Enhanced Hydrogen Generation Rate and Stability of Cu/MgO/Cubic-ZrO2 Methanol Steam Reforming Catalyst─Promotion Effect of MgO

Methanol reformation is one of the sustainable methods to produce hydrogen on board as a fuel in automobiles. This study found that MgO as a promoter can enhance the hydrogen production rate and stability of the copper catalyst supported on ZrO₂ stabilized in the cubic phase (c-ZrO₂). To investigate the effect of different promoters, a series of copper-based catalysts, Cu/X/c-ZrO₂ (X = Al₂O₃, Y₂O₃, MgO, NiO, and ZnO), were prepared and examined. The physicochemical properties of the catalysts were studied using X-ray diffraction, N₂ adsorption, H₂-temperature-programmed reduction, and X-ray photoelectron spectroscopy. To provide insights on the structure–activity relationship, steam reforming of methanol on these catalysts was carried out under the same experimental conditions and compared. The addition of the secondary metal oxide promoters to Cu/c-ZrO₂ caused notable variations in physicochemical properties and catalytic