Role of formaldehyde in promoting aromatic selectivity during methanol conversion over gallium-modified zeolites
Wu Wen, Tianci Xiao, Beibei Feng, Chaoqun Zhou, Jian Li, Hao Ma, Zhongyue Zhou, Ying Zhang, Jiuzhong Yang, Zhandong Wang, Fei Qi, Jun Bao, Chengyuan Liu, Yang Pan
Abstract
Abstract 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 Ga 2 O 3 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 Ga 2 O 3 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.