In situ Ga K-edge XANES study of Ga-exchanged zeolites at high temperatures under different atmospheres including vacuum, CO, and pressurized H2

Ga-exchanged zeolites are promising catalysts for dehydrogenative alkane transformations. Reduced Ga species, such as Ga hydrides and Ga+ cations, are possible active sites for alkane dehydrogenation based on in situ spectroscopic studies. However, most of the reported studies were conducted at lower temperatures (<300 degrees C) compared with those encountered in actual operating conditions (>600 degrees C). In this study, the in situ Ga K-edge XANES analysis of Ga-exchanged MFI zeolite was performed under actual operating temperatures (>700 degrees C) and different atmospheres (H-2, He, CO, vacuum, and C2H6). The absorption edge appeared at similarly lower energy values than that of Ga2O3 in all atmospheres, whereas the main absorption peak intensity differed depending on the presence or absence of a hydride source in the gas phase. Higher intensities were observed under H-2 and C2H6 atmospheres than under CO and vacuum atmospheres. It was also noted that the main absorption peak intensity increased with increasing H-2 pressure, indicating that the higher intensity was responsible for the presence of Ga-hydride species. Similar in situ XANES measurements were conducted for other Ga-exchanged zeolites. The obtained results were compared with our previously reported data on the relative formation amounts and steady-state activity for ethane dehydrogenation.

Automated summary

This study investigates the catalytic performance of Ga-exchanged zeolites at actual operating temperatures using in situ analysis. The results show that Ga-exchanged zeolites exhibit higher absorption peak intensity under hydrogen and ethane atmospheres, indicating the importance of hydride species in their catalytic activity.