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Highlights: [•] NO x reduction to N2 in H2-C3H6-SCR increases with decreasing Ag loadings. [•] Changes in the kinetic parameters remarkably correlate to the changes in NO x uptakes. [•] C3H6 and H2 are activated on Ag species, while NO x are activated on Al2O3. [•] The number of active sites on Al2O3 accounts for the observed catalytic activities. [Copyright &y& Elsevier]

Abstract: Out-of-pile tritium release experiments under different water uptake contents and purge gas chemistry were performed on Li4SiO4. Water measurement was performed on samples under different experimental procedures. It was found that water was adsorbed on the sample during its transferring and storage process. A strong dependence of tritium release behavior on water uptake was determined. By doping H2 in the sweep gas, the formation of water in orthosilicate was observed in addition to the isotope exchange reaction with H2 gas. Thermal desorption peaks of the water formation reaction and H2 isotope exchange reaction appeared at 668°C and 463°C, respectively, at ramping rate of 5°C/min. [Copyright &y& Elsevier]

Abstract: The role of hydrogen in promoting the reduction by ammonia of NO x on silver catalysts has been investigated using a Short Time on Stream (STOS) technique to allow differentiation between potentially reactive intermediates and relatively inactive spectator species. Under these conditions, we have used DRIFTS to identify surface nitrate species that are formed and removed on a timescale of seconds. This is in contrast to nitrate species observed under normal steady-state conditions which can continue to form over many tens of minutes. Since this timescale of seconds is very similar to the response rate at which the NH3/NO x to N2 reaction is accelerated when H2 is added, or decelerated when H2 is removed, we conclude that this fast-forming and fast disappearing nitrate species is most probably adsorbed on or close to the active Ag sites. The removal of such a blocking nitrate species from the active sites can explain the effect of H2 in greatly increasing the rate of the overall de-NO x reaction. [Copyright &y& Elsevier]

Abstract: In recent years, the impact of H2 on α-radiation induced dissolution of UO2-based spent nuclear fuel has been studied and debated extensively. Experimental results on the effect of H2 on the concentration of H2O2 during α-radiolysis have been shown to disagree with numerical simulations. For this reason, the reaction scheme used in simulations of aqueous radiation chemistry has sometimes been questioned. In this work, we have studied the impact of H2 on the H2O2 concentration in α-irradiated aqueous solution using numerical simulations. The effects of H2 pressure, α-dose rate and concentration were investigated by performing systematic variations in these parameters. The simulations show that the discrepancy between the previously published experimental result and numerical simulations is due to the use of a homogeneous dose rate (the energy is assumed to be equally distributed in the whole volume). Taking the actual dose rate of the α-irradiated volume into account, the simulation is in perfect agreement with the experimental results. This shows that the H2 effect is strongly α-dose rate dependent, and proves the reliability of the reaction scheme used in the simulations. The simulations also show that H2 influences the H2O2 concentration under α-radiolysis. The magnitude of the effect depends on the dose rate and the H2 pressure as well as on the concentration of . The impact of the radiolytic H2 effect on the rate of α-radiation induced dissolution of spent nuclear fuel is discussed along with other (α- and γ-) radiation induced processes capable of reducing the concentration of uranium in solution. The radiolytic H2 effect is quantitatively compared to the previously presented noble metal catalyzed H2 effect. This comparison shows that the noble metal catalyzed H2 effect is far more efficient than the radiolytic H2 effect. Reduction of U(VI) in solution due to low dose rate γ-radiolysis in the presence of H2 is proposed to be the cause of the H2 effect observed in leaching experiments on α-doped UO2. [Copyright &y& Elsevier]

Abstract: The effect of temperature and transient addition of H2 on the NOx–SCR reaction was investigated over a 2-wt.% Ag/Al2O3 catalyst using isotopically labelled 15NO. The addition and removal of hydrogen had a marked effect on the nitrogen balance at temperatures ranging from 245 to 400°C. At a low temperature (245°C), the addition of hydrogen resulted in the storage of NOx, whereas, the reverse was true at 400°C, where NOx was stored upon removal of hydrogen from the feed. The transient NOx storage effect could be harnessed to allow continuous high NOx conversion with intermittent hydrogen addition. In particular, an average NOx conversion of 79% could be achieved during transient experiments in which H2 was switched in and out of the feed in 6-s intervals at 300°C. [Copyright &y& Elsevier]

Abstract: The H2-assisted hydrocarbon selective catalytic reduction (HC-SCR) of NO x was investigated using fast transient kinetic analysis coupled with isotopically labelled 15NO. This allowed monitoring of the evolution of products and reactants during switches of H2 in and out of the SCR reaction mix. The results obtained with a time resolution of less than 1 s showed that the effect on the reaction of the removal or addition of H2 was essentially instantaneous. This is consistent with the view that H2 has a direct chemical effect on the reaction mechanism rather than a secondary one through the formation of “active” Ag clusters. The effect of H2 partial pressure was investigated at 245 °C, it was found that increasing partial pressure of H2 resulted in increasing conversion of NO and octane. It was also found that the addition of H2 at 245 °C had different effects on the product distribution depending on its partial pressure. The change of the nitrogen balance over time during switches in and out of hydrogen showed that significant quantities of N-containing species were stored when hydrogen was introduced to the system. The positive nitrogen balance on removal of H2 from the gas phase showed that these stored species continued to react after removal of hydrogen to form N2. [Copyright &y& Elsevier]

Abstract: In this work we present the results obtained with 3 catalysts (Pt, Rh and Ag on alumina) tested in ranges of temperatures and gas hourly space velocities typical of diesel engines in real trucks. NO concentration was 500ppm, C3H6 ranged between 500 and 2000ppm, while oxygen was always 5%. All the catalysts were active and showed high conversions. Both Pt and Rh were active at low temperature (T 50 =200–250°C) but had quite high selectivity towards NO2. Silver was active at higher temperature, but showed very high selectivity towards N2. A strong boosting effect on NO conversion was recorded if H2 was added to the gas mixture. [Copyright &y& Elsevier]