T.Yu. Kardash

Metal–support interaction in Pd/CeO2 model catalysts for CO oxidation: from pulsed laser-ablated nanoparticles to highly active state of the catalyst

Palladium and cerium oxide nanoparticles obtained by pulsed laser ablation (PLA) in liquid (water or ethanol) have been used as nanostructured precursors for the synthesis of composite Pd/CeO2 catalysts. The initial mixture of Pd and CeO2 nanoparticles does not show catalytic activity at temperatures lower than 100 °C. It has been found that the composites prepared by PLA in alcohol are easily activated by calcination in air at 450–600 °C, demonstrating a high level of activity at room temperature. Application of XRD, TEM and XPS reveals that laser ablation in water leads to the formation of large and well-crystallized nanoparticles of palladium and CeO2, whereas ablation in alcohol results in the formation of much smaller PdCx nanoparticles. The activation of the composites takes place due to the strong Pd–ceria interaction which occurs more easily for highly dispersed defective particles obtained in alcohol. Such an interaction implies the introduction of palladium ions into the ceria lattice with the formation of a mixed phase of PdxCe1−xO2−x−δ solid solution at the contact spaces of palladium and cerium oxide nanoparticles. TPR-CO and XPS data show clearly that on the surface of the PdxCe1−xO2−x−δ solid solution the oxidized PdOx(s)/Pd–O–Ce(s) clusters are formed. These clusters are composed of highly reactive oxygen which is responsible for the high level of catalytic activity in LTO CO.

Formation of active component of MoVTeNb oxide catalyst for selective oxidation and ammoxidation of propane and ethane

Abstract The effect of slurry pH on the formation of active component of MoVTeNbO catalyst for selective (amm)oxidation of ethane and propane has been studied. pH affects the nature and composition of the crude and dry precursors as well as chemical and phase composition of the final catalyst. The most effective catalyst is prepared at pH = 3.0, which is characterized by a maximum content of M1 phase.

Enhanced Thermal Stability of Pd/Ce–Sn–O Catalysts for CO Oxidation Prepared by Plasma-Arc Synthesis

The plasma-arc (PA) method was applied for the highly efficient synthesis of Pd/Ce–Sn–O catalysts for CO oxidation. Using the PA sputtering of a graphite electrode together with Pd, Ce and Sn metallic components in inert atmosphere, a PdCeSnC composite was obtained. After the subsequent calcination in oxygen over the temperature range of 600–1000 °C, the initial composites were transformed into active catalysts of CO oxidation at low temperatures (LTO CO). Catalytic testing showed that these PA-prepared Pd/Ce–Sn–O catalysts were characterized by unusually high thermal stability. The catalysts demonstrated the excellent LTO CO performance after calcination at 1000 °C. According to the XRD and HRTEM observations, the Pd/Ce–Sn–O catalysts can be described as heterogeneous structures consisting of small CeO2 and SnO2 particles that interact with each other, forming extended grain boundaries and a composite structure. The TPR-CO and XPS methods detected highly dispersed Pd species in the active catalysts, namely Pd2+ in the lattice of ceria (a Pd-ceria solid solution) and the PdOx clusters on the surface. Deactivation of the Pd/Ce–Sn–O is governed by decomposition of the Pd-ceria solid solution accompanied by the sintering of the PdOx clusters and formation of the metallic and oxide palladium nanoparticles. Oxygen species with high mobility in the Pd/Ce–Sn–O catalyst were detected by a TPR-CO method. The amount of the highly mobile oxygen species is in five times higher for the Pd/Ce–Sn–O catalyst then for the Pd/CeO2 sample. Promising perspectives of the plasma-arc application for catalyst the synthesis of with improved properties are discussed.