Theodore R. Krause

Experimental assessment of a combined plasma/catalytic system for hydrogen production via partial oxidation of hydrocarbon fuels

A combined reformation system, which includes both auto-thermal catalytic and non-equilibrium plasma units, is studied experimentally. The system is assessed for the practical application of hydrogen production via reforming of liquid gasoline-like fuels. The catalyst has been previously used for reforming of different types of hydrocarbons, demonstrating good performances in terms of hydrogen production for temperatures as high as 800°C. In this work, a non-equilibrium plasma source is coupled to the catalytic unit. A pulsed corona reactor is used as a non-equilibrium plasma source at atmospheric pressure. The performances of combined reformation system are characterized experimentally in terms of hydrogen yield and electric power consumption. Hydrogen conversion and byproduct composition are determined and quantified with respect to power consumption, reactor temperature, input reactant composition, and configuration of the experimental setup.

Discovery of Highly Selective Alkyne Semihydrogenation Catalysts Based on First‐Row Transition‐Metallated Porous Organic Polymers

Five different first-row transition metal precursors (V(III), Cr(III), Mn(II), Co(II), Ni(II)) were successfully incorporated into a catechol porous organic polymer (POP) and characterized using ATR-IR and XAS analysis. The resulting metallated POPs were then evaluated for catalytic alkyne hydrogenation using high-throughput screening techniques. All POPs were unexpectedly found to be active and selective catalysts for alkyne semihydrogenation. Three of the metallated POPs (V, Cr, Mn) are the first of their kind to be active single-site hydrogenation catalysts. These results highlight the advantages of using a POP platform to develop new catalysts which are otherwise difficult to achieve through traditional heterogeneous and homogeneous routes.

Organometallic model complexes elucidate the active gallium species in alkane dehydrogenation catalysts based on ligand effects in Ga K-edge XANES

Gallium-modified zeolites are known catalysts for the dehydrogenation of alkanes, reactivity that finds industrial application in the aromatization of light alkanes by Ga-ZSM5. While the role of gallium cations in alkane activation is well known, the oxidation state and coordination environment of gallium under reaction conditions has been the subject of debate. Edge shifts in Ga K-edge XANES spectra acquired under reaction conditions have long been interpreted as evidence for reduction of Ga(III) to Ga(I). However, a change in oxidation state is not the only factor that can give rise to a change in the XANES spectrum. In order to better understand the XANES spectra of working catalysts, we have synthesized a series of molecular model compounds and grafted surface organometallic Ga species and compared their XANES spectra to those of gallium-based catalysts acquired under reducing conditions. We demonstrate that changes in the identity and number of gallium nearest neighbors can give rise to changes in XANES spectra similar to those attributed in literature to changes in oxidation state. Specifically, spectral features previously attributed to Ga(I) may be equally well interpreted as evidence for low-coordinate Ga(III) alkyl or hydride species. These findings apply both to gallium-impregnated zeolite catalysts and to silica-supported single site gallium catalysts, the latter of which is found to be active and selective for dehydrogenation of propane and hydrogenation of propylene.

On the Optimal On-Line Management of Photovoltaic-Hydrogen Hybrid Energy Systems

We present an on-line management strategy for photovoltaic-hydrogen (PV-H2) hybrid energy systems. The strategy follows a receding-horizon principle and exploits solar radiation forecasts and statistics generated through a Gaussian process model. We demonstrate that incorporating forecast information can dramatically improve the reliability and economic performance of these promising energy production devices.

