Heterogeneous oxidation catalysis on ruthenium: bridging the pressure and materials gaps and beyond

Abstract

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.

Preparation of Nanoporous Ruthenium Catalyst and Its CO Oxidation Characteristics

“…7(b). The E a determined from the Arrhenius plots was 82 kJ mol ¹1 , and is similar to those obtained in previous CO oxidation experiments with various Ru catalysts, summarized by Assmann et al 41) including single crystal Ru, 2) polycrystalline Ru 42) and supported Ru nanoparticles. 9,43) Various factors affect the activity of catalysts, including the catalyst surface oxidation state which is crucially important for CO oxidation over Ru catalysts.…”

“…However, further analyses such as in-situ infrared spectroscopy are required to elucidate the CO oxidation mechanism over np-Ru, because the metallic Ru surface oxidation state is very sensitive to the atmosphere. 9,10,41) On the other hand, a measurable amount of residual Mn was also detected by XPS [ Fig. 8(b)], although strict elemental composition cannot be calculated due to overlap of Ru 3d and C 1s peaks, unfortunately.…”

On the CO-Oxidation over Oxygenated Ruthenium

“…Whereas these aforementioned studies dealt with ruthenium single crystals, in more recent work on polycrystalline ruthenium dioxide [8] the authors proposed a core-shell model consisting of an about 1nm thick RuO 2 layer covering a metallic core as the most active state of RuO 2 in the CO oxidation. Again, the cus-oxygen was suggested as the active species, thus the authors concluded that the "pressure gap" was bridged [9,10]. The observed deactivation behavior, especially under net-oxidizing conditions, was attributed to the formation of the completely inactive RuO 2 (100)-c(2x2) surface [10,11].…”

“…Again, the cus-oxygen was suggested as the active species, thus the authors concluded that the "pressure gap" was bridged [9,10]. The observed deactivation behavior, especially under net-oxidizing conditions, was attributed to the formation of the completely inactive RuO 2 (100)-c(2x2) surface [10,11]. 3.…”

Growth and thermal oxidation of Ru and ZrO2 thin films as oxidation protective layers

“…This side corresponds to (110) crystal plane, taking into account the rutile-like structure of the oxide. For this structure, (110) surface has the lowest energy, 324 which explains why it is the most abundant surface of the observed columns.…”