NMR for Catalyst Studies
EMSL Project ID
9103
Abstract
A detailed understanding of the mechanisms involved in a catalytic reaction requires that we identify the nature of the active sites and of reaction intermediates, and that we probe dynamic processes starting when reactants enter the reaction zone until final products elute from the system. For reactions involving simple species, in-situ techniques such as UV-visible and IR spectroscopies are typically used to probe the nature of adsorbed intermediates. For many important reactions, especially selective oxidations of organics, reaction products and intermediates are complex and difficult to identify using a single spectroscopic tool. Nuclear magnetic resonance spectroscopy at high field and under simulated reaction conditions can contribute in critical ways to the required analysis. Several well established surface-sensitive solid-state NMR techniques will be used to investigate the catalytic systems of interest. For example, singly- or doubly- labeled (13C or 2H) organic molecules can be adsorbed at ~5% monolayer coverage. The absorbed species mobility can be quenched by dropping the temperature to 50K or lower. The purpose of these experiments is simple: are the data consistent with proposed reaction mechanisms? Is there a single species on the surface or multiple forms? The results of these experiments (shielding tensors, bond distances and angles) can be used as boundary conditions for calculations and for comparison of analogous experiments using IR and other methods. Another experiment of particular interest is the adsorption of 15N-labelled NOx molecules on NOx conversion catalyst materials as probed by 15N NMR. Already, we have performed what we believe to be the first experiments to provide specific detail on the nature of the adsorbed NOx species on these important materials.
There are two specific current catalysis programs of interest as this EMSL use begins:
1) Early Transition Metal Oxides as Catalysts: Crossing Scales from Clusters to Single Crystals to Functioning Materials, a program funded by the DOE/OS/Basic Energy Sciences/Chemical Sciences; and
2) Fundamental Studies of NOx Adsorber Materials; a program funded by the DOE/EE/Office of FreedomCar and Vehicle Transportation.
Project Details
Start Date
2004-08-30
End Date
2006-10-11
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members