Micro-mesoporous

Microporous nanoparticles with ordered zeolitic structure such as Ti-Beta are used for incorporation into walls or deposition into pores of mesoporous materials to form the micro/mesoporous composite materials [1-3], Microporous particles need to be small enough to be successfully incorporated in the composite structure. This means that the zeolite synthesis has to be stopped as soon as the particles exhibit ordered zeolitic structure. To study the growth of Ti-Beta particles we used 29Si solid-state and liquid-state NMR spectroscopy combined with x-ray powder diffraction (XRPD) and high-resolution transmission electron microscopy (HRTEM). With these techniques we monitored zeolite formation from the initial precursor gel to the final Ti-Beta product. 

With the combined methods of 29Si NMR spectroscopy, X-ray diffraction, HRTEM and SAED we were able to characterize the Ti-Beta particle growth. 29Si NMR spectroscopy gave us an opportunity to see the formation of nanoparticles even before they were detectable with other techniques such as XRD. The above mentioned techniques enabled us to obtain sufficient knowledge to prepare Ti-Beta nanoparticles which were than successfully incorporated in novel micro/mesoporous materials [1],... 

Methodology for the characterization of micro-mesoporous acidic materials... 

The studied solids exhibit great differences in term of porosity (purely microporous, micro-mesoporous and mesoporous). As it is well known, mesoporosity of USY (CBV series) increases as the aluminum content decreases. Large part of mesoporosity is in the range 2-3.6 nm according to the difference between mesoporous volume obtained by N2 or Hg measurements. Pore size estimation gave similar results whatever the technique. 

Nickel containing MCM-36 zeolite was used as new catalyst in the ethylene oligomerization reaction performed in slurry semi-batch mode. This catalyst, with micro-mesoporous structure, mild acidity and well balanced Ni2+/acid sites ratio, showed good activity (46 g of oligomers/gcataLh) and selectivity (100% olefins with even number of carbon atoms). The NiMCM-36 behaviour was compared to those obtained with NiMCM-22, NiY, NiMCM-41 and NiMCM-48 catalysts. 

Hydroisomerization of n-octane over Pt-containing micro/mesoporous molecular sieves... 

Hydroisomerization of n-octane over Pt-containing micro/mesoporous catalysts obtained by recrystallization of zeolites BEA and MOR was investigated in the temperature range of 200-250 °C under 1-20 bar. Composite materials showed remarkably high activity and selectivity with respect to both pure microporous and pure mesoporous materials. The effect is due to high zeolitic acidity combined with improved accessibility of active sites and transport of bulky molecules provided by mesopores. 

The development of composite micro/mesoporous materials opens new perspectives for the improvement of zeolytic catalysts. These materials combine the advantages of both zeolites and mesoporous molecular sieves, in particular, strong acidity, high thermal and hydrothermal stability and improved diffusivity of bulky molecules due to reduction of the intracrystalline diffusion path length, resulting from creation of secondary mesoporous structure. It can be expected that the creation of secondary mesoporous structure in zeolitic crystals, on the one hand, will result in the improvement of the effectiveness factor in hydroisomerization process and, on the other hand, will lead to the decrease of the residence time of products and minimization of secondary reactions, such as cracking. This will result in an increase of both the conversion and the selectivity to isomerization products. 

Partial recrystallization of zeolites into composite micro/mesoporous materials leads to 1,3-2 fold increase of n-octane conversion and 2-3 fold increase of the yield of target products - branched octanes, indicating improved accessibility of active sites and transport of bulky molecules provided by mesopores. In the case of BEA series recrystallization in mild conditions leads to remarkable increase in selectivity to i-octane from 40 to 67%. On the contrary, complete recrystallization results in low catalytic activity, comparable with MCM-41 catalyst. 

In view of the numerous advantages of POMs the development of strategies for converting them to solid catalysts is of primaiy interest. First, catalytically active POMs can be heterogenized in the form of insoluble salts using Cs, Ag, K, NH/ and some organic cations [37,49, 58-64]. Such salts possess micro/mesoporous structure and their smface area is typically in the range of 10-150 mVg. 

