Synthesis of Zeolite Catalysts Containing Zn and Ga for Aromatization of <i>n</i>-Hexane

Abstract

MFI-type zeolites and MWW-type zeolites containing Zn and/or Ga species were directly synthesized through the hydrothermal treatment of an amorphous gel containing Zn and/or Ga species with a high metal content in the absence of Al species. The metal-containing zeolites were applied to the aromatization of n-hexane to evaluate the catalytic performances. Ga-containing zeolites exhibited much higher catalytic activities than Zn-containing zeolites. The Ga-containing zeolites predominantly produced benzene through the dehydrocyclization of n-hexane among benzene, toluene, and xylenes (BTX), although cracked compounds were mainly produced. Higher crystallinity of the MFI zeolite containing both Zn and Ga species led to higher catalytic performances for both the dehydrocyclization and cracking. Furthermore, higher Ga content in the MFI zeolite containing both Zn and Ga species, which corresponds to lower Zn/Ga molar ratio, improved the catalytic activity for the aromatization of the cracked compounds to produce toluene and xylenes, whereas the selectivity for benzene was independent of the Ga content.