| Because of the unique pore channal structures, high surface ares, abundent active sites and great hydrothermal stability, Zeolites molecule seives have been used as heterogeneous catalyst, adsorption and seperation materials and ion-exchange materials world widely, and the application of zeolites will be expanded in the fields of fine chemical industry, petroleum chemical industry and the daily chemicals. However, the small micropore size and long pore channal directly limited its application in the catalytic reactions which having larger reaction molecules involved. Traditional mesoporous materials have well-organized mesoporous aperture structure, but the essence of its amorphous structure result in a great difference between this kind of material and zeolite molecular sieves on hydrothermal stability and the number of catalytic activity center s, which not only makd the efficiency of the catalytic reaction reduced greatly but also the structure of catalysts became more easily collapsed and carbon deposition.The mesoporous zeolite molecule seives or hierarchical-pore zeolites materials take the advantages of conventional zeolites and uniformly mesoporous materials. The essence of framework of materials are of zeolites crystallinity, and the abundent mesopores introduced into the structures of micropores not only could maintain the advantages of zeolites such as the plentiful active sites and great hydrothermal stability, but also could accelerate the mass transport rates and catalytic reaction rates. However, accrodding to the experiences in synthesis of mesoporous zeolites, the consuming and destruction of parts of micropores is inevitable after mesopores introduced, so the synthesis of mesoporous zeolites with great microporosity and also mesoporosity with varied method and templates became research hotspots.This paper focuses on the current research hotspot, and refer to a large number of excellent literature works in the fields, combined with our own group advantages, has made the detailed research works in the preparation of core-shell mesoporous LTA zeolite molecular sieve and mesoporous/multistage aperture ZSM-5 zeolite molecular sieve. Works mainly focused on the synthesis of organic siloxane template pore-forming agent and the control and optimization conditions of zeolite materials preparation and the analysis of the phenomenon, through the tests of hydrothermal stability and ion-exchange rate of materials and also the characterization of the conversion and selectivity in catalytic reaction. Through the mesoporous zeolites materials preparation method and the expansion of template agent, for subsequent efficient synthesis of zeolite catalyst provided ideas and direction. In this paper the experiment work content is divided into six parts to discuss:1. In the chapter three, a novel mesoporous core-shell LTA (CSLTA) zeolite was synthesized successfully. Through the employment of KH560-660 as mesoporogen and with ultrasonic treatment, the mesoporous LTA zeolite was of 100-200 nm microporous shell and mesoporous LTA core. Different from the conventional core-shell materials, the CSLTA in this paper was of single crystalline and the core was not amorphous. In experiment, the ultrasonic treatment time played a very important role in the formation of core-shell morphology. Sufficient ultrasonic treatment not only helped with the development of microporous framework but also made the particle size transforming from micrometer to nanometer (ab.800 nm), and meanwhile, the thickness of shell could be ab.100 nm. The crystallization time should be 5 days and insufficient crystallization would cause the formation of a incomplete shell. As the increase of template adding amounts, the total BET of Ca2+-CSLTA samples maintained at a high level (531 m2/g-545 m2/g) and the mesopore BET also increased obviously (from 35 m2/g to 213 m2/g), however, the micropore BET and volume showed a slightly decrease, which implying that the introducing of abundent mesopores had influence of micropores. In the Mg2+ ion-exchange test, the exchange rate of Na+-CSLTA was 9.6 times of conventional LTA zeolite. We also elucidated the synthetic mechanism of this novel core-shell structure. Ultrasonic treatment could forcus the silica source combined with template molecule on the centre of alumino silicate gel, and in the following process, crystallizaiton method was from inside to outside and with this way, the redundant alumino silicate materials formed the microporous shell outside, then the mesoporous core would be formed with the calcination of template. This novel core-shell structure had more effective ability in sieving molecules