High Activity and Stability of PdOx Anchored in Porous NiO Nanofibers for Catalyzing Suzuki Coupling Reactions
Heterogeneous Pd-based catalysts are receiving great attention in cross-coupling reactions due to their distinct advantages of relatively low cost, high stability, easy separation, and recycling. Nonetheless, great challenges still remain in developing heterogeneous catalysts with excellent performance and revealing the origin for efficient catalysis. Herein, we have synthesized a PdOx/NiO NFs catalyst consisting of porous NiO nanofibers and in situ anchored PdOx species by a facile electrospinning–pyrolysis strategy. The electron transfer from NiO to PdO created during the calcination step results in the formation of Pdδ+ (δ < 2) in the PdOx/NiO NFs, validated by both spectroscopic analyses and computational modeling. The PdOx/NiO NFs catalyst exhibits much higher activity than the commercial 5.0 wt % Pd/C and other as-prepared Pd-based catalysts in Suzuki coupling reactions. The turnover frequency (TOF) values for the conversions of iodo-, bromo-, and chlorobenzenes over the PdOx/NiO NFs catalyst are 6.6–7.3 times those over the commercial 5 wt % Pd/C catalyst. Theoretical calculations demonstrate that the configuration of PdO(101)/NiO(111) surface is more propitious to the adsorption and activation of arylhalide and phenylboronic acid than that of Pd(111)/NiO(111) surface. The compelling performance of PdOx/NiO NFs is mainly attributed to the special surface configuration of PdOx and unique electronic state of Pdδ+ species. These traits can be well retained in a long-term reaction owing to the strong metal–support interaction, ensuring the good durability of the catalyst. This study not only develops a promising heterogeneous catalyst with high performance for green synthesis of fine chemicals but also provides insights into the enhancement of catalytic activity achieved by modulating the active centers.
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