Addition of Fe to Ni- and Co-based (oxy)hydroxides has been shown to enhance the activity of these materials for electrochemical oxygen evolution. Here we show that Fe cations bound to the surface of oxidized Au exhibit enhanced oxygen evolution reaction (OER) activity. We find that the OER activity increases with increasing surface concentration of Fe. Density functional theory analysis of the OER energetics reveals that oxygen evolution over Fe cations bound to a hydroxyl-terminated oxidized Au (Fe–Au₂O₃) occurs at an overpotential ∼0.3 V lower than over hydroxylated Au₂O₃ (0.82 V). This finding agrees well with experimental observations and is a consequence of the more optimal binding energetics of OER reaction intermediates at Fe cations bound to the surface of Au₂O₃. These findings suggest that the enhanced OER activity reported recently upon low-potential cycling of Au may be due to surface Fe impurities rather than to “superactive” Au^III surfaquo species.

Aviation fuel (i.e., jet fuel) requires a mixture of C₉–C₁₆ hydrocarbons having both a high energy density and a low freezing point. While jet fuel is currently produced from petroleum, increasing concern with the release of CO₂ into the atmosphere from the combustion of petroleum-based fuels has led to policy changes mandating the inclusion of biomass-based fuels into the fuel pool. Here we report a novel way to produce a mixture of branched cyclohexane derivatives in very high yield (>94 %) that match or exceed many required properties of jet fuel. As starting materials, we use a mixture of n-alkyl methyl ketones and their derivatives obtained from biomass. These synthons are condensed into trimers via base-catalyzed aldol condensation and Michael addition. Hydrodeoxygenation of these products yields mixtures of C₁₂–C₂₁ branched, cyclic alkanes. Using models for predicting the carbon number distribution obtained from a mixture of n-alkyl methyl ketones and for predicting the boiling point distribution of the final mixture of cyclic alkanes, we show that it is possible to define the mixture of synthons that will closely reproduce the distillation curve of traditional jet fuel.

Gold nanoparticles (NPs) supported on hydrotalcite (Au/HT) are highly active and selective catalysts for the continuous, gas-phase, non-oxidative dehydrogenation of bioderived C₂–C₄ alcohols. A sharp increase in turn over frequency (TOF) is noted when the size of Au NPs is less than 5 nm relating to the strong synergy between metallic Au NPs and the acid–base groups on the support surface. It is shown that catalytic activity depends critically on Au NP size, support composition, and support pretreatments. A reaction pathway elucidated from kinetic isotope effects suggests that the abstraction of β-H by Au NPs (C−H activation) is the rate-determining step in the dehydrogenation of bioderived C₂–C₄ alcohols.

The catalytic activity of secondary amines supported on mesoporous silica for the self-condensation of n-butanal to 2-ethylhexenal can be altered significantly by controlling the Brønsted acidity of MOH species present on the surface of the support. In this study, MOH (M=Sn, Zr, Ti, and Al) groups were doped onto the surface of SBA-15, a mesoporous silica, prior to grafting secondary propyl amine groups on to the support surface. The catalytic activity was found to depend critically on the synthesis procedure, the nature and amount of metal species introduced and the spatial separation between the acidic sites and amine groups. DFT analysis of the reaction pathway indicates that, for weak Brønsted acid groups, such as SiOH, the rate-limiting step is CC bond formation, whereas for stronger Brønsted acid groups, such as Ti and Al, hydrolysis of iminium species produced upon CC bond formation is the rate-limiting step. Theoretical analysis shows further that the apparent activation energy decreases with increasing Brønsted acidity of the MOH groups, consistent with experimental observation.

Invited for this month′s cover is the group of Alexis T. Bell at The University of California, Berkeley in Berkeley, California. The image shows the utility of gold nanoparticles deposited on hydrotalcite (Au/HT) for the continuous gas-phase non- oxidative dehydrogenation reaction of bioderived C₂–C₄ alcohols to the respective carbonyl compounds and hydrogen. The Communication itself is available at 10.1002/cssc.201500786.

In this study, we demonstrate that while the energy density and lubricity of the C₁₅ and C₁₆ products of furan condensation of biomass-derived aldehydes with 2-methylfuran are consistent with requirements for diesel, these products do not meet specifications for cetane number and pour point due to their aromatic furan rings. However, a novel class of products that fully meet or exceed most specifications for diesel can be produced by converting the furan rings in these compounds to cyclic ether moieties. Full hydrodeoxygenation of furan condensation products to alkanes would require 55–60 % higher hydrogen demand, starting from biomass, compared to the products of furan ring saturation, providing an additional incentive to support the saturated products. We also report here on a tunable class of catalysts that contain Pd nanoparticles supported on ionic liquid-modified SiO₂ that can achieve complete saturation of the furan rings in yields of 95 % without opening these rings.

