Stabilization of the supported nanocatalysts with minimal impact on their activity represents a significant challenge. Herein, we report a strategy of in situ depositing two-dimensional covalent organic frameworks (2D COFs) on heterogeneous catalysts for suppressing the agglomeration and sintering of the supported metal nanoparticles. An imine-based rigid 2D COF with a theoretical pore size of 1.5 nm has been deposited onto the silica-supported copper (Cu/SiO2) and palladium (Pd/SiO2) nanocatalysts controllably. The COF-decorated nanocatalysts are used for various hydrogenation reactions including the reduction of dimethyl oxalate (DMO), furfural, and other chemicals. We find that the deposition of a very small amountof 2D COFs, i.e., less than 1.2 wt% of the supported catalyst, can effectively inhibit the migration and agglomeration of metal nanocatalysts during the hydrogenation at 200-300 °C. For instance, the average size of the Cu nanoparticles only increases from 5.1 ± 0.9 nm to 7.7 ± 0.9 nm after 150 h, compared with an increase from 4.4 ± 1.2 nm to 17.8 ± 2.1 nm for Cu/SiO2. The COF-modified nanocatalysts also exhibit the improved activity and selectivity, e.g., the conversion of DMO approaches 99.6% with a target-product selectivity exceeding 95.4%, both higher than that of the control group. Besides, such high conversion and selectivity can remain for at least 300 h in the reaction. Similar results are achieved for the COF-modified Pd nanocatalysts. Our method provides a new way to addressing the critical issue of nanocatalyst sintering and deactivation in heterogeneous catalysis.

Surface deposition of 2D covalent organic frameworks for minimizing nanocatalyst sintering during hydrogenation

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