Li Huang,Jia Wang,Qi Liu,Peng Sun,Mengnan Nie,Guang Gao,Zelun Zhao,Zhiwei Huang,Fuwei Li
Olefin hydroformylation is one of the most important industrial processes for aldehyde synthesis. Heterogeneous catalysts are easy to separate compared with homogeneous catalysts, yet with limited success in activity and regioselectivity control. In the present work, a zeolite-encapsulated rhodium carbide species (RhC x @S-1) catalyst was developed, demonstrating not only relatively high catalytic activity but also good regioselectivity and stability in heterogeneous hydroformylation. The unique microenvironment of rhodium carbide species was formed in situ during the catalyst carbonization reduction process, tuning the steric and electronic characteristics of Rh species to obtain more linear aldehydes. This work shows an alternative strategy to promote the regioselectivity of olefin hydroformylation catalyzed by zeolite-confined catalysts and provides insights into the selective regulation of heterogeneous catalysts.
The homogeneous catalytic hydroformylation of formaldehyde to glycolaldehyde is a key intermediate step for one-step synthesis of ethylene glycol from syngas. The effect of solvent nature on the catalytic response and mechanistic pathway has been rarely studied. A group of parameters (e.g., ε r , μ, α, β) describing the solvent electronic features were achieved for a descriptor database and correlated with the hydroformylation activity. The net electron donating ability has been found to govern the selectivity to glycolaldehyde. The DFT calculation demonstrates the stronger electron-donating solvents serve to lower the energy required for the dissociation of Rh-H to form the anionic rhodium species, which induces the anion mechanism that preferentially facilitates the glycolaldehyde generation. The polar aprotic solvents can be protonated in the dissociation of Rh-H to the anionic species and participate in the HCHO activation through the proton transfer from solvent molecules to HCHO, resulting in the formation of hydroxymethyl species.
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