Ionothe Mal Synthesis Of Heteroatom-containing Aluminumphosj Lite Molecular Sieves By Microwave Heating And Using Deep Eutectic Mixture

Molecular sieves have property of particular shape-selective catalysis becauseof their special composition, structure and property, so they have been playing animportant role in modern petrochemical industry. Ionothermal synthesis is a novelmethod for the preparation of molecular sieves using ionic liquids or deep-eutecticmixtures as solvents and structure-directing agents without adding other organictemplates. The extremely low vapor pressure and polarity of ionic liquid ordeep-eutectic mixtures allow the reactions taking place under conditions ofmicrowave heating and common opening vessel. Compared with the traditionalhydrothermal or solvothermal synthesis, this novel synthetic method has manyunique properties. Therefore, studying ionothermal synthesis of molecular sieves hasimportant significance of science and application.In this paper, SAPO-5molecular sieve with AFI topology had beenionothermally synthesized by microwave irradiation and using eutectic mixturebased on pentaerythritol and choline chloride as reaction medium. The resultantSAPO-5molecular sieve was characterized by X-ray diffraction （XRD）,²⁹Simagic-angle spinning nuclear magnetic resonance (²⁹Si MAS-NMR), N2physisorption, scanning electron microscopy （SEM）, energy disperse spectroscopy（EDS）, and thermogravimetry-differential thermal analysis （TG-DTA）. It wasdemonstrated that the synthesized molecular sieve was SAPO-5molecular sieve,and which contained mesopores with a pore radius of about3–30nm. Moreover, thefactors affecting the crystallization of aluminophosphate molecular sieve such as themolar ratio of raw materials, crystallization time and crystallization temperaturewere investigated in detail. By experimental analysis, we got the optimal synthesisconditions for the synthesis of SAPO-5molecular sieve which are as follows: themolar ratio of raw materials was54EU:aP₂O₅:Al₂O₃:0.5HF:0.4SiO₂（a=1.0².0）, thetemperature and time of the molecular sieve crystallization was150²00℃and30⁶0min, respectively.FeAPO-5molecular sieve with AFI topology was ionothermally prepared under microwave irradiation in a three-component eutectic mixture consisting of succinicacid, choline chloride and tetraethylammonium bromide. The structure andmorphology of FeAPO-5molecular sieve were characterized in detail by X-Raydiffraction （XRD）, N₂physisorption, Electron spin resonance （ESR）, diffusereflectance UV-visible spectroscopy （DR UV-vis）, thermogravimetry-differentialthermaanalysis （TG-DTA）, Fourier transform infrared spectroscopy （FT-IR）, andscanning electron microscopy （SEM）. It was demonstrated that the synthesizedmolecular sieve was hierarchical FeAPO-5molecular sieve, and the resultantsamples exhibited meso-microporous characteristic. The influencing factors ofsynthesis conditions such as reactants, the molar ratio of reaction raw materials; thecrystallization time and crystallization temperature on the synthesis of molecularsieve were systematically investigated. The optimal reactionconditions were asfollows: Al₂O₃:xP₂O₅:yHF:0.4Fe₂O₃:62EU （x=1.1².2, y=0.5¹.0）, the temperatureand time of the molecularsieve crystallization was180¹90℃and40-60min,respectively.In this paper, we studied the catalytic properties for phenol hydroxylation usingthe hierarchical FeAPO-5samples as catalyst. The results showed that, FeAPO-5molecular sieve, which was ionothermally prepared under microwave irradiation ina three-component eutectic mixture consisting of succinic acid, choline chloride andtetraethylammonium bromide, achieved good results on catalytic hydroxylation ofPhenol. The molecular sieve with ferric nitrate as the iron source showed highercatalytic activity. The conversion of phenol was up to41.6%, and the selectivity forcatechol was higher.