J. Haber

Abstract: Solid oxide fuel cells (SOFCs) are a rapidly emerging energy technology for a low carbon world, providing high efficiency, potential to use carbonaceous fuels, and compatibility with carbon capture and storage. However, current state-of-the-art materials have low tolerance to sulfur, a common contaminant of many fuels, and are vulnerable to deactivation due to carbon deposition when using carbon-containing compounds. In this review, we first study the theoretical basis behind carbon and sulfur poisoning, before examining the strategies toward carbon and sulfur tolerance used so far in the SOFC literature. We then study the more extensive relevant heterogeneous catalysis literature for strategies and materials which could be incorporated into carbon and sulfur tolerant fuel cells.

Abstract: In this paper, I review recent progress in joint theoretical and experimental studies aiming at atomic structure determination of low-dimensional metal oxides. Low-dimensional systems can be generally defined as materials of unusual structure that extend to less than three dimensions. In recent years low-dimensional systems have attracted increasing attention of physicists and chemists, and the interest is expected to rise in the near future. Two- and one-dimensional structures in form of thin oxide films or elongated oxide chains have many potential applications including model supports for heterogeneous catalysts and insulating layers in semiconductor industry. The interest in zero-dimensional gas-phase oxide clusters ranges from astrophysics to studies of elementary steps in catalysis. The key prerequisite for understanding physical and chemical properties of low-dimensional systems is a detailed knowledge of their atomic structures. However, such systems frequently present complex structures to solve. Only in a few cases experimental data can provide some information about possible arrangement of atoms, but data interpretation relies to a large extent on intuition. Therefore, in the recent years quantum chemical calculations became an indispensable tool in structure identification of low-dimensional systems, yet the accuracy of theoretical tools is often limited. The results reviewed here demonstrate that often the only way of an unambiguous atomic structure determination of low-dimensional systems are experimental studies combined with theoretical calculations. Particularly the global optimization methods such as genetic algorithm in combination with the density functional theory prove very useful in automatic structure determination of the observed surface structures and gas-phase clusters.

Abstract: The detailed analysis of the experimental XPS envelopes of the model MoO3/Al2O3 and MoO3/SiO2 systems was performed using a curve fitting procedure. It appeared possible to fit the XPS spectrum of MoO3/Al2O3 system with a single Mo 3d5/2-Mo 3d3/2 doublet which indicates the presence of only one type of molybdenum(VI) oxo-species In contrast, curve fitting for MoO3/SiO2 system required two individual Mo 3d5/2-Mo 3d3/2 doublets. The first Mo 3d5/2-Mo 3d3/2 doublet with the binding energy close to that of bulk MoO3 was attributed reflects the to three-dimensional molybdenum(VI) oxo-species. The second Mo 3d5/2-Mo 3d3/2 doublet, shifted to higher binding energy, presence of monomeric or two-dimensional molybdenum(VI) oxo-species which strongly interact with silica surface.

Abstract: Isolated molybdenum centers bearing either one (oxomolybdenum system) or two (dioxomolybdenum system) terminal oxo ligands are considered, which are modeled by appropriate mononuclear oxomolybdenum methoxides and oxomolybdasilsesquioxanes. Although the oxidation process in both systems is characterized by the same fundamental steps, that is, dissociative addition of methanol followed by rate-determining hydrogen abstraction from the methoxy group, the mechanism of the oxidation reaction differs in each case. In the oxomolybdenum system, the first step leads to cleavage of a bond in a Mo−O−Si sequence and the formation of a surface molybdenum methoxide species. Hydrogen is then abstracted from the methoxide ligand by a terminal oxo ligand in a process entailing a closed-shell transition structure. In contrast, the preferred mechanism in the dioxomolybdenum system involves a hydroxomolybdenum methoxide intermediate formed without cleavage of a bond in a Mo−O−Si sequence. Furthermore, the hydrogen abstractio...

Abstract: Density functional theory in combination with genetic algorithm is applied to determine the atomic models of p(1x2) and p(1x3) surface structures observed upon oxygen adsorption on a Mo(112) surfac