We report the catalytic oxidation of cyclohexane to CO and CO2 over size-selected palladium clusters (PdN clusters, N = 10–120) supported on graphite as a function of cluster size. The stability of the pinned clusters (nanoparticles) under reaction conditions is investigated by scanning tunnelling microscopy measurement both before and after reaction. Temperature-programmed reaction experiments at 800 Torr show that the turnover rates (per surface Pd atom) for both CO and CO2 increase significantly as cluster size decreases and correlate with the number of Pd perimeter atoms at the graphite interface. Under oxygen-rich conditions, the activity of the clusters increases by a factor of 3 while the product ratio CO:CO2 rises by an order of magnitude. 相似文献
Benzaldehyde byproduct is an imperative intermediate in the production of fine chemicals and additives. Tuning selectivity to benzaldehyde is therefore critical in alcohol oxidation reactions at the industrial level. Herein, we report a simple but innovative method for the synthesis of palladium hydride and nickel palladium hydride nanodendrites with controllable morphology, high stability, and excellent catalytic activity. The synthesized dendrites can maintain the palladium hydride phase even after their use in the chosen catalytic reaction. Remarkably, the high surface area morphology and unique interaction between nickel-rich surface and palladium hydride (β-phase) of these nanodendrites are translated in an enhanced catalytic activity for benzyl alcohol oxidation reaction. Our Ni/PdH0.43 nanodendrites demonstrated a high selectivity towards benzaldehyde of about 92.0% with a conversion rate of 95.4%, showing higher catalytic selectivity than their PdH0.43 counterparts and commercial Pd/C. The present study opens the door for further exploration of metal/metal-hydride nanostructures as next-generation catalytic materials.
We study the catalytic capability of unsupported single-walled helical gold nanotubes Au(5,3) by using density functional theory. We use the CO oxidation as a benchmark probe to gain insights into high catalytic activity of the gold nanotubes. The CO oxidation, catalyzed by the Au(5,3) nanotube, proceeds via a two-step mechanism, CO + O2 --> CO2 +O and CO + O --> CO2. The CO oxidation is initiated by the CO + O2 --> OOCO --> CO2 + O reaction with an activation barrier of 0.29 eV. On the reaction path, a peroxo-type O-O-CO intermediate forms. Thereafter, the CO + O --> CO2 reaction proceeds along the reaction pathway with a very low barrier (0.03 eV). Note that the second reaction cannot be the starting point for the CO oxidation due to the energetically disfavored adsorption of free O2 on the gold nanotube. The high catalytic activity of the Au(5,3) nanotube can be attributed to the electronic resonance between electronic states of adsorbed intermediate species and Au atoms at the reaction site, particularly among the d states of Au atom and the antibonding 2pi* states of C-O and O1-O2, concomitant with a partial charge transfer. The presence of undercoordinated Au sites and the strain inherent in the helical gold nanotube also play important roles. Our study suggests that the CO oxidation catalyzed by the helical gold nanotubes is likely to occur at the room temperature. 相似文献
Bifunctional catalysts containing (0.5-1.5 wt%) palladium and 15 wt% of Nickel supported on gamma-Al2O3 were prepared via an impregnation technique and catalysts were characterzed by XRD BET surface area and SEM, respectively. The aqueous phase reforming of glycerol (APR) was conducted over alumina-supported catalysts at different reaction conditions for catalytic activity. Finally, we concluded that the 1.0 wt% Pd 15 wt% Ni/gamma-Al2O3 catalyst evidences higher conversion, hydrogen selectivity, lower alkane selectivity and CO production. This indicate that Pd loaded Ni/gamma-Al2O3 could be a potential catalyst for the APR of glycerol. 相似文献