New palladium-Gold Nanoparticle Catalysts Recycle High Value Products from Glycerol

Rice University scientists (from left) Michael Wong, Zhun Zhao and James Clomburg discovered a palladium and gold nanocatalyst that is 10 times faster converting glycerol into high-value products Credit: Jeff Fitlow/Rice University Researchers at Rice University in Houston, Texas have found that a palladium-gold nanoparticle catalyst can recycle waste from the production of biodiesel into high value chemicals. The university explained that chemical engineer, Michael Wong, has spent a decade amassing evidence that palladium-gold nanoparticles are excellent catalysts for cleaning polluted water, but that even he was surprised at how well the particles converted biodiesel waste into valuable chemicals. According to the researchers, Wong’s latest study found that a palladium and gold nanocatalyst is about 10 times faster at converting glycerol, a waste byproduct of biodiesel production, into high-value products than catalysts of either metal alone. The university said, that in scientific parlance, the data from the study produced a ‘volcano plot,’ a graph with a sharp spike that depicts a ‘Goldilocks effect’, a ‘just righ’ balance of palladium and gold. “We’ve now seen this volcano plot at least four times now, first with TCE, then with the dry cleaning contaminant ‘perc,’ and more recently with chloroform and nitrites,” Wong said. “The remarkable thing is that the reaction, in each case, is very different.” In previous studies, researchers explained that the nanocatalysts were used in reduction reactions, chemical processes marked by the addition of hydrogen. In the latest tests on glycerol conversion, the nanocatalysts spurred an oxidation reaction, which involves adding oxygen. “Oxidation and reduction aren’t just dissimilar; they’re often thought of as being in opposite directions,” Wong said. Matchmaking The scientists explained that in chemistry the role of the catalyst is much like that of a matchmaker; catalysts cause other compounds to react with one another, often by bringing them into close proximity, but the catalysts themselves don’t take part in the reaction. Palladium and gold - and mixtures of the two - have long been recognised as extremely effective catalysts. Among catalysts, gold is said to be valued because it doesn’t tarnish or oxidise, a process that can shorten a catalyst’s lifespan. Palladium is typically prized because it is especially good at binding and inducing molecules to reduce or oxidise. Wong and colleagues claimed to have demonstrated a way to bring these two metals together with better control. The hybrid catalysts are built on gold spheres that are about four nanometers in diameter. The spheres are partially covered with palladium, so that the particles’ surface contains some gold and some palladium. The team said that they have shown that covering 60% to 80% of the gold’s surface area with palladium typically produces the ideal catalyst - though the exact percentage varies for different reactions. The synthesis knob “Our synthesis knob, the thing we use to dial in the efficiency, is the coverage area, and the precision of that knob is really what sets us apart from other people who are studying bimetallic catalysis,” Wong said. “That precision is what produces these beautiful volcano plots, but it also helps in another way because it allows us to develop a rigorous explanation for the effects that we’re measuring.” In the latest study, Wong, along with Rice graduate student and lead author Zhun Zhao and colleagues from Rice, Argonne National Laboratory and the University of Groningen in Holland used high-powered X-ray spectroscopy and other techniques to show that the ‘Goldilocks’ coverage area for glycerol catalysis was about 60%. “Palladium by itself oxidizes, which is not good because it slows down the catalysis,” Zhao said. “We found that the gold in our catalysts helps stabilise the palladium and prevents it from degrading. The catalysts in our tests had extremely high durability.” “Our best catalyst produced a glycerol product with higher purity and in less time than anything else we found in the literature,” he continued. Wong added that the research opens up an exciting new area of exploration for his lab. “Now that we understand how these work with glycerol, we can study reactions of other biomass molecules like glucose, a building block of plants,” Wong said. Read More MSU Scientists Researching Hungry Microbes that Eat Nuclear Waste & Produce Biofuel A new fuel-cell concept, developed by a Michigan State University (MSU) researcher, could put an end to the production of hazardous glycerol wastes from biodiesel plants while removing their dependence on fossil fuel from their production process. 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