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Issue 40, 2020
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An experimental approach for controlling confinement effects at catalyst interfaces

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Abstract

Catalysts are conventionally designed with a focus on enthalpic effects, manipulating the Arrhenius activation energy. This approach ignores the possibility of designing materials to control the entropic factors that determine the pre-exponential factor. Here we investigate a new method of designing supported Pt catalysts with varying degrees of molecular confinement at the active site. Combining these with fast and precise online measurements, we analyse the kinetics of a model reaction, the platinum-catalysed hydrolysis of ammonia borane. We control the environment around the Pt particles by erecting organophosphonic acid barriers of different heights and at different distances. This is done by first coating the particles with organothiols, then coating the surface with organophosphonic acids, and finally removing the thiols. The result is a set of catalysts with well-defined “empty areas” surrounding the active sites. Generating Arrhenius plots with >300 points each, we then compare the effects of each confinement scenario. We show experimentally that confining the reaction influences mainly the entropy part of the enthalpy/entropy trade-off, leaving the enthalpy unchanged. Furthermore, we find this entropy contribution is only relevant at very small distances (<3 Å for ammonia borane), where the “empty space” is of a similar size to the reactant molecule. This suggests that confinement effects observed over larger distances must be enthalpic in nature.

Graphical abstract: An experimental approach for controlling confinement effects at catalyst interfaces

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Supplementary files

Article information


Submitted
28 Jul 2020
Accepted
04 Sep 2020
First published
11 Sep 2020

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2020,11, 11024-11029
Article type
Edge Article

An experimental approach for controlling confinement effects at catalyst interfaces

T. K. Slot, N. Riley, N. R. Shiju, J. W. Medlin and G. Rothenberg, Chem. Sci., 2020, 11, 11024
DOI: 10.1039/D0SC04118A

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