Engineering Frustrated Lewis Pair Active Sites in Porous Organic Scaffolds for Catalytic CO2 Hydrogenation

TL;DR

This paper presents a method to design immobilized Frustrated Lewis Pair active sites in porous materials for efficient CO2 hydrogenation.

Contribution

The study formulates practical design guidelines for immobilized FLPs through large-scale screening of 25,000 candidates.

Findings

Boron-containing acidic sites near nitrogen bases in MOFs are effective for CO2 hydrogenation.

Simple descriptors like acidity, basicity, and spatial arrangement predict active site performance.

Design principles derived from top-performing candidates can guide future FLP catalyst development.

Abstract

Frustrated Lewis pairs (FLPs), featuring reactive combinations
of Lewis acids and Lewis bases, have been utilized for myriad metal-free
homogeneous catalytic processes. Immobilizing the active Lewis sites
to a solid support, especially to porous scaffolds, has shown great
potential to ameliorate FLP catalysis by circumventing some of its
inherent drawbacks, such as poor product separation and catalyst recyclability.
Nevertheless, designing immobilized Lewis pair active sites (LPASs)
is challenging due to the requirement of placing the donor and acceptor
centers in appropriate geometric arrangements while maintaining the
necessary chemical environment to perform catalysis, and clear design
rules have not yet been established. In this work, we formulate simple
guidelines to build highly active LPASs for direct catalytic hydrogenation
of CO2 through a large-scale screening of a diverse library
of 25,000 immobilized FLPs. The library is built by introducing boron-containing
acidic sites in the vicinity of the existing basic nitrogen sites
of the organic linkers of metal–organic frameworks collected
in a “top-down” fashion from the CoRE MOF 2019 database.
The chemical and geometrical appropriateness of these LPASs for CO2 hydrogenation is determined by evaluating a series of simple
descriptors representing the intrinsic strength (acidity and basicity)
of the components and their spatial arrangement in the active sites.
Analysis of the leading candidates enables the formulation of pragmatic
and experimentally relevant design principles which constitute the
starting point for further exploration of FLP-based catalysts for
the reduction of CO2.

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