Converting waste plastic into new chemicals could help alleviate pollution while providing products — such as hydrogen and various carbon-based materials — that are valuable to an energy transition away from fossil fuels. One approach is to first pyrolyse the plastic, which involves heating it to a high temperature in the absence of oxygen to break it down, before carrying out a catalytic process that yields the desired products. However, the catalysts used in the latter process tend to have poor product recovery efficiencies and limited reusability. Now, Huiyan Zhang and colleagues across China and Europe report a reusable stainless-steel catalyst that can be employed in a pyrolytic-catalytic process to produce hydrogen and multiwalled carbon nanotubes (MWCNTs) with high efficiency.
The team test different plastic feedstocks including polyethylene, polypropylene and polystyrene. The plastics are first pyrolysed, forming volatile compounds that then pass over the catalyst. To prepare the catalyst, the researchers take a grade 316 stainless-steel mesh and apply an acid etch followed by calcination, which increases the surface roughness and exposes more active sites for catalysis. The result is that they achieve high carbon and hydrogen atom recovery efficiencies — calculated from the total mass of carbon in the MWCNTs and total mass of hydrogen in the H2 product compared to the amounts in the feedstock — of up to 86% and 70%, respectively. Zhang and colleagues also show that the catalyst can be separated from the MWCNTs by simple ultrasonic treatment and can be re-used at least ten times.
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