Synthesis and characterization of MCM-41-supported nano zirconia catalysts

Series of MCM-41 supported sulfated Zirconia (SZ) catalysts with different loadings (2.5–7.5% wt.) were prepared using direct impregnation method. The acquired solid catalysts were characterized structurally and chemically using X-RD, HRTEM, BET, FT-IR, Raman spectroscopy and TPD analysis. The acidity of the solid catalysts was investigated through cumene cracking and isopropanol dehydration at different temperatures. As the SZ loading increases, the surface acidity of the mesoporous catalysts was enhanced, this was reflected by the higher catalytic activity toward cumene cracking and isopropanol dehydration.     

Mineralization of Para-Chlorobenzoic Acid in Water by Cobalt-Incorporated MCM-41 Catalyzed Ozonation

Cobalt-incorporated MCM-41(Co-MCM-41) was used as a heterogeneous catalyst for the ozonation of para-chlorobenzoic acid (p-CBA) in aqueous solution. Cobalt oxide supported on MCM-41(Co/MCM-41) was synthesized for comparison. Their textural properties were elucidated by various characterization techniques to understand the relationship between surface texture and catalytic activity. TOC removal at 60 min reached 91% with Co-MCM-41, 83% with Co/MCM-41 and only 52% with ozone alone, respectively. Observations from diffuse reflection spectroscopy demonstrated that different metal phases were formed in these cobalt-modified molecular sieves samples. Radical scavenger experiments indicated the formation of hydroxyl radicals that were responsible for the effective degradation of p-CBA. An integrated approach to the catalytic mechanism was proposed by considering the variation of pH in the course of ozonation as well as its subsequent influence on the dissociation of targeted compounds and surface charge of the catalyst. In the reusability experiments, the reused Co-MCM-41 was able to regain the same catalytic capability as the fresh one within 5 cycles. X-ray photoelectron spectroscopy results indicated that a part of Co²⁺ was oxidized to Co³⁺ after oxidation reaction.     

Ru/MCM-41催化剂上苯的液相加氢反应

 以Si-MCM-41、Al-MCM-41(1) (n(Si)/n(Al)=15)、Al-MCM-41(2) (n(Si)/n(Al)=10)以及用NH4NO3或HAc的醇溶液分别与Si-MCM-41离子交换所得的H-MCM-41(N)和H-MCM-41(H)为载体制备了系列Ru/MCM-41催化剂。采用N2吸附、XRD和H2-TPR表征了负载Ru前后催化剂的结构及Ru在各种载体表面上的分散状态。以0.5%（质量分数）苯的环己烷溶液为模型化合物，在298K、3.0MPa反应条件下，考察了上述催化剂的苯液相加氢反应性能，并与Ru/HY、Ru/H和Pt/MCM-41催化剂进行了比较。结果表明，载体MCM-41的n(Si)/n(Al)和表面化学组成等性质对Ru在其表面上的分散状态、还原性及催化性能均有影响。对苯的转化率与反应时间的关系曲线进行拟合，发现其遵循一级动力学方程，加氢反应速率常数按照Ru/Al-MCM-41(2)MCM-41(1)MCM-41MCM-41(H)MCM-41(N)的顺序递增；Ru/Si-MCM-41较高的催化活性来自于Si-MCM-41的高比表面积和Ru的高分散性；由于载体酸性的增加，H-MCM-41负载催化剂的加氢活性进一步提高。     

Na+、K+离子交换对Co-Mo/MCM-41加氢脱硫催化剂的影响

 用偏硅酸钠和正硅酸乙酯作硅源制备了MCM-41（分别记作MCM-41(S)和MCM-41(T)）分子筛，并用Na₂C₂O₄和K₂C₂O₄对MCM-41(S)进行了碱金属离子交换改性。以质量分数0.8 %的二苯并噻吩（DBT）的十氢萘溶液为模型化合物，考察了不同MCM-41担载的Co-Mo硫化物催化剂对DBT的加氢脱硫反应性能。结果表明，MCM-41担载的Co-Mo催化剂加氢活性较低，DBT主要通过直接脱硫反应路径脱硫。其活性顺序为：Co-Mo/MCM-41(T)>Co-Mo/MCM-41(S)>Co-Mo/MCM-41(K)>Co-Mo/MCM-41(Na)。UV-Vis结果表明，部分Co与MCM-41(S)中少量Al发生相互作用，生成了CoAl₂O₄，是造成Co-Mo/MCM-41(S)活性降低的重要因素。而在Co-Mo/MCM-41(K)和Co-Mo/MCM-41(Na)中，除CoAl₂O₄物种之外，碱金属的引入还促进了Co₃O₄物种的形成，使其活性进一步降低。     

