Anthony J. Crisci

Stabilization of Copper Catalysts for Liquid‐Phase Reactions by Atomic Layer Deposition

Atomic layer deposition (ALD) of an alumina overcoat can stabilize a base metal catalyst (e.g., copper) for liquid-phase catalytic reactions (e.g., hydrogenation of biomass-derived furfural in alcoholic solvents or water), thereby eliminating the deactivation of conventional catalysts by sintering and leaching. This method of catalyst stabilization alleviates the need to employ precious metals (e.g., platinum) in liquid-phase catalytic processing. The alumina overcoat initially covers the catalyst surface completely. By using solid state NMR spectroscopy, X-ray diffraction, and electron microscopy, it was shown that high temperature treatment opens porosity in the overcoat by forming crystallites of γ-Al2 O3 . Infrared spectroscopic measurements and scanning tunneling microscopy studies of trimethylaluminum ALD on copper show that the remarkable stability imparted to the nanoparticles arises from selective armoring of under-coordinated copper atoms on the nanoparticle surface.

A Tailored Microenvironment for Catalytic Biomass Conversion in Inorganic–Organic Nanoreactors†

The efficient and selective conversion of biomass-derived renewable feedstocks into chemicals and fuels remains a major techno-economic challenge. Fructose, a simple carbohydrate that can be obtained from cellulose, can be dehydrated to a potential platform chemical, 5-hydroxymethylfurfural (HMF). The selectivity for HMF is a function of the fructose tautomer distribution, which varies with solvent polarity and temperature. Near-quantitative conversion of fructose into HMF has only been obtained in non-aqueous, polar aprotic solvents (such as, DMSO or NMP), or in ionic liquids. However, HMF separation from such high-boiling and/or costly solvents is energy-intensive and lowers the yield, even when combined with immiscible, low-boiling solvents. Herein, we describe an organic–inorganic nanocomposite catalyst that converts fructose selectively (> 80 %) into HMF in a flow reactor, while eliminating separation issues and the need for environmentally unfriendly solvents. We obtain the highest reported HMF yields to date in a monophasic, readily separable solvent, avoiding the undesirable use of salts. Our previous studies of fructose dehydration to HMF employed silicas and organosilicas with pore-directed alkylsulfonic acid groups as heterogeneous catalysts. Ordered mesoporous silica-based catalysts were found to be more selective and robust than catalysts with similar chemical compositions but non-ordered pores. Upon incorporating bifunctional organosilanes containing both alkylsulfonic acid groups and thioether/sulfone groups to promote fructose tautomerization to the desired furanose tautomers, we observed further, modest selectivity improvements relative to propylsulfonic acid-functionalized silicas. We hypothesized that in order to achieve HMF selectivities comparable to those reported with homogeneous systems, the microenvironment throughout the pore channels (rather than just localized near the active sites) should promote fructose tautomerization. Soluble organic polymers have been reported to act as pseudo-solvents, encapsulating reactants in a local microenvironment that can be favorably tailored for catalysis. Furthermore, the pores of acid-functionalized ordered mesoporous materials (both silicas and organosilicas) are large enough to accommodate such macromolecules. Poly(vinylpyrrolidone) (PVP), a polar aprotic polymer, was intercalated by incipient wetness impregnation into the pores of unmodified SBA-15 silica (Scheme 1), as well as into