engleski

Effect of Nickel(II) ions on properties of nanosized FAU type zeolite

Introduction Due to its’ 12-member ring cage faujasite type zeolite is one of the best catalysts for fluid catalytic cracking (FCC) and is often used as support for platinum or palladium in a hydrocracking process. Depending on the Si/Al ratio synthetic FAU is classified as X, if ratio is between 2 and 3, or Y if ratio is 3 or higher. High aluminum content in X type zeolite results in large number of Brønsted’s acid sites which often leads to unwanted cyclic byproducts and formation of coke. In order to avoid this problem postsynthetic modifications to the zeolite structure are needed. One of the most promising methods to do this is wet impregnation with metal cations that increase the number of Lewis’ and reduce the number of Brønsted’s acid sites [1] in order to create more controlled catalytic conditions. Experimental The zeolite for post synthetic treatment (HF-AS) was isolated from a gel with following composition 8Na2O:0.7Al2O3:10SiO2:160H2O adopted from Awala and co-workers [2]. Previously prepared HF-AS was added in the water solution of nickel(II) chloride (1:50, 0.5 mol dm-3) and stirred. After 45 minutes the crystals were separated from solution and the process was repeated once more. The prepared product HF-Ni1 was then washed two times with 40 cm3 of redistilled water and then calcined at 550°C for 6 hours. Thus prepared product (HF-Ni1iz) was then ion exchanged with 0.8 mol dm-3 water solution of ammonium nitrate (1:10) for 3 hours after which it was again calcined at 450°C for 5 hours. The same procedure as described above was also used for the synthesis of HF-Ni2, HF-Ni3 and HF- Ni4 with the exception that before washing the products with redistilled water they were hydrothermally treated at 100°C for 24, 1.5 and 3 hours respectively. Results and discussion It was observed that calcination following wet impregnation with nickel(II) ions leads to increase of intensity of (111) peak and disappearance of peaks at 10.3° and 11.7° which may indicate the migration of nickel cations from double-6 rings to supercage. The shift in the peak positions from 0.2° to 0.4° varying on sample was also observed (Fig.1.). The diffraction peaks of the nickel(II) oxide were not observed in any of the samples (Fig.2.). The samples were also analyzed using atomic absorption spectroscopy and vacuum FTIR.

zeolite ; faujasite ; wet impregnation ; nickel(II)

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