官能团化MCM-41在分离低碳醇-水混合物中的应用

采用一步法水热合成了介孔材料氯丙基官能团化的MCM-41(Cl(CH2)3-MCM-41)、氨丙基官能团化MCM-41(NH2(CH2)3-MCM-41)、甲基官能团化MCM-41(CH3-MCM-41)和氯丙基官能团化硅胶,并考察了它们作为气相色谱固定相分离低碳醇-水混合物的情况。实验结果表明,Cl(CH2)3-MCM-41能够分离低碳醇-水混合物中的各组分,随水、甲醇、乙醇、异丙醇、正丁醇极性的减小,各分子与Cl(CH2)3-MCM-41的作用力增强,保留时间延长。氯丙基官能团化硅胶、NH2(CH2)3-MCM-41)和CH3-MCM-41均不能分离低碳醇-水混合物,表明介孔材料规则的孔道结构、表面嫁接基团等对低碳醇-水混合物的分离有重要影响。同时考察了Cl(CH2)3-MCM-41的氯丙基负载量对低碳醇-水混合物分离效果的影响,结果表明,当氯丙基的摩尔分数为15%时,分离效果最佳。     

Epoxidation of β-ionone using molecular oxygen over Pt/MCM-41 catalyst under mild conditions

The epoxidation of β-ionone over the Pt/MCM-41 catalyst using molecular oxygen in the liquid phase had been studied. The results indicated that the β-ionone was catalytically oxidized to 5,6-epoxy-β-ionone, 4-oxo-β-ionone, 4-hydroxy-β-ionone and dihydroactinidiolide using molecular oxygen as the sole oxidant. The effects of solvent, content of Pt, reaction temperature and time on the catalytic activity and product selectivity had also been investigated in detail.     

模板剂在介孔分子筛合成中的作用机理

以模板法合成分子筛不但能够有效的控制其介观结构,而且环境友好,操作简单,成本低廉,但由于反应在高压釜中进行,模板剂对分子筛合成的作用机理尚未被认清。本文总结了目前提出的可能的模板剂作用机理,并加以分类讨论,以对分子筛合成过程提供指导。     

Cooperative effect of crystallization temperature and NaF addition in the formation process and hydrothermal stability of MCM-48 mesoporous molecular sieve

The hydrothermal stability of MCM-48 was conveniently and effectively improved by increasing the crystallization temperature and directly adding NaF to the synthesis gel. The crystallization temperature varied from 373 K to 403 K. The influences of NaF addition, crystallization temperature and crystallization time on the formation process and hydrothermal stability of MCM-48 were systematically studied here to solve the problem of poor reproducibility. Results from XRD patterns indicated that the crystallization temperature and crystallization time were very critical factors for the improvement of the hydrothermal stability besides NaF addition. The formation process of MCM-48 was significantly accelerated and the pore structure ordering was also greatly improved by increasing the crystallization temperature and F⁻/Si ratio. A high hydrothermally stable MCM-48 mesoporous molecular sieve was obtained after being crystallized at 393 K for 36 h in the presence of NaF, which endured the hydrothermal treatment in boiling water at least for 4 days. However, only an amorphous product was obtained when the crystallization temperature was further increased to 403 K. Results from Si MAS NMR, N₂ adsorption isotherms, TEM, Raman spectra and XRD patterns manifested that the improved stability of MCM-48 was attributed to the high silicates condensation degree and the excellent pore structure ordering. The possible reason for the successful formation of hydrothermally stable MCM-48 sample by controlling the crystallization temperature, time and F⁻/Si ratio was explained here.     

钒硅中孔分子筛的合成、表征及其催化性能研究

在碱性环境中，采用水热合成法制备得到了不同硅钒比的钒硅中孔分子筛V－MCM－41，利用XRD，IR，TG等表征方法考察了钒的搀杂量与其结构和性能之间的关系，该催化剂对苯乙烯氧化反应具有较好的催化活性，在一定的反应条件下，以H2O2溶液（30％）为氧化剂，以乙腈为溶剂，V－MCM－41（Si/V=25)能使苯乙烯的转化率达到95％以上，产物（苯甲醛＋苯甲酸）的选择性不低于90％。     

Isobutane/2-butene alkylation on MCM-22 catalyst. Influence of zeolite structure and acidity on activity and selectivity

The catalytic behavior of the novel MCM-22 zeolite for the continuous alkylation of isobutane with 2-butene has been investigated at a temperature of 50°C, 2.5 MPa total pressure, and a variety of olefin space velocities. At high olefin conversions the MCM-22 zeolite showed a very high initial cracking activity attributable to strong Brønsted acid sites, as well as to the existence of strong diffusional restrictions of the TMP's (formed inside the zeolite) to exit through the channels. At short times on stream (TOS), TMP's account for ca. 40% of the C₈ fraction. The olefin conversion and the cracking activity rapidly decline with TOS, while the alkylate product became richer in dimethylhexenes, indicating a predominance of 2-butene dimerization and a loss of hydrogen transfer activity as the catalyst aged. Moreover, MCM-22 gives less TMP's than large-pore zeolites (USY, beta, mordenite), but more than the mediumpore ZSM-5 at similar 2-butene conversion. The latter catalyst was much more selective for olefin dimerization than for isobutane alkylation, presumably because formation of the bulkier TMP's was strongly impeded in its smaller pores.