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Physical Sciences
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August 2015

Energy in Chemical Bonds and the Plant-Pollution Connection

PNNL scientists share fundamental insights in energy and atmospheric science at ACS National Meeting

Model of a zeolite
Zeolite, a sieve-like material made of aluminum and silicon, is one of the most common catalysts, and chemists are eager to determine how to modify it to control chemical reactions of interest. Image created by Amity Andersen, PNNL. Enlarge Image.

Energy Storage: Putting molecular hydrogen together, taking it apart

Storing electrical energy in chemicals and pulling it back out again to use for renewable energy requires inexpensive catalysts, which are molecules that can speed up the chemical reactions in either direction. PNNL researchers have been exploring the nuts and bolts of how catalysts do this for hydrogen fuel (talk number CATL 241), many of whom will be participating in a special one-and-a-half-day symposium. In recognition of work that draws inspiration from biological catalysts called hydrogenases (CATL 111, 236), ACS has awarded a PNNL-led team of researchers the ACS Catalysis Lectureship.

This is the first time this has been awarded to a team. Members of the PNNL-led hydrogen catalysis team will discuss developing catalysts using abundant metals rather than spendy ones such as platinum. They have explored in detail proton relays (CATL 74, 75), where complicated molecules surround the catalyst's metal center and relay positively charged protons in a route through the catalyst that guide negatively charged electrons-the energy-containing bits-into chemical bonds, or back out again. Branching out from hydrogen, other PNNL researchers have begun exploring related reactions that convert carbon dioxide (CO2) to formate (HCO2-) (CATL 117).

Reference: Various speakers, CATL 74-79, 111-117, 236-241: 2015 ACS Catalysis Lectureship, Monday, Aug. 17, 8:00 a.m. - 11:20 a.m., 1:00 p.m. - 4:45 p.m.; Tuesday, Aug. 18, 8:00 a.m. - 11:30 a.m., Atlantic Blrm 3 - Renaissance Boston Waterfront.

Catalysis in zeolites imitating enzymes

Petroleum processing and industrial chemicals production use catalysts to convert raw materials into useful products such as gasoline or chemicals for various uses. Zeolite, a sieve-like material made of aluminum and silicon, is one of the most common catalysts, and chemists are eager to determine how to modify it to control chemical reactions of interest. Recently, researchers have been exploring how the rates and selectivity of chemical transformations in zeolites are determined by the chemical nature of the active site as well as the confined space around the sites, called the steric environment. PNNL chemist Johannes Lercher will discuss results that show how the nature of sites can be used to enhance reaction rates by directed interactions and by steric constraints-both principles common in biological systems.

Reference: Johannes Lercher, CATL 95: Influencing catalytic rates by tailoring steric constraints, Monday, Aug. 17, 8:35 a.m. - 9:20 a.m., Pacific Blrm A - Renaissance Boston Waterfront.

The connection between plants, pollution, and aerosols

A large portion of secondary organic aerosols-tiny particles in the air we breathe that contribute to cloud formation and precipitation-arise from a combination of man-made pollution and molecules given off by plant matter. Researchers find that when these two sources work in consort they produce significantly more particles than expected. The mechanism behind this phenomenon remained a mystery for a long while. Based on laboratory experiments, PNNL chemist Alla Zelenyuk has found that manmade pollutants, like polycyclic aromatic hydrocarbons, also known as PAHs, can dramatically increase the number and mass of particles produced by plant-based alpha-pinene-the chemical that gives pine trees their scent. The effect is especially pronounced when alpha-pinene is low. A dash of pyrene added to a low concentration of alpha-pinene yields aerosols that are five times the mass, and 200 times as many, than that produced by alpha-pinene alone. Zelenyuk will discuss the chemical reactions that lead to these findings, direct evidence of the non-linear interactions between manmade pollution and natural airborne particles.

Reference: Alla Zelenyuk, PHYS 377: New experimentally-based secondary organic aerosol paradigm, Wednesday, Aug. 19, 1:30 p.m. - 2:00 p.m., Room 252B - Boston Convention & Exhibition Center.

This work was supported by the Department of Energy Office of Science.

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