Frank S. Stone

Bio: Frank S. Stone is an academic researcher from University of Bath. The author has contributed to research in topics: Adsorption & Catalysis. The author has an hindex of 20, co-authored 56 publications receiving 1513 citations. Previous affiliations of Frank S. Stone include Sapienza University of Rome & Keele University.

Reflectance spectra of carbon monoxide adsorbed on alkaline earth oxides

Abstract: The adsorption of carbon monoxide at room temperature on well-outgassed specimens of MgO, CaO, SrO and BaO gives rise to a strong absorption spectrum between text-decoration:overlineν= 15000 and text-decoration:overlineν= 40000 cm–1. The stronger the outgassing conditions, the more intense is the absorption which can be developed.The spectrum consists of two main envelopes, one comprising absorption at text-decoration:overlineν= 29000–40000 cm–1 and the other, more composite in character, at text-decoration:overlineν= 15000–29000 cm–1. Changes in the CO pressure affect the two spectral regions differently, showing that two different kinds of adsorbed species are involved.The formation of the new spectrum as CO is dosed is accompanied by a simultaneous decrease in the absorption due to surface states (coordinatively unsaturated surface oxide ions). The effect on the oxide absorption is more pronounced with SrO and CaO than with MgO. The bulk states are unaffected, showing that the process is entirely a surface reaction.The results are interpreted as an electron donor process in which CO accepts electrons from surface oxide ions and forms anionic clusters in the adsorbed state. The high-text-decoration:overlineν absorption (ν > 29 000 cm–1) is ascribed to the dimer (CO)2–2, and the low-text-decoration:overlineν absorption to polymeric oxocarbon anions (CO)xn, where n > 2. The latter are considered to include cyclic, resonance-stabilized structures. The reactivity of the oxide towards CO increases with increase in basic character: on the MgO surface there are relatively few sites of sufficient donor potential to react with CO, but on the more strongly basic CaO and SrO the reaction is much more extensive.

Oxide solid solutions as catalysts

Abstract: This review traces the development of oxide solid solutions as catalysts from their first use in the 1960s to their current application in basic and applied research. Oxide solid solutions provide the means to control the properties of catalytically active ions in defined surface environments. When applied to transition metal (TM) ions, interaction with neighbors can be suppressed or progressively developed, depending on the concentration chosen for the active solute and the structure of the insulating matrix selected as solvent oxide. Simple examples are nickel, cobalt and chromium ions in MgO and MgAl 2 O 4 . The successful preparation of solid solutions demands a knowledge of the reactivity of solids and the behavior of crystal defects. This is exemplified in the methods described for preparing solid solutions of low and high specific surface area, respectively. Characterization receives detailed attention and the methods specific to oxide solid solutions are illustrated. Emphasis is placed on quantitative determination of surface composition for which X-ray photo-electron spectroscopy is the most widely applicable technique. The acidity and basicity of oxide solid solution surfaces is linked with coordinative unsaturation and this aspect of characterization involves adsorption calorimetry and infra-red spectroscopy. The account of oxide solid solutions as catalysts is divided into two parts. The first comprises studies where solid solutions have been used as model catalysts to identify and compare the catalytic properties of individual TM ions. For this purpose the catalysis of N 2 0 decomposition, CO oxidation and H 2 D 2 equilibration have long served as prototypical test reactions. These simple reactions enable issues such as the distinctive behavior of isolated ions, pairs and chains to be addressed and matrix effects to be explored. The motivation here is detailed understanding of catalysis on highly characterized microcrystalline oxides. The second catalytic part is broader in scope and focuses to a greater extent on the application of oxide solid solutions as catalysts for reactions of industrial interest. Combustion of hydrocarbons is a high-temperature reaction for which perovskite-structured solid solution catalysts are especially attractive since they accommodate a wide range of TM and main group ions in solid solution. A second sector covered is selective oxidation of hydrocarbons. Oxide solid solutions containing TM ions made an early entry as catalysts for alkene conversion and remained when interest switched to alkanes. The solid solution approach featured strongly in the search for methane coupling catalysts and currently contributes in a new guise in titanium silicalite. The acidity developed at solute sites is the source of activity for carbenium ion catalysis. SAPOs and McAPOs fall within the solid solution domain as covalently-bonded counterparts of ionic solid solutions. Finally, reduced solid solutions with phase-separated transition metal clusters are effective catalysts for reforming of alkanes.

Recent advances in catalytic hydrogenation of carbon dioxide

Abstract: Owing to the increasing emissions of carbon dioxide (CO2), human life and the ecological environment have been affected by global warming and climate changes. To mitigate the concentration of CO2 in the atmosphere various strategies have been implemented such as separation, storage, and utilization of CO2. Although it has been explored for many years, hydrogenation reaction, an important representative among chemical conversions of CO2, offers challenging opportunities for sustainable development in energy and the environment. Indeed, the hydrogenation of CO2 not only reduces the increasing CO2 buildup but also produces fuels and chemicals. In this critical review we discuss recent developments in this area, with emphases on catalytic reactivity, reactor innovation, and reaction mechanism. We also provide an overview regarding the challenges and opportunities for future research in the field (319 references).

Quantum Dot Solar Cells. Tuning Photoresponse through Size and Shape Control of CdSe−TiO2 Architecture

Abstract: Different-sized CdSe quantum dots have been assembled on TiO2 films composed of particle and nanotube morphologies using a bifunctional linker molecule. Upon band-gap excitation, CdSe quantum dots inject electrons into TiO2 nanoparticles and nanotubes, thus enabling the generation of photocurrent in a photoelectrochemical solar cell. The results presented in this study highlight two major findings: (i) ability to tune the photoelectrochemical response and photoconversion efficiency via size control of CdSe quantum dots and (ii) improvement in the photoconversion efficiency by facilitating the charge transport through TiO2 nanotube architecture. The maximum IPCE (photon-to-charge carrier generation efficiency) obtained with 3 nm diameter CdSe nanoparticles was 35% for particulate TiO2 and 45% for tubular TiO2 morphology. The maximum IPCE observed at the excitonic band increases with decreasing particle size, whereas the shift in the conduction band to more negative potentials increases the driving force and favors fast electron injection. The maximum power-conversion efficiency

Sustainable Conversion of Carbon Dioxide: An Integrated Review of Catalysis and Life Cycle Assessment

Abstract: CO2 conversion covers a wide range of possible application areas from fuels to bulk and commodity chemicals and even to specialty products with biological activity such as pharmaceuticals. In the present review, we discuss selected examples in these areas in a combined analysis of the state-of-the-art of synthetic methodologies and processes with their life cycle assessment. Thereby, we attempted to assess the potential to reduce the environmental footprint in these application fields relative to the current petrochemical value chain. This analysis and discussion differs significantly from a viewpoint on CO2 utilization as a measure for global CO2 mitigation. Whereas the latter focuses on reducing the end-of-pipe problem “CO2 emissions” from todays’ industries, the approach taken here tries to identify opportunities by exploiting a novel feedstock that avoids the utilization of fossil resource in transition toward more sustainable future production. Thus, the motivation to develop CO2-based chemistry does...

Heterogeneous catalytic decomposition of nitrous oxide

Abstract: An overview is given on the ongoing activities in the area of the decomposition of nitrous oxide, N2O, over solid catalysts. These catalysts include metals, pure and mixed oxides, supported as well as unsupported, and zeolitic systems. The review covers aspects of the reaction mechanism and kinetics, focusing on the role of surface oxygen, the inhibition by molecular oxygen, water and other species, poisoning phenomena and practical developments.