Regulating the Electronic Structure of Pd Nanoparticles on NH3-Pretreated Nano-Flake TiO2 for Efficient Hydrogenation of Nitrile Butadiene Rubber

The heterogeneous selective hydrogenation of nitrile butadiene rubber (NBR) is an efficient method to generate high value-added hydrogenated NBR. Nevertheless, the inherent large molecular size and high spatial hindrance of polymers lead to poor activity and metal loss. Herein, we report a simple support ammonia pretreatment strategy for the synthesis of efficient N-doped Pd catalyst and applied for the NBR hydrogenation. The results reveal that N doping enhances electron transfer from the support to Pd more effectively than oxygen-rich vacancy support, thereby substantially enhancing the electron cloud density and stability of the Pd sites. The formation of more electron-rich Pd sites not only significantly enhances the adsorption-activation ability of C=C and H2, but also lowers the apparent activation energy of the reaction. As a result, the Pd/N-TiO2-R demonstrates best activity with a hydrogenation degree (HD) of 98 % and a TOF value of 335 h-1, significantly higher than that of Pd/TiO2-R (HD=83 %, 282 h-1) and Pd/TiO2 (HD=74 %, 204 h-1). This strategy will provide new inspiration to improve the activity and stability of Pd/TiO2 catalysts for the hydrogenation of unsaturated polymers.