Evidence for and mitigation of the encapsulation of gold nanoparticles within silica supports upon high-temperature treatment of Au/SiO2 catalysts: Implication to catalyst deactivation

Silica is one of the most widely used catalyst supports for metal nanocatalysts. Although the sintering of metal nanoparticles on various silica supports has been extensively studied, the restructuring of silica supports and its effect on supported metal nanoparticles have been seldom investigated. In this paper, silica-supported gold catalysts were used as a model system to probe the interplay of silica supports and metal nanoparticles under high-temperature treatment conditions. Gold was loaded onto mesoporous SiO2 (SBA-15) using Au(en)2Cl3 as the precursor in the presence of aqueous NaOH (pH ∼ 10). The influence of high-temperature treatment on the textural and structural changes of SBA-15 and Au/SBA-15 was studied by X-ray diffraction (XRD), N2 adsorption-desorption, and transmission electron microscopy (TEM). Control experiments were conducted using an amorphous SiO2 (Cab-O-Sil) as the support. It was found that SBA-15 undergoes significant phase transformation to crystalline cristobalite upon high-temperature treatment, resulting in the dramatic decrease in surface area. More interestingly, the crystallization of SiO2 leads to the encapsulation of gold nanoparticles inside the SiO2 matrix. This conclusion was proven by aqua regia leaching, EDX, and SEM/TEM experiments. Gold nanoparticles can also be encapsulated into the SiO2 matrix when using Cab-O-Sil as the support, but the process takes place under much higher temperatures. The encapsulation of gold nanoparticles can be mitigated by coating Au/SBA-15 with amorphous Al2O3 or by coating SBA-15 with Al2O3 before loading gold. Our findings shed new light on the deactivation of supported gold catalysts under high-temperature conditions. © 2010 Elsevier B.V. All rights reserved.

Duke Scholars

Author Miaofang Chi Thomas Lord Department of Mechanical Engineering and Materia ...