부산대학교 도서관

Gallium-modified HZSM-5 zeolites are known to increase aromatic selectivity in methanol conversion. However, there are still disputes about the exact active sites and the aromatic formation mechanisms over Ga-modified zeolites. In this work, in situ synchrotron radiation photoionization mass spectrometry (SR-PIMS) experiments were carried out to study the behaviors of intermediates and products during methanol conversion over Ga-modified HZSM-5. The increased formaldehyde (HCHO) yield over Ga-modified HZSM-5 was found to play a key role in the increase in aromatic yields. More HCHO was deemed to be generated from the direct dehydrogenation of methanol, and Ga2O3 in Ga-modified HZSM-5 was found to be the active phase. The larger increase in aromatic production over Ga-modified HZSM-5 after reduction‒oxidation treatment was found to be the result of redispersed Ga2O3 with smaller size generating a larger amount of HCHO. This study provides some new insights into the internal driving force for promoting the production of aromatics over Ga-modified HZSM-5. Gallium-modified HZSM-5 zeolites demonstrate increased selectivity towards aromatics during methanol conversion, but the mechanism and the nature of the active sites that lead to this enhanced selectivity are poorly understood. Here, in situ synchrotron radiation photoionization mass spectrometry experiments reveal that increased formaldehyde generation over Ga2O3 species plays a key role in promoting the production of aromatic compounds. [ABSTRACT FROM AUTHOR]