Ceria-supported Pd is a promising heterogeneous catalyst for CO oxidation relevant to environmental cleanup reactions. Pd loaded onto a nanorod form of ceria exposing predominantly (111) facets is already active at 50 °C. Here we report a combination of CO-FTIR spectroscopy and theoretical calculations that allows assigning different forms of Pd on the CeO2(111) surface during reaction conditions. Single Pd atoms stabilized in the form of PdO and PdO2 in a CO/O2 atmosphere participate in a catalytic cycle involving very low activation barriers for CO oxidation. The presence of single Pd atoms on the Pd/CeO2-nanorod, corroborated by aberration-corrected TEM and CO-FTIR spectroscopy, is considered pivotal to its high CO oxidation activity.

The evaluation of the stability of emerging earth-abundant metal phosphide electrocatalysts by solely electrochemical current–potential sweeps is often not conclusive. In this study, we investigated Co2P to evaluate its stability under both acidic (0.5 M H2SO4) and alkaline (1.0 M KOH) hydrogen evolution (HER) conditions. We found that the electrochemical surface area (ECSA) of Co2P only slightly increased in acidic conditions but almost doubled after electrolysis in alkaline electrolyte. The surface composition of the electrode remained almost unchanged in acid but was significantly altered in alkaline during current–potential sweeps. Analysis of the electrolytes after the stability test shows almost stoichiometric composition of Co and P in acid, but a preferential dissolution of P over Co could be observed in alkaline electrolyte. Applying comprehensive postcatalysis analysis of both the electrode and electrolyte, we conclude that Co2P, prepared by thermal phosphidization, dissolves stoichiometrically in acid and degrades to hydroxides under alkaline stability testing.

Catalyst stability in the liquid phase under polar conditions, typically required for the catalytic conversion of renewable platform molecules, is a major concern but has been only sparsely studied. Here, the activity, selectivity, and stability of Ru-based catalysts supported on TiO2, ZrO2, and C in the conversion of levulinic acid (LA) to γ-valerolactone (GVL) has been studied at 30 bar of H2 and 423 K in dioxane as solvent. All catalysts showed excellent yields of GVL when used fresh, but only the Ru/ZrO2 catalyst could maintain these high yields upon multiple recycling. Surprisingly, the widely used Ru/TiO2 catalyst showed quick signs of deactivation already after the first catalytic test. XPS, CO/FT-IR, TGA, AC-STEM, and physisorption data showed that the partial deactivation is not due to Ru sintering or coking but rather due to reduction of the titania support in combination with partial coverage of the Ru nanoparticles, i.e. due to a detrimental strong metal–support interaction. In contrast, the zirconia support showed no signs of reduction and displayed high morphological and structural stability even after five recycling tests. Remarkably, in the fresh Ru/ZrO2 catalyst, Ru was found to be fully atomically dispersed on the fresh catalyst even at 1 wt % Ru loading, with some genesis of Ru nanoparticles being observed upon recycling. Further studies with the Ru/ZrO2 catalyst showed that dioxane can be readily replaced by more benign solvents, including GVL itself. The addition of water to the reaction mixture was furthermore shown to promote the selective hydrogenation reaction.

Low-temperature controllable synthesis of monolayer-to-multilayer thick MoS2 with tuneable morphology is demonstrated by using plasma enhanced atomic layer deposition (PEALD). The characteristic self-limiting ALD growth with a growth-per-cycle of 0.1 nm per cycle and digital thickness control down to a monolayer are observed with excellent wafer scale uniformity. The as-deposited films are found to be polycrystalline in nature showing the signature Raman and photoluminescence signals for the mono-to-few layered regime. Furthermore, a transformation in film morphology from in-plane to out-of-plane orientation of the 2-dimensional layers as a function of growth temperature is observed. An extensive study based on high-resolution transmission electron microscopy is presented to unravel the nucleation mechanism of MoS2 on SiO2/Si substrates at 450 °C. In addition, a model elucidating the film morphology transformation (at 450 °C) is hypothesized. Finally, the out-of-plane oriented films are demonstrated to outperform the in-plane oriented films in the hydrogen evolution reaction for water splitting applications.

Ultrathin single-crystalline RuO 2 (110) films supported on Ru(0001) are employed as model electrodes to extract kinetic information about the industrially important chlorine evolution reaction (CER) in a 5M concentrated NaCl solution under well-defined electrochemical conditions and variable temperatures. A combination of chronoamperometry (CA) and online electrochemical mass spectrometry (OLEMS) experiments provides insight into the selectivity issue: At pH = 0.9, the CER dominates over oxygen evolution, whereas at pH = 3.5, oxygen evolution and other parasitic side reactions contribute mostly to the total current density. From temperaturedependent CA data for pH = 0.9, we determine the apparent free activation energy of the CER over RuO 2 (110) to be 0.91 eV, which compares reasonably well with the theoretical value of 0.79 eV derived from first-principles microkinetics. The experimentally determined apparent free activation energy of 0.91 eV is considered as a benchmark for assessing future improved theoretical modeling from first principles.