Daniel Ostgard

Structure sensitive hydrogen effect during Pt/SiO2 catalyzed hydrogenolysis of methyloxirane: Absence of effect with EuroPt-1

On Pt/SiO2 catalysts, with the exception of EuroPt-1, rates of methyloxirane hydrogenolysis go through maxima at 33.3 kPa of hydrogen and the size of the maximum depends on platinum dispersion. Therefore, structure sensitivity is related not only to the clean metal surface, but also to the metal-hydrogen system. These relationships suggest that hydrogenand/or methyloxirane-induced surface restructuring may occur and offer a method by which supported platinum catalysts may be characterized. Thus, carefully chosen chemical reactions distinguish among ambiguous and conflicting physical characterizations and are essential components in complete catalyst characterization. Additionally, optimum flexibility of 60%D particles explains the failure of EuroPt-1 to perform according to its dispersion and explains why diverse reactions exhibit rate maxima at approximately 60%D.

The Mechanism of Hydrogenolysis and Isomerization of Oxacycloalkanes on Metals, Part X. Nature of the Active Sites in the Regioselective Hydrogenation of Oxiranes

Summary The hydrogenolysis and isomerization of methyloxirane were studied over various Pt catalysts in order to determine the number and nature of the active sites. The steps were found to be the probable active sites and the transformation is structure-sensitive. The regioselectivity is not affected by variation in the catalyst structure, so it is determined by the nature of the metal.

Active sites on well-characterized Pd/SiO2 determined by (−)-apopinene deuteriumation, cyclohexene hydrogenation, and CS2 titration

Cyclohexene and (−)-apopinene were hydrogenated over various Pd/SiO 2 catalysts, and their turnover frequencies (TOFs) and numbers of active sites, from CS 2 titration (CS 2 -sites), are reported. (−)-Apopinene TOFs and CS 2 -sites increase with increasing dispersion, but with the same increase in dispersion cyclohexene TOFs decrease and CS 2 -sites pass through a maximum. The more complex structure of (−)-apopinene makes it difficult to adsorb on the planes, on which cyclohexene can adsorb readily. Thus (−)-apopinene exhibits lower activity than cyclohexene on planes but higher activity on edges and corners.

The effects of raney alloy structure on the activation process and the properties of the resulting catalyst

Abstract The rate of nitrobenzene hydrogenation over activated base metal catalysts (ABMC) was found to be strongly influenced by the residual Al content of the catalyst, whereas higher Al contents resulted in lower activities. It was also shown that the ability to leach Al from an alloy was dependent on its initial Al content, the percentage of the Ni2Al3 phase, and the size of the Ni2Al3 domains. For alloys with ∼60%Ni2Al3, the larger Ni2Al3 domains leached Al faster than the smaller ones. Additionally, the larger Ni2Al3 domains required longer activation times to reach optimal activity suggesting a restructuring process. In principle, the leaching of alloys with smaller phase domains should produce catalysts with higher surface areas and activities, however it has been demonstrated that one can make equally or more active catalysts from alloys with larger phases by incrasing the activation time.