Jennifer D. Lee

Unraveling the surface state and composition of highly selective nanocrystalline Ni–Cu alloy catalysts for hydrodeoxygenation of HMF

The selective hydrodeoxygenation (HDO) of 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF) is an important step in cellulosic biomass upgrading to biofuels, where bimetallic oxophilic catalysts have shown promising performance. Well controlled bimetallic NiCu and NiCu3 nanocrystals supported on carbon are shown to give high yields and selectivities to DMF. To shed light on the active phase, near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) was used to characterize the surface composition of these highly selective base-metal catalysts under reducing conditions relevant to the HDO reaction. Reactions were performed in a continuous flow reactor under reasonable conditions of 33 bar and 180 °C. The Ni alloys were significantly more selective for DMF compared to monometallic Ni or Cu catalysts. With a well-controlled surface composition, the nanocrystal NiCu3/C catalyst exhibited a maximum DMF yield of 98.7%. NAP-XPS characterization showed that the Ni–Cu nanocrystals were completely reduced below 250 °C in H2; this, together with bulk thermodynamic calculations, implies that the catalysts were completely reduced under the reaction conditions. NAP-XPS also indicated that the NiCu3 nanocrystal structure consisted of a Cu-rich core and a 1 : 1 molar Ni : Cu shell.

A Study of Tetrahydrofurfuryl Alcohol to 1,5-Pentanediol Over Pt–WO x /C

The hydrogenolysis of tetrahydrofurfural alcohol to 1,5-pentanediol was studied over a series of carbon-supported metal/metal-oxide pairs. In agreement with previous reports, specific pairs, especially Pt and Ir paired with WOx, MoOx and ReOx, exhibited high activity and selectivity, even though the individual components were not active or selective. Only reducible oxides produced selective catalysts. A more comprehensive study of the Pt–WOx system indicated that the active form of the catalyst exists as a thin, submonolayer film of the oxide on the Pt surface. This film could be formed by atomic layer deposition (ALD) of W(CO)6 onto the Pt nanocrystals and STEM–EDS mapping demonstrated that ALD deposition occurred selectively on the Pt. When the catalyst was formed by impregnation of Pt and W salts, the WOx was mobile and able to move onto the Pt. The implications of these result for preparing selective catalysts are discussed.Graphical Abstract

Improved Chemical and Colloidal Stability of Gold Nanoparticles Through Dendron Capping

Nanoparticle (NP) stability is imperative for commercialization of nanotechnology. In this study, we compare the stability of Au NPs with surfaces functionalized with oleylamine, dodecanethiol, and two dendritic ligands of different generations. Dendrimer ligands provide a significant increase in the chemical stability of Au NPs when analyzed by cyanide-induced NP decomposition as well as an investigation into their colloidal stability at ambient conditions. These results were supported by absorption measurements, transmission electron microscopy, thermogravimetric analysis, nuclear magnetic resonance, and small-angle transmission X-ray scattering and show that dendrimers play a key role in improving the chemical and colloidal stability of NPs.