Investigation of Supported Metal Oxide Species with Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy

Raman spectroscopy is a widely employed tool for characterization of heterogeneous catalysts, although it suffers somewhat from poor sensitivity at low concentrations or under in situ conditions. In this article, we describe the use of a variation of surface-enhanced Raman spectroscopy known as shell-isolated nanoparticle-enhanced Raman spectroscopy for enhancing the sensitivity of supported metal oxide catalysts. We present a general method in which we drop-cast Au@SiO2 nanoparticles onto metal oxide-functionalized 2D films, monoliths, or pelletized powder samples to increase the Raman signal. These Au@SiO2 shell-isolated nanoparticles act as optical antennae that receive far-field radiation from the Raman laser and enhance the local electromagnetic field at the catalyst surface. We observe enhancements in Raman signals for vanadium and niobium oxide on various supports including monolithic materials, as well as the enhancement of interfacial V-O-Si vibrations on powdered silica supported vanadium oxide catalysts that contain dispersed vanadium oxide species at ambient conditions and dehydrated up to 400 degrees C.