S. Beau Waldrup

In situ study of Nitrile Adsorption and Hydrogenation on Supported Metal Catalyst Surfaces Using Sum Frequency Spectroscopy (SFS)

MELANIE SCHAAL

YARITZA LOPEZ

Beau Waldrup began his work in December of 2003. The first year he spent the majority of the time familiarizing himself with the concepts of lasers and optics as well as the basics of SFG.

    The first major thrust of Beau's research dealt with studying the adsorption behavior of acetonitrile on a model support. The results from this work have been published in paper 1 in the Papers in press shown below. The abstract of the paper is given below.

    Sum-Frequency spectroscopy (SFS) has been used to probe the interface between a model catalyst support (Al₂O₃-coated CaF₂) and liquid consisting of neat acetonitrile and acetonitrile in ethanol.  Vibrational features associated with both C≡N stretching (~2242 and 2281) and C-H stretching (~2942 and 2989) are observed for adsorbed nitrile.  The peak positions are only slightly shifted from the bulk values, indicating weak adsorption to the model support.  In the case of the neat liquid, the C-H stretching vibrations have also been probed using various polarization combinations of the sum frequency, visible and infrared beams in order to determine the orientation of the nitrile with respect to the surface.  The average molecular angle calculated (~39^o) shows the off-normal alignment of acetonitrile on the surface of the model support.  Finally, an attempt has been made to obtain qualitative information about the adsorption isotherm of acetonitrile on Al₂O₃/CaF₂.  The lack of curvature in the isotherm indicates the lack of affinity for the surface by acetonitrile in ethanol.

    The second thrust of Beau's work will be to again examine acetonitrile adsorption on Pt films that have been deposited on the model support used previously. In doing this we can begin to work towards the addition of hydrogen into the mixture thus completing the study.

    One other areas Beau has been working in is developing SFG to be used for studying high surface area supported metal catalysts. There will be more to come on this in a later update.

Commonly proposed surface adsorbates and intermediates for the hydrogenation of nitriles on supported transition metal catalysts.

Proposed mechanistic pathways for the formation of primary, secondary and tertiary amine products (dashed box) from aliphatic nitriles (dashed circle). Adapted from De Bellefon et. al.

References:

1. C. De Bellefon, P. Fouilloux, Catal. Rev. – Sci. Eng., 36 (3), 459-506 (1994).

Papers in Press:

1. “Solubility of chemical warfare agent simulates in supercritical carbon dioxide: experiments and modeling”, Z. Shen, G. Sandhu, D. Li, C. E. Bara, S. B. Waldrup, S. Siddiqui, C. R. Dillon, K. B. MacIver and M. A. McHugh, J. of Sup. Fluids, 30(3), 273-280 (2004).

2. “In-situ Investigation of Acetonitrile Adsorption on Al₂O₃-coated CaF₂ Using Sum-Frequency Spectroscopy”,  S. B. Waldrup and C. T. Williams,  J. Phys. Chem. B, 110, 16633-16639 (2006) .