Abstract
SAPO-34/ZSM-5 composite was synthesized with nano-sized ZSM-5 zeolite as seeds and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen sorption, Fourier transform infrared (FTIR) and temperature-programmed desorption of ammonia (NH3-TPD); its catalytic performance in the conversion of methanol to hydrocarbons (MTH) was investigated. The results indicated that the as-synthesized SAPO-34/ZSM-5 composite takes the form of sphere-like particles with a diameter ranging from 2.3 to 4.8 µm, through the accumulation of tiny ZSM-5 and SAPO-34 crystals; a large quantity of mesopores was formed in the interspaces between the ZSM-5 and SAPO-34 crystals. Owing to its proper acidity and porosity, the SAPO-34/ZSM-5 composite exhibits higher stability in MTH and favors the formation of aromatics and alkanes, compared with the parent SAPO-34 and ZSM-5 zeolites and their mechanical mixture.
Highlights
As methanol can be expediently produced via syngas from multifarious carbon sources such as coal, natural gas, and biomass, the conversion of methanol to hydrocarbons (MTH) over acidic zeolite catalysts has been turning into an increasingly important alternative to petrochemical processing to get hydrocarbons.[1,2] Relying on the catalyst and reaction conditions employed, the MTH process may be designed to get light olefins, gasoline, aromatics, and so on.Usually, the molecular sieves of 8 to 12-membered ring are employed as the catalysts in MTH;[3,4,5,6] among them, SAPO-34 and ZSM-5 zeolites have proved to be uniquely effective
The SAPO-34/ZSM-5 composite was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen sorption, Fourier transform infrared (FTIR), and temperature-programmed desorption of ammonia (NH3-TPD); its catalytic performance in MTH was investigated and compared with that of the mechanical mixture of SAPO-34 and ZSM-5
ZSM-5 zeolite with a Si/Al ratio of 200 was hydro thermally synthesized with tetraethyl orthosilicate (TEOS) as the Si source, aluminum isopropoxide as the Al source, and tetrapropylammonium hydroxide (TPAOH) as the template according to the composition of 6 TPAOH:0.1 NaOH:[25] SiO2:0.0625 Al2O3:480 H2O:100 EtOH
Summary
As methanol can be expediently produced via syngas from multifarious carbon sources such as coal, natural gas, and biomass, the conversion of methanol to hydrocarbons (MTH) over acidic zeolite catalysts has been turning into an increasingly important alternative to petrochemical processing to get hydrocarbons.[1,2] Relying on the catalyst and reaction conditions employed, the MTH process may be designed to get light olefins (methanol to light olefins, MTO), gasoline (methanol to gasoline, MTG), aromatics (methanol to aromatics, MTA), and so on. Fan et al prepared various composite molecular sieves consisting of SAPO‐11, Hβ, HMOR and HZSM-5;8,9 among them, ZSM‐5/SAPO-11 composite exhibited a core-shell structure, large quantity of mesopores, moderate acidity, and excellent catalytic performance in fluid catalytic cracking gasoline hydro-upgrading. It is expected that a composite catalyst of SAPO‐34/ZSM-5 may take the advantages of both SAPO‐34 and ZSM-5 and performs efficiently in MTH, giving high selectivity to specified products and long lifetime.[13,14] A SAPO-34/ZSM-5 composite, i.e., submicron-scale agglomerates of SAPO-34 and ZSM-5, was prepared and used as an efficient catalyst in MTO.[13] it is well accepted that nano-sized crystal zeolites may show high activity and long lifetime because of the large external surface and short diffusion length.[15]. The SAPO-34/ZSM-5 composite was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen sorption, Fourier transform infrared (FTIR), and temperature-programmed desorption of ammonia (NH3-TPD); its catalytic performance in MTH was investigated and compared with that of the mechanical mixture of SAPO-34 and ZSM-5
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