Synthesis Of Mic/Mesoporous Composite And NaY Zeolite Nanocrystal

Nowadays zeolite microporous molecular sieve have been widely adopted toimportant industrial applications such as adsorption and catalysis due to their strongacidity and high hydrothermal stability. However, the small pore size (less then 1nm)renders them useless as catalysts in the conversion of larger sized reactants, whichlimit potential application in petroleum refining and chemicals synthesis. Severalapproaches aim at solving the problem. One approach is to synthesize zeolitenanocrystal. The reduction of zeolite particle size from the micrometer to thenanometer scale leads to substantial changes in the properties of the materials, whichhave an impact on the performance of zeolites in tradition areas such as catalysis andseparation. Due to zeolite nanocrystals: 1) the ratio of external to internal number ofatoms increase rapidly as the particle size decreases, 2) zeolite nanoparticles havelarge external surface areas and high surface activity, 3) smaller zeolite crystals havereduced diffusion path lengths relative to conventional micrometer-sized zeolites.Another approach is to prepare new zeolite-type materials with larger pores. In 1992,the Mobil Corporation reported the synthesis of mesoporous M41s by the use ofself-assembled surfactant molecular aggregates as the structure-directing agents. Thematerials have attracted considerable attention because of its excellent structuralording, tunable pore size (1.5-20nm), high surface area and pore volume.However, as compared with conventional zeolites, these mesostructured materialshave relatively low acidity and hudrothermal stability, which can be attributed to theamorphous nature of the pore walls. These drawbacks severely hinder the applicationof the mesoporous materials in the petroleum industry. It is thus very attractive tosynthesize new materials which can combine the advantages of both zeolites andmesoporous materials.In this article, using a two-step crystalline method to synthesize NaA(Si/Al=1)/MCM-41 composites. We integrated zeolite and mesoporous synthesisconditions and studied the different synthesis procedures. Finally, finding only whenwe stop the crystallization at middle period of crystalline NaA zeolite to synthesizeMCM-41 that NaA/MCM-41 composites can be obtained.Two-step method has been adopt to synthesis NaY/MCM-41 composite. First NaYzeolite is prepared at 100°C and then reducing the basicity of synthesis system tosynthesize MCM-41 at 100°C. The NaY/MCM-41 composite is obtained. The ratioof SiO2/Al2O3(10-14) is higher in all synthesis procedure. By varying the ratio ofSiO2/Al2O3 (10, 12, 14) of gel composition, we were able to modify the compositionof the NaY/MCM-41composite materials. The result of experiment indicates that theratio of MCM-41 of the materials is higher when the ratio of SiO2/Al2O3 of in thecomposite materials is higher. When the time of first-step is longer the crystalinityNaY zeolite is higher, because of NaY zeolite is mainly crystallized in the first-step.By varying the crystalline time of the second-step (the first-step time unchanged),the results indicate that crystalinity of MCM-41and NaY of the composites is higher.The above results only are primary and it is need to quest for the synthesisconditions in order to obtain ultrafine composite of NaY covered by MCM-41. Thecomposite with mesoporous and microporous structure is also prepared by usingcarbon mesoporous molecular sieves as template and heat treatment method.Here we also report a novel method to prepare nanosized NaY zeolite by usingNaY seeds solution as a silica source, it is needn't to add other silica sources. Theconventional method for preparing nanosized NaY zeolite is add organic material tothe gel, which increase the cost and pollute the environment. By varying the agingtime (3d, 5d, 9d, 24d) of seeds solution, we synthesize 600nm, 490nm, 140nm,100nm NaY zeolite. The particle size of NaY is bigger when the aging time of seedssolution is longer, but the relationship of the particle with the aging time is not alinear relationship. The crystalline temperature is varied at 85oC, 100oC, 120oC andthe results indicate that the crystal obtained at 85oC is smallest. When the gel iscrystalizes at 140oC, the composite of ? zeolite and P zeolite is obtained. Thedifferent crystalline time (12h, 1d, 2d) at 85oC is investigated, The particle sizes ofNaY are 550nm, 640nm and 850nm at the crystalline time 12h, 1d, and 2drespectively. The above results are primary, The composition and aging condition ofNaY seeds solution are need to continuative study in the future.