In-situ Studies of the Reactions of Bifunctional and Heterocyclic Molecules over Noble Metal Single Crystal and Nanoparticle Catalysts Studied with Kinetics and Sum-Frequency Generation Vibrational Spectroscopy

Abstract

found that the ring-cracking product butylamine is a reaction poison over both surfaces studied.Furan hydrogenation was studied over Pt(111), Pt(100), 10 nm cubic platinum nanoparticles and 1 nm platinum nanoparticles. The product distribution was observed to be highly structure sensitive and the acquired SFG-VS spectra reflected this sensitivity.Pt(100) exhibited more ring-cracking to form butanol than Pt(111), while the nanoparticles yielded higher selectivities for the partially saturated ring dihydrofuran.Pyridine hydrogenation was investigated over Pt(111) and Pt(100). The α-pyridyl surface adsorption mode was observed with SFG-VS over both surfaces. 1,4-dihydropyridine was seen as a surface intermediate over Pt (100) but not Pt(111). Upon heating the surfaces to 350K, the adsorbed pyridine changes to a flat-lying adsorption mode. No evidence was found for the pyridinium cation.The hydrogenation of the α,β-unsaturated aldehydes acrolein, crotonaldehyde, and prenal were investigated over Pt(111) and Pt(100). The selectivity for the hydrogenation of the C=C bond was found to depend on the number of methyl groups added to the bond. The adsorption modes of the three aldehydes were determined. The hydrogenation of crotonaldehyde was found to be nearly structure insensitive as the TOF and selectivity were very close to the same over Pt(111) and Pt(100). SFG-VS indicated identical surface intermediates over the two crystal faces during crotonaldehyde hydrogenation.

In Situ Studies of Surface Mobility on Noble Metal Model Catalysts Using STM and XPS at Ambient Pressure

“…Few surface characterization techniques other than STM are sensitive to the observed morphological changes observed on the surface which are likely to play a role in its catalytic behavior. The spontaneous formation of a high density of edge sites could explain the selectivity of the Pt(100) surface towards hydrocarbon cracking products [23]. Since active catalysts have mobile surface layers that restructure in response to high temperatures and pressures, ex-situ characterization is insufficient to develop an accurate description of catalytic behavior.…”