Synthesis Of Nano-size HZSM-5 Molecular Sieve

Methanol to propylene(MTP)reaction is an important way to obtain propylene,it means a lot for increasing propylene yield while reducing the dependence on petroleum routes.Nano-size HZSM-5 is considered to be one of the most important molecular sieve catalysts because of its advantages,such as small grain size,short channels and rational distribution of acid sites.As the catalyst for MTP reaction,nano-size HZSM-5 has drawn much attention in recent years.In this study,nano-size HZSM-5 samples were prepared by adding different components in the initial gel.These samples were characterized by X-ray diffraction(XRD),field emission scanning electron microscope(FE-SEM),transmission electron microscope(TEM),N2 adsorption/desorption measurements,temperature programmed ammonia desorption(NH3-TPD)and inductively coupled plasma-atomic emission spectrosmetry(ICP-AES),in order to study the effect of different composition of raw materials on the synthesis of nano-size HZSM-5.These samples were tested under 450?,0.1 MP and WHSV 0.1 h-1 in MTP reaction to observe the catalytic performance.It showed that tetrapropylammonium hydroxide(TPAOH)could be used as the template agents to prepare the nano-size HZSM-5,when TPAOH/SiO2 molar ratio was 0.25,the average crystal size was 50 nm.When TPAOH/SiO2 molar ratio was 0.15,the propylene selectivity reached at 38.1%.Sodium aluminate,aluminum isopropoxide and aluminum nitrate could act as aluminum sources to prepare the nano-size HZSM-5 whose average crystal size was 50 nm.The sample prepared from sodium aluminate showed the highest propylene selectivity.TEOS and silica sol were used as silica sources to prepare nano-size HZSM-5,the average crystal size of them were 50nm and 110 nm,respectively.Propylene selectivity of the sample prepared from silica was up to 37.8%.When SiO2/Al2O3 molar ratio increased from 100 to 300,the average crystal size remained 50 nm,indicating that SiO2/Al2O3 molar ratio exerted little influence on average crystal size.Meanwhile,the sample with high SiO2/Al2O3 molar ratio showed higher propylene selectivity in MTP reaction.