ABSTRACT
In polymer electrolyte fuel cell (PEFC) systems, small amounts of ammonia (NH3 ) present in the reformate gas deactivate the supported ruthenium catalysts used for preferential oxidation (PROX) of carbon monoxide (CO). In this study, we investigated how the addition of a small amount of platinum to a Ru/α-Al2 O3 catalyst (Pt/Ru=1:9 w/w) affected the catalyst's PROX activity in both the absence and the presence of NH3 (130 ppm) under conditions mimicking the reformate conditions during steam reforming of natural gas. The activity of undoped Ru/α-Al2 O3 decreased sharply upon addition of NH3 , whereas Pt/Ru/α-Al2 O3 exhibited excellent PROX activity even in the presence of NH3 . Ruthenium K-edge X-ray absorption near-edge structure (XANES) spectra indicated that in the presence of NH3 , some of the ruthenium in the undoped catalyst was oxidized in the presence of NH3 , whereas ruthenium oxidation was not observed with Pt/Ru/α-Al2 O3 . These results suggest that ruthenium oxidation is retarded by the platinum, so that the catalyst shows high activity even in the presence of NH3 .
Subject(s)
Aluminum Oxide/chemistry , Ammonia/analysis , Carbon Monoxide/chemistry , Electric Power Supplies , Platinum/chemistry , Ruthenium/chemistry , Oxidation-ReductionSubject(s)
Butanes/chemistry , Cerium/chemistry , Green Chemistry Technology/methods , Oxides/chemistry , Rhenium/chemistry , Zirconium/chemistry , Carbon Dioxide/chemistry , Catalysis , Conservation of Energy Resources/methods , Hydrogen/chemistry , Models, Chemical , Oxidation-Reduction , TemperatureABSTRACT
SF(6) was selectively hydrolyzed to SO(3) over rare earth (RE) phosphates above 800 K. CePO(4) was the most active catalyst, followed by GdPO(4), YbPO(4), DyPO(4), ErPO(4), SmPO(4), PrPO(4), TbPO(4), NdPO(4), and LaPO(4). The middle RE phosphates were found to be more active than the light RE phosphates, but the reason for the high activity of CePO(4), which belongs to the light RE group, is not clear. The catalytic activity was independent of the specific surface area (SSA), acid amount, and acid concentration of the catalysts. RE phosphates were single-phase, and a broad inversely proportional relation was observed between the crystallite size and SSA, except in the case of CePO(4). The combination of highly active AlPO(4) and CePO(4) creates synergetic effects in the catalytic activity and SO(3) selectivity over all ranges of composition. Binary catalysts were a mixture of small crystalline AlPO(4) and CePO(4). The addition of Ce promoted the crystallization of AlPO(4), which was controlled to about 10 nm at 10-50% Ce content. The turnover frequency for SF(6) decomposition was proportional to the surface concentration of hydroxyls of binary catalysts. Therefore, synergy effects may come from the number of hydroxyl (OH) pair sites on which a bidentate intermediate of hydrolysis of SF(6) may be formed by the moderate crystallization of AlPO(4). The addition of Ce, Pr, or Y to AlPO(4) brings about a small promotion effect for SF(6) decomposition, but the addition of La, Nd > Gd > Yb diminishes the activity. The addition of Gd, Pr, or Nd greatly improved the SO(3) selectivity. A linear relationship between catalytic activity and the concentration of surface hydroxyls of the catalysts supports a reaction mechanism in which two F atoms of an SF(6) molecule interact with two surface hydroxyls to form a bidentate intermediate.
ABSTRACT
Hydrogen storage into multi-walled carbon nanotubes obtained by the decomposition of hydrocarbons using Ni-Li/SiO2 was investigated. The optimized reaction conditions for the synthesis of carbon nanotubes were 873K and W/F=40 g-cat.h/mol, and carbon nanotubes obtained by C2H6 decomposition were found to exhibit fairly large H2 storage capacity of 1 wt% at room temperature. The storage capacity increased with decreasing temperature and a capacity of 5 wt% was achieved at 77K, with 66% of adsorbed hydrogen being desorbable. Hydrogen adsorption by pi orbital in C-C bond coordination is proposed, observing both weakened Raman adsorption C-C peaks and the thermal release of CH4 after H2 storage.
Subject(s)
Energy-Generating Resources , Hydrogen/chemistry , Nanotechnology , Adsorption , Carbon , Hydrogen/analysis , Lithium/chemistry , Nickel/chemistry , Silicon Dioxide/chemistryABSTRACT
In our previous study, we found that Ti(OH)(4) exhibited fluoride ion exchange properties. In order to improve the ion exchange capacity, mesoporous Ti oxohydroxide (TiOx(OH)y) had been prepared by using dodecylamine as template. Zirconia and silica had been introduced into the mesoporous Ti oxohydroxide to enhance the ion exchange capacity. The mesoporous structure and the morphology of the mesoporous materials obtained were confirmed using XRD and SEM, respectively. A fluoride ion exchange study was done on each sample. Results showed that mesoporous Ti oxohydroxide containing zirconia exhibited the highest fluoride ion exchange capacity, as it has the smallest particle size, with high uniformity among the mesoporous materials prepared.
