Hydrogenation of commercial polystyrene on Pd/TiO2 monolithic ceramic foam catalysts: catalytic performance and enhanced internal mass transfer

Mechanism of NCNTs Growth on Foamed Nickel and Thus-Prepared PS Hydrogenation High-Performance Carrier NCNTs@FN

Traditional heterogeneous catalysts are affected in the catalytic hydrogenation of PS by the scale effect, viscosity effect, adhesion effect, and conformational effect, resulting in poor activity and stability. Monolithic Pd-CNTs@FN catalysts could eliminate or weaken the impact of these negative effects. We grew nitrogen-doped carbon nanotubes (NCNTs) on monolithic-foamed nickel (FN) and investigate their growth mechanism. Meanwhile, the feasibility of using the NCNTs@FN carrier for PS hydrogenation reaction was also verified. The growth of NCNTs on FN can be divided into 3 stages: initial growth stage, stable growth stage, and supersaturation stage. Finally, a three-layer structure of NCNT layer, dense carbon layer, and FN skeleton is formed. Two types of structures, nickel-doped carbon nanotubes (NiCNTs) and C-Ni alloy, are formed by combining C and Ni, while four nitrogen-doped structures, NPD, NPR, NG, and NO, are formed by C and N. The prepared carrier exhibited an extremely outstanding specific surface area (2.829 × 106 cm2/g) and strength (no NCNTs falling off after 24 h 500 rpm agitation), as well as high catalytic activity for PS hydrogenation after loaded with Pd (2.13 ± 0.95 nm), with a TOF of up to 27.6 gPS/(gPd•h). After 8 repetitions of the catalyst, there was no significant decrease in activity. This proves the excellent performance of Pd-NCNTs@FN in polymer hydrogenation reactions, laying a solid foundation for further research on the mechanism of NCNTs promoting PS hydrogenation and regulating the growth of NCNTs.