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Catalyst Cracks Coking Challenge

Feb. 23, 2018
New platinum-copper catalyst resists coking when converting shale gas to methane

Researchers at University College London (UCL), London, and Tufts University, Medford, Mass., say they have found a coking-resistant catalyst that’s also more energy- and cost-efficient for converting the methane in shale gas into hydrocarbon fuels.

The catalyst, a PtCu alloy, is able to retain activity as it deters carbon buildup, and uses less energy to break the carbon-hydrogen (C-H) bonds than other materials, they report. In addition, current methods require temperatures of about 900°C; the new material could lower this to 400°C, saving energy.

To investigate the performance of the alloy, UCL researchers, led by Michail Stamatakis, traced the reaction using computers, while Tufts chemists and chemical engineers, led by Charles Sykes, ran surface science and micro-reactor experiments to demonstrate the catalyst’s viability.

Platinum-Copper Catalyst

Figure 1. A scanning tunneling microscope reveals three platinum atoms on the surface of a model copper single atom alloy catalyst. Source: Charles Sykes, Tufts University.

Results showed the platinum breaks the C-H bonds, while the copper helps couple hydrocarbon molecules of different sizes, allowing conversion to fuels. The researchers also report that the single atom alloy was very stable and only required a small amount of platinum to work.

“Our scanning tunneling microscope allowed us to visualize how single platinum atoms were arranged in copper. Given that platinum is over $1,000 an ounce, versus copper at 15 cents, a significant cost saving can be made,” notes Sykes.

A recent issue of Nature Chemistry contains more details.

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The team now plans to further develop coking-resistant catalysts. Bench-scale trials of the PtCu single-atom alloys for dehydrogenation of alkanes currently are underway. “The first one, dehydrogenation of butane at 400°C, is reported in the Nature Chemistry paper; the catalyst showed 100% stability over 48 hours,” says Sykes. “We have yet to try C-H activation chemistry/shale gas dehydrogenation on NiCu and RhCu single atom alloys. Calculations suggest that these will be even more active than PtCu,” he adds.

In addition to coking resilience, the single-atom alloys suit many types of hydrogenations and reforming of alcohols. Narrowing down which alloy combination and which chemical reaction to try next is a challenge. “There are so many possibilities. Our theory collaborators are helping guide us to find the most impactful ones, as theory is much faster than experiments,” notes Sykes.

“At UCL, we are performing theoretical studies on a large class of single atom alloy catalysts that consist of Cu, Ag, and Au as hosts, doped with Ni, Pd, Pt, Rh and Ir. In terms of chemical processes, again we are approaching this from a very broad perspective, studying reactions of interest in hydrogenation processes, selective couplings, partial oxidations, conversion of biomass to useful chemicals, and CO2 utilization,” elaborates Stamatakis.

Making the catalyst on a larger scale pose doesn’t pose any major issues. “The only challenge we see with scale up is deactivation of PtCu catalytic nanoparticles via sintering; this could be addressed with the use of appropriate supports. Also, there are thermodynamic limitations when converting methane to higher hydrocarbons, and we have recently started performing calculations to help us understand the effect of temperature and reactor design. We have had unofficial discussions with industrial contacts, who have shown keen interest in our work, but there is no specific timeline from lab to pilot as of yet. We will keep publishing our work so that everyone can benefit from the results,” concludes Stamatakis.

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