A highly efficient solid-base organocatalyst for the gas-phase aldol self-condensation of n-butanal to 2-ethylhexenal was developed by grafting site-isolated amines on tailored silica surfaces. The catalytic activity depends largely on the nature of amine species, the surface concentration of amine and silanol groups, and the spatial separation between the silanol and amine groups. In situ FTIR measurements demonstrated that the formation of nucleophilic enamines leads to the enhanced catalytic activity of secondary amine catalysts, whereas the formation of imines (stable up to 473 K) leads to the low activity observed for silica-supported primary amines. Blocking the silanol groups on the silica support by silylation or cofeeding water into the reaction stream drastically decreased the reaction rates, demonstrating that weaker acidic silanol groups participate cooperatively with the amine groups to catalyze the condensation reaction. This work demonstrates that the spatial separation of the weakly acidic silanols and amines can be tuned by the controlled dehydration of the supporting silica and by varying the linker length of the amine organosilane precursor used to graft the amine to the support surface. A mechanism for aldol condensation was proposed and then analyzed by DFT calculations. DFT analysis of the reaction pathway suggested that the rate-limiting step in aldol condensation is carboncarbon bond formation, which is consistent with the observed kinetics. The calculated apparent activation barrier agrees reasonably with that measured experimentally.

Supported Co is an effective catalyst for the Fischer–Tropsch synthesis of various hydrocarbon products that can be converted to diesel. Recent studies have shown that the formation of methane can be suppressed and the formation of C₅₊ products enhanced by promoting Co with Mn. Because the activity and product selectivity of Co-based catalysts are dependent on the size of Co nanoparticles and the extent of Co promotion by Mn, it is desirable to understand these effects by investigating the performance of Co nanoparticles with well-defined size and elemental composition. The present study was undertaken with the aim of producing well-defined nanoparticles of Co and Co–Mn and then supporting them on silica. Co and Co–Mn particles were synthesized through the polyol reduction of Co and Mn acetylacetonates. By controlling synthesis conditions, Co particles with diameters of 7–10 nm and similarly sized Co–Mn (Mn/Co=0.1) particles were prepared. XRD and elemental mapping with scanning TEM-energy-dispersive X-ray spectroscopy and scanning TEM-electron energy loss spectroscopy studies suggested that most of the Mn species was associated with the Co particles. Ex situ prepared Co and Co–Mn nanoparticles were first supported on silica and then investigated for the catalytic activity for the Fischer–Tropsch synthesis. The turnover frequencies and product distributions obtained with silica-supported Co and Co–Mn nanoparticles were similar to those obtained with catalysts prepared by using the conventional incipient wetness impregnation method. However, the rate of CO consumption per mass of Co was much lower for the catalysts produced by supporting ex situ prepared nanoparticles. This effect was attributed to the sintering of the nanoparticles during their calcination and reduction. Magnetic interactions among nanoparticles during their immobilization and thermal pretreatment were identified as the primary cause of sintering.

A series of alkali metal or alkaline earth-exchanged NiX (X=faujasite zeolite, Si/Al=1.2) zeolites containing approximately 0.6 wt % Ni as Ni²⁺ cations were examined as catalysts for propene oligomerization at 453 K and 5 bar (500 kPa). In the presence of propene, the activity of alkali metal-exchanged zeolites (NiLiX, NiNaX, and NiKX) increased with time on stream, reached a maximum, then decreased, and finally reached steady state. In contrast, the activity of alkaline earth-exchanged zeolites (NiMgX, NiCaX, and NiSrX) was high initially and then decreased until steady-state activity was achieved. The primary product formed in all cases was hexene (90 %), and nonene was the only other product observed (10 %). Both the rate of propene dimerization and the ratio of branched to linear hexene isomers were determined to depend on the identity of the charge-compensating cation, with the dimerization rate and degree of dimer branching increasing with increasing free volume in the zeolite supercages. The apparent activation energy for trimer formation was greater than that for dimer formation, which suggests that steric constraints imposed by the zeolite may inhibit the growth of larger oligomers.

An investigation was carried out into the hydrolysis of cellulose dissolved in 1-ethyl-3-methylimidazolium chloride ([Emim][Cl]) and 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) catalyzed by mineral acids. Glucose, cellobiose, and 5-hydroxymethylfurfural (5-HMF) were observed as the primary reaction products. The initial rate of glucose formation was determined to be of first order in the concentrations of dissolved glucan and protons and of zero order in the concentration of water. The absence of a dependence on water concentration suggests that cleavage of the β-1,4-glycosidic linkages near chain ends is irreversible. The apparent activation energy for glucose formation is 96 kJ mol⁻¹. The absence of oligosaccharides longer than cellobiose suggests that cleavage of interior glycosidic bonds is reversible due to the slow diffusional separation of cleaved chains in the highly viscous glucan/ionic liquid solution. Progressive addition of water during the course of glucan hydrolysis inhibited the rate of glucose dehydration to 5-HMF and the formation of humins. The inhibition of glucose dehydration is attributed to stronger interaction of protons with water than the 2-OH atom of the pyranose ring of glucose, the critical step in the proposed mechanism for the formation of 5-HMF. The reduction in humin formation associated with water addition is ascribed to the lowered concentration of 5-HMF, since the formation of humins is suggested to proceed through the condensation polymerization of 5-HMF with glucose.