Statistical analysis of the influence of synthesis conditions on the properties of hierarchical zeolite Y

Commercial zeolite USY (CBV500, Si/Al = 2.6) was dealuminated with oxalic acid, desilicated with ammonium hydroxide assisted by cetyltrimethylammonium bromide, and acid washed with lactic acid for obtaining hierarchical zeolite Y. The samples were characterized by X-ray diffraction, N2-physisorption, temperature programmed desorption of NH3, transmission electronic microscopy and diffuse reflectance infrared Fourier transform spectroscopy Ppyridine adsorption. A central composite experimental design was used for obtaining the influence of the concentration of the three solutions used in each step of the synthesis, on the relative crystallinity (%RC), mesopore volume (Vmeso), and total acidity of the synthesized materials. All the materials conserved the %RC and total acidity between 51-89% and 51–80%, respectively; modified materials showed an increase of up to 300 m2/g of external surface area and 0.17 cm3/g of the Vmeso with respect to the CBV500 sample. The statistical analysis showed that all the properties are influenced by oxalic acid concentration, whereas ammonium hydroxide concentration affects Vmeso, and lactic acid concentration affects %RC and total acidity in the modified samples. According to the optimization of the process, the material synthesized and labeled as MZ-OP, showed a %RC = 82%, Vmeso = 0.21 cm3/g, and total acidity of 1.430 mmol/g. The catalytic cracking of n-dodecane was tested over CBV500, MZ-OP, and MZ-10-100-500 and the obtained conversion at 300 min was 65%, 95% and 82%, respectively. Deactivation rate of the modified samples was significantly lower than the values obtained with CBV500, showing that the modified samples were more stable under tested reaction conditions.