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 the hydrogen recombination rates of catalytic recombiners and deliberate ignition
A study is being carried out by the Department of Nuclear and Mechanical Constructions at the University of Pisa on catalytic recombiners and on deliberately induced weak deflagration. These are the most practical methods for recombining hydrogen released into large nuclear containments during severe accidents. The recombination rates of different types of catalytic device were obtained from a thorough analysis of published experimental data. The main parameter that affects the effectiveness of these devices seems to be the molar density of the deficiency reactant rather than its volumetric concentration. The recombination rate of weak deflagrations in vented compartments has been assessed with experimental tests carried out in a small-scale glass vessel. Through a computerized system of analysis of video recordings of the deflagrations, the flame surface and the burnt gas volume were obtained as functions of time. These values of flame surface and burnt gas volume were used as inputs for a computer code to calculate the recombining rate, the burning velocity and the pressure transient in the experimental test. The code is being validated with a methodology principally based on a comparison of the measurements of pressure with the calculated values.
Decomposition of dimethyl methylphosphonate on Pt, Au, and Au-Pt clusters supported on TiO2(110).
The decomposition of dimethyl methylphosphonate (DMMP) was studied by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) on TiO(2)-supported Pt, Au, and Au-Pt clusters as well as on TiO(2)(110) itself. In agreement with previous work, TPD experiments for DMMP on TiO(2)(110) showed that methyl and methane were the main gaseous products. Multiple DMMP adsorption-reaction cycles on TiO(2)(110) demonstrated that active sites for DMMP decomposition were blocked after a single cycle, but some activity for methyl production was sustained even after five cycles. Furthermore, the activity of the TiO(2) surface could be regenerated by heating in O(2) at 800 K or heating in vacuum to 965 K to remove surface carbon and phosphorus, which are byproducts of DMMP decomposition. On 0.5 ML Pt clusters deposited on TiO(2)(110), TPD studies of DMMP reaction showed that CO and H(2) were the main gas products, with methyl and methane as minor products. The Pt clusters were more active than TiO(2) both in terms of the total amount of DMMP reaction and the ability to break C-H, P-O, and P-OCH(3) bonds in DMMP. However, the Pt clusters had no sustained activity for DMMP decomposition, since the product yields dropped to zero after a single adsorption-reaction cycle. This loss of activity is attributed to a combination of poisoning of active sites by surface phosphorus species and encapsulation of the Pt clusters by reduced titania after heating above 600 K due to strong metal support interactions (SMSI). On 0.5 ML Au clusters, CO and H(2) were also the main products detected in TPD experiments, in addition to methane and methyl produced from reaction on the support. The Au clusters were less active for DMMP decomposition to CO and H(2) as well as P-O bond scission, but surface phosphorus was removed from the Au clusters by desorption at approximately 900 K. Au-Pt bimetallic clusters on TiO(2)(110) were prepared by depositing 0.25 ML of Pt followed by 0.25 ML of Au, and the bimetallic surfaces exhibited activity intermediate between that of pure Pt and pure Au in terms of CO and H(2) desorption yields. However, there is evidence that the production of methane from DMMP decomposition occurs at Au-Pt sites.