Enzyme-Inspired Microporous Polymer Layers Determine the Reactivity of Encapsulated Metallic Surfaces

Published

August 5, 2019

Author(s)

Andrew Herzing, Andrew Riscoe, Cody Wrasman, Adam Hoffman, Aditya Menon, Alexey Boubnov, Maria Vargas, Simon Bare, Matteo Cargnello

Abstract

Enzymes are natural catalysts that govern precise, biological chemistry through accurate control of transport and activation of species within three-dimensional active sites, but their use in industrial applications is limited by their stability1. Mimicking the chemical diversity and three-dimensional nature of enzyme active sites in heterogeneous catalysts is a pathway to higher performing and more stable systems2. Previous work has focused on using organometallic complexes3, molecularly imprinted silica4, functional tethered complexes5, and metal-exchanged zeolites 6 to achieve this goal. Despite the successes, these systems are limited in functional group selection and/or stability. In this work, we introduce a modular approach for the systematic synthesis of three-dimensional active sites by encapsulating colloidal nanocrystals (NCs) within microporous polymer layers (Porous Organic Frameworks, POFs). We are able to tune POF morphology and chemical functionality, as well as nanocrystal size and composition. The polymer layers provide a confined environment that drastically changes the catalytic performance of the metal surfaces. In particular, we observe an increase in intrinsic rate of palladium nanocrystal surfaces for CO oxidation and the appearance of reaction oscillations, only when specific POF layers cover their surface. Kinetic analysis demonstrates that the increase in rate is related to entropic stabilization of product-like intermediates by the polymer layers surrounding the palladium surface. Reaction oscillations are also shown to depend on the polymer layer chemistry, with POF layers rich in amino groups controlling the diffusion of reactants and products through the confined pockets containing the active sites, in analogy to enzymatic behavior. We demonstrate the ability to regulate these changes in reactivity by controlling the POF layers, as suggested by CO2 adsorption experiments. This approach has a broad scope of catalyst design and is there

Citation

Nature

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Journals

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Citation

Herzing, A. , Riscoe, A. , Wrasman, C. , Hoffman, A. , Menon, A. , Boubnov, A. , Vargas, M. , Bare, S. and Cargnello, M. (2019), Enzyme-Inspired Microporous Polymer Layers Determine the Reactivity of Encapsulated Metallic Surfaces, Nature, [online], https://doi.org/10.1038/s41929-019-0322-7 (Accessed May 7, 2024)