The spreading of micron-sized MoO3 particles deposited
on model supports, alumina and titania thin films,
has been studied by scanning photoemission spectromicroscopy. It
was shown that Mo species released
from the MoO3 crystals spread over the thin oxide film
under conditions (heating to 720 K for 6 h in air)
similar to those used for catalysts on powdered supports. The
changes in the surface morphology were followed
by elemental mapping and photoelectron spectroscopy from submicron
spots where the intensities and kinetic
energies of the Mo 3d, Al 2p, Ti 3d, and O 1s photoelectrons were used
as fingerprints for the chemical
composition of the surface. The high spatial resolution when
imaging the spread phase on the laterally
inhomogeneous samples made it possible to throw light onto the active
transport mechanism of the wetting
Mo oxide species during heat treatment of the model
systems.
The initial stage of spreading of micron-sized MoO3 crystals deposited on a flat Al2O3 support have been studied by synchrotron radiation spectromicroscopy. The lateral resolution of 150 nm and the surface sensitivity of the microscope allowed us to detect submonolayer quantities of Mo–oxide, spread on the support in the vicinity of the MoO3 crystals after annealing in oxygen atmosphere. Detailed analyses of the Mo–oxide wetting the support have been performed combining chemical imaging with spectroscopy. The concentration of the spread Mo–oxide was quantified as a function of the distance from the MoO3 crystals. The determined concentration profiles were fitted to the analytical solution of an equivalent diffusion model for the MoO3 mass transport in dry oxygen at 630 K yielding a diffusion constant of D=7.8×10−11 cm2/s. The results are discussed in the framework of the possible mass transport mechanisms causing the spreading. The simple unrolling carpet was ruled out as an active process.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.