Synthesis Of Mesoporous Molecular Seive Al-MCM-41 With Coal Kalin And Catalytic Application

Mesoporous molecular seive MCM-41 with larger surface area, uniform pore size distribution and one-dimensional ordered pore system, had attracted extensive attention in the fields of catalysis and adsorption. In Inner Mongolia, coal-kaolin with abundant reserve and good quality was a better resource for the preparation of Si-Al molecular seive. In this paper, Al-doped mesoporous molecular seive (Al-MCM-41) was successfully prepared by the method of hydrothermal synthesis using Inner Mongolia coal-kaolin as the aluminum resource, tetraethylsilicate(TEOS) as the complement of silicon resource and cetyltrimethylammonium bromide(CTAB) as the template. XRD, FT-IR, SEM and TEM were taken to analyze the structure and morphology of the samples and also investigated the effect of the preparation condition on the sample's structure. The thermal stability and the static hydrothermal stability of the sample were discussed and the effect of Al-MCM-41 as the support in the CO-PROX was studied preliminarily.The characterization of raw material showed that kaolin had 18.44m2/g surface area, 0.05cm3/g pore volume, 9.96nm average pore diameter. It mainly consisted of highly crystallinity lamellar kaolinite,which possessed trigonal spacegroup, Al4OH8(Si4O10) molecular formula and had a little of iron oxide and titanium oxide. Calcined in the range of 466.9oC~971.4oC, kaolin was transformed to armorphous activated aluminum and silicon, which can be used as the resource of aluminum and part resource of silicon to synthesize Al-MCM-41 mesoporous molecular sieve.The effect of kaolin's calcination temperature, Si/Al ratio of raw material, reaction temperature, pH value, crystallization time, crystallization temperature and calcination method on the structure of mesoporous molecular seive Al-MCM-41 were investigated. The main influence operation factors were kaolin's calcination temperature, raw material Si/Al ratio, reaction temperature and pH value. However, crystallization time, crystallization temperature and calcination method did not have significant impact on the structural characteristic, and had little effect on the structural parameters.The experiments confirmed that optimized operation condition for Al-MCM-41 synthesis was as follows: 550oC kaolin's calcination temperature, 45oC reaction temperature, 2g calcined kaolin, 10.00 pH value, 110oC crystallization temperature, 72h crystalization time, 2oC/min heating rate and 550oC sample's calcination temperature. The target product Al-MCM-41 prepared under optimized condition had 580.65m2/g BET surface area, 0.54cm3/g pore volume, 3.57nm average pore diameter and Si/Al atom ratio of 9 and it exhibited high crystallinity and nonuniform sphere particles. Most of the aluminum had incorporated into the framework.The thermal stability of Al-MCM-41 was studied. With the increase of sample's calcination temperature, silicon hydroxyl excessively shrank and the ordered structure partly collapsed. XRD results suggested that the sample still retained the highly ordered structure after calcined at 700oC for 2 hours.The static hydrothermal stability was also investigated. The orderliness of the sample decreased significantly after impregnation in the boiling water for 12 hours. This suggested that the sample's hydrothermal stability needed improving.The feasibility of Al-MCM-41 used as the support in the CO-PROX was studied and the influence of Al-MCM-41 on the catalyst's structure and activity performance was investigated.