Electrochemical hydrogenation (ECH) of biomass-derived platform molecules is a burgeoning route for the sustainable utilization of hydrogen, as the active hydrogen in-situ generated on the electrocatalyst surface from water and participated in hydrogenating adsorbed organic substrates using electricity under ambient condition.
However, the most carbon- and energy-rich component-;the lignin fraction of the biomass, are not utilized effectively due to the carbon-based inactive property and the noble metal catalyzed ECH of phenolic compounds suffers from intense competition with hydrogen evolution reaction (HER).
Very recently, Prof. Yuqin Zou and colleagues in Hunan University elaborately prepared PtRh/MCN bimetallic catalysts (nanoparticles dispersed on highly ordered mesoporous carbon nanospheres (MCN) support) with the goals of distinguishing mechanisms of product formation and densifying competition mechanism between ECH and HER.
By careful experimental mechanistic studies and active adsorbed hydrogen (Had) behavior analysis, PtRh/MCN improved the utilization efficiency of Had to ECH in H-UPD region (> 0 V vs. RHE) with high FEECH of ~88%. The strong overlapping between the d-orbitals electron density of Pt and Rh with a suitable adsorption hydrogen enhanced specific adsorption of phenol, which promoted intrinsic activity for producing Had from water electrolysis.
The phenol ECH pathway and the variation of adsorption energy for the phenol and reaction intermediates on catalysts was confirmed by the operando synchrotron-radiation Fourier transform infrared spectroscopy (SR-FTIR), in-situ SFG, and density functional theory calculations (DFT) for the first time.
DFT calculations confirmed the selectivity difference and the ECH parallel pathways: cyclohexanol and cyclohexanone were formed via hydrogenation/dehydrogenation of intermediates *C6H10OH. These findings deepen our fundamental understanding of the ECH process, and cast new light on exploration of highly efficient electrocatalysts for biomass upgrading.
See the article: Zhou L, Zhu X, Su H, Lin H, Lyu Y, Zhao X, Chen C, Zhang N, Xie C, Li Y, Lu Y, Zheng J, Johannessen B, Jiang SP, Liu Q, Li Y, Zou Y, Wang S. Identification of the Hydrogen Utilization Pathway for the Electrocatalytic Hydrogenation of Phenol. Sci. China Chem., 2021, DOI: 10.1007/s11426-021-1100-y.