Microwave Synthesis of Micro-Mesoporous Composite Material... 

However, there have been only a few reports about the synthesis of the micro-mesoporous materials. Bekkum group have reported that the FAU zeolite overgrown with small content of... 

Based on those propositions mentioned above, we tried to design a mesoporous material having micro crystalline wall by controlling the ratio of Q4 silicate species formed around TPA and Q2,3 silicate species interact with the micelles. To synthesize micro-mesoporous composite material through the control of Q2-3 and Q4 groups, two different templates were used and nucleation step of microporous material was introduced prior to the crystallization. And also we have attempted to monitor microenvironment of micro-mesoporous composite materials during the nucleation and crystallization steps using TG-DTA and photoluminescence with pyrene probe. 

Micro-mesoporous composite materials was prepared in a CEM microwave oven (MDS-2000) by using 50 - 100% of the maximum power of the oven (Wmax = 630 watts, frequency = 2.45 GHz, Pmax = 200 psi). The percentage power of microwave was programmed in percent increments to control the rate of heating. The fiber optic probe with a type of phosphor sensor was used for controlling the temperature of microwave oven. 

Synthesis of micro-mesoporous composite materials via microwave irradiation... 

Fig. 2. XRD patterns of as-synthesized micro-mesoporous composite materials prepared with increasing the time of microwave irradiation (a) sample 1, (b) sample II, (b ) calcined (b), (c) sample III, (c1) calcined (c), and (d) sample IV. See Table 1 for the notations of I, II, III and IV.

Fig. 3. SEM images of micro-mesoporous composite materials (a) sample II, (b) sample III, and (c) sample IV.

Fig. 4. N2 adsorption-desorption isotherms of (a) sample 11, (b) sample III, and (c) sample IV, and pore size distribution of (a ) sample II, (b1) sample III, and (c ) sample IV of micro-mesoporous composite materials.

In principle, the micro-mesoporous composite materials can be synthesized by the... 

Fig. 6. Variation of III/I ratio in pyrene PL Spectra from the various micro-mesoporous gels (a) TPA solution, (b) sample 1, (c) mixture of (b) and micelle, (d) sample II, and (e) sample IV.

This study demonstrated that the micro-mesoporous composite materials could be synthesized with two-step treatment by microwave using two different templates system with TPABr and MTAB. This formation was controlled by the self-assembly formation of supramolecular templates between MTA micelles and SiO /TPA gels. As varying microwave irradiation time of micro-mesoporous materials, gradually transition from the mesophase to micro-mesophase was occurred. These materials have higher dm spacing of mesoporous materials and lead to transition from mesophase to micro-microphase by an increment of synthetic time, while the calcined products is formed with bimodal and trimodal pore size distribution under microwave irradiation within 3 h. From TG-DTA and PL analysis, the self-assembly formation of supramolecular templates between MTA+ micelles and SiO /TPA+ gels were monitored. 

Serrano D.P., Galleja G., Sanz R., Pizzarro P. (2004) Preparation of bimodal micro-mesoporous Ti02 with tailored crystalline properties, Chem.Comm., (8), 1000-1001. 

Dias, A. S., Pillinger, M., and Valente, A. A., Dehydration of xylose into furfural over micro-mesoporous sulfonic acid catalysts. J Catalysis 2005, 229 (2), 414-423. 

The strategy of this method is to utilize the inherent porosity of bulky substrates in the construction of hierarchical stractures by incorporating additional pore systems. Diatoms are unicellular algae whose walls are composed of silica with an internal pore diameter at submicron to micron scales. Zeolitization of diatoms, in which zeolite nanoparticles are dispersed on the surface of diatoms followed by a hydrothermal conversation of a portion of the diatom silicas into zeolites, resulted in the formation of a micro/mesoporous composite material. Similarly, wood has also been used as a substrate to prepare meso/macroporous composites and meso/macroporous zeolites. After the synthesis, wood is removed by calcination. ... 

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