of small size, and the outside microporous-shell was beneficial to the access of small-sized molecules and the inside mesoporous-core could accelerate the transfer rate of intracrystal, and then enhanced the adsorption-separation of gas molecule.2. In chapter four, a series of mesoporous ZSM-5 zeolite has been synthesized with KH560-660 as mesoporogen and the preparation conditions has also been modulated and optimized. (1)At first, the silica sol was used to be the silica source, and under the optimal synthesis conditions, the microporous BET of the samples could maintain at around 340 m2/g and the largest mesoporous BET was 234 m2/g; the samples were composed of good-dispersed 1 μm microsphere particles with obviously gully-like surface. (2)The TEOS was used to be the silica source, and under the optimal synthesis conditions, the microporous BET of the samples could maintain at 340-325 m2/g and the largest mesoporous BET was 216 m2/g; the samples were composed of good-dispersed 500-900 nm nanosphere particles with smooth surface. (3)The grafted silica was used to be the silica source, and under the optimal synthesis conditions, the best microporous BET of the sample was 342 m/g and the largest mesoporous BET was 247 m2/g; the samples were composed of good-dispersed 5-10 μm microsphere particles with relatively smooth surface. The most distinguishing feature of the samples prepared in this chapter was that the microporous property was not weakened and the mesopores introduced were all of intracrystalline mesopore with 5 nm pore sized distribution.3. In chapter five, a series of mesoporous ZSM-5 zeolite has been synthesized with KH560-540 as mesoporogen and the preparation conditions has also been modulated and optimized. Although only one more oxygen atom in KH560-540 than KH560-660, the one more methoxyl group could bring great differences in the synthesis process. (1)The silica sol was used to be the silica source, and under the optimal synthesis conditions, the microporous BET of the samples could maintain at around 315-338 m2/g and the largest mesoporous BET was 300 m2/g; the samples were composed of good-dispersed 1-2 μm microsphere particles which was further consisted of 20 nm nanocrystallines; and under the directly high-temperature crystallization method, the microporous BET of the samples maintained at a very high level (400 m2/g) and the mesoporous BET reached to 176 m2/g, and the samples were composed of good-dispersed 8-10 μm microsphere particles with a layer of nanocrystalline surrounded outside. (2)The TEOS was used to be the silica source, and under the optimal synthesis conditions, the microporous BET of the samples could maintain at 358-398 m2/g and the largest mesoporous BET was 265 m2/g and the largest total BET reached to 632 m2/g; the samples were composed of good-dispersed 5 um twinned microsphere particles with obviously nanocrystalline surface; under the directly high-temperature crystallization method, the optimal mesoporous BET reached to 217 m2/g, however the microporous BET only had 267 m2/g which was far less than that of conventional ZSM-5 and the samples were composed of good-dispersed 3 um microsphere particles with not rough enough surface. (3)The grafted silica was used to be the silica source, and under the optimal synthesis conditions, the best microporous BET of the sample was at around 350 m2/g and the mesoporous BET could adjust at 100-263 m2/g; the samples were composed of good-dispersed 1 μm microsphere particles with rough surface which was further consisted of dozens of nanocrystallines. The pore parameters of the samples synthesized in this chapter were more outstanding than that of chapter four, especially had great boost in micropores, and the disadvantage was that the adjustment of TPAOH adding amounts had difficulty and many factors changed in small scale causing tremendous differences.4. In chapter six, there was a large adjustment on the structure of template molecule. The polyether amine D230 was reacted with KH560 to synthesis a new template KH560-D230, and we applied this template to synthesis mesoporous ZSM-5 zeolite looking forward to have larger pore size of mesopores. (1)The silica sol was used to be the silica source, and under the optimal synthesis conditions, the best microporous BET of the samples was 330 m2/g and the largest mesoporous BET was 463 m2/g, meanwhile, the total pore volume reached to 0.8 cm3/g, and the mesopores were of intracrystalline; the samples were composed of good-dispersed 1 μm microsphere particles which was further consisted of 50 nm nanocrystallines; and under the directly high-temperature crystallization method, the