Combined studies of DFT atomistic modelling and in situ FTIR spectroscopy on surface oxidants and CO oxidation at Ru electrodes

We report the combined studies of density functional theory (DFT) calculations and electrochemical in situ FTIR spectroscopy on surface oxidants and mechanisms of CO oxidation at the Ru(0001) electrodes. It is shown that CO can co-adsorb with both O and OH species at lower potential region where a low coverage of the (2 x 2)-O/OH adlayer formed; the oxidation of CO adsorbates takes place at higher potentials where a high coverage of the (1 x 1)-O/OH adlayer formed. Surface O species are not the active oxidants under all coverages studied, due to the high reaction barriers between CO and O (>1 eV). However, surface OH species with higher coverage are identified as the active oxidants, and CO oxidation takes place via a two-steps' mechanism of CO + 3OH -> COOH + 2OH -> CO2 + H2O + OH, in which three nearby OH species are involved in the CO2 formation: CO reacts with OH, forming COOH; COOH then transfers the H to a nearby OH to form H2O and CO2, at the same time, another H in the H2O transfers to a nearby OH to form a weak adsorbed H2O and a new OH. The reaction barrier of these processes is reduced significantly to around 0.50 eV. These new results not only provide an insight into surface active oxidants on Ru, which is directly relevant to fuel cell catalysis, but also reveals the extra complexity of catalytic reactions taking place at solid/liquid electrochemical interface in comparison to the relatively simpler ones at solid/gas phase. 

In Situ Single-Crystal Diffraction Studies of the Structural Transition of Metal-Organic Framework Copper 5-Sulfoisophthalate, Cu-SIP-3

The flexibility of the metal-organic framework Cu-2(OH)(C8H3O7S)(H2O)center dot 2H(2)O (Cu-SIP-3) toward reversible single-crystal to single-crystal transformations is demonstrated using in situ diffraction methods at variable temperature. At temperatures below a dehydration-induced phase transition (T < 370 K) the structure is confirmed as being hydrated. In the temperature range where the transition takes place (370 K < T < 405 K) no discrete, sharp Bragg peaks can be seen in the single-crystal X-ray diffraction pattern, indicating significant loss of long-range order. At temperatures higher than 405 K, the Bragg peaks return and the structure can be refined as dehydrated Cu-SIP-3. The loss of guest water molecules can be followed at temperatures below the phase transition giving insight into the mechanism of the dehydration. Addition of nitric oxide gas to the material above the gating opening pressure of 275 mbar also leads to loss of Bragg scattering in the diffraction pattern.

An in situ spatially resolved method to probe gas phase reactions through a fixed bed catalyst

A new method to spatially probe heterogeneous catalysed reactions within a packed bed of catalyst has been developed. The spatial resolution is achieved using a stationary perforated capillary coupled to a mass spectrometer while the catalyst bed is moved. The oxidation of CO promoted by H-2 over a Pd catalyst has been used to demonstrate the technique.

An in situ spatially resolved analytical technique to simultaneously probe gas phase reactions and temperature within the packed bed of a plug flow reactor

This paper reports the detailed description and validation of a fully automated, computer controlled analytical method to spatially probe the gas composition and thermal characteristics in packed bed systems. As an exemplar, we have examined a heterogeneously catalysed gas phase reaction within the bed of a powdered oxide supported metal catalyst. The design of the gas sampling and the temperature recording systems are disclosed. A stationary capillary with holes drilled in its wall and a moveable reactor coupled with a mass spectrometer are used to enable sampling and analysis. This method has been designed to limit the invasiveness of the probe on the reactor by using the smallest combination of thermocouple and capillary which can be employed practically. An 80 mu m (O.D.) thermocouple has been inserted in a 250 mu m (O.D.) capillary. The thermocouple is aligned with the sampling holes to enable both the gas composition and temperature profiles to be simultaneously measured at equivalent spatially resolved positions. This analysis technique has been validated by studying CO oxidation over a 1% Pt/Al2O3 catalyst and the spatial resolution profiles of chemical species concentrations and temperature as a function of the axial position within the catalyst bed are reported.

