Selective Hydrogenation Catalysis for Alkynes

Selective hydrogenation of alkynes to alkenes occupies a central role in organic synthesis and industrial chemistry, enabling the conversion of triple bonds into double bonds with high precision. The key challenge is to achieve semi-hydrogenation that yields the desired alkene without further reduction to the alkane. Traditional catalysts, such as Lindlar catalysts, rely on palladium poisoned with lead or other modifiers to suppress overhydrogenation, but they often suffer from limited activity, environmental concerns and catalyst deactivation. Recent advances have focused on structural and electronic modulation of catalytic sites, including the generation of isolated metal ensembles, incorporation of interstitial atoms and development of two-dimensional interfaces. Materials such as MXene-supported metallenes, sulphide-modified nanoparticles and atomic overlayers of cuprous oxide on palladium have demonstrated remarkable improvements in selectivity and turnover frequency. These breakthroughs not only reduce the energy footprint and hazardous waste associated with alkyne hydrogenation but also open pathways to more sustainable processes for pharmaceuticals, agrochemicals and fine chemicals. Interdisciplinary efforts continue to refine catalyst design principles, balancing activity, selectivity and stability under mild conditions.

Research from Nature Portfolio

Tripodal palladium metallenes on niobium carbides exhibit a chair-like six-membered ring structure with low coordination numbers, which both facilitates alkene desorption and curbs overhydrogenation. This material achieves turn-over frequencies exceeding 10 000 h⁻¹ and alkene selectivities around 96 % at room temperature, demonstrating scalable synthesis across the MXene family.

Catalysts engineered with interstitial modification of palladium by boron and carbon atoms break traditional scaling relationships between key intermediates. A co-modified palladium achieves a seventeen-fold increase in turn-over frequency compared to conventional poisoned catalysts and sustains alkene selectivities above 95 % at near-complete conversions.

An atomic-thick cuprous oxide overlayer on palladium constitutes a two-dimensional microporous interface that synergistically weakens hydrogen adsorption and enhances activity. The overlayer also mitigates catalyst deactivation by passivation of defect sites with terminal alkynes, delivering sustained performance in semi-hydrogenation reactions.

Selective Hydrogenation Catalysis for Alkynes publication trend

The graph below shows the total number of articles in selective hydrogenation catalysis for alkynes across all publications each year (not limited to Nature Index journals).

Technical terms

Semi-hydrogenation: Partial addition of hydrogen to an alkyne to yield an alkene without further reduction to an alkane.

Overhydrogenation: Undesired full hydrogenation of an alkene product into the corresponding alkane.

Turn-over frequency: Number of catalytic cycles per active site per unit time, indicating catalyst activity.

Metal–support interaction: Electronic and structural effects at the interface between metal nanoparticles and their supporting material.

Intermetallic ensemble: A specific arrangement of metal atoms that constitutes the active site for selective reactions.

Scaling relationship: A linear correlation between adsorption energies of reaction intermediates that limits simultaneous optimisation of activity and selectivity.

References

1. Selective photosynthesis of Z‐olefins through crystalline metal–organic cage‐initiated expeditious cascade reactions. Carbon Energy (2023).
2. Tripodal Pd metallenes mediated by Nb2C MXenes for boosting alkynes semihydrogenation. Nature Communications (2023).
3. Selective ensembles in supported palladium sulfide nanoparticles for alkyne semi-hydrogenation. Nature Communications (2018).
4. Breaking scaling relationships in alkynol semi-hydrogenation by manipulating interstitial atoms in Pd with d-electron gain. Nature Communications (2022).
5. Atomic overlayer of permeable microporous cuprous oxide on palladium promotes hydrogenation catalysis. Nature Communications (2022).
6. Pd-functionalized polydopamine-coated polyurethane foam: a readily prepared and highly reusable structured catalyst for selective alkyne semi-hydrogenation and Suzuki coupling under air. Green Chemistry (2023).
7. Parts-Per-Million of Soluble Pd0 Catalyze the Semi-Hydrogenation Reaction of Alkynes to Alkenes. The Journal of Organic Chemistry (2022).