Multistage nanoreactor catalyst and preparation and application thereof
The present disclosure discloses a multistage nanoreactor catalyst and preparation and application thereof, belonging to the technical field of synthesis gas conversion. The catalyst consists of a core of an iron-based Fischer-Tropsch catalyst, a transition layer of a porous oxide or porous carbon material, and a shell layer of a molecular sieve having an aromatization function. The molecular sieve of the shell layer can be further modified by a metal element or a non-metal element, and the outer surface of the molecular sieve is further modified by a silicon-oxygen compound to adjust the acidic site on the outer surface and the aperture of the molecular sieve, thereby inhibiting the formation of heavy aromatic hydrocarbons. According to the disclosure, the shell layer molecular sieve with a transition layer and a shell layer containing or not containing auxiliaries, and with or without surface modification can be prepared by the iron-based Fischer-Tropsch catalyst through multiple steps. The catalyst can be used for direct preparation of aromatic compounds, especially light aromatic compounds, from synthesis gas; the selectivity of light aromatic hydrocarbons in hydrocarbons can be 75% or above, and the content in the liquid phase product is not less than 95%; and the catalyst has good stability and good industrial application prospect.
1. A method for preparing a multistage nanoreactor catalyst, comprising the following steps:
step 1, admixing an iron-based catalyst into an organic solvent containing a transition layer oxide precursor, then performing rotary evaporation to remove the organic solvent and drying at 30 to 250° C. for 0 to 24 h to obtain a sample;
step 2, admixing the sample prepared in step 1 into an alkaline solution comprising an alkali, a template, a silicon source and an aluminum source, and stirring for 0 to 24 h, wherein weight ratio of the sample, the template, the silicon source, the aluminum source, the alkali and water is (0.5-50):(0.05-1): 1:(0.01-1):(0.001-0.5):(10-500); then charging into a hydrothermal kettle, sealing, heating to 110 to 300° C., and hydrothermally crystallizing for 5 to 120 h; filtering a solid product after crystallization and cooling, washing till pH value of washing liquid is 4 to 11, then drying at 30 to 200° C. for 0 to 24 h, and calcining at 300 to 800° C. for 0 to 24 h to obtain a powder;
step 3, admixing the powder obtained in step 2 into a solution containing a soluble salt of a metal element by an incipient wetness impregnation method or an ion exchange method or an excess impregnation method; and
step 4, admixing the sample powder obtained in step 3 into an organic solvent containing a silicon source, stirring, then removing the solvent by rotary evaporation and drying at 30 to 250° C. for 0 to 24 h, and finally calcining at 350 to 650° C. for 0 to 24 h.
2. The method for preparing a multistage nanoreactor catalyst according to claim 1 , wherein in step 1, the organic solvent is selected from the group consisting of ethanol, propanol, acetone, cyclohexane, n-hexane, n-heptane, n-pentane and a combination thereof.
3. The method for preparing a multistage nanoreactor catalyst according to claim 1 , wherein in step 2, the template adopted is selected from the group consisting of tetrapropylammonium hydroxide, n-propylamine, isopropylamine, hexamethyleneimine, triethylamine, tetraethylammonium hydroxide and a combination thereof; the silicon source is selected from the group consisting of silicon oxide, sodium silicate, propyl orthosilicate, hexamethyldisiloxane, ethyl orthosilicate, isopropyl orthosilicate and a combination thereof; the aluminum source is selected from the group consisting of alumina, aluminum isopropoxide trihydrate, sodium aluminate, aluminum sulfate, boehmite, gibbsite and a combination thereof; and the alkali is selected from the group consisting of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate, potassium bicarbonate, sodium acetate and a combination thereof.
4. The method for preparing a multistage nanoreactor catalyst according to claim 1 , wherein in step 3, the soluble salt is selected from the group consisting of nitrate, carbonate, acetate, sulfate, molybdate, tungstate, chloride and a combination thereof.