Methanol to hydrocarbon conversion on Fe-silicates prepared from Fe 2+ and Fe 3+ sources

Abstract

By using the rapid crystallization method, Fe-silicates having the pentasil pore-opening structure and a high content of Fe(7.8− 10.4 wt% as Fe 2O 3) were prepared from both Fe 2+ and Fe 3+ salts as the starting materials. A significant effect of the different kinds of salt was observed on the preparation, physical properties, and catalytic performances in methanol to hydrocarbon conversion and syngas to hydrocarbon conversion. As for the catalyst from Fe 3+ salt[Fesilicate(III)], almost all of the charged Fe ions were incorporated in the silicate crystal. As for the catalyst from Fe 2+ salt[Fe-silicate(II)], on the other hand, only 75% of the charged Fe ions were incorporated in the crystal. Chemical analysis of the intermediate products and s lutions in the preparation procedures of Fe-silicate revealed th t 72% of Fe 2+ are oxidized to Fe 3+ during the hydrothermal synthesis, and Fe 3+ thus produced is incorporated in the crystal while most of the remaining Fe 2+ is effused from the crystal to washing water after the hydrothermal synthesis. Characterizations of the Fe-silicates indicated the following differences between Fe-silicate(III) and Fe-silicate(II): Fesilicate(II) has a higher crystallinity and a stronger acidity than Fesilicate(III). In accordance with the differences, Fe-silicate(II) exhibited a higher activity than Fe-silicate(III) in the methanol to hydrocarbon conversion; Fe-silicate(II) was favorable for the formation of aromatics and gasoline, while Fe-silicate(III) produced more C 2-C 4 olefins than Fe-silicate( between Fe-silicate(II) and Fe-silicate(III) was also observed in the selectivity of syngas to hydrocarbon conversion; Fe-silicate(II) produced aromatics much more than Fe-silicate(III). Consequently, the difference in Fe source affects the crystallinity and acidity of Fe-silicates which in turn determine the catalytic performance of Fe-silicates.