Vinyloxy radicals unveiled as critical intermediates in Ni/La2O3-catalyzed ethanol steam reforming for hydrogen production

Ethanol steam reforming (ESR) offers a sustainable route for hydrogen production, yet its complex reaction network and elusive intermediates hinder catalyst optimization. Here, we identify the vinyloxy radical (CH₂CHO) as the critical chain-carrying intermediate in ESR over Ni/La₂O₃ catalysts, challenging the conventional view of acetyl radical (CH₃CO) dominance. Through in situ synchrotron vacuum ultraviolet photoionization mass spectrometry with molecular beam sampling (SVUV-PI-MBMS), combined with density functional theory (DFT) calculations and microkinetic modeling, the dynamic speciation of gas-phase radicals and stable products are resolved across 473-1073 K. Experimental results reveal CH₂CHO as the predominant intermediate, absent CH₃CO detection. DFT calculations provide a theoretical foundation that supports the experimental observations, demonstrating that the CH₂CHO-mediated pathway has a kinetic advantage over the CH₃CO pathway. This finding aligns with kinetic simulation results, which reveal that CH₂CHO controls 75% of the formaldehyde conversion flux. This work redefines the ESR mechanistic framework, offering a strategy to tailor catalytic pathways via intermediate control.