Preparation Of Highly Ordered Molecular Sieves With High Content Of Metal And Its Catalytic Performance

Molecular sieve materials have received considerable attentions in basic scientificresearch and industrial applications on account of their acidity and structure features.However, their weak surface acidity restricts the applications of pure silica zeolite;on the other hand, the pore-restrictions of microporous zeolite and lowerhydrothermal stability of mesoporous molecular sieves also hindered theirapplications.The incorporation of foreign atoms into the silica framework was found to be aneffective strategy to promote the surface activity. The acidities of molecular sieveswere related to the metal content in the framework; more metal atoms in theframework could be conducive to the generation of more catalytically. Thus,metal-rich incorporation molecular sieves are desirable. A number of papers dealwith the synthesis of composite materials, which should combine the advantages ofmicroporous zeolite and mesoporous molecular sieves.In the present studies, we show that high content of iron can successfully beincorporation into the microporous zeolite and mesoporous molecular sievesframework using a simple hydrothermal method, avoiding co-precipitation of iron oxides during the synthesis. Micro-mesoporous composites were prepared using adual templating method through a process of two-step crystallization. Mesoporoussilica with crystalline zeolitic framework was synthesized through one-pot process.The obtained products were characterized by using X-ray fluorescence spectroscopy(XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), high-powertransmission electron microscopy (HR-TEM), N2adsorption/desorption(N₂-sorption), infrared absorption spectroscopy (FT-IR), UV-visible absorptionspectroscopy (UV-vis), electron paramagnetic resonance spectroscopy (EPR), X-rayabsorption fine structure (XAFS), thermogravimetric-differential scanningcalorimetry (TG-DSC), H₂temperature-programmed desorption (H₂-TPR). And thecatalytic activities were investigated through the hydroxylation of phenol and residuehydrocracking reaction. The main research results are as following:1) The mesoporous ferrisilicates (MFS) with high iron content were synthesizedby pH-modification method and the iron content could be up to10.5wt%(Si/Fe=8).The pH was kept less than2at pre-hydrothermal synthesis step and was adjusted to11during hydrothermal step. The characterized results suggested that the MFSmaterials were ordered2D-hexagonal mesophase of MCM-41, and the iron ionswere tetrahedral coordinated in the silica framework. This material could efficientlycatalyze the hydroxylation of phenol in water medium using H₂O₂as an oxidant, andthe phenol conversion could be up to52wt%under the optimal experimentalconditions.2) A series of Fe-MFIs with a high content of iron were synthesized using TBAB as the structure directing agent. The optimum limit of iron incorporation in theframework was7.2wt%. Characterization results showed the Fe³⁺was tetrahedralcoordination in the silica framework. The crystallinity of Fe-MFI decreased with theiron content increases; the crystalline sizes also change with the iron contentincreases.3) The MFI/MCM-41composites with bimetallic Fe and Co were prepared usinga templating method through a process of two-step crystallization. Characterizationresults showed that two kinds of stable MFI/MCM-41composites can be synthesizedduring the course of recrystallization. The iron and cobalt were incorporated into thesilicon framework according to the characterization data. The composites presentedexcellent activities in hydrocracking of residual oil, which were superior to the purematerials of silicate-1/MCM-41.4) Mesoporous molecular sieves Cry-Ni-MCM-41with crystalline zeoliticframework was synthesized using one pot process. The obtained products possesseda good crystal particle with uniform mesoporous channel. The alkali stability of thesample wss much higher than the amorphous pore walls of mesoporous molecularsieves.5) A method of incorporating iron onto the mesoporous silica network usingpotassium ferricyanide (K₃Fe(CN)₆) as the iron source was established. TheFe(CN)₆³+ions interact with the template and attached onto the silica network afterthe as-synthesized sample calcined at823K. FT-IR spectroscopy provided a clearevidence for the interaction between cyanide ligands and template. XANES spectroscopic displayed that the Fe³⁺changed from octahedral to tetrahedralcoordinated during thermal treatment. XRD and HRTEM results indicated that theiron ions incorporated onto the silica network without destroying the lattice structureof the parent MCM-41. The synthesized material exhibited a good activity for phenolhydroxylation.6) According to the results of the characterizations, the formation mechanisticof the samples was described.