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Grubbs-type catalysts are being studied as tools for breaking down unsaturated rubber in waste tyres, but this is still laboratory research—not an established industrial recycling process. Two recent studies show different approaches: one converts tire-like rubber into an intermediate that can be pyrolyzed to make isoprene; another reports a tandem reaction that produces C5–C7 cycloalkenes.
How does Grubbs’ catalyst help recycle tyre rubber?
Many tyre rubbers contain carbon–carbon double bonds. Olefin metathesis rearranges those bonds, and researchers have used it to break rubber networks into soluble intermediates or smaller cyclic molecules. The catalyst does not simply melt or remove the rubber: the outcome depends on the feedstock, catalyst, reaction sequence and any downstream processing.
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In the studies discussed here, metathesis is a chemical route for recovering molecules from rubber waste. It is distinct from mechanical grinding and from any blanket claim that tyres are already being recycled this way at commercial scale.
Two reported routes, with different products
| Route | Feedstock and sequence | Reported outcome | Evidence status |
|---|---|---|---|
| Isoprene route | Putro and colleagues used tire-like isoprene rubber containing sulfur cross-links and carbon black. Successive ring-closing metathesis was followed by pyrolysis. | The metathesis step solubilized organic components without heating, allowing separation from carbon black. The organic fraction had a reported number-average molecular weight (Mn) of 1,000 Da; its main cyclodepolymerization product was an isoprene cyclic tetramer. Subsequent pyrolysis produced isoprene as the main monomer product, alongside benzene, toluene and xylene. | Laboratory research report; commercial operation is not established. |
| Tandem cycloalkene route | Park and colleagues report tandem isomerization and ring-closing metathesis for synthetic rubber, including post-consumer vulcanized rubber such as tyres. The catalyst context includes second-generation Hoveyda–Grubbs catalyst (HG2). | The paper reports C5–C7 cycloalkene products. This product slate is distinct from the isoprene route. | Research report; commercial operation is not established. |
The first route is not simply another description of the second. In the isoprene work, metathesis creates a cyclic intermediate that is then pyrolyzed; in the tandem work, the reported products are cycloalkenes from a different reaction design. Their feedstocks and outputs should not be conflated.
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What the isoprene experiment demonstrates
Putro and colleagues studied tire-like isoprene rubber with sulfur cross-links and carbon black. Their reported metathesis step dissolved the organic part without heating, which made it possible to separate that fraction from the carbon black. The resulting organic fraction had Mn of 1,000 Da, and the principal cyclodepolymerization product was an isoprene cyclic tetramer. Pyrolyzing that intermediate yielded isoprene as the main monomer product, with benzene, toluene and xylene also reported.
The sequence matters: metathesis first produces an intermediate, and pyrolysis then produces the monomer-rich output. The study therefore demonstrates a possible chemical pathway, not a direct one-step conversion of mixed scrap tyres into reusable tyre material. The authors’ abstract calls it “a promising approach for repurposing waste tires as a renewable feedstock.”
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What the tandem route adds
Park and colleagues describe tandem isomerization and ring-closing metathesis for synthetic rubber, including post-consumer vulcanized rubber such as tyres. The paper reports C5–C7 cycloalkenes and identifies second-generation Hoveyda–Grubbs catalyst, or HG2, in its catalyst context.
This route targets cyclic hydrocarbons rather than the isoprene monomer pathway reported by Putro and colleagues. The two studies illustrate that catalyst choice and reaction sequence can steer rubber deconstruction toward different chemical products; the available evidence does not establish that either product slate is commercially viable.
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Why catalyst and feedstock details matter
Grubbs’ catalyst is a family of ruthenium-based metathesis catalysts, not one universal recipe for every rubber. The cited studies address particular materials and conditions. Tyres contain different rubber formulations and additives, so results for tire-like isoprene rubber or a studied synthetic-rubber sample do not prove that the same reaction will work equally well on every tyre.
Other research broadens the context but does not remove that qualification. A 2016 Green Chemistry study reported first- and second-generation Grubbs catalysts breaking down polybutadiene networks through cross-metathesis; it also tested a styrene-butadiene rubber sheet using G2 and a diester accelerator. A 2026 study reports G2-mediated deconstruction and upcycling of chloroprene rubber. These are examples of research on other rubber systems, not evidence that one method applies unchanged to all tyre formulations.
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Competing reactions can also affect results. One study reports that isomerization side reactions and catalyst decomposition can interfere with ring-closing metathesis outcomes. In practice, the desired product depends not just on naming a catalyst, but on controlling the reaction chemistry for the specific rubber and target molecule.
Does this mean tyres are already being recycled this way?
No. These papers demonstrate experimental chemical routes; the records cited here do not establish commercial-scale deployment, cost competitiveness or lifecycle advantages. A reported laboratory product is not, by itself, proof that a process can handle the volume, mixed composition, contamination and economics of discarded tyres.
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A 2025 Chem article’s “bigger picture” section reports 1.5 billion discarded tyres per year. That is the figure as stated by that article, not an independently verified current global inventory. The scale of the waste problem helps explain the interest in recovering molecules, but it does not establish readiness of these catalyst-based methods.
What to take from the headline
“Grubbs’ catalyst drives tyre recycling” is best read as a shorthand for a promising area of chemical-recycling research. Metathesis can act on double bonds in unsaturated rubber, and researchers have reported routes to soluble intermediates, isoprene after pyrolysis, and C5–C7 cycloalkenes. Those are distinct laboratory demonstrations, not proof that Grubbs-catalyst tyre recycling is a widespread or commercially proven practice.
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