The Critical Role of Water at the Gold-titania Interface in Catalytic CO Oxidation

We provide direct evidence of a water-mediated reaction mechanism for room-temperature CO oxidation over Au/TiO2 catalysts. A hydrogen/deuterium kinetic isotope effect of nearly 2 implicates O-H(D) bond breaking in the rate-determining step. Kinetics and in situ infrared spectroscopy experiments showed that the coverage of weakly adsorbed water on TiO2 largely determines catalyst activity by changing the number of active sites. Density functional theory calculations indicated that proton transfer at the metal-support interface facilitates O2 binding and activation; the resulting Au-OOH species readily reacts with adsorbed Au-CO, yielding Au-COOH. Au-COOH decomposition involves proton transfer to water and was suggested to be rate determining. These results provide a unified explanation to disparate literature results, clearly defining the mechanistic roles of water, support OH groups, and the metal-support interface

NaBr Poisoning of Au/TiO\u3csub\u3e2\u3c/sub\u3e Catalysts: Effects on Kinetics, Poisoning Mechanism, and Estimation of the Number of Catalytic Active Sites

Sodium bromide was used to intentionally poison a commercial Au/TiO2 catalyst with the goals of understanding the nature of halide poisoning and evaluating the number and nature of the catalytic active sites. A series of eight poisoned catalysts were prepared by impregnating the parent catalyst with methanolic solutions of NaBr. Each catalyst was tested with CO oxidation catalysis under differential reactor conditions; O2 reaction orders and Arrhenius activation energies were determined for each material. All of the kinetic data, including a Michaelis−Menten analysis, indicated that the primary effect of adding NaBr was to reduce the number of catalytically active sites. Density functional theory calculations, employed to evaluate likely binding sites for NaBr, showed that NaBr binds more strongly to Au corner and edge atoms than it does to the titania support or to exposed Au face atoms. Infrared spectroscopy of adsorbed CO, along with a Temkin analysis of the data, was also used to evaluate changes to the catalyst upon NaBr deposition. These studies suggested that NaBr addition induces some subtle changes in the coverage dependent properties of CO adsorption, but that these did not substantially impact the CO coverage of the CO binding sites. The experimental and computational results are discussed in terms of possible poisoning mechanisms (siteblocking vs off-site binding and modification); the nature and number of active sites are also discussed in the context of the results

H\u3csub\u3e2\u3c/sub\u3e Oxidation Over Supported Au Nanoparticle Catalysts: Evidence for Heterolytic H\u3csub\u3e2\u3c/sub\u3e Activation at the Metal-Support Interface

Water adsorbed at the metal-support interface (MSI) plays an important role in multiple reactions. Due to its importance in CO preferential oxidation (PrOx), we examined H2 oxidation kinetics in the presence of water over Au/TiO2 and Au/Al2O3 catalysts, reaching the following mechanistic conclusions: (i) O2 activation follows a similar mechanism to that proposed in CO oxidation catalysis; (ii) weakly adsorbed H2O is a strong reaction inhibitor; (iii) fast H2 activation occurs at the MSI, and (iv) H2 activation kinetics are inconsistent with traditional dissociative H2 chemisorption on metals. Density function theory (DFT) calculations using a supported Au nanorod model suggest H2 activation proceeds through a heterolytic dissociation mechanism, resulting in a formal hydride residing on the Au and a proton bound to a surface TiOH group. This potential mechanism was supported by infrared spectroscopy experiments during H2 adsorption on a deuterated Au/TiO2 surface, which showed rapid H-D scrambling with surface hydroxyl groups. DFT calculations suggest that the reaction proceeds largely through proton-mediated pathways and that typical Brønstednsted-Evans Polanyi behavior is broken by introducing weak acid/base sites at the MSI. THe kinetics data were successfully reinterpreted in the context of the heterolytic H2 activation mechanism, tying together the experimental and computational evidence and rationalizing the observed inhibition by physiorbed water on the support as blocking the MSI sites required for heterolytic H2 activation. In addition to providing evidence for the unusual H2 activation mechanism, these results offer additional insight into why water dramatically improves CO PrOx catalysis over Au

When It Rains, It Pours: Future Climate Extremes and Health

Background: The accelerating accumulation of greenhouse gases in the Earth’s atmosphere is changing global environmental conditions in unprecedented and potentially irreversible ways. Climate change poses a host of challenges to the health of populations through complex direct and indirect mechanisms. The direct effects include an increased frequency of heat waves, rising sea levels that threaten low-lying communities, anticipated extremes in the global hydrologic cycle (droughts, floods, and intense storms), and adverse effects on agricultural production and fisheries due to environmental stressors and changes in land use. Indirectly, climate change is anticipated to threaten health by worsening urban air pollution and increasing rates of infectious (particularly waterborne and vector-borne) disease transmission. Objective: To provide a state-of-the-science review on the health consequences of a changing climate. Findings: Environmental public health researchers have concluded that, on balance, adverse health outcomes will dominate under these changed climatic conditions. The number of pathways through which climate change can affect the health of populations makes this environmental health threat one of the largest and most formidable of the new century. Geographic location plays an influential role the potential for adverse health effects caused by climate change, and certain regions and populations are more vulnerable than others to expected health effects. Two kinds of strategies are available for responding to climate change: mitigation policies (which aim to reduce greenhouse gas emissions) and adaptation measures (relating to preparedness for anticipated impacts). Conclusions: To better understand and address the complex nature of health risks posed by climate change, interdisciplinary collaboration is critical. Efforts to move beyond our current reliance on fossil fuels to cleaner, more sustainable energy sources may offer some of the greatest health opportunities in more than a century and cobenefits beyond the health sector. Because the nations least responsible for climate change are most vulnerable to its effects, the challenge to reduce greenhouse gas emissions is not merely technical, but also moral

