealed several advantages including short reaction times, simple workup, easy isolation and reusability.     

Activity of Mo(II) allylic complexes supported in MCM-41 as oxidation catalysts precursors

[Mo(η³-C₃H₅)X(CO)₂(NCCH₃)₂] (X = Br, 1a; X = Cl, 1b) complexes reacted with the bidentate ligand RNC(Ph)–C(Ph)NR, R = (CH₂)₂CH₃ (DAB, 2) affording [Mo(η³-C₃H₅)X(CO)₂(DAB)] (X = Br, 4a; X = Cl, 4b), which were characterized by elemental analysis, FTIR and ¹H and ¹³C NMR spectroscopy. The modified silylated ligand RNC(Ph)C(Ph)NR, R = (CH₂)₃Si(OCH₂CH₃)₃ (DAB–Si, 3), was used to immobilize the two complexes in MCM-41 (MCM) mesoporous silica. The new materials were characterized by powder X-ray diffraction, N₂ adsorption analysis, FTIR and ²⁹Si and ¹³C CPMAS solid state NMR spectroscopy. Both the materials and the complexes were tested in the oxidation of cyclooctene and styrene and behaved as active catalyst precursors for cyclooctene and styrene epoxidation with TBHP (t-butylhydroperoxide), leading selectively to epoxides with high conversions and TOFs. Although the homogeneous systems reach 100% conversion of cyclooctene and slightly less for styrene, the loss of catalytic activity in the heterogeneous systems is small, with a 98% conversion of styrene achieved by the chloride containing material.     

非晶态Ni-B/MCM-22催化剂上二氧化碳甲烷化的研究

本文采用固定床反应装置考察了非晶态镍基催化剂CO2甲烷化催化反应活性。研究结果表明:以化学还原法制备的非晶态镍基催化剂的二氧化碳甲烷化活性较高;由XRD及TEM结果可知,非晶态镍基催化剂中镍的分散度较高;以MCM-22分子筛为催化剂载体的非晶态镍基催化剂CO2的转化率高于以γ-Al2O3为载体的非晶态催化剂。     

用于芳烃中微量烯烃脱除的MCM-22催化剂的研究

考察了用氯化铵离子交换处理的MCM-22分子筛催化剂在脱除芳烃中微量烯烃的催化活性,对分子筛催化剂进行了表征.结果表明离子交换增加了催化剂固体酸中心的量,而第2次离子交换的MCM-22分子筛催化剂脱烯烃效果最佳,其固体酸中心的量为最大.失活的分子筛催化剂通过焙烧再生处理,可恢复其活性.     

MCM-22、MCM-49和MCM-56三种分子筛的合成

MWW结构分子筛是一类新型的催化材料,具有独特的10元环孔道和12元环孔穴结构,在多种反应中表现出良好的催化活性。以六亚甲基亚胺作为模板剂,合成了MCM-22、MCM-49和MCM-56三种分子筛,并详细考察了不同硅源、凝胶配比、晶化温度和晶化时间对合成过程的影响。结果表明,凝胶配比和晶化温度对分子筛物相的影响较大。以硅胶粉为硅源,无论在何种晶化时间下都不能得到MCM-56,只能合成出MCM-49。而以碱性硅溶胶为硅源,在较短的晶化时间内就可以得到MCM-56。     

Cerium-containing MCM-41 materials as selective acylation and alkylation catalysts

The synthesis of Ce–MCM-41, Al–MCM-41 and Ce–Al–MCM-41-type mesoporous materials was carried out hydrothermally by refluxing the gel with magnetic stirring under atmospheric pressure for 24–36 h. The samples were characterized thoroughly in order to obtain the structural and textural properties, which reveal the presence of well-ordered M41S-type materials. The Ce–MCM-41 samples were used for catalytic acylation of alcohols, thiols, phenols and amines show good activity and selectivity including high chemoselectivity towards selective monofunctional acylation of bifunctional compounds. Quite importantly the acylation of bulky molecules such as cholesterol, ergesterol and β-sitosterol could be achieved using Ce–MCM-41 as solid catalyst. The presence of Ce along with Al in Ce–Al–MCM-41 was found to have synergistic effect as Ce–Al–MCM-41samples were more active catalysts for alkylation of naphthalene compared to either Ce–MCM-41 or Al–MCM-41 with comparable Si/Al or Si/Ce molar ratio.     

