New environmentally friendly catalysts containing Pd-interstitial carbon made from Pd-glucose precursors for ultraselective hydrogenations in the liquid phase.

We report a novel preparation of a Pd nanocatalyst modified with subsurface C via blending a glucose precursor at the molecular level: the catalyst is demonstrated for the first time to be stereoselective in the hydrogenation of alkynes to cis-alkenes in the liquid phase.

Geometric and electronic effects on hydrogenation of cinnamaldehyde over unsupported Pt-based nanocrystals.

It is reported that catalytic hydrogenation of cinnamaldehyde to cinnamyl alcohol is a structural sensitive reaction dependent on size and type of metal doper of unsupported platinum nanocrystals used. Smaller sizes of platinum nanocrystals are found to give lower selectivity to cinnamyl alcohol, which suggests the high index Pt sites are undesirable for the terminal aldehyde hydrogenation. A plot of reaction selectivity across the first row of transition metals as dopers gives a typical volcano shape curve, the apex of which depicts that a small level of cobalt on platinum nanocrystals can greatly promote the reaction selectivity. The selectivity towards cinnamyl alcohol over the cobalt doped Pt nanocrystals can reach over 99.7%, following the optimization in reaction conditions such as temperature, pressure and substrate concentration. Detailed studies of XRD, CO chemisorption (for FTIR), TEM, SEM, AES and XPS of the nanostructure catalyst clearly reveal that the decorated cobalt atoms not only block the high index sites of Pt nanocrystals (sites for Co deposition) but also exert a strong electronic influence on reaction pathways. The d-band centre theory is invoked to explain the volcano plot of selectivity versus metal doper.

Engineering preformed cobalt-doped platinum nanocatalysts for ultraselective hydrogenation.

Bimetallic heterostructures are used as industrial catalysts for many important transformations. However, conventional catalysts are primarily prepared in cost-effective manners without much appreciation in metal size control and metal-metal interaction. By employing recent nanotechnology, Pt nanocrystals with tailored sizes can be decorated with Co atoms in a controlled manner in colloid solution as preformed nanocatalysts before they are applied on support materials. Thus, we show that the terminal CO hydrogenation can be achieved in high activity, while the undesirable hydrogenation of the CC group can be totally suppressed in the selective hydrogenation of alpha,beta-unsaturated aldehydes to unsaturated alcohols, when Co decorated Pt nanocrystals within a critical size range are used. This is achieved through blockage of unselective low coordination sites and the optimization in electronic influence of the Pt nanoparticle of appropriate size by the Co decoration. This work clearly demonstrates the advantage in engineering preformed nanoparticles via a bottom-up construction and illustrates that this route of catalyst design may lead to improved catalytic processes.