Neutron Scattering Studies of the Porous Silica Catalyst Support SBA-15

Rachel A. Pollock (University of Maine)

Mesoporous materials are interesting as catalyst supports because molecules can move efficiently in and out of the pore network. However many supports, including the porous silica SBA-15, have a broad distribution of secondary pores that affects both its stability and transport properties. By using different size molecules in contrast matching SANS experiments as direct probes of the size of micropores the onset of the pore size distribution was determined to be 6± 0.2Å , consistent with cylindrical pores formed from polymer template strands that unravel into the silica matrix. Diffraction intensity analysis of SANS measurements, combined with pore size distributions calculated from nitrogen sorption isotherms using non-local density functional theory, show that the secondary pores are distributed relatively uniformly throughout the silica framework.

Quasielastic neutron scattering (QENS) measurements of methane in SBA-15 probe the rotational and translational motion as a function of temperature and loading. For polydisperse systems, the resolution and spectral width of an instrument define a “window” that selects the pore size and temperature range where diffusion can be measured. Current Monte Carlo simulations of methane in cylindrical silica pores model the filling of a polydisperse pore size distribution. The simulations will provide information regarding the occupancy of pores as temperature is increased, from which the spectral window selects the range of pore sizes that are observed in QENS experiments.

Back to Seminar Home Page

Last modified 08-August-2012 by website owner: NCNR (attn: )