Specification and optimization of the active centers of a catalyst have long been a challenge in catalysis. Thus far, numerous efforts have been spent on trying to modify the active sites in heterogeneous catalysts. Complementarily, the conversion of CO2 into value-added chemicals such as lower olefins and liquid fuels is attractive due to its potential in mitigating CO2 emissions. However, limitations on rates and selectivity arise due to limited control on individual active site motifs. Herein we report the first example of uniformly encapsulating a metal/metal oxide Ru/TiO2 supported catalyst within a tunable layer of an imine-based porous organic framework (IPOF) with controllable morphology and chemical functionality. Such polymer confinement offers the opportunity to modify the CO2 hydrogenation behavior of the Ru surface, significantly enhancing the C2+ productivity of such a conventional methanation catalyst. Kinetic measurements of the encapsulated catalyst demonstrate a 10-fold increase in the C2-C4 production turnover frequency. Moreover, operando DRIFTS experiments reveal that IPOF encapsulation not only modifies the binding strength of surface intermediates, but also changes the CO2 hydrogenation pathway on Ru surfaces, favoring C-C coupling and subsequent C2+ production. We further demonstrate that the polymer effect is general and occur on several Ru/metal oxide supported catalysts with similar magnitude of selectivity control. Such polymer-induced reactivity control provides promising opportunities for the rational engineering of active sites and selectivity tuning not only for CO2 conversion but as a general tool for other selective transformations in supported catalyst systems.

Tuning CO2 hydrogenation at polymer/metal interfaces

ACS Spring Meeting 2021

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