Pore-size dependent catalytic activity of supported Pd catalysts for selective hydrogenation of nitrile butadiene rubber

Pore diffusion effect plays a crucial role in heterogeneous hydrogenation of unsaturated polymers. However, how large pore size can eliminate the pore diffusion limitation remains a controversial issue. Herein, we prepared a series of Pd/SiO2 catalysts with graded pore sizes and investigated the effect of pore size on hydrogenation activity of nitrile butadiene rubber (NBR). It is found that when the catalyst pore size (Dcat) is 7 times of the diameter of NBR chains (DNBR), the Weisz modulus 0 can be reduced to < 0.3 thus the internal mass transfer limitation can be eliminated, making NBR easier to approach the active sites. Consequently, the catalysts with the Dcat/DNBR > 7 exhibit excellent catalytic activity (96.7%) and selectivity (100%) to C = C. This work emphasizes that the pore size of catalysts can regulate the pore transfer limitation and the accessibility of internal active sites, providing useful guidance for the design of efficient macromolecular hydrogenation catalysts. CO 2023 Elsevier Ltd. All rights reserved.

Automated summary

Pore diffusion plays a significant role in the heterogeneous hydrogenation of unsaturated polymers. The influence of pore size on the hydrogenation activity of nitrile butadiene rubber (NBR) was investigated using a series of Pd/SiO2 catalysts with graded pore sizes. It was found that when the catalyst pore size was 7 times larger than the diameter of NBR chains, the internal mass transfer limitation could be eliminated, resulting in excellent catalytic activity (96.7%) and selectivity (100%) towards C=C. This study highlights the importance of pore size in regulating pore diffusion limitation and the accessibility of internal active sites in macromolecular hydrogenation catalyst design.