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The exsolution process enables to produce and control the formation of stable and catalytically active nano particles via reductive extraction of uniformly incorporated precious metal ions from a solid oxide solution. Here we consider the simple and stable perovskite LaFeO3(LFO) where 10% of Fe on B sites are substituted by ruthenium (LFRO). Hydrogen reduction of LFRO at 800 °C leads to the formation of socketed ruthenium particles whose low-temperature activity in the total propane oxidation reaction at 210 °C is substantially lower than that of the original LFRO. Upon increasing the reaction temperature once to 400 °C, the exsolved catalyst undergoes self-activation so that the activity at 210 °C turns out to be five times higher than that of the original LFRO. High-resolution transmission electron microscopy and nanometer-resolved element mapping, together with averaging characterization methods, including X-ray diffraction and X-ray photoelectron spectroscopy, Raman spectroscopy, and diffuse infrared spectroscopy, unveil that after reduction at 800 °C the exsolved Ru particles are slightly alloyed with Fe and encapsulated by an inert and protecting LaOxlayer. Mild oxidative treatment at 400 °C leads to the removal of the conforming LaOxlayer, while the uncovered RuFe alloy particle transforms to catalytically active oxidic Ru species, with no indication of a separate FeOxphase. We exemplify with our case study of LaFe0.9Ru0.1O3that careful redox treatment enables to control the exsolution process and to avoid deactivation. This may be of importance for the whole class of exsolvable materials.

The solid solution of a reducible oxide with a (non or) less reducible oxide may open the way to incorporate substantial amounts of hydrogen by the simple exposure to H2at elevated temperatures, as exemplified with the mixture of RuO2and TiO2. We are able to incorporate 17.6 mol% hydrogen into the mixed oxide Ru0.3Ti0.7O2by H2exposure at 250 °C, while this is not possible for pure RuO2and rutile TiO2that is either reduced to metallic Ru or does not allow for hydrogen absorption, respectively. Hydrogenated Ru0.3Ti0.7O2may be utilized in hydrogenation catalysis. In this study, however, we demonstrate that hydrogen-incorporated Ru0.3Ti0.7O2improves substantially the catalytic performance in oxidation reactions such as the total oxidation of propane and HCl oxidation reaction. Hydrogen induced lattice strain in Ru0.3Ti0.7O2accompanied with altered electronic properties is likely to be the reason for the observed enhancement in catalytic activity. Hydrogen treatment can also be performed in the reactor, thus providing an additional parameter to fine-tune in situthe catalytic performance of a mixed oxide catalyst.

With operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and online gas analysis, we studied the catalytic methane combustion over 2 mol % IrO2supported on rutile TiO2under reducing (CH4:O2= 1:1) and oxidizing (CH4:O2= 1:4) reaction conditions. Two types of catalysts are studied: the samples are pretreated at 320 °C either with O2(ox-IrO2@TiO2) to ensure full oxidation or with CH4(red-IrO2@TiO2) to partially reduce IrO2. Ox-IrO2@TiO2and red-IrO2@TiO2are stable under oxidizing and reducing methane oxidation conditions, respectively. DRIFTS indicates, however, that under reducing conditions CO is formed on red-IrO2@TiO2, while no CO formation is observed for ox-IrO2@TiO2under oxidizing conditions. Methane oxidation under reducing conditions transforms ox-IrO2@TiO2into red-IrO2@TiO2showing strong CO bands in DRIFTS and higher activity than oxidized IrO2. This latter observation is in stark contrast to methane oxidation studies over single crystalline IrO2(110), thus manifesting a material gap in terms of chemical reducibility. Highest methane conversion is achieved with red-IrO2@TiO2under the oxidizing reaction feed. The formation of adsorbed CO on the catalyst evidences that the reaction mechanism proceeds via the formaldehyde intermediate.