Troy A. Semelsberger

Potassium(I) amidotrihydroborate: structure and hydrogen release.

Potassium(I) amidotrihydroborate (KNH(2)BH(3)) is a newly developed potential hydrogen storage material representing a completely different structural motif within the alkali metal amidotrihydroborate group. Evolution of 6.5 wt % hydrogen starting at temperatures as low as 80 degrees C is observed and shows a significant change in the hydrogen release profile, as compared to the corresponding lithium and sodium compounds. Here we describe the synthesis, structure, and hydrogen release characteristics of KNH(2)BH(3).

Equilibrium products from autothermal processes for generating hydrogen-rich fuel-cell feeds

Abstract This work presents thermodynamic analyses of autothermal processes using five fuels—natural gas, methanol, ethanol, dimethyl ether, and gasoline. Autothermal processes combine exothermic and endothermic reactions. The processes considered here couple endothermic steam reforming with exothermic oxidation to create hydrogen-rich fuel-cell feeds. Of the fuels treated here, methanol, ethanol, and dimethyl ether are pure compounds. Methane simulates natural gas and a mixture of 7% neopentane, 56% 2,4 dimethyl pentane, 7% cyclohexane, 30% ethyl benzene simulates gasoline. In the computations, sufficient oxygen is fed so the energy generated by the oxidation exactly compensates the energy absorbed by the reforming reactions. The analyses calculate equilibrium product concentrations at temperatures from 300 to 1000 K , pressures from 1 to 5 atm , and water–fuel ratios from 1 to 9 times the stoichiometric value. The thermodynamic calculations in this work say that any of the five fuels, when processed autothermally, can give a product leading to a hydrogen-rich feed for fuel cells. The calculations also show that the oxygen-containing substances (methanol, ethanol, and dimethyl ether) require lower temperatures for effective processing than the non-oxygenated fuels (natural gas and gasoline). Lower reaction temperatures also promote products containing less carbon monoxide, a desirable effect. The presence of significant product CO mandates the choice of optimum conditions, not necessarily conditions that produce the maximum product hydrogen content. Using a simple optimum objective function shows that dimethyl ether has the greatest potential product content, followed by methanol, ethanol, gasoline, and natural gas. The calculations point the way toward rational choices of processes for producing fuel-cell feeds of the necessary quality.

Improved Hydrogen Release from Ammonia–Borane with ZIF-8

The promotion for hydrogen release from ammonia-borane (AB) was observed in the presence of ZIF-8. Even at concentrations of ZIF-8 as low as 0.25 mol %, a reduction of the onset temperature for dehydrogenation accompanies an increase in both the rate and amount of hydrogen released from AB.

The effect of functional groups in bio-derived fuel candidates

Interest in developing renewable fuels is continuing to grow and biomass represents a viable source of renewable carbon with which to replace fossil-based components in transportation fuels. During our own work, we noticed that chemists think in terms of functional groups whereas fuel engineers think in terms of physical fuel properties. In this Concept article, we discuss the effect of carbon and oxygen functional groups on potential fuel properties. This serves as a way of informing our own thinking and provides us with a basis with which to design and synthesize molecules from biomass that could provide useful transportation fuels.

Physical, structural, and dehydrogenation properties of ammonia borane in ionic liquids

Ionic liquids (ILs) are excellent solvents for the dehydrogenation of ammonia borane (AB); however, the basic properties that allow efficient dehydrogenation are still unclear. In this report, density, viscosity, melting/freezing/glass transition temperature, solubility, and the dehydrogenation properties, including impurity gas quantification, of AB-imidazolium-based IL solutions were studied. Note that ILs can solubilize 32–35 wt% of AB, and the liquid AB–IL solutions have densities of ∼0.9 g cm−3, viscosities similar to motor oil (100–250 cP), and glass transition temperatures below −50 °C. AB–ILs are stable at room temperature for several weeks with minimal hydrogen generation, although some hydrolysis occurs immediately upon mixing as a result of trace water content. Between 80 and 130 °C, more than 2 mol H2/AB are desorbed from AB–ILs with limited impurity emissions. Furthermore, there is no reaction between AB and ILs upon dehydrogenation, and structural analysis reveals a complex solid solution.

Enabling ammonia-borane: co-oligomerizaiton of ammonia-borane and amine-boranes yield liquid products

In contrast to neat ammonia-borane (AB), the thermal decomposition of AB with N-substituted amine-boranes yields a liquid product after extended heating and H2 release. NMR and GPC data indicate that co-oligomerization has occurred. These results show promise for developing high energy density AB-based fuel formulations for automotive applications.

Acetaldehyde as an ethanol derived bio-building block: an alternative to Guerbet chemistry

In this work, we describe a highly selective poly-aldol condensation of acetaldehyde, which can readily be obtained via dehydrogenation of ethanol. The process operates under mild temperatures (100 °C or less) using commercially available catalysts and exhibits excellent total carbon yield of C4+ products with good selectivity for C6 products. The products derived from the reactions described herein are shown to be candidate drop-in fuel replacements for compression ignition engines and precursors to valuable chemicals.

Heterogeneous Ketone Hydrodeoxygenation for the Production of Fuels and Feedstocks from Biomass

In this work, we describe a simple, heterogeneous catalytic system for the hydrodeoxygenation (HDO) of 5‐nonanone and 2,5‐hexanedione, which we use as model compounds for more complex biomass‐derived molecules. We present the stepwise reduction of ketones by using supported metal and solid acid catalysts to identify the intermediates en route to hydrocarbons. Although monoketone HDO can be achieved rapidly using moderate conditions (Ni/SiO2.Al2O3, HZSM‐5, 200 °C, 1.38 MPa H2, 1 h), quantitative γ‐polyketone HDO requires higher pressures and longer reaction times (Pd/Al2O3, HZSM‐5, 2.76 MPa H2, 5 h), although these are more facile conditions than have been reported previously for γ‐polyketone HDO. Stepwise HDO of the γ‐polyketone shows the reaction pathway occurs through ring‐closure to a saturated tetrahydrofuran species intermediate, which requires increased H2 pressure to ring‐open and subsequently to fully HDO. This work allows for further understanding of bio‐derived molecule defunctionalization mechanisms, and ultimately aids in the promotion of biomass as a feedstock for fuels and chemicals.

Synthesis of Acetone‐Derived C6, C9, and C12 Carbon Scaffolds for Chemical and Fuel Applications

A simple, inexpensive catalyst system (Amberlyst 15 and Ni/SiO2 -Al2 O3 ) is described for the upgrading of acetone to a range of chemicals and potential fuels. Stepwise hydrodeoxygenation of the produced ketones can yield branched alcohols, alkenes, and alkanes. An analysis of these products is provided, which demonstrates that this approach can provide a product profile of valuable bioproducts and potential biofuels.

A simple, solvent free method for transforming bio-derived aldehydes into cyclic acetals for renewable diesel fuels

The acetalization of 2,3-butanediol with bio-derived C4–8 aldehydes has yielded a route to substituted 1,3-dioxolanes from small bio-building blocks. The reported reaction system features excellent carbon yields (>93%), atom economy (>89%) and phase separation of the analytically pure product which eliminates elaborate purification processes and facilitates simple catalyst recycling. The 1,3-dioxolanes offer performance advantages over traditional diesel and have the potential to augment petroleum derived fuels.