General insight into CO oxidation: A density functional theory study of the reaction mechanism on platinum oxides

CO oxidation on PtO2(110) has been studied using density functional theory calculations. Four possible reaction mechanisms were investigated and the most feasible one is the following: (i) the O at the bridge site of PtO2(110) reacts with CO on the coordinatively unsaturated site (CUS) with a negligible barrier; (ii) O-2 adsorbs on the bridge site and then interacts with CO on the CUS to form an OO-CO complex; (iii) the bond of O-OCO breaks to produce CO2 with a small barrier (0.01 eV). The CO oxidation mechanisms on metals and metal oxides are rationalized by a simple model: The O-surface bonding determines the reactivity on surfaces; it also determines whether the atomic or molecular mechanism is preferred. The reactivity on metal oxides is further found to be related to the 3rd ionization energy of the metal atom.

General trends in the barriers of catalytic reactions on transition metal surfaces

A catalyst preparation by design is one of the ultimate goals in chemistry. The first step towards this goal is to understand the origin of reaction barriers. In this study, we have investigated several catalytic reactions on some transition metal surfaces, using density functional theory. All the reaction barriers have been determined. By detailed analyses we obtain some insight into the reaction barrier. Each barrier is related to (i) the potential energy surface of reactants on the surface, (ii) the total chemisorption energy of reactants, and (iii) the metal d orbital occupancy and the reactant valency. (C) 2001 American Institute of Physics.

General trends in CO dissociation on transition metal surfaces

Dissociative adsorption is one of the most important reactions in catalysis. In this communication we propose a model aiming to generalize the important factors that affect dissociation reactions. Specifically, for a dissociation reaction, say AB -->A + B, the model connects the dissociation barrier with the association barrier, the chemisorption energies of A and B at the final state and the bonding energy of AB in the gas phase. To apply this model, we have calculated CO dissociation on Ru(0001), Rh(111), Pd(111) (4d transition metals), Os(0001), Ir(111), and Pt(111) (5d transition metals) using density function theory (DFT). All the barriers are determined. We find that the DFT results can be rationalized within the model. The model can also be used to explain many experimental observations. (C) 2001 American Institute of Physics.

Using the opinions of coronary heart disease patients in designing a health education booklet for use in general practice consultations.

Objective This study explored how coronary heart disease (CHD) patients’ views would inform the design of an information booklet aimed at providing patients and practitioners with a resource to help influence positively patients’ health behaviour outcomes. Methods Opinions of patients (N=23) with CHD about their information needs, particularly lifestyle advice, were explored using a qualitative approach in four general practices. This information was used in designing a booklet for a pilot study intervention aimed at promoting healthy lifestyle behaviours and medication adherence among people with CHD. Subsequent focus groups explored patients’ (N=17) opinions about the booklet’s ‘fitness for purpose’; semi-structured interviews with practitioners (N=10) examined their views on the booklet’s usefulness. Results In initial focus groups patients identified gaps in their information provision regarding coping with stress, available local community support and medication purpose. A booklet, prepared on the basis of previous literature, was modified to address these gaps. Pilot study patients were satisfied with the re-designed booklet and practitioners reported that its use in consultations enabled change implementation and facilitated patients’ understanding of connections between lifestyle and health outcomes. Conclusion Acknowledging the opinions of CHD patients in producing health information booklets which emphasised a patient centred approach supported practitioner-patient partnerships for choosing healthy lifestyle choices.

Radiotherapy in the presence of contrast agents: a general figure of merit and its application to gold nanoparticles

Delivering sufficient dose to tumours while sparing surrounding tissue is one of the primary challenges of radiotherapy, and in common practice this is typically achieved by using highly penetrating MV photon beams and spatially shaping dose. However, there has been a recent increase in interest in the possibility of using contrast agents with high atomic number to enhance the dose deposited in tumours when used in conjunction with kV x-rays, which see a significant increase in absorption due to the heavy element's high-photoelectric cross-section at such energies. Unfortunately, the introduction of such contrast agents significantly complicates the comparison of different source types for treatment efficacy, as the dose deposited now depends very strongly on the exact composition of the spectrum, making traditional metrics such as beam quality less valuable. To address this, a 'figure of merit' is proposed, which yields a value which enables the direct comparison of different source types for tumours at different depths inside a patient. This figure of merit is evaluated for a 15 MV LINAC source and two 150 kVp sources (both of which make use of a tungsten target, one with conventional aluminium filtration, while the other uses a more aggressive thorium filter) through analytical methods as well as numerical models, considering tissue treated with a realistic concentration and uptake ratio of gold nanoparticle contrast agents (10 mg ml(-1) concentration in 'tumour' volume, 10: 1 uptake ratio). Finally, a test case of human neck phantom is considered with a similar contrast agent to compare the abstract figure to a more realistic treatment situation. Good agreement was found both between the different approaches to calculate the figure of merit, and between the figure of merit and the effectiveness in a more realistic patient scenario. Together, these observations suggest that there is the potential for contrast-enhanced kilovoltage radiation to be a useful therapeutic tool for a number of classes of tumour on dosimetric considerations alone, and they point to the need for further research in this area.