The addition of lead and calcium to an industrial catalyst can improve its ability to support propylene production at very high temperatures.
This is the claim of scientists at Hokkaido University in Japan who said their catalyst design for propylene production is highly stable, even at 600°C. Their findings have been published in Angewandte Chemie International Edition.
Propylene is a raw material and building block for products including in textiles, plastics and electronics. It was originally produced as a by-product of breaking down saturated hydrocarbons using steam cracking, but this process no longer provides the quantities needed by industry.
More recently, the industry has been making propylene from shale gas, which contains a large amount of methane, and smaller amounts of ethane and propane. Propylene can be produced from propane by removing two hydrogen atoms from it through propane dehydrogenation, a process that requires temperatures of around 600°C. Platinum is widely used as a catalyst in propane dehydrogenation as it is very good at breaking hydrogen atoms away from carbon. A drawback is rapid deactivation by side reactions that occur at high temperatures.
Associate Professor Shinya Furukawa led a team of scientists at Hokkaido University’s Institute for Catalysis to improve currently available platinum catalysts. Specifically, they worked with a platinum catalyst that is alloyed with gallium, one of several inactive metals that can help reduce the unwanted side reactions that deactivate the catalyst at high temperatures by separating the platinum atoms from each other. However, gallium’s separation of platinum atoms is not complete.
Furukawa and his colleagues added lead atoms to platinum-gallium nanoparticles placed on a silicon oxide base. The lead atoms attached to the surface of the nanoparticles wherever three platinum atoms occurred together. This blocks the side reactions that occur at the sites of the aggregated platinum atoms, leaving single atoms to do the dehydrogenation work.
The team said it further improved the catalyst by depositing calcium ions on its silicon oxide base. The calcium ions donate electrons to the platinum-gallium nanoparticles, improving their stability.
“Our ‘doubly decorated’ platinum-gallium catalyst had a significantly superior stability, of one month at 600°C, compared to other reported propane dehydrogenation catalysts which are deactivated within several days,” Furukawa said in a statement.
The researchers tested additives and bases other than calcium ions and silicon oxide respectively, but none had the superior catalytic ability and stability of the doubly decorated platinum gallium catalyst.
“Our catalyst design concept paves the way for enhancing the catalytic performance of intermetallics in saturated hydrocarbon dehydrogenation,” said Furukawa.