Ethylene oxidation over platinum: In situ electrochemically controlled promotion using Na-beta'' alumina and studies with a Pt(111)/Na model catalyst

Electrochemically modified ethylene oxidation over a PI film supported on the Na+ ion conductor beta '' alumina has been studied over a range of conditions encompassing both promotion and poisoning, The system exhibits reversible behavior, and the data are interpreted in terms of (i) Na-enhanced oxygen chemisorption and (ii) poisoning of the surface by accumulation of Na compounds. At low Na coverages the first effect results in increased competitive adsorption of oxygen at the expense of ethylene, resulting in an increased rate, At very negative catalyst potentials (high Na coverage) both effects operate to poison the system: the increased strength of the Pt-O bond and coverage of the catalytic surface by compounds of Na strongly suppress the rate, Kinetic and spectroscopic results for ethylene oxidation over a Pt(111)-Na model catalyst shed light on important aspects of the electrochemically controlled system, Low levels of Na promote the reaction and high levels poison it, mirroring the behavior observed under electrochemical control and strongly suggesting that sodium pumped from the solid electrolyte is the key species, XP and Auger spectra show that under reaction conditions, the sodium exists as a surface carbonate. Post-reaction TPD spectra and the use of (CO)-C-13 demonstrate that CO is formed as a stable reaction intermediate, The observed activation energy (56 +/- 3 kJ/mol) is similar to that measured for CO oxidation under comparable conditions, suggesting that the rate limiting step is CO oxidation. (C) 1996 Academic Press, Inc.

Evaluation of in Situ DGT Measurements for Predicting the Concentration of Cd in Chinese Field-Cultivated Rice: Impact of Soil Cd:Zn Ratios

DGT (diffusive gradients in thin-films) has been proposed as a tool for predicting Cd concentrations in rice grain, but there is a lack of authenticating data. To further explore the relationship between DGT measured Cd and concentrations in rice cultivated in challenging, metal degraded, field locations with different heavy metal pollutant sources, 77 paired soil and grain samples were collected in Southern China from industrial zones, a "cancer village" impacted by mining waste and an organic farm. In situ deployments of DGT in flooded paddy rice rhizospheres were compared with a laboratory DGT assay on dried and rewetted soil. Total soil concentrations were a very poor predictor of plant uptake. Laboratory and field deployed DGT assays and porewater measurements were linearly related to grain concentrations in all but the most contaminated samples where plant toxicity occurred. The laboratory DGT assay was the best predictor of grain Cd concentrations, accommodating differences in soil Cd, pollutant source, and Cd:Zn ratios. Field DGT measurements showed that Zn availability in the flooded rice rhizospheres was greatly diminished compared to that of Cd, resulting in very high Cd:Zn ratios (0.1) compared to commonly observed values (0.005). These results demonstrate the potential of the DGT technique to predict Cd concentrations in field cultivated rice and demonstrate its robustness in a range of environments. Although, field deployments provided important details about in situ element stoichiometry, due to the inherent heterogeneity of the rice rhizosphere soils, deployment of DGT in dried and homogenized soils offers the best possibility of a soil screening tool.

Dual-colour HER2/chromosome 17 chromogenic in situ hybridisation assay enables accurate assessment of HER2 genomic status in gastric cancer and has potential utility in HER2 testing of biopsy samples

Determination of HER2 protein expression by immunohistochemistry (IHC) and genomic status by fluorescent in situ hybridisation (FISH) are important in identifying a subset of high HER2-expressing gastric cancers that might respond to trastuzumab. Although FISH is considered the standard for determination of HER2 genomic status, brightfield ISH is being increasingly recognised as a viable alternative. Also, the impact of HER2 protein expression/genomic heterogeneity on the accuracy of HER2 testing has not been well studied in the context of gastric biopsy samples.

‘CLAM’ tests for measuring in-situ permeation properties of concrete

This paper descirbes a simple test measuring the sorptivity (a measure of the absorption property if concrete) and the air and water permeability of concrete on site. Using this test, the decay of pressure is monitired for the air permeability test.whereas water penetrating into the concrete at a constant pressure of 0.01 bar and 1.5 bar are recorded for the sorptivity and the water permeability tests respectively. These tests are essentially non-destructive in nature and a skilled operator is not needed. It is possible to carry out a number of tests quickly and efficiently on site without prior planning. It has been found that statistically satisfactory results can be obtained from a mean of three tests. As the flow lines are largely concentrated within 40 mm from the surface, reasonably reliable results can be obtained by drying the surface even if the surface under test is initially wet.

