William S. Willis

Bio: William S. Willis is an academic researcher from University of Connecticut. The author has contributed to research in topics: Catalysis & Hydrogen. The author has an hindex of 18, co-authored 48 publications receiving 1806 citations.

Electron transfer from electrodes to myoglobin: facilitated in surfactant films and blocked by adsorbed biomacromolecules.

Abstract: In previous work, greatly enhanced rates of electron transfer were found for myoglobin (Mb) in ordered films of surfactants on pyrolytic graphite (PG) electrodes. Direct electron transfer is now reported for Mb in films of didodecyldimethylammonium bromide (DDAB) on platinum, tin-doped indium oxide, and gold electrodes. Rates of electron transfer in these films were similar on all electrodes. In the absence of surfactant, electron transfer was observed on bare electrodes only when Mb was purified by chromatography, and only on hydrophilic tin-doped In 2 O 3 or PG. Treatment of tin-doped In 2 O 3 or PG electrodes with unpurified protein solutions blocked electron transfer to Mb in the purified solutions. Reflectance-absorbance infrared and X-ray photoelectron spectroscopy revealed proteinaceous adsorbates on electrodes exposed to unpurified solutions of Mb. This adsorbate blocks electron transfer to Mb and to ferricyanide in solution. Results suggest that electron transfer in the Mb-DDAB films may be facilitated partly by strong adsorption of surfactants on electrodes. Surfactant adsorbed at electrode-film interfaces appears to inhibit adsorption of macromolecules from Mb solutions which could otherwise block electron transfer between Mb and electrodes.

Pyrolytic decomposition of ammonia borane to boron nitride.

Abstract: The thermal decomposition of ammonia borane was studied using a variety of methods to qualitatively identify gas and remnant solid phase species after thermal treatments up to 1500 °C. At about 110 °C, ammonia borane begins to decompose yielding H2 as the major gas phase product. A two step decomposition process leading to a polymeric -[NH═BH]n- species above 130 °C is generally accepted. In this comprehensive study of decomposition pathways, we confirm the first two decomposition steps and identify a third process initiating at 1170 °C which leads to a semicrystalline hexagonal phase boron nitride. Thermogravimetric analysis (TGA) was used to identify the onset of the third step. Temperature programmed desorption-mass spectroscopy (TPD-MS) and vacuum line methods identify molecular aminoborane (H2N═BH2) as a species that can be released in appreciable quantities with the other major impurity, borazine. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was used to identify th...

Efficient Stable Catalysts for Low Temperature Carbon Monoxide Oxidation

Abstract: Octahedral molecular sieves (OMS), doped with Ag+, Co2+, and Cu2+, have been tested for their catalytic activity for carbon monoxide oxidation at low temperatures for long times on stream. Metal loaded OMS materials are highly active for this catalytic reaction and compare favorably with other catalysts such as Hopcalite-like CuMn2O4 catalysts, supported Ag catalysts, and supported noble-metal catalysts, especially with respect to resistance to deactivation in a long run. Co-doped OMS-2 has been tested for selective oxidation in the presence of a large surplus of hydrogen in the feed gas. This catalyst shows nearly exclusive oxidation of CO versus hydrogen with oxygen present in stoichiometric amounts with carbon monoxide. Its stability against reduction in CO or H2 containing gas is demonstrated from comparisons of X-ray diffraction patterns and X-ray photoelectron spectra before and after exposure to these gases. Average oxidation numbers and populations of Mn valence states were determined for these catalysts. Catalytic activity of doped OMS catalysts toward CO oxidation shows a correlation among average oxidation number of Mn and the position and nature of the doped cation. The structure of the active sites and the mechanism of the reaction are proposed.