MCM-22、MCM-49和MCM-56分子筛的表征

MWW结构分子筛是一类新型的催化材料,具有独特的10元环孔道和12元环孔穴结构、优良的水热稳定性和特殊的酸中心分布,在多种反应中表现出良好的催化活性。以六亚甲基亚胺为模板剂,合成了具有MWW结构的MCM-22、MCM-49和MCM-56三种分子筛,并采用XRD、BET、TG/DTG和SEM手段对合成分子筛进行了表征,表明它们具有相同的单层结构,彼此之间的区别只有层间排列的结合层度和结合方式不同。MCM-56是薄层结构,晶体的层数少,MCM-22和MCM-49是多层结构,层数多。MCM-22的层间结合比较疏松,MCM-49的层间结合比较紧密。     

以哌啶为模板剂静态合成MCM-22和MCM-36分子筛

以来源易得的哌啶(PI)取代六亚甲基亚胺(HMI)为模板剂,采用静态合成的方法制备MCM-22分子筛,并进一步以十六烷基三甲基氯化铵(CTMACL)、四丙基氢氧化铵(TPAOH)作为溶胀剂,以正硅酸乙酯(TEOS)为柱撑剂合成MCM-36分子筛,以探索MCM-22和MCM-36的新合成途径。通过XRD、IR、SEM、N2吸附-脱附、NH3-TPD、正丁胺回滴法对MCM-22和MCM-36结构形貌、比表面积、孔径、表面酸量进行表征。结果表明,采用静态法以哌啶为模板剂是合成MCM-22和MCM-36的有效途径,MCM-22结晶度达到98.5%。合成的MCM-22比表面积为382 m2?g-1,孔容为0.25 cm3?g-1,外表面酸量为0.78 mmol?g-1;合成的MCM-36比表面积为468 m2?g-1,孔容为0.39 cm3?g-1,外表面酸量为0.94 mmol?g-1,介孔孔径达2.7 nm。     

SHS-produced β-sialons as supports for oxidation catalysts

SHS-produced β-sialons Si_6−z Al _z O _z N_8−z (z = 1, 3, 4) were tested as supports for oxidation catalysts comprising of unary, binary or ternary mixtures of transition metal (Cr, Mn, Fe, Co, Ni, Cu) oxides and also KMnO₄ and K₂Cr₂O₇. In oxidation of CO and propane (C₃H₈), the highest activity was exhibited by the catalysts based on cobalt oxides. Suggested are some methods for activation of the above catalysts.      

Novel utilization of MCM-22 molecular sieves as supports of cobalt catalysts in the Fischer–Tropsch synthesis

Cobalt catalysts (2–10 wt% Co) supported on silica-rich MCM-22 zeolites have been prepared by impregnation with aqueous Co(NO₃)₂ solutions. The catalysts are characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), nitrogen adsorption, solid state nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The catalytic properties for the Fischer–Tropsch synthesis (FTS) at 280 °C, 12.5 bar and H₂/CO = 2 are evaluated. The catalysts supported on MCM-22 exhibit the highest selectivity to long-chain (C₅₊) hydrocarbons when MCM-22 supports are synthesized with the appropriate Si/Al ratio.     

Alkaline carbon nanotubes as effective catalysts for H2S oxidation

Carbon nanotubes (CNTs) were made alkaline by impregnation with Na₂CO₃ and used for the direct oxidation of H₂S into sulfur at 30 °C. The alkaline CNTs before and after H₂S oxidation were characterized by N₂ adsorption, scanning and transmission electron microscopy, X-ray diffraction, and thermogravimetry analysis. The effects of Na₂CO₃ loading and the structure of the CNTs on the catalytic activity of alkaline CNTs were investigated. Results indicated that the saturation sulfur capacity of alkaline CNTs was up to 1.86 g H₂S/g catalyst, which was about 3.9 times higher than that of a common commercial H₂S oxidation catalyst. The introduction of Na₂CO₃, which provided alkalinity needed for H₂S dissociation, significantly enhanced the catalytic performance. The optimum content of Na₂CO₃ loading was determined to be 20 wt.% in the CNTs. The catalytic performance was also dependent on the structure of the CNTs, and the single-walled CNTs with the smallest tube diameter exhibited the highest sulfur capacity. Tangled CNTs provided their external voids to store the sulfur produced, which was a key feature of this high-performance CNT catalyst.