Morphology change and phase transformation of alumina related to defect sites and its use in catalyst preparation

Abstract

The surface properties of support have a large influence on the catalyst properties and the catalyst properties are usually interpreted based on the characterization results of the support surface. However, in many cases, especially when gamma-Al2O3 is used as the support, the alumina surface can be changed during catalyst preparation. Here, the significant changes in the physical and chemical properties of gamma-Al2O3 were observed during catalyst preparation by using incipient wetness impregnation, which follows the general protocols of catalyst production. These changes were confirmed with transmission electron microscopy (TEM) and X-ray diffraction (XRD) analyses. To investigate the origin of such changes from hydrolysis, low-crystalline gamma-Al2O3 (A600) was prepared, which has abundant defect sites (Al-V) on its surface and bulk. Through Al-27 magic angle spinning nuclear magnetic resonance (MAS-NMR) and XRD studies, it could be demonstrated that defect sites (Al-V) play a crucial role in the hydrolysis of alumina. Further, the hydrolysis of the alumina surface could be controlled by altering the solvent properties like changing the volume ratio of ethanol. These results suggest that the change in the support's surface during the catalyst preparation should be considered carefully when correlating the characteristics of the alumina surface with the characteristics of an alumina-based catalyst.