Contact Us

Center for Catalysis
0755 Gilman Hall
Ames, IA 50011
515-294-3135
vsylin@iastate.edu

Green Chemistry Catalysis Laboratory

More about the Green Chemistry Catalysis Laboratory can be found at http://www.external.ameslab.gov/Catalysishome.htm

Funded Projects

Oxidation and Oxidative Degradation

William Jenks, Iowa State University Department of Chemistry

William Jenks (left) in his laboratory, with graduate student Chaly Oh.

We are investigating the use of new catalysts for the total oxidative decomposition of organic pollutants in water. Two types of catalysts are under investigation, homogeneous systems relying on hydrogen peroxide as the oxidant, and heterogeneous titanium dioxide based catalysts that rely on light for activation but use molecular oxygen as the oxidant.

Chlorinated phenols are persistent and toxic pollutants in the environment for which efficient chemical treatment methods are needed. Soluble iron(III) porphine catalysts have been investigated, and it has been found that exposure to light increases the rate of oxidation, probably because of the accumulation of quinones during the process. A mechanism focusing on the role of the catalyst has been proposed for the early stages of the degradation.

Tungsten-doped titanium dioxide semiconductor catalysts have been prepared by the sol-gel method and characterized by a variety of physical methods, and we have shown that the tungsten is distributed homogeneously throughout the catalyst. These materials should have the property of carrying out photocatalytic degradations using visible light and we are currently investigating both the efficiency of these reactions and the comparison of the chemical outcomes of the early steps, comparing doped and undoped samples. Our goal is to understand the role of the tungsten in the catalyst and how it affects the balance of electron transfer vs. hydroxyl radical chemistry.

Photocatalytic, Heterogeneous Oxidation of Hydrocarbons

Andreja Bakac, Ames Laboratory
Brent Shanks, Iowa State University Dept. of Chemical Engineering
Marek Pruski, Ames Laboratory
Victor Lin, Iowa State University Department of Chemistry

Andreja Bakac (right), with postdoctoral associates Oleg Pestovsky (left) and Kelemu Lemma.

The development of efficient, economical, and environmentally friendly methods for the oxidation of hydrocarbons would constitute a major advance in catalytic chemistry. Such developments could convert the large available supplies of hydrocarbons into valuable industrial feedstocks. Compared to the current technology, the new catalytic oxidations would operate with greatly reduced energy consumption without generating hazardous wastes. The costly disposal procedures and potential contamination of the soil and underground water supplies would be avoided.

Our goal is to develop a catalyst which would not only use inexpensive and environmentally friendly oxidants - oxygen and hydrogen peroxide - but would also utilize light, ideally sunlight, instead of heat as energy source. Such a process would avoid the burning of non-renewable fossil fuels and provide additional economic and environmental benefits. The catalytic process should operate under heterogeneous conditions employing a solid or supported catalyst which can be easily removed from the reaction mixture by standard separation techniques.

This project uses uranium ions, UO₂²⁺, to catalyze photochemical oxidations. We have demonstrated the feasibility of the proposed chemistry in homogeneous solution. Under illumination with visible or ultraviolet light in the presence of uranium ions, hydrocarbons (HC) are oxidized catalytically with molecular oxygen and/or hydrogen peroxide. The only oxidant-derived product is water, which makes the process truly "green" (environmentally safe). Light absorption by UO₂²⁺ converts it into the excited state, *UO₂²⁺, an extremely potent oxidant and hydrogen-abstracting agent. After the initial oxidation step, which usually generates radicals (HC^o), a series of reactions ensue and convert the radicals to final products. At the same time, the reduced uranium is reoxidized to UO₂²⁺ and returned to the beginning of the cycle.

In this multi-investigator effort, we are preparing solid uranium-containing materials to be examined as catalysts for photochemical oxidations. Several synthetic approaches and support materials are being used to optimize both catalyst preparation and activity. If the chemistry works well under heterogeneous conditions, then, in addition to economic and environmental benefits , the project also has a potential to put to use some of the nation's large stockpiles of depleted uranium.