Low-temperature redox activity and alcohol ammoxidation performance on Cu- and Ru-incorporated ceria catalysts.

Transition-metal-incorporated cerium oxides with Cu and a small amount of Ru (Cu0.18Ru0.05CeOz) were prepared, and their low-temperature redox performance (<423 K) and catalytic alcohol ammoxidation performance were investigated. Temperature-programmed reduction/oxidation under H2/O2 and in situ X-ray absorption fine structure revealed the reversible redox behavior of the three metals, Cu, Ru, and Ce, in the low-temperature redox processes. The initially reduced Ru species decreased the reduction temperature of Cu oxides and promoted the activation of Ce species. Cu0.18Ru0.05CeOz selectively catalyzed the production of benzonitrile in the ammoxidation of benzyl alcohol. H2-treated Cu0.18Ru0.05CeOz showed a slightly larger initial conversion of benzyl alcohol than O2-treated Cu0.18Ru0.05CeOz, suggesting that the reduced structure of Cu0.18Ru0.05CeOz was active for the ammoxidation. The integration of both Cu and Ru resulted in the efficient promotion of ammoxidation, in which the Ru species were involved in the conversion of benzyl alcohol and Cu species were required for selective production of benzonitrile.

Reversible low-temperature redox activity and selective oxidation catalysis derived from the concerted activation of multiple metal species on Cr and Rh-incorporated ceria catalysts.

The ceria-based catalyst incorporated with Cr and a trace amount of Rh (Cr0.19Rh0.06CeOz) was prepared and the reversible redox performances and oxidation catalysis of CO and alcohol derivatives with O2 at low temperatures (<373 K) were investigated. In situ X-ray absorption fine structure (XAFS), ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM)-EDS/EELS and temperature-programmed reduction/oxidation (TPR/TPO) revealed the structures and redox mechanisms of three metals in Cr0.19Rh0.06CeOz: dispersed Rh3+δ species (<1 nm) and Cr6-γO3-x nanoparticles (∼1 nm) supported on CeO2 in Cr0.19Rh0.06CeOz were transformed to Rh nanoclusters, Cr(OH)3 species and CeO2-x with two Ce3+-oxide layers at the surface in a concerted activation manner of the three metal species with H2.

Tuning the structure and catalytic activity of Ru nanoparticle catalysts by single 3d transition-metal atoms in Ru12-metalloporphyrin precursors.

Ru nanoparticle catalysts were prepared from Ru12-metalloporphyrin complex precursors containing 3d transition-metal atoms attached to SiO2 surfaces. The single 3d metal atoms at the central position of the Ru12-metalloporphyrin complex precursors exerted a significant influence on the structures and hydrogenation performance of the Ru nanoparticles on the SiO2 surfaces. The Ru12-Cu-porphyrin complex afforded positively charged Ru nanoparticles, which would provide high activity toward aromatic hydrogenation.

Molecular Adsorbates Switch on Heterogeneous Catalysis: Induction of Reactivity by N-Heterocyclic Carbenes.

We report the N-heterocyclic carbene (NHC)-induced activation of an otherwise unreactive Pd/Al2O3 catalyst. Surface analysis techniques demonstrate the NHC being coordinated to the palladium particles and affecting their electronic properties. Ab initio calculations provide further insight into the electronic effect of the coordination with the NHC injecting electron density into the metal nanocluster thus lowering the barrier for bromobenzene activation. By this NHC modification, the catalyst could be successfully applied in the Buchwald-Hartwig amination of aryl chlorides, bromides, and iodides. Various heterogeneity tests could additionally show that the reaction proceeds via a heterogeneous active species.