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An experimental approach for controlling confinement effects at catalyst interfaces.

Thierry K Slot¹, Nathan Riley¹, N Raveendran Shiju¹

¹Van 't Hoff Institute for Molecular Sciences, University of Amsterdam Science Park 904 Amsterdam 1098 XH The Netherlands g.rothenberg@uva.nl.

Chemical Science

|June 14, 2021

Summary

This summary is machine-generated.

This study reveals that controlling molecular confinement around platinum (Pt) catalyst active sites primarily impacts entropy, not enthalpy. This entropy effect is significant only at very small distances, comparable to reactant molecule size.

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Area of Science:

Catalysis Science
Materials Science
Chemical Kinetics

Background:

Conventional catalyst design focuses on enthalpic effects (Arrhenius activation energy).
The role of entropic factors in catalyst performance is often overlooked.
Designing catalysts to control the pre-exponential factor offers a new avenue for optimization.

Purpose of the Study:

To investigate a novel method for designing supported platinum (Pt) catalysts with tunable molecular confinement.
To analyze the kinetics of the platinum-catalyzed hydrolysis of ammonia borane under varying confinement conditions.
To elucidate the influence of molecular confinement on the enthalpy/entropy trade-off in catalysis.

Main Methods:

Fabrication of supported Pt catalysts with controlled molecular confinement using organophosphonic acid barriers.
Utilizing organothiols as sacrificial layers to precisely control barrier height and distance.
Performing kinetic analysis of ammonia borane hydrolysis using fast, online measurements and generating detailed Arrhenius plots (>300 points).

Main Results:

Molecular confinement significantly influences the entropic component of the enthalpy/entropy trade-off, while enthalpy remains largely unchanged.
The entropic contribution to catalysis is only relevant at short distances (<3 Å for ammonia borane), where the confinement space matches the reactant size.
Confinement effects observed at larger distances are likely enthalpic in nature.

Conclusions:

Catalyst design can be advanced by controlling entropic factors through molecular confinement.
Precise control over the nanostructure around active sites is crucial for tuning catalytic performance.
Understanding distance-dependent confinement effects is key to designing efficient heterogeneous catalysts.