Atomically dispersed Ni(i) as the active site for electrochemical CO2 reduction

Abstract: Electrochemical reduction of CO2 to chemical fuel offers a promising strategy for managing the global carbon balance, but presents challenges for chemistry due to the lack of effective electrocatalyst. Here we report atomically dispersed nickel on nitrogenated graphene as an efficient and durable electrocatalyst for CO2 reduction. Based on operando X-ray absorption and photoelectron spectroscopy measurements, the monovalent Ni(i) atomic center with a d9 electronic configuration was identified as the catalytically active site. The single-Ni-atom catalyst exhibits high intrinsic CO2 reduction activity, reaching a specific current of 350 A gcatalyst−1 and turnover frequency of 14,800 h−1 at a mild overpotential of 0.61 V for CO conversion with 97% Faradaic efficiency. The catalyst maintained 98% of its initial activity after 100 h of continuous reaction at CO formation current densities as high as 22 mA cm−2. Electrocatalysts with improved activity and stability for the conversion of CO2 to CO are being sought. Using operando spectroscopies, the authors identify atomically dispersed Ni(i) as the active site in a nitrogenated-graphene-supported catalyst with high intrinsic activity and stability over 100 hours.

A Multiplet Analysis of Fe K-Edge 1s → 3d Pre-Edge Features of Iron Complexes

Abstract: X-ray absorption Fe−K edge data on ferrous and ferric model complexes have been studied to establish a detailed understanding of the 1s → 3d pre-edge feature and its sensitivity to the electronic structure of the iron site. The energy position and splitting, and intensity distribution, of the pre-edge feature were found to vary systematically with spin state, oxidation state, geometry, and bridging ligation (for binuclear complexes). A methodology for interpreting the energy splitting and intensity distribution of the 1s → 3d pre-edge features was developed for high-spin ferrous and ferric complexes in octahedral, tetrahedral, and square pyramidal environments and low-spin ferrous and ferric complexes in octahedral environments. In each case, the allowable many-electron excited states were determined using ligand field theory. The energies of the excited states were calculated and compared to the energy splitting in the 1s → 3d pre-edge features. The relative intensities of electric quadrupole transitions...

Heterogeneous Catalyst Deactivation and Regeneration: A Review

Abstract: Deactivation of heterogeneous catalysts is a ubiquitous problem that causes loss of catalytic rate with time. This review on deactivation and regeneration of heterogeneous catalysts classifies deactivation by type (chemical, thermal, and mechanical) and by mechanism (poisoning, fouling, thermal degradation, vapor formation, vapor-solid and solid-solid reactions, and attrition/crushing). The key features and considerations for each of these deactivation types is reviewed in detail with reference to the latest literature reports in these areas. Two case studies on the deactivation mechanisms of catalysts used for cobalt Fischer-Tropsch and selective catalytic reduction are considered to provide additional depth in the topics of sintering, coking, poisoning, and fouling. Regeneration considerations and options are also briefly discussed for each deactivation mechanism.

Functionalization of Porous Carbon Materials with Designed Pore Architecture

Abstract: Recent progress in syntheses of porous carbons with designed pore architecture has rejuvenated the field of carbon chemistry and promises to provide new advanced materials. In order to reap the full benefit of designer carbons, it is necessary to develop chemistries for functionalizing the porous carbon surfaces. This Review examines methods of functionalizing porous carbon through direct incorporation of heteroatoms in the carbon synthesis, surface oxidation and activation, halogenation, sulfonation, grafting, attachment of nanoparticles and surface coating with polymers. Methods of characterizing the functionalized carbon materials and applications that benefit from functionalized nanoporous carbons with designed architecture are also highlighted.

Carbon nanotube electrode for oxidation of dopamine

Abstract: Carbon nanotube electrodes were constructed using bromoform as binder, and the oxidative behaviour of dopamine was examined at these electrodes. The two-electron oxidation of dopamine to dopaminequinone showed ideal reversibility in cyclic voltammetry, and was significantly superior to that observed at other carbon electrodes. The electrode treated with goat's brain tissue homogenate showed the same features as the untreated electrode. The results illustrate the potential of nanotube electrodes for in vitro and in vivo neurotransmitter investigations involving dopamine.