In this paper, micro-mesoporous HZSM-5/MCM-41 zeolites were prepared by a
two-step hydrothermal method using commercial HZSM-5 with two different
silica/alumina ratios (38 and 50) as starting materials. The structures,
morphologies and acidity of as-prepared zeolites were analyzed using XRD,
FT-IR, SEM, N2-adsorption/desorption and NH3-TPD. The HZSM-5/MCM-41 zeolites
combined the acidity of microporous HZSM-5 with the pore advantages of
mesoporous MCM-41. Mesopores and microspores of 3.34 and 0.95 nm in diameter
were found to be present in HZSM-5/MCM-41 zeolites. When they were used to
catalyze the pyrolysis of waste tires, the selectivity of light olefins for
HZSM-5/MCM-41 prepared using HZSM-5 with the silica/alumina ratio of 50 as
starting materials was 21.42%, higher than 18.43% of
HZSM-5/MCM-41synthesized using HZSM-5 with the silica/alumina ratio of 38.
In order to further overcome the pore size constraints and mass transfer
limitations of HZSM-5/MCM-41 zeolites for catalyzing pyrolysis of waste
tires, macroporous ?-Al2O3 were mixed with HZSM-5/MCM-41 and used as
catalysts. The selectivity to light olefins for the mixture of ?-Al2O3 and
HZSM-5/MCM-41 prepared using HZSM-5 with the silica/alumina ratio of 50 as
starting materials was 33.65%, which was obviously enhanced by the
introduction of ?-Al2O3.
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