It is shown that both the materials and the pressure gaps can be bridged for ruthenium in heterogeneous oxidation catalysis using the oxidation of carbon monoxide as a model reaction. Polycrystalline catalysts, such as supported Ru catalysts and micrometer-sized Ru powder, were compared to single-crystalline ultrathin RuO 2 films serving as model catalysts. The microscopic reaction steps on RuO 2 were identified by a combined experimental and theoretical approach applying density functional theory. Steady-state CO oxidation and transient kinetic experiments such as temperature-programmed desorption were performed with polycrystalline catalysts and single-crystal surfaces and analyzed on the basis of a microkinetic model. Infrared spectroscopy turned out to be a valuable tool allowing us to identify adsorption sites and adsorbed species under reaction conditions both for practical catalysts and for the model catalyst over a wide temperature and pressure range. The close interplay of the experimental and theoretical surface science approach with the kinetic and spectroscopic research on catalysts applied in plug-flow reactors provides a synergistic strategy for improving the performance of Ru-based catalysts. The most active and stable state was identified with an ultrathin RuO 2 shell coating a metallic Ru core. The microscopic processes causing the structural deactivation of Ru-based catalysts while oxidizing CO have been identified.

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Research on new reaction routes and precursors to prepare catalysts for CO 2 hydrogenation has enormous importance. Here, we report on the preparation of the permanganate salt of the urea-coordinated iron(III), [hexakis(urea- O )iron(III)]permanganate ([Fe(urea-O) 6 ](MnO 4 ) 3 ) via an affordable synthesis route and preliminarily demonstrate the catalytic activity of its (Fe,Mn)O x thermal decomposition products in CO 2 hydrogenation. [Fe(urea-O) 6 ](MnO 4 ) 3 contains O-coordinated urea ligands in octahedral propeller-like arrangement around the Fe 3+ cation. There are extended hydrogen bond interactions between the permanganate ions and the hydrogen atoms of the urea ligands. These hydrogen bonds serve as reaction centers and have unique roles in the solid-phase quasi-intramolecular redox reaction of the urea ligand and the permanganate anion below the temperature of ligand loss of the complex cation. The decomposition mechanism of the urea ligand (ammonia elimination with the formation of isocyanuric acid and biuret) has been clarified. In an inert atmosphere, the final thermal decomposition product was manganese-containing wuestite, (Fe,Mn)O, at 800 °C, whereas in ambient air, two types of bixbyite (Fe,Mn) 2 O 3 as well as jacobsite (Fe,Mn) T-4 (Fe,Mn) OC-6 2 O 4 ), with overall Fe to Mn stoichiometry of 1:3, were formed. These final products were obtained regardless of the different atmospheres applied during thermal treatments up to 350 °C. Disordered bixbyite formed first with inhomogeneous Fe and Mn distribution and double-size supercell and then transformed gradually into common bixbyite with regular structure (and with 1:3 Fe to Mn ratio) upon increasing the temperature and heating time. The (Fe,Mn)O x intermediates formed under various conditions showed catalytic effect in the CO 2 hydrogenation reaction with <57.6% CO 2 conversions and <39.3% hydrocarbon yields. As a mild solid-phase oxidant, hexakis(urea- O )iron(III) permanganate, was found to be selective in the transformation of (un)substituted benzylic alcohols into benzaldehydes and benzonitriles.

In situ reflection-absorption infrared spectroscopy (RAIRS) experiments identify the most abundant surface species during the CO oxidation on RuO 2 (110) in a wide pressure range from 10 -7 mbar to 10 -3 mbar. Under reaction conditions with highest catalytic activity most of the undercoordinated (bridging) surface O atoms of the RuO 2 (110) surface are shown to be replaced by bridging CO molecules, thereby modifying the operating catalyst. The observed replacement of bridging O by bridging CO contradicts recently published ab initio kinetic Monte Carlo (k-MC) simulations on the same catalytic system. The C-O stretching frequency depends not only on the adsorption site but also on the local adsorption environment on the surface. This allows us to gain unprecedented information about the distribution and local configuration of the adsorbed reactants on the catalyst's surface during the CO oxidation reaction, which may serve as benchmarks for future k-MC simulations. Under reaction conditions the catalyst surface exposes areas which are catalytically active and areas which are poisoned by densely packed bridging CO and on-top CO. The actual reaction proceeds via the so-called Langmuir-Hinshelwood mechanism in that neighboring on-top O and on-top CO preferentially recombine to form CO 2 . The thermally induced restoration of the mildly reduced RuO 2 (110) surface was studied in situ on the atomic scale.