Boyang Liu,Yu Wang,Ning Huang,Xiaocheng Lan,Tiefeng Wang
The development of a highly active heterogeneous catalyst for styrene hydroformylation is a major challenge, and we previously found that Rh2P was a good candidate. By doping a second metal of Co, we further improved the activity by 1.7 times, and the highest TOF reached 2563 h–1 on Rh7Co1P4/SiO2. The addition of Co tuned the electronic environment of surface Rh atoms without changing the crystal structure, and the reaction activity showed a volcano relationship with the Co ratio. DFT calculations showed that Co doping decreased the overall activation energy of surface reactions and destabilized H2 adsorption simultaneously. When x ≤ 2 for Rh8–xCoxP4/SiO2 catalysts, surface Rh atoms had positive valence and H2 adsorption was exothermic. Therefore, the hydroformylation rate was mainly determined by surface reaction with a first order of styrene concentration. When x > 2, however, surface Rh atoms were negatively charged and H2 adsorption became thermodynamically unfavorable. The reaction activity was then determined by H2 adsorption and was independent of styrene concentration. We introduced δE, which was the sum of overall activation energy and H2 coadsorption energy with styrene, to predict activity. Moderate addition of Co decreased the value of δE and promoted the activity, while excessive doping would increase δE.
Quansheng Wu,Songhua Zhou,Chengbing Fu,Jiesong Zhang,Bo Chen,Hongyan Pan,Qian Lin
For the mono-metal Pd based catalysts, the O–O bond in O2 and H2O2 is easily dissociated due to the higher energy sites of Pd, which decreases the selectivity and productivity of H2O2. 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 O2, and both the adsorption and dissociation ability for H2 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 Pd2+/Pd0 ratio. The influence of the nPd/nSn 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 nPd/nSn ratio was 2. The catalyst's H2 conversion, H2O2 selectivity, and productivity were 35%, 97%, and 3961 mmol gPd−1 h−1, respectively. After 10 cycles, the H2O2 productivity of this catalyst remained at 92.1%, which was greater than the H2O2 productivity of the typical Pd-based catalyst Pd/C, which stayed at 37% under the same conditions.
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