title: Hydrothermal stability investigation of micro- and mesoporous silica containing long-range ordered cobalt oxide clusters by XAS.
abstract: This work investigates the hydrothermal stability of cobalt doped silica materials with different Co/Si molar ratios (0, 0.05, 0.10, and 0.25). The resultant materials were characterized by N2 sorption and chemical structures by Raman and X-ray absorption spectroscopy before and after a harsh hydrothermal exposure (550 °C, 75 mol% vapour and 40 h). The cobalt silica materials showed a lower surface area loss from 48% to 12% with increasing Co/Si molar ratio from 0.05 to 0.25 and relatively maintaining their pore size distribution, while pure silica exhibited significant surface area reduction (80%) and pore size broadening. For low cobalt loading sample (Co/Si = 0.05), the cobalt was highly dispersed in the silica network in a tetrahedral coordination with oxygen and a small proportion of Co-Co interaction in the second shell. Long range order Co3O4 was observed when Co/Si molar ratio increased to 0.10 and 0.25. The hydrothermal exposure did not affect the local cobalt environments and no cobalt-silicon interaction was observed by X-ray absorption spectroscopy. The hydrothermal stability of the silica matrix was attributed to the physical barrier of cobalt oxide in opposing densification and silica mobility under harsh hydrothermal conditions.
authors.affiliation: The University of Queensland, FIM2Lab - Functional Interfacial Materials and Membranes Laboratory, School of Chemical Engineering, Brisbane, QLD 4072, Australia. j.dacosta@eng.uq.edu.au.
authors.forename: Liang
authors.initials: L
authors.lastname: Liu
authors.forename: David K
authors.initials: DK
authors.lastname: Wang
authors.forename: Peter
authors.initials: P
authors.lastname: Kappen
authors.forename: Dana L
authors.initials: DL
authors.lastname: Martens
authors.forename: Simon
authors.initials: S
authors.lastname: Smart
authors.forename: João C
authors.initials: JC
authors.lastname: Diniz da Costa