چكيده به لاتين
Sol-gel/oil-drop granulation technique was used to prepare mesoporous γ-Al2O3 granules of 1.5-2 mm with high surface area and pore volume of 295 m2.g-1 and 0.47 cm3.g-1, respectively. A response surface methodology (RSM) holding CCD approach was used for modeling the influence of process variables on the granules' pore structure, having a quadratic function relating the independent variables (calcination temperature, acid amount, and ammonia concentration) to the responses (surface area, mean pore diameter, and pore volume). The granules synthesized using 20 ml of nitric acid, aged in a 9.25 wt% ammonia solution, and calcined at 450 ○C showed the best properties. The predicted values for the responses were 315.6 m2.g-1, 7 nm, and 0.53 cm3.g-1, respectively, which were compatible with experimental values. Furthermore, to clarify the role of the additives and their content on the porous structure as well as on the chemical, structural, and microstructural behavior of γ-alumina, a series of undoped, La-, Sn-, Ce-, Zr, and B-doped as well as Zr-Ce and Zr-La co-doped alumina granules were synthesized via sol-gel/oil drop method. XRD, DSC, N2 adsorption/desorption NMR, and HRTEM techniques were hired to investigate alumina granules’ characteristics. XRD results indicated that the introduction of 1 wt% of Zr, La, or Zr-La dopants improves the thermal stability of transition aluminas up to 1200 °C. DSC/TG results revealed that the incorporation of 1 wt% zirconium along with 1 wt% lanthanum retarded α-Al2O3 phase transformation temperature to around 1335 °C. Compared to the pure sample, the BET surface area of alumina containing 3 wt% boron, 3 wt% tin, 1 wt% zirconium, and 1 wt% zirconium along with 1 wt% lanthanum increased to 246, 238.1, 234.4, and 232.4 m2/g at 750 °C, respectively. Moreover, the sample containing 1 wt% of Zr along with 1 wt% of La dopants maintained a higher specific surface area after calcination at 1000 °C (133.6 m2/g) and 1200 °C (64.7 m2/g). According to NMR and HRTEM investigations, the capability of the co-doped Zr-La alumina to preserve the mesoporous structure and thermal stability as well as suppressing α-alumina formation up to 1200 °C is due to the stabilization of OH groups in alumina structure via Zr-O-Al and La-O-Al bonds. The reported Zr-Al co-doped alumina granules in this study with high thermal and porous structural stability can be good candidates as a support for the industrial catalysts, namely iridium catalyst in the hydrazine degradation process.
