Science Concentrates: ACS meeting news CATALYSIS
Generating energy where rivers meet the sea As a river flows into the ocean, freshwater and saltwater mix, an entropic process that releases about as much energy as water flowing over a 270-meter-tall dam, according to Christopher A. Gorski of Pennsylvania State University. At the American Chemical Society national meeting in Philadelphia last week, Gorski’s group reported a new strategy to extract that energy. The team has built a battery-like device that consists of two copper hexacyanoferrate electrodes, with a high-salt solution flowing past one and a low-salt solution flowing past the other (Environ. Sci. Technol. 2016, DOI: 10.1021/acs.est.6b02554). This creates a so-called concentration cell, which generates an electrochemical potential between the two electrodes based on the difference in concentrations of the salt solutions. As the device discharges and electrical current flows, the highsalt electrode takes up sodium ions while the low-salt one releases them. When the potential between the electrodes approaches zero, the researchers flip the solutions so that the electrode that was in contact with the high-salt solution is then bathed by the low-salt solution and vice versa. This regenerates the electrical potential, and the process starts over. In a talk in the Division of Environmental Chemistry, Taeyoung Kim, a postdoc in Gorski’s group, reported that the device produces about 0.4 W of power per m2 of membrane separating the device’s two channels. Previous methods to tap into the energy of mixing freshwater and saltwater have produced between 0.03 and 10 W/m2.—MICHAEL TORRICE
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C&EN | CEN.ACS.ORG | AUGUST 29, 2016
Supercool catalysts oxidize CO Nanoparticles with catalytic gold cores drive reactions at cryogenic temperatures Chemical processes often need to be and protects the gold particles from fusing coaxed into action with heat. Catalysts together, a common problem that deactican reduce the amount of heat required vates nanoparticle catalysts. to drive a reaction, enabling an ordinarily The amorphous titania shell contains high-temperature reaction to run at lower sodium titanate and silicon impurities temperatures. that prove critical to the cryogenic activiAt the American Chemical Society naty. Removing the impurities kills the cataltional meeting in Philadelphia last week, ysis. Spectroscopy measurements indicate Francisco Zaera of the University of Calthat the mechanism governing cryogenic ifornia, Riverside, described an extreme CO oxidation differs from the one active low-temperature example: a gold catalyst at room temperature. that drives carbon monoxide oxidation at Jeffrey G. Weissman, manager of cat–150 °C below zero. alyst development at Precision CombusThe finding broadens basic understand- tion in North Haven, Conn., remarked ing of low-temperature chemistry and may that catalysts working at cryogenic temlead to applications in space exploration. Catalytic reactions that run at cryogenic temperatures are rare. One example is the esoteric interconversion of spin isomers of dihydrogen. Reactions These yolk-shell particles catalyze CO oxidation at –150 °C. involving gold catalysts used to be rare. But in recent peratures could find applications in space years, researchers have discovered sevexploration. For example, in an extended eral reactions mediated by nanosized manned mission to an asteroid or Mars, gold particles. Those reactions, including astronauts may need to collect ice and othCO oxidation, tend to run close to room er materials found on location and convert temperature. them to oxygen, water, fuel, and possibly The UC Riverside group’s catalysts plant growth medium. Weissman’s team are also nanosized, but they do their job has conducted research in support of such at a frigid 120 K. Speaking at a session a mission and has developed cabin-air sponsored by the Division of Catalysis cleaning devices for the International Science & Technology, Zaera explained Space Station. that his group prepares the catalysts by “One aspect I find intriguing,” Weissgrowing gold particles roughly 15 nm in man said, “is that the yolk-shell morpholodiameter and encapsulating them in a gy provides a means to exclude certain gas 200-nm-wide silica sphere, which they in species from reaching the catalyst.” For turn coat with a 20-nm thick titania shell. example, larger hydrocarbons or sulfur The team then etches away the silica, contained in a gas mixture may be physleaving a yolk-shell structure—so named ically blocked from reaching the catalyst because it resembles an egg without the surface thereby preventing catalyst deactiegg white (Surf. Sci. 2016, DOI: 10.1016/j. vation. Such a capability could be importsusc.2015.10.008). ant in devices that clean up exhaust gas The porous titania shell allows gases or air in confined living spaces.—MITCH to diffuse to and from the catalytic cores JACOBY
CREDIT: SURF. SCI.
ENERGY
