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

[Display omitted] •A series of Pd/SiO2 catalysts with graded pore sizes were successfully prepared.•Macroporous catalysts facilitate NBR diffusion and improve metal utilization.•The correlation between Dcat/DNBR with HD and Weisz modulus Φ were revealed.•Pd/N-SiO2-70 shows excellent activity (96.7%) and selectivity (100 %) to C = C. 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 Φ can be reduced to 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.