COMPARATIVE ENERGY BARRIERS FOR HYDROGEN ACTIVATION BY HOMOGENEOUS AND HETEROGENEOUS METAL OXIDE CATALYSTS

Triethylene glycol solutions of alkali and alkaline earth metal hydroxide complexes are well-defined soluble oxide water-gas shift catalysts which equilibrate the reaction of carbon monoxide and water to yield hydrogen and carbon dioxide at temperatures ranging from 150 ° to 250 °C and carbon monoxide pressures of 1 to 300 atm. Significantly, catalysis proceeds cleanly, even in the complete absence of a metal center in the soluble oxide system. Thus, the rate of hydroxide ion catalyzed hydrogen evolution is highest in the presence of a noncoordinating organic cation: BuΔN+>Cs+>Na+>H+>Ca+2. Furthermore, the activation energy for the homogeneous sodium hydroxide catalyst in triethylene glycol solution, 26±1 kcal, is comparable to that exhibited by a commercially used heterogeneous iron oxide catalyst, 27±0.2 kcal. The alkali metal hydroxide system may be modified for metal cocatalysis. Thus, lead (II) oxide dissolves in the triethylene glycol solutions to yield a new species which exhibits a207Pb NMR resonance shifted 3350 ppm downfield from lead perchlorate. The activity of this lead modified system is improved by three orders of magnitude. Yet, the activation energy is unchanged, 26±1 kcal, suggesting that entropic factors may be important in these homogeneous metal oxide hydrogen evolution/activation systems.

Fuel Processing for Mobile Fuel Cell Systems

Fuel cells may in the future compete with heat engines in automobiles and motor generators and with batteries in portable electronics. Hydrogen, either in compressed, cryogenic, or chemically stored form is a good fuel if the storage density can be improved. Alternatively, the hydrogen could be obtained by converting gasoline, alcohols or other liquid hydrocarbons into a hydrogen-rich gas in a fuel processor that is a component of the fuel cell system. Such processors will have to be small, light, and inexpensive, and will have to have rapid ramp-up and ramp-down capabilities to follow the power demands of the applications. Traditional steam reforming technology does not meet these requirements, but newly developed catalytic auto-thermal reformers do. The principles of operation and the status of the technology are discussed.Copyright

In situ S/TEM Reduction Reaction of Calcined Cu/BEA-zeolite Catalyst

Zeolite-catalyzed processes represent promising approaches to convert C1 species (e.g., methanol, dimethyl ether (DME)) from syngas into targeted classes of high-value fuels and chemicals. H-BEA, large pore acidic zeolites, can be used to convert methanol and/or DME to branched C4–C7 alkanes with high selectivity to isobutane and 2,2,3-Trimethylbutane [1,2]. Recent research has demonstrated that the addition of Cu to the BEA zeolite catalyst can further improve hydrocarbon productivity by incorporation of co-fed H2 into the desired products [3]. Advanced catalyst synthesis coupled with advanced characterization are key to advancing catalyst research and development; thus, to better understand the mechanism of Cu species incorporation into the BEA zeolite, high-resolution and in situ scanning transmission electron microscopy (S/TEM) are being used to provide insight.

Distributed Reforming of Diesel, JP-8, and Other Heavy Hydrocarbon Fuels for Fuel Cell Applications: Challenges and Issues

Reforming diesel, JP-8 (Jet Propellant 8 – standard U.S. military kerosene-based jet fuel), and other heavy hydrocarbon fuels is one option being investigated for providing H2 for distributed mobile and stationary fuel cell systems for military and civilian applications. Unlike natural gas, which is another hydrocarbon fuel being investigated, these fuels are high-boiling-point, multi-component liquids that contain high concentrations of refractory sulfur and aromatic compounds that can negatively impact the efficiency and operating lifetime of the fuel processor. Fuel injection, desulfurization, and carbon deposition are major issues that fuel processor developers must address when designing fuel processors for these fuels. The fuel injection system must prevent direct injection of liquid onto the catalyst surface and poor mixing of the fuel and oxidants (i.e., air and/or steam), both of which can result in excessively high temperatures that can damage or destroy the reforming catalyst. A highly efficient desulfurization process is required that can reduce the sulfur concentration to acceptable levels for both fuel processor and fuel cell catalysts without requiring large amounts of materials or complicated processes, and without generating excessive amounts of disposable waste. Highly active reforming catalysts and the proper choice of operating conditions (i.e., ratio of fuel to oxidant[s], temperature, residence time) are required for effective reforming of aromatic compounds to prevent carbon deposition on the reforming catalyst as well as in the fuel processor downstream of the reformer. In this paper, we will discuss how the chemical and physical properties of these fuels influence the design of the fuel processor focusing on the fuel injection system, the choice of desulfurization process, and the design and operation of the reformer. We will also discuss various approaches and design options for developing highly efficient fuel processors for reforming these fuels for both polymer electrolyte and solid oxide fuel cells.Copyright