Observation of an optical phonon band in situ in TiO electrochemistry:A possible indicator of strongly trapped intermediates in the O evolution reaction

This Letter reports in situ Fourier transform infrared (FTIR) spectroscopic data on thermal TiO films fabricated by heating titanium plates in air at 475, 700 and 800 °C. The films were studied in the dark and under UV-irradiation in aqueous 0.1MNaClO in the presence and absence of 0.1 M Na(OOC) and at 10, 25 and 50 °C. The film fabricated at 800 °C showed a broad feature near 1580cm under UV-irradiation that was not observed in the dark, whilst the films fabricated at lower temperatures, 475 and 700 °C, showed no such feature. This feature appears to be associated with the accumulation of surface-mobile holes at the complex, porous film-electrolyte interface and the capacity of such holes to enhance the absorption cross-section of optical phonons characteristic of the rutile crystal form at and near the surface of the TiO/electrolyte interface. © 2001 Elsevier Science B.V.

Catalysis of CO electrooxidation at Pt, Ru, and PtRu alloy. An in situ FTIR study

A comparative study of CO electrooxidation on different catalysts using in situ FTIR spectroscopy is presented. As electrode materials, polycrystalline Pt and Ru and a PtRu (50:50) alloy are used. The latter is one of the well-known active alloys for CO oxidation. The potential dependence of the band frequencies for the CO stretch indicates the formation of relatively compact islands at pure Pt and Ru, and a loose adlayer structure at the alloy. This loose structure has a positive effect on the rate of oxidative desorption. CO submonolayer coverages are obtained by integrating the absorption bands for CO produced upon oxidation of adsorbed CO. The band intensities measured at Pt, Ru, and PtRu indicate an influence of the substrate on the absorption coefficient of the CO stretch. It is shown that for a correct description of the catalyst properties toward CO electrooxidation, it must be distinguished between bulk and adsorbed CO. In contrast to the statement of most of the recent papers that a PtRu alloy (50:50) is the material with the highest activity for CO oxidation, it is demonstrated and rationalized in the present paper that for bulk CO oxidation pure Ru is the best catalyst. © 1999 American Chemical Society.

Quantum chemistry and in situ FTir spectroscopy studies on potential-dependent properties of CO adsorbed on Pt electrodes

The electronic and vibrational properties of CO adsorbed on Pt electrodes at different potentials have been studied, by using methods of self-consistent-charge discrete variational Xa (SCC-DV-Xa) cluster calculations and in situ FTir spectroscopy. Two new models have been developed and verified to be successful: (1) using a "metallic state cluster" to imitate a metal (electrode) surface; and (2) charging the cluster and shifting its Fermi level (e{lunate}) to simulate, according to the relation of -d e{lunate}e dE, quantitatively the variation of the electrode potential (E). It is shown that the binding of PtCO is dominated by the electric charge transfer of dp ? 2p, while that of s ? Pt is less important in this binding. The electron occupancy of the 2p orbital of CO weakens the CO bond and decreases the v. Variation of E mainly influences the charge transfer process of dp ? 2p, but hardly influences that of s ? Pt. A linear potential-dependence of v has been shown and the calculated dv/dE = 35.0 cm V. All results of calculations coincide with the ir experimental data. © 1993.

In situ FTIRS investigations of surface processes of Rh electrode - Novel observation of geminal adsorbates of carbon monoxide on Rh electrode in acid solution

With the help of in situ multi-step FTIR Spectroscopy, two types of adsorbed geminal CO have been observed for the first time at an electrochemically modified Rh electrode. A doublet band of two broad peaks at 2166 and 2112cm is assigned to geminal CO on Rh surface oxide (or hydroxide) produced by the electrochemical modification process, and a doublet band of two peaks near 2103 and 2033cm is ascribed to geminal CO on surface clusters of Rh formed by reduction of Rh surface oxide. Based on the evolution of FTIR spectra with the electrode potential, the surface processes of a Rh electrode, subjected to a potential cycling treatment at 1.5Vs between -0.275 and 2.4V for 2min, have been elucidated. The present results at the solid/liquid electrochemical interface were compared with those obtained at the solid/gas interface, and consistent conclusions were achieved.

In situ FTIR spectroscopy studies on electrochemical redox processes of high nuclearity osmium carbonyl clusters

The electrochemical redox processes of two high nuclearity osmium carbonyl clusters [(PhP)N[OsC(CO) ]·PPN (1) and Os(CO) (6) have been studied by electrochemical in situ FTIR. The five oxidation states of 1, i.e., [OsC(CO)], have been characterized. There are no significant structural changes for these species. Hence, the ability of this decanuclear cluster to act as an electron reservoir has been demonstrated. The structural rearrangement associated with the two-electron reduction of bicapped tetrahedral 6 to octahedral dianion [Os(CO)] and [Os(CO)] tetraanion has also been investigated. © 1996 American Chemical Society.