Recombination of hydrogen over Pt/TiO2 catalysts under ambient conditions
It has been reported that H2, which is very explosive gas in nuclear power plants. Therefore, in this study, we prepared a catalyst under different conditions its ability to oxide H2 at room temperature. And it was characterized by means of X-Ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and CO-chemisorptions. The catalyst consisted of Pd or Pt/TiO2 and was prepared by the wet impregnation method. To assess the effects of pretreatment, the catalyst were prepared at 873K in a hydrogen atmosphere and at 673K in air atmosphere. When the conversion rate of H2 to H2O was compared for these catalysts, the catalyst prepared in hydrogen atmosphere displayed the perfect conversion rate at room temperature and pressure.
A study on evaluating a passive autocatalytic recombiner PAR-system in the PWR large-dry containment
A systematic step-by-step framework for analyzing hydrogen behavior and implementing passive autocatalytic recombiners (PARs) to mitigate hydrogen deflagration or detonation risk in severe accidents (SAs) is presented. The procedure can be subdivided into five main steps: (1) modeling the containment based on the plant design characteristics, (2) selecting the typical severe accident sequences, (3) calculating the hydrogen generation including in- and ex-vessel period, (4) modeling the gas distribution in containment atmosphere and estimating the hydrogen combustion modes and (5) evaluating the efficiency of the PAR-system to mitigate the hydrogen risk with and without catalytic recombiners, according to the safety criterion. For the Chinese 600MWe pressurized water reactor (PWR) with a large-dry containment, large break loss-of-coolant accident (LB-LOCA) is screened out as the reference severe accident sequence, considering the nature of hydrogen generation and the probabilistic safety assessment (PSA) result on accident sequences. The results show that a certain number of recombiners could remove effectively hydrogen and oxygen, to protect the containment integrity against hydrogen deflagration or detonation.
Effect of varying titania surface coverage on the chemisorptive behavior of nickel
Abstract Temperature-programmed desorption (TPD) of CO and H2 from nickel surfaces containing varying amounts of titania showed that the effects of titania adspecies are predominantly short-ranged. Titania surface species block CO adsorption at strongly bound sites (believed to be sites atop individual Ni atoms) corresponding to heats of adsorption in the range 134–139 kJ · mol−1; in addition, titania enhances adsorption into more weakly bound sites (believed to be bridging and hollow sites between Ni atoms) with heats of adsorption from 91 to 107 kJ · mol−1. For hydrogen adsorption, overall adsorption strength was increased with increasing concentration of surface titania. In addition, a new, activated adsorption state was created and is believed to be associated with hydrogen at sites on titania. The variations of the initial sticking coefficients of CO and H2 as a function of titania precoverages show that at low titania coverage each Tiox moiety influences approximately 4–10 Ni surface atoms. The long-range electronic influence of titania at a concentration of 0.1 monolayer was estimated to be responsible for only a 6-kJ · mol-1 decrease in the CO heat of adsorption. Qualitatively, similar results were found for an alumina-containing Ni surface, although alumina appears to be more poorly dispersed than titania on Ni. This suggests that the effects of metal oxide species on metal surfaces may be generalized to include irreducible support materials.