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