This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Australian researchers and international collaborators have demonstrated a solar-driven approach to convert glycerol, a low-value byproduct of biodiesel production, into hydrogen and higher-value chemicals. Using advanced techniques at the Australian Synchrotron, they revealed how the catalyst changed while it was working.
The study, led by researchers at the University of New South Wales, investigated a process known as photoreforming, in which light energy is used to drive chemical reactions to simultaneously produce hydrogen and transform organic feedstocks into useful products. The research was published in Applied Catalysis B: Environment and Energy. Glycerol is produced in large quantities by the growing biodiesel industry, with approximately 100 kilograms (220 pounds) generated for every ton of biodiesel.
Crude glycerol can be worth as little as US$0.11 per kilogram. Chemicals can be produced from it, such as glyceraldehyde and dihydroxyacetone, which have applications in the chemical and pharmaceutical industries and are valued at approximately US$75 and US$150 per kilogram, respectively. Denny Gunawan from UNSW said the opportunity was to use sunlight not only to produce hydrogen, but also to extract greater value from an existing industrial byproduct.
"Rather than using an expensive feedstock simply to produce hydrogen, photoreforming gives us the opportunity to do two useful things at once: generate hydrogen and convert a low-value byproduct into more valuable chemicals," said Gunawan. "The challenge is that glycerol can follow several different reaction pathways. If we understand what controls those pathways, we can start designing catalysts that steer the reaction toward the products we want." The researchers developed a photocatalyst based on zinc indium sulfide, which was modified with very small amounts of nickel and cobalt.
Under visible light, adding the nickel-cobalt cocatalyst increased the hydrogen evolution rate by approximately 10 times compared with the unmodified material. It also changed the chemistry of the reaction, substantially increasing the proportion of glycerol converted through pathways producing glyceraldehyde and dihydroxyacetone. Tests under simulated sunlight demonstrated the simultaneous production of hydrogen and useful organic products, with the catalyst achieving a hydrogen production rate competitive with other reported solar-driven glycerol photoreforming systems.
To understand why nickel and cobalt changed the reaction, researchers needed to observe the catalyst while it was operating. At the X-ray Absorption Spectroscopy (XAS) Beamline, the researchers used two techniques, in situ XAS and Fixed Energy XAS (FE-XAS), to investigate what happened to the nickel and cobalt sites when the photocatalyst was illuminated. By measuring at selected X-ray energies rather than scanning across the full absorption spectrum, FE-XAS can follow changes in the catalyst much faster than conventional XAS.
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