Structure of germanium oxide on CVD zeolites by extended X-ray absorption fine structure and X-ray photoelectron spectroscopy

Abstract

Chemical vapour deposition of GeO₂ from Ge(OCH₃)₄ on two kinds of H-mordenite with different silica to alumina ratios has been accomplished, and the deposited GeO₂ has been characterized by EXAFS and XPS measurements. Shape-selectivity in cracking of octane isomers was strongly dependent on the composition of mordenite and similar in behaviour to the deposited silica from Si(OCH₃)₄. The amount of deposited GeO₂ required to achieve the shape-selectivity on HM10 (Si/Al = 4.9) was less than that on HM20 (Si/Al = 10.0). On the other hand, the XPS measurement on these CVD mordenites yielded similar results as for the depth distribution of deposited GeO₂. Furthermore, from the EXAFS measurement, the coordination numbers of the second-nearest Ge neighbours around the deposited Ge atoms on these CVD mordenites was less than that in α-quartz type GeO₂. Based upon these findings, we can make some speculations about the structure of deposited GeO₂ on these CVD mordenites: GeO₂ is deposited on the external surface, apparently as a thin layer. Therefore, the difference in the shape-selectivity is caused by a difference not in the location but in the structure of the deposited GeO₂ between these CVD mordenites.