microporous BET of the samples maintained at a low level (240 m2/g) and the mesoporous BET was 374 m2/g, but the total pore volume reached up to 1.1 cm3/g, and the samples were composed of 2-3 μm irregular particles with obviously amorphous materials formed around. (2)The TEOS was used to be the silica source, and under the optimal synthesis conditions, the best microporous BET of the samples only was 250 m2/g which was obviously lower than that of conventional ZSM-5 zeolite and the mesoporous BET was 363 m2/g, meanwhile, the total pore volume reached only to 0.63 cm3/g, and the mesopores were also of intracrystalline; the samples were composed of good-dispersed 1-2 μm microsphere particles with rock stratum-like morphology and no amorphous material was found. (3)The grafted silica was used to be the silica source, and under the optimal synthesis conditions, the best microporous BET of the sample was 299 m2/g and the mesoporous BET was 501 m2/g and the total pore volume reached only to 0.71 cm3/g, along with the increase amounts of template, the samples transformed to amorphous eventually. The samples were composed of-1 μm regular particles with obviously amorphous materials formed around.5. In chapter seven, the polyether amine D403 was employed to react with KH560 to synthesis another new template KH560-D403, and we also applied this template to synthesis hierarchical ZSM-5 zeolite. (1)The silica sol was used to be the silica source, and under the optimal synthesis conditions, the best microporous BET of the samples was 341 m2/g and the largest mesoporous BET was 437 m2/g, meanwhile, the total pore volume only had 0.58 cm3/g, and the mesopores were consisted of intracrystalline and aggregates mesopores; the samples were composed of good-dispersed 1-2 μm microsphere particles with obviously nanovoid inner and no amorphous materias had been found; and under the directly high-temperature crystallization method, the microporous BET of the samples maintained at a high level (450 m/g) and the total BET was 570 m2/g, but the total pore volume only had 0.3 cm3/g which further demonstrating that the samples were typical microporous aggregates, and the samples were composed of 5 μm particles. (2)With TEOS as silica source, the as-prepared sample had great destruction on the micropores and always along with the formation of amorphism. The mesopores of sample synthesized within 7 mL template were of intracrystalline, and after the amounts exceeding 7 mL the amorphous component became formed with microporous BET decreasing from 285 m2/g to 242 m2/g; under the directly high-temperature crystallization method, the optimal mesoporous BET reached to 468 m2/g, and the microporous BET had 354 m2/g, and after the adding amounts of template exceeding 20 mL the samples were composed of plate-like mixture of amorphism and microporous zeolite. (3)The grafted silica was used to be the silica source, and under the optimal synthesis conditions, the best microporous BET of the sample was 320 m2/g and the mesoporous BET was 372 m2/g and the pore size distribution centered at 16-32 nm; under the directly high-temperature crystallization method, the optimal mesoporous BET reached to 207 m2/g, and the microporous BET had 399 m2/g, however the samples were transformed to mesoporous Beta zeolite totally.6. In chapter eight, we synthesized a series samples of different Si/Al ratios with KH560-660 and silica sol. At the process of preparation contions adjustment, the NaOH instead of part of TPAOH as alkali source was not work. We also employed lots of characteration methods to analysis the samples, then ion-exchange rate and hydrothermal stability test were also employed to investigate the perfiormance. In the experiment of Mg2+ exchange, it was found that the total exchange amounts was inversely proportional to the Si/Al ratios, such as that the total exchange amounts of MZ-20 was 8 times of MZ-600 sample, and compared with the 0.28 exchange rate of conventional ZSM-5 zeolite, the MZ-(20-320) samples were in the range of 1.35-0.53. In hydrothermal stability test, it was demonstrated that the samples of lower Si/Al ratios the worse stability had. After boiling for 80 hours, the microporous BET of MZ-20 sample decreased for 25% and total BET for 6.5%, however, the MZ-600 sample showed excellent hydrothermal stability. At last we also analysis the different catalytic activity among the as-synthesized samples with the reaction of 1,3,5-triisopropylbenzene craking. And we also discuss the detailed synthetic mechanism of the mesoporous ZSM-5 zeolite with the organic templates used in this paper. |
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