Deciphering the role of Cu⁰ and Cu^σ+ in engendering the hydrogen production from glycerol reforming over Cu/CeO₂: The effect of different Cu precursors

Copper-based catalysts have been widely reported as remarkable candidates in reforming processes; however, they often suffer from poor stability, sintering, and deactivation over extended periods under high-temperature conditions. Hitherto, the information of the mechanism of the Cu precursor that induces the strong metal-support interaction over the Cu-based catalysts, the role of Cu⁰ and Cu^σ+ that engendered the reforming, and the stabilization of Cu facets remain limited in the literature. Here, we demonstrate that copper-acetate-based catalyst supported on CeO₂ (Cu/CeO₂(A)) is a promising candidate for glycerol reforming in terms of stability and reforming efficiency compared to sulphate and nitrate-based Cu/CeO₂ catalysts. Through a series of characterization analyses (H₂-TPR, H₂-TPD, XPS, N₂O, HRTEM, Raman spectroscopy, in-situ DRIFTS, and variable-temperature PXRD), the presence of Cu^δ+ species in the Cu/CeO₂ were found to be the main active sites for promoting the reforming and CO activation. Whereas the Cu⁰ and oxygen vacancies of CeO₂ were to aid in facilitating the glycerol decomposition. Moreover, the in-situ synchrotron-FTIR microspectroscopy further shows that the ratio of Brönsted: Lewis acidic active sites ratio of Cu/CeO₂(A) (in high spatial-resolution mode) remained stable between 0.17 and 0.18, for both physisorbed and chemisorbed, indicating that the main acidic sites promoting the glycerol dissociative and adsorption were on the LS sites. Notably, a remarkable performance of 95.1 % of glycerol conversion and 80.8 vol.% H₂ production were obtained under the reaction condition of Cu species loading = 10 wt.%, reaction temperature 600 °C, glycerol concentration = 10 wt.%, and WHSV =1.953 h⁻¹.