Overview
A Nature paper (ITQ, Universidad de Cádiz, ALBA synchrotron) describes KRh@MFI: a potassium-exchanged MFI-type zeolite (ZSM-5 family) containing trace rhodium locked in its straight and zigzag channels. Using the industrial solvent NMP as a molecular plug, the team blocked the misbehaving site and achieved:
- Linear-to-branched ratio: 817:1 (described as state of the art)
- Linear aldehyde (undecanal) selectivity: 96%
- 1-Decene conversion: 99.8%
- Scope: C6 to C10 alpha-olefins
- Rh+ avidly migrates double bonds along the carbon chain; once an alpha-olefin becomes an internal olefin, subsequent hydroformylation yields a messy aldehyde mixture and linearity collapses.
- Rh3+ is specific to hydroformylation and indifferent to isomerization.
- Performance retained over repeated batches; semi-continuous operation demonstrated (solid stays in the reactor, liquid feeds in and out) — a realistic industrial configuration.
- The additive screen covered a family of organic molecules, including fluoro- and bromo-substituted variants, mapping how structure controls preference for Rh+ vs. Rh3+.
- Zhao M., Millán R., et al., Rh3+ stabilized in KRh@MFI catalyses regioselective hydroformylation, Nature (2026), DOI 10.1038/s41586-026-11136-9
- Scienmag: Zeolite-Trapped Rhodium Ions Deliver Record Selectivity in Industrial Hydroformylation, 2026-10-16
- Corma group 2023: Rh-(O)-P-MFI one-pot low-temperature ethylene hydroformylation, Nature Communications
- Corma group 2024: rhodium-zeolite regioselective propene hydroformylation, Nature
- ALBA synchrotron CLÆSS beamline X-ray absorption spectroscopy characterization (as relayed above)
The reaction is hydroformylation — adding a formyl group and a hydrogen across a C=C double bond to make aldehydes. It is one of the largest-volume homogeneous catalytic processes in industry, and for decades it has relied on dissolved rhodium complexes with bulky, expensive, often toxic phosphine ligands to steer the reaction toward the valuable linear aldehyde.
Two site types emerge from the zeolite
Spectroscopy (IR, X-ray absorption at ALBA's CLÆSS beamline) plus DFT calculations show that the sub-nanometric Rh2O3 clusters in the channels are not inert containers: under reaction atmosphere they fragment into isolated ions in two oxidation states, Rh3+ and Rh+. Both can catalyze hydroformylation with comparable energetics — the difference is the side reaction.
Plugging the side reaction instead of purifying sites
The counterintuitive move: rather than synthesizing a purely Rh3+ material, the team let both states coexist and selectively switched off the troublesome one. Nitrogen-containing additives (MP or NMP) preferentially coordinate to Rh+ in the channels, capping those sites like molecular plugs. The solid itself is unchanged, and the switch is reversible and molecular-scale. Measured apparent activation energies support the mechanism: after additive dosing, the isomerization barrier rises far more than the hydroformylation barrier.
Engineering notes
For context, heterogeneous catalysts on this reaction historically stabilize tens-to-one regioselectivity; homogeneous phosphine systems do better at the cost of expensive ligand synthesis, metal loss to product, and extra purification. With global alpha-olefin hydroformylation supporting a large share of aldehyde production, an 817:1 ratio re-opens the accounting on separation energy and feedstock waste.
A design philosophy
The takeaway is not the number but the philosophy: instead of forcing every site to be identical, let site types coexist and switch off unwanted functionality with small, reversible ligands — analogous to allosteric effectors in enzymes, implemented on an industrial zeolite with nothing more exotic than a lactam solvent. The work builds on the team's 2023 Nature Communications Rh-(O)-P-MFI study and 2024 Nature propene regioselective hydroformylation paper.
Assessment
817:1 is a single-substrate, paper-scale result; industrialization still faces long-term stability, additive cost, and scale-up. What makes it memorable: "turning off side reactions" is cheaper than "purifying the active site," and that idea transfers.
Sources and caveats: Zhao M., Millán R., et al., *Rh3+ stabilized in KRh@MFI catalyses regioselective hydroformylation*, Nature, DOI 10.1038/s41586-026-11136-9, as detailed by Scienmag (2026-10-16); the 817:1, 96%, 99.8% figures and C6–C10 scope reflect that secondary report; "credible heterogeneous challenger" is the secondary source's wording, stated conditionally.
References