UC Irvine

Propylene and butylene thermal dehydrogenation have been studied on Pt(111) single crystal using Scanning Tunneling Microscopy (STM). Propylene and butylene were heated to 1000 K on the Pt single crystal. Both olefins formed uniform sized carbon clusters, with less than a monolayer coverage on the Pt surface. With cycles of continued dosing and heating, particles grew in number but not size. The catalytic activity stopped by the third saturation dose, leaving areas of bare Pt. Carbon clusters generated from the dehydrogenated propylene and butylene were approximately 1 Å in height and 12 Å in diameter. Propylene and butylene clusters contained an average of 44 and 51 carbon atoms per cluster respectively.

The reactions of Pt nanoparticles on Al2O3/NiAl(110) were compared with those on the Pt single crystal. An Al2O3 thin film was formed with similar properties to previous alumina reported in literature. Ethlyene did not adsorb to the clean alumina regardless of dosing temperature. The Pt nanoparticles formed were circular, flat, and uniform in size (13 Å) and shape, corresponding to approximately 20 atoms. Annealing the Pt particles up to 1100 K did not produce any change in the size or arrangement of the particles. The Pt nanoparticles deposited only onto crystalline Al2O3 surfaces. Ethylene was then dosed onto the Pt. At 1000 K, ethylene deposited only onto the Pt nanoparticles and not onto the oxide layer. The thermally dehydrogenated ethylene covered the Pt nanoparticles and particles grew to a maximum of 20 Å. Particle density did not increase at an annealing temperature of 1000 K. At 1100 K the density of particles increased and decorated the step edges.

Another set of experiments examined the dehydrogenation of ethylenediamine at 300-500 K on Ni(111). The goal of this study was to form cyanogen. The end result was unidentifiable via imaging by STM and cyanogen formation was not observed.