Substrate-Dependent Selectivity in Alkyne Semihydrogenation Over a Hydrogen-Competent Pd₃Sn₂ Intermetallic Catalyst.

Area of Science:

• Catalysis
• Materials Science
• Surface Chemistry

Background:

• Heterogeneous hydrogenation faces challenges in balancing rapid H2 activation with preventing product overhydrogenation.
• Site isolation strategies can compromise hydrogen competence, and selectivity is often assumed transferable across similar substrates.

Purpose of the Study:

• To establish a substrate-dependent selectivity framework on Pd-Sn intermetallic catalysts.
• To integrate theoretical predictions with experimental validation for catalyst design.

Main Methods:

• Theoretical calculations to identify active sites and understand reaction mechanisms.
• Synthesis of phase-pure Pd3Sn, Pd3Sn2, and PdSn2 intermetallic catalysts.
• Characterization using aberration-corrected electron microscopy and X-ray absorption spectroscopy.
• Experimental validation of catalytic performance and kinetic studies.

Main Results:

• Pd3Sn2 exhibits a unique surface structure facilitating efficient H2 dissociation and favoring propylene desorption over further hydrogenation.
• Pd3Sn2 achieved 98.0% propylene selectivity at 100% propyne conversion under excess-propylene conditions.
• Other catalysts (Pd, Pd3Sn, PdSn2) showed severe overhydrogenation or sluggish activity.
• Pd3Sn2 demonstrated poor selectivity for acetylene hydrogenation, leading to significant ethane formation.

Conclusions:

• The Pd-Sn intermetallic framework, particularly Pd3Sn2, offers a viable strategy for selective hydrogenation by tuning surface properties.
• Substrate-dependent selectivity is crucial and can be predicted through integrated theoretical and experimental approaches.
• Understanding active site cooperation and intermediate binding is key to designing efficient hydrogenation catalysts.