AFM and SEM-EDS examination of highly dispersed heteropolyacids supported on MCM 41 and SBA 15 mesoporous materials

Abstract

Heteropolyacids (HPAS) H(3)PMo(12)O(40) (HPM) and H(4)PVMo(11)O(40) (HPVM) supported on mesoporous pure-silica and Al, Fe modified molecular sieve MCM-41 and SBA-15 have been prepared and characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM) with EDS. All supported HPAs were prepared by impregnation using the incipient wetness techniques with a mixture of water: ethanol = 1:1. AFM features show that nanoclusters of HPA-molecular sieves composites of various heights were formed on the surface. The morphology of the pure molecular sieves and HPA-molecular sieves composites surface, respectively, has an island-like structure. SEM studies confirmed the uniformity of the distribution of active phase in the supported samples. It is found that most of HPM and HPVM (active phases) in supported samples are well dispersed on all supports. HPAs supported on MCM-41 ans SBA-15 have still kept their Keggin structure. A relatively uniform distribution of active phase in the supports pores was confirmed by EDS analysis.