Stacked but not Stuck: Unveiling the Role of π→π* Interactions with the Help of the Benzofuran–Formaldehyde Complex

The 1:1 benzofuran–formaldehyde complex has been chosen as model system for analyzing π→π* interactions in supramolecular organizations involving heteroaromatic rings and carbonyl groups. A joint “rotational spectroscopy–quantum chemistry” strategy unveiled the dominant role of π→π* interactions in tuning the intermolecular interactions of such adduct. The exploration of the intermolecular potential energy surface led to the identification of 14 low-energy minima, with 4 stacked isomers being more stable than those linked by hydrogen bond or lone-pair→π interactions. All energy minima are separated by loose transition states, thus suggesting an effective relaxation to the global minimum under the experimental conditions. This expectation has been confirmed by the experimental detection of only one species, which was unambiguously assigned owing to the computation of accurate spectroscopic parameters and the characterization of 11 isotopologues. The large number of isotopic species opened the way to the determination of the first semi-experimental equilibrium structure for a molecular complex of such a dimension

Search for corannulene (C20H10) in the Red Rectangle

Polycyclic Aromatic Hydrocarbons (PAHs) are widely accepted as the carriers of the Aromatic Infrared Bands (AIBs), but an unambiguous identification of any specific interstellar PAH is still missing. For polar PAHs, pure rotational transitions can be used as spectral fingerprints for identification. Combining dedicated experiments, detailed simulations and observations, we explore d the mm wavelength domain to search for specific rotational transitions of corannulene (C20H10). We performed high-resolution spectroscopic measurements and a simulation of the emission spectrum of ultraviolet-excited C20H10 in the environment of the Red Rectangle (RR), calculating its synthetic rotational spectrum. Based on these results, we conducted a first observational campaign at the IRAM 30-m telescope towards this source to search for several high-J rotational transitions of C20H10. The laboratory detection of the J = 112 ← 111 transition of corannulene showed that no centrifugal splitting is present up to this line. Observations with the IRAM 30-m telescope towards the RR do not show any corannulene emission at any of the observed frequencies, down to a rms noise level of Tmb= 8 mK for the J =135 → 134 transition at 137.615 GHz. Comparing the noise level with the synthetic spectrum, we are able to estimate an upper limit to the fraction of carbon locked in corannulene of about 1.0 × 10−5 relative to the total abundance of carbon in PAHs. The sensitivity achieved in this work shows that radio spectroscopy can be a powerful tool to search for polar PAHs. We compare this upper limit with models for the PAH size distribution, emphasizing that small PAHs are much less abundant than predicted. We show that this cannot be explained by destruction but is more likely related to the chemistry of their formation in the environment of the R

The planarity of the stickface motion in the field hockey hit

The field hockey hit is an important but poorly understood stroke. This study investigated the planarity of the stickface motion during the downswing, in order to better characterise the kinematics and to assess the suitability of planar pendulum models for simulating the hit. Thirteen experienced female field hockey players were filmed executing hits with a single approach step, and the kinematics of the centre of the stickface were measured. A method was developed for identifying how far back from impact the stickface motion was planar. Orthogonal least-squares regression was used to determine best-fit planes for sections of the stickface path of varying length, each of which ended at impact, and these sections were considered planar if the mean residual between the stickface path and the fitted plane was less than 0.25% of the distance traveled by the stickface during that period. On average the stickface motion was planar for the last 83±12% of its downswing path, with the length of the planar section ranging from 1.85 m to 2.70 m. The suitability of a planar model for the stickface motion was supported, but further investigation of the stick and arm kinematics is warranted

Ancillary health effects of climate mitigation scenarios as drivers of policy uptake: a review of air quality, transportation and diet co-benefits modeling studies

Background: Significant mitigation efforts beyond the Nationally Determined Commitments (NDCs) coming out of the 2015 Paris Climate Agreement are required to avoid warming of 2 °C above pre-industrial temperatures. Health co-benefits represent selected near term, positive consequences of climate policies that can offset mitigation costs in the short term before the beneficial impacts of those policies on the magnitude of climate change are evident. The diversity of approaches to modeling mitigation options and their health effects inhibits meta-analyses and syntheses of results useful in policy-making. Methods/Design: We evaluated the range of methods and choices in modeling health co-benefits of climate mitigation to identify opportunities for increased consistency and collaboration that could better inform policy-making. We reviewed studies quantifying the health co-benefits of climate change mitigation related to air quality, transportation, and diet published since the 2009 Lancet Commission 'Managing the health effects of climate change' through January 2017. We documented approaches, methods, scenarios, health-related exposures, and health outcomes. Results/Synthesis: Forty-two studies met the inclusion criteria. Air quality, transportation, and diet scenarios ranged from specific policy proposals to hypothetical scenarios, and from global recommendations to stakeholder-informed local guidance. Geographic and temporal scope as well as validity of scenarios determined policy relevance. More recent studies tended to use more sophisticated methods to address complexity in the relevant policy system. Discussion: Most studies indicated significant, nearer term, local ancillary health benefits providing impetus for policy uptake and net cost savings. However, studies were more suited to describing the interaction of climate policy and health and the magnitude of potential outcomes than to providing specific accurate estimates of health co-benefits. Modeling the health co-benefits of climate policy provides policy-relevant information when the scenarios are reasonable, relevant, and thorough, and the model adequately addresses complexity. Greater consistency in selected modeling choices across the health co-benefits of climate mitigation research would facilitate evaluation of mitigation options particularly as they apply to the NDCs and promote policy uptake