Gasoline could soon come from... gasoline exhaust

Fossil fuels aren’t forever. There were only so many dead dinosaurs and other organisms that morphed into sludge over millions of years, and burning them only produces carbon dioxide emissions that gnaw away at our ozone layer, but there might be a way to reverse that.

You can turn CO₂ right back into gasoline if you can just capture it and re-morph it (without the process taking 70 million years). Burn the gasoline, capture the carbon, and repeat infinitely. With that in mind, chemical engineers Michael Cargnello and Chengshuang Zhou of Stanford University, along with their research team, created a catalyst that can change CO₂ into 1,000 times more butane than the next most efficient catalyst, given the same exact process.

“For the catalytic reaction to happen at high rates, the catalyst should be able to activate reactants (like CO₂ and H₂) effectively,” Zhou told SYFY WIRE. “Most metals that activate H₂ easily are not as active when it comes to activating CO₂, since CO₂ is much more inert than H₂.”

Zhou, who led a study recently published in PNAS, kept experimenting with a catalyst created by Cargnello. CO₂ needs something to set off the chemical reaction which forms the long-chain hydrocarbons gasoline is made of. Under maximum pressure, butane is the longest hydrocarbon it can produce. This happens when the CO₂ is hydrogenated — it reacts with hydrogen when set off by a catalyst, then reduced so its carbon bonds with hydrogen and forms a hydrocarbon. The catalyst had to be engineered to produce longer hydrocarbons like butane. Enter ruthenium.

Ruthenium (Ru) is a rare transition metal that, when coated in plastic, can catalyze a reaction between CO₂ and hydrogen to produce hydrocarbons like butane (C₄H₁₀). It can activate both H₂ and CO₂ for hydrogenation without a problem. Catalysts need to remain stable and not be eaten up by the reaction. Ruthenium won’t bond with the reactants, and when it does, the bond is destroyed by hydrogen. Hydrogenation doesn’t happen anywhere near its melting point, so its atoms stay where they are, but it can really make the reaction take off when coated in plastic.

“After polymer encapsulation, openings in the polymer create many confined areas on the Ru surface and the interactions between the polymer and Ru seem to affect the activation pattern of H₂ and CO₂ in a way that the overall C to H ratio is notably increased,” said Zhou.

Butane is the ideal fuel to produce with hydrogenation because it is liquid at room temperature, unlike gaseous short-chain hydrocarbons like methane, ethane, and propane. This makes storage much easier and eliminates worry about it leaking into the atmosphere. Ruthenium may activate both CO₂ and H₂  but plays favorites. On its own, it is more likely to activate H₂ and end up with mostly hydrogen and not much carbon on its surface. Because carbon bonds to carbon in butane and other long hydrocarbons, you need something to give CO₂ activation an assist.

Add plastic to ruthenium and you get a super-catalyst. With an increased C to H ratio on the surface, there is a drastic increase in how many carbon atoms are likely to bond to each other, which will create those long hydrocarbons needed for butane, and that could produce a whole lot of gasoline. The thing about plastic is that this process might be able to actually produce plastic in the future. There are other alternative plastics being explored, and some have even proven to be superior to the plastics we’re used to. Zhou and his team are still working on it.

“Of all the CO₂ hydrogenation products, only methane cannot be readily utilized for plastics, so its formation needs to be further suppressed,” he said. “I intend to systematically introduce functional groups into the polymer to further modulate the C to H ratio on the catalyst.”

Maybe we really do have a chance at saving the planet before we get hit with another mass extinction.