Oxygen storage in reducible oxides studied by ultra-thin film growth on single-crystal oxide substrates

Thermal desorption and steady-state CO oxidation measurements were performed on model catalysts to gain a better understanding of the redox properties of oxygen-storage components in three-way, automotive-emissions-control catalysts. The interactions of these components with group VIII metals, and the effect of those interactions on catalytic properties, was also examined. Thermal desorption of O\sb2 was used to probe directly the oxidation and reduction of ceria, the primary oxygen-storage component used in emissions-control catalysts. For the first time, it was shown that there is a weakly bound form of lattice oxygen on small ceria crystallites, not found on inactive forms of ceria, and that this species of oxygen results in the enhanced CO oxidation activity of ceria-supported metals. Furthermore, interactions with zirconia, which is known to promote ceria in commercial catalysts, were found to greatly increase the fraction of weakly bound oxygen on ceria, as well as the CO oxidation activity. Metal-support interactions, unique to single-crystalline ceria and Rh, were found to promote unusually high CO dissociation activity. Insights gained from these measurements were used to design a novel, ceria-based anode for a solid-oxide fuel cell which could oxidize methane directly, with performance comparable to that obtained using hydrogen. In addition to ceria, the catalytic properties of other reducible oxides, praseodymia and lanthana, were examined to determine the potential of these oxides as oxygen-storage components. While it was determined that praseodymia likely cannot be utilized in its pure form due to slow reoxidation, the results provided further insights into why ceria-based mixed oxides are such effective oxygen-storage components. While lanthana is normally considered to be non-reducible, lanthana could be reduced in CO and could promote the steady-state reduction of NO by CO. However, like ceria, the ability of lanthana to promote redox chemistry is dependent on its structure. Finally, the interaction of oxygen with Rh, Pt, and Pd was studied as a function of particle size. Desorption from Pt and Pd was found to be strongly structure sensitive, whereas desorption from Rh was roughly independent of particle size

Oxygen storage in reducible oxides studied by ultra-thin film growth on single-crystal oxide substrates

Thermal desorption and steady-state CO oxidation measurements were performed on model catalysts to gain a better understanding of the redox properties of oxygen-storage components in three-way, automotive-emissions-control catalysts. The interactions of these components with group VIII metals, and the effect of those interactions on catalytic properties, was also examined. Thermal desorption of O\sb2 was used to probe directly the oxidation and reduction of ceria, the primary oxygen-storage component used in emissions-control catalysts. For the first time, it was shown that there is a weakly bound form of lattice oxygen on small ceria crystallites, not found on inactive forms of ceria, and that this species of oxygen results in the enhanced CO oxidation activity of ceria-supported metals. Furthermore, interactions with zirconia, which is known to promote ceria in commercial catalysts, were found to greatly increase the fraction of weakly bound oxygen on ceria, as well as the CO oxidation activity. Metal-support interactions, unique to single-crystalline ceria and Rh, were found to promote unusually high CO dissociation activity. Insights gained from these measurements were used to design a novel, ceria-based anode for a solid-oxide fuel cell which could oxidize methane directly, with performance comparable to that obtained using hydrogen. In addition to ceria, the catalytic properties of other reducible oxides, praseodymia and lanthana, were examined to determine the potential of these oxides as oxygen-storage components. While it was determined that praseodymia likely cannot be utilized in its pure form due to slow reoxidation, the results provided further insights into why ceria-based mixed oxides are such effective oxygen-storage components. While lanthana is normally considered to be non-reducible, lanthana could be reduced in CO and could promote the steady-state reduction of NO by CO. However, like ceria, the ability of lanthana to promote redox chemistry is dependent on its structure. Finally, the interaction of oxygen with Rh, Pt, and Pd was studied as a function of particle size. Desorption from Pt and Pd was found to be strongly structure sensitive, whereas desorption from Rh was roughly independent of particle size

Unique preservation of siliceous dinoflagellate motile cells from the Oligocene fossil-lagerstätte of Sieblos, Germany

The Triassic to Recent fossil record of the dinoflagellates is represented overwhelmingly by geologically resistant, organic-walled, non-motile resting cysts; such cysts are formed following the sexual phase in the life cycle. Very few confirmed records exist of the motile stage being preserved in the fossil record. This paper reports the occurrence of two very unusual dinoflagellate taphofacies, one developed in bituminous shales and the other in micrites, from the Oligocene fossil lagerstätte at Sieblos, Hesse, Germany. A new dinoflagellate taxon, Sieblososphaera martini sp. nov. has been identified through analysis of dissociated skeletal elements in the bituminous shales and external moulds and casts in the micrites. The unique preservation of these fossils confirms them not only as primary biogenically silicified motile thecate cells, but also indicates that there was a much greater range of tabulation present within the subfamily Lithoperidiniaceae than has hitherto been recognised