Direct synthesis of HO over Pd-M@HCS (M = Sn, Fe, Co, or Ni): effects of non-noble metal M on the electronic state and particle size of Pd

For the mono-metal Pd based catalysts, the O-O bond in O 2 and H 2 O 2 is easily dissociated due to the higher energy sites of Pd, which decreases the selectivity and productivity of H 2 O 2 . To address this issue, non-noble metals M (M = Sn, Fe, Co, Ni) were doped into palladium precursors to create a series of yolk-shell structure bimetallic catalysts Pd-M@HCS (H = hollow; C = carbon; S = sphere) with Pd-M as the core and porous carbon as the shell. The results indicated that the catalyst Pd-M@HCS doped with Sn, Fe, Co, and Ni has a weak dissociation ability for O 2 , and both the adsorption and dissociation ability for H 2 are improved. Of these catalysts, the catalyst Pd-Sn@HCS gives the best performance, which is benefited by the suitable Pd-Sn nanoparticle size and the best Pd 2+ /Pd 0 ratio. The influence of the n Pd / n Sn ratio in the Pd-Sn@HCS system on catalyst performance was further explored, and the findings revealed that Pd-Sn@HCS had the best catalytic activity and stability when the n Pd / n Sn ratio was 2. The catalyst's H 2 conversion, H 2 O 2 selectivity, and productivity were 35%, 97%, and 3961 mmol g Pd −1 h −1 , respectively. After 10 cycles, the H 2 O 2 productivity of this catalyst remained at 92.1%, which was greater than the H 2 O 2 productivity of the typical Pd-based catalyst Pd/C, which stayed at 37% under the same conditions. Direct synthesis of H 2 O 2 in a yolk-shell structure assisted by M (M = Fe,Co,Ni,Sn) metal doping.