6 research outputs found
Reactions of ethanol over CeO2 and Ru/CeO2 catalysts
The reaction of ethanol has been investigated on Ru/CeO2 in steady state conditions as well as with temperature programmed desorption (TPD). High resolution transmission electron microscopy (HRTEM) images indicated that the used catalyst contained Ru particles with a mean size of ca. 1.5 nm well dispersed on CeO2 (of about 12â15 nm in size). Surface uptake of ethanol was measured by changing exposure to ethanol followed by TPD. Saturation coverage is found to be between 0.25 and 0.33 of a monolayer for CeO2 that has been prior heated with O2 at 773 K. The main reactions of ethanol on CeO2 during TPD are: re-combinative desorption of ethanol; dehydrogenation to acetaldehyde; and dehydration to ethylene. The dehydration to ethylene occurs mainly in a small temperature window at about 700 K and it is attributed to ethoxides adsorbed on surface-oxygen defects. The presence of Ru considerably modified the reaction of ceria towards ethanol. It has switched the desorption products to CO, CO2, CH4 and H2. These latter products are typical reforming products. Ethanol steam reforming (ESR) conducted on Ru/CeO2 indicated that optimal reaction activity is at about 673 K above which CO2 production declines (together with that of H2) due to reverse water gas shift. This trend was well captured during ethanol TPD where CO2 desorbed about 50 K below than CO on both oxidized and reduced Ru/CeO2 catalysts.Peer ReviewedPostprint (author's final draft
A Stable Integrated Photoelectrochemical Reactor for Hâ Production from Water Attains a SolarâtoâHydrogen Efficiency of 18â% at 15 Suns and 13â% at 207 Suns
The major challenge in solar water splitting to H_{2} and O_{2} is in making a stable and affordable system for largeâscale applications. We have designed, fabricated, and tested a photoelectrochemical reactor characterized as follows: 1)â
it comprises an integrated device to reduce the balance of the system cost, 2)â
it utilizes concentrated sunlight to reduce the photoabsorber cost, and 3)â
it employs and alkaline electrolyte to reduce catalyst cost and eliminate external thermal management needs. The system consists of an IIIâVâbased photovoltaic cell integrated with Ni foil as an O_{2} evolution catalyst that also protects the cell from corrosion. At low light concentration, without the use of optical lenses, the solarâtoâhydrogen (STH) efficiency was 18.3â%, while at high light concentration (up to 207 suns) with the use of optical lenses, the STH efficiency was 13â%. Catalytic tests conducted for over 100 hours at 100â200 suns showed no sign of degradation nor deviation from product stoichiometry (H_{2}/O_{2}=2). Further tests projected a system stability of years
Reactions of ethanol over CeO2 and Ru/CeO2 catalysts
The reaction of ethanol has been investigated on Ru/CeO2 in steady state conditions as well as with temperature programmed desorption (TPD). High resolution transmission electron microscopy (HRTEM) images indicated that the used catalyst contained Ru particles with a mean size of ca. 1.5 nm well dispersed on CeO2 (of about 12â15 nm in size). Surface uptake of ethanol was measured by changing exposure to ethanol followed by TPD. Saturation coverage is found to be between 0.25 and 0.33 of a monolayer for CeO2 that has been prior heated with O2 at 773 K. The main reactions of ethanol on CeO2 during TPD are: re-combinative desorption of ethanol; dehydrogenation to acetaldehyde; and dehydration to ethylene. The dehydration to ethylene occurs mainly in a small temperature window at about 700 K and it is attributed to ethoxides adsorbed on surface-oxygen defects. The presence of Ru considerably modified the reaction of ceria towards ethanol. It has switched the desorption products to CO, CO2, CH4 and H2. These latter products are typical reforming products. Ethanol steam reforming (ESR) conducted on Ru/CeO2 indicated that optimal reaction activity is at about 673 K above which CO2 production declines (together with that of H2) due to reverse water gas shift. This trend was well captured during ethanol TPD where CO2 desorbed about 50 K below than CO on both oxidized and reduced Ru/CeO2 catalysts.Peer Reviewe