Gang Wu,Shasha Liu,Jie Ren,Jiawei Zhu,Yun Yu,Suzana Yusup,Dengyu Chen,Shu Zhang,Yong Huang
The development of efficient and recyclable heterogeneous catalysts for the catalytic conversion of cellulose into high-value platform chemicals has garnered significant attention. Cobalt sulfide, recognized for its earth-abundance and recyclability, has emerged as a promising catalyst for the production of methyl levulinate (ML) from cellulose, albeit with a noted disparity in catalytic performance when compared to conventional homogeneous catalysts. In this study, various phosphorus-doped cobalt sulfides (CoS x P 2-x ) were employed to enhance the production of ML from cellulose, with a particular focus on the sulfide-phosphorus ratio. Notably, an optimal ML yield of 48.9 wt% and a complete conversion of cellulose were achieved at a sulfide-to-phosphorus ratio of 1:1. Comprehensive characterization of the synthesized CoS x P 2-x materials revealed that CoS 1.00 P 1.00 exhibited distinctive properties, such as the presence of ternary acid sites and the lowest Co 3+ /Co 2+ ratio among the series. Density functional theory (DFT) calculations elucidated that the bound electrons within the P-Co bonds were activated by the synergistic effects among Co, P, and S atoms, thereby diminishing the free energy barrier for the adsorption of reaction intermediates.
Zhao Nannan,Wang Songbo,Cheng Penggao,Zhang Jianping,Zhang Lei,Du Wei,Tang Na
Co 3− x Mn x O 4 is a bimetal oxide with excellent electrochemical activity in alkaline solution, has been regarded as a promising alternative in the field of ion-air batteries and proton exchange membrane fuel cell (PEMFC). Herein, we report a simple solvothermal-calcination method to fabricate Co 3− x Mn x O 4 with tunable external Co 3+ /Co 2+ and Mn 3+ /Mn 2+ ratio. The tunable ratio of element valence in the bimetal results in a higher exposure of active center for oxygen redox reaction (ORR), and thus lead to a better ORR activity, which was confirmed by X-ray photoelectron spectroscopy characterizations and electrochemical measurements. Specially, Co 1.8 Mn 1.2 O 4 with a Co 3+ /Co 2+ ratio of 2.08 showed an overpotential of 0.37 V at benchmark ORR current density of 3 mA/cm 2 in 0.1 M KOH, which is lower than that of pure oxide (Mn 3 O 4 0.53 V and Co3O4 0.56 V). In addition, the as prepared Co 1.8 Mn 1.2 O 4 exhibited a positive half-wave potential (0.83 V vs RHE) due to their more active sites, promotes charge transfer, adsorption and desorption of oxygen species. This work provides a strategy for the design and fabrication of earth-abundant, low-cost electrocatalysts for PEMFC in practical applications. Graphic Abstract Co 3− x Mn x O 4 was fabricated by tuning external Co 3+ /Co 2+ and Mn 3+ /Mn 2+ ratio, and the activity initially shows a positive correlation with the ration of Co 3+ /Co 2+ in Co 3− x Mn x O 4 .
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