William Tumas

Figures-of-merit for the technical development and application of advanced oxidation technologies for both electric- and solar-driven systems (IUPAC Technical Report)

Advanced oxidation technologies (AOTs), which involve the in situ generation of highly potent chemical oxidants, such as the hydroxyl radical (áOH), have emerged as an important class of technologies for accelerating the oxidation (and hence removal) of a wide range of organic contaminants in polluted water and air. In this report, standard figures-of-merit are proposed for the comparison and evaluation of these waste treatment technologies. These figures-of-merit are based on electric-energy consumption (for electric-energy-driven systems) or collector area (for solar-energy-driven systems). They fit within two phenomenological kinetic order regimes: 1) for high contaminant concentrations (electric energy per mass, EEM, or collector area per mass, ACM) and 2) for low concentrations (electric energy per order of magnitude, EEO, or collector area per order of magnitude, ACO). Furthermore, a simple understanding of the overall kinetic behavior of organic contaminant removal in a waste stream (i.e., whether zero- or first-order) is shown to be necessary for the description of meaningful electric- or solar-energy efficiencies. These standard figures-of-merit provide a direct link to the electric- or solar-energy efficiency (lower values mean higher efficiency) of an advanced oxidation technology, independent of the nature of the system, and therefore allow for direct comparison of widely disparate AOTs. These figures-of-merit are also shown to be inversely proportional to fundamental efficiency factors, such as the lamp efficiency (for electrical systems), the fraction of the emitted light that is absorbed in the aqueous solution, and the quantum yield of generation of active radicals.

Figures-of-Merit for the Technical Development and Application of Advanced Oxidation Processes

Abstract Advanced oxidation processes (AOPs), which involve the in-situ generation of highly potent chemical oxidants such as the hydroxyl radical (•OH), have recently emerged as an important class of technologies for accelerating the oxidation and hence destruction of a wide range of organic contaminants in polluted water and air. We propose generally applicable standard figures-of-merit for comparing these waste treatment technologies. These figures-of-merit are based on electrical energy consumption within two phenomenological kinetic order regimes: one for high contaminant concentrations (electrical energy per mass, EE/M) and one for low concentrations (electrical energy per order of magnitude per m3, EE/O). We also point out that a simple understanding of the overall kinetic behavior of organic destruction in a waste stream (i.e. whether zero or first order) is necessary for describing meaningful electrical efficiencies. These standard figures-of-merit provide a direct link to the electrical efficiency (lower values mean higher efficiency) of an advanced oxidation process, independent of the nature of the system and therefore allow for direct comparison of widely disparate AOP technologies. We have also shown that the EE/M and EE/O parameters are inversely proportional to fundamental efficiency factors, such as the lamp efficiency, the fraction of the emitted light flux that is absorbed in the water and the quantum yield of generation of active radicals.

Phase-separable catalysis using room temperature ionic liquids and supercritical carbon dioxide

A new phase-separable catalysis concept is demonstrated using nsupercritical carbon dioxide and the room temperature ionic liquid n1-butyl-3-methylimidazolium hexafluorophosphate for hydrogenation of nalkenes and carbon dioxide.

Metalloporphyrin-catalyzed homogeneous oxidation in supercritical carbon dioxide

We report results from a study of the reactivity of the halogenated porphyrins tetrakis(pentafluorophenyl)porphyrinato iron(III) chloride [Fe(TFPP)Cl] and β-octabromo-tetrakis(pentafluorophenyl)porphyrinato iron(III) chloride [Fe(TFPPBr8)Cl] with dioxygen and cyclohexene in supercritical carbon dioxide. A lower limit for the solubility of the iron porphyrins in sc CO2 was determined. Both halogenated metalloporphyrins were active catalysts for oxidation of cyclohexene to epoxide and allylic oxidation products in sc CO2. In 12 h at 80°C, up to 350 and 580 turnovers were observed for Fe(TFPP)Cl and Fe(TFPPBr8)Cl, respectively. We have also explored several organic solvent reactions at high temperature and pressure to benchmark relative activity and selectivity. Activity is higher in organic solvent, but accompanied by substantial oxidation of, or reaction with the solvent. Selectivity for epoxidation with Fe(TFPPBr8)Cl is higher in sc CO2 than in organic solvents, with up to 34% cyclohexene oxide produced.

C–H activation of a 2,2′-bipyridine ligand within (mono)pentamethylcyclopentadienyl lutetium complexes

We report the activation of a 2,2-bipyridine ligand within a class of (mono)cyclopentadienyl lanthanide complexes when reacted with carbon monoxide.

Hydrogen evolution from organic "hydrides".

Benzimidazolines (dihydrobenzimidazoles) are shown for the first time to eliminate hydrogen (H2) by catalyzed reaction with protic compounds.

Non-covalent immobilization of homogeneous cationicchiral rhodium–phosphine catalysts on silica surfaces

Non-covalent immobilization of n[(R,R)-Me-(DuPHOS)Rh(COD)]OTf by interaction of the ntriflate counter ion with surface silanols of silica supports leads to an nactive, stable, enantioselective, asymmetric hydrogenation catalyst.

Selective epoxidation in dense phase carbon dioxide

Selective epoxidations with transition metal catalysts (V, Ti, Mo) and ButOOH proceed with high conversions and high selectivity in dense phase carbon dioxide.

Heterogenization of Homogeneous Catalysts: the Effect of the Support

We have studied the influence of placing a soluble, homogeneous catalyst onto a solid support. We determined that such a heterogenized homogeneous catalyst can have improved activity and selectivity for the asymmetric hydrogenation of enamides to amino acid derivatives. The route of heterogenization of RhDuPhos(COD){sup +} cations occurs via electrostatic interactions with anions that are capable of strong hydrogen bonding to silica surfaces. This is a novel approach to supported catalysis. Supported RhDuPhos(COD){sup +} is a recyclable, non-leaching catalyst in non-polar media. This is one of the few heterogenized catalysts that exhibits improved catalytic performance as compared to its homogeneous analog.