Controlled Synthesis of Palladium Phosphides with Tunable Crystal Phases and Their Sulfur-Tolerant Performance
Zhenbo Guo, Ruifeng Wang, Yuanyi Guo, Jiawei Jiang, Zhiqiang Wang, Wei Li, Minghui Zhang
Abstract
The development of sulfur-tolerant heterogeneous noble metal catalysts with high activity and stability has always been a major challenge. Herein, PdmPn/carbon nanofiber (CNF) catalysts with tunable crystal phases (Pd6P, Pd3P, Pd5P2, and PdP2) were synthesized by a simple impregnation–pyrolysis method, and their sulfur resistance was systematically studied in hydrogenation of sulfur-containing substrates and hydrogenation of aromatic compounds in a sulfur-containing system. Structural analysis showed that all PdmPn/CNF catalysts with phase-pure phosphides exhibited a similar morphology and physicochemical properties. However, the obvious differences in hydrogenation activity (Pd > Pd6P > Pd3P > Pd5P2 > PdP2) and anti-sulfur (Pd < Pd6P < Pd3P < Pd5P2 < PdP2) performance are presented. Overall, Pd5P2/CNFs exhibited the optimal catalytic hydrogenation activity of sulfur-containing substrates and aromatic compounds in sulfur-containing systems, and its turnover frequency (1043.9 h–1) was 20 times higher than that of Pd/CNFs (51.8 h–1) in 4-nitrothioanisole hydrogenation. Combining systematical characterizations with density functional theory calculation, the enhanced resistance to sulfur poisoning of PdmPn/CNFs is attributed to the reduced adsorption strength and adsorption energy of the sulfur-containing molecules. Meanwhile, when sulfur-containing molecules are adsorbed on PdmPn/CNFs, the weakened Pd–S and enhanced C–S bond suggest that it is more difficult to form palladium sulfide from being poisoned. This work was valuable for guiding the design and manipulation of noble metal-based anti-sulfur catalysts.