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Microwaves Improve CO2 To CO Conversion

Efficient heating of industrial process could significantly reduce energy costs

by Elizabeth K. Wilson
December 9, 2013 | A version of this story appeared in Volume 91, Issue 49

The proposed mechanism for the microwave-driven Boudouard reaction invokes the generation of electron-hole pairs.
These schemes show how thermal and microwave exposure affect the Boudouard reaction.
The proposed mechanism for the microwave-driven Boudouard reaction invokes the generation of electron-hole pairs.

The conversion of carbon dioxide to carbon monoxide over a solid carbon substrate, known as the Boudouard reaction, is a key component of coal gasification and smelting processes. Scientists are also interested in harnessing the reaction to remediate excess CO2 because it’s a greenhouse gas. But the reaction CO2 + C → 2 CO normally requires temperatures above 600 °C, making it costly. Albert E. Stiegman and colleagues at Florida State University show they can reduce the temperature at which the equilibrium favors CO production to a mere 213 °C by using micro­waves instead of heat sources such as steam (J. Phys. Chem. C 2013, DOI: 10.1021/jp4076965). Although microwaves have been known to increase rates of hetero­geneous gas-phase reactions, the altered thermodynamics based on this type of heating method have not been observed before, the researchers say. Because microwaves rapidly heat the solid carbon substrate while CO2 gas passes through unheated, this reaction lends itself well to the study of microwave heating mechanisms—determining whether microwaves are just heating the reactants or exerting an irradiation effect. Stiegman’s team posits that microwave heating could be causing the carbon substrate to generate a steady supply of electron-hole pairs with which the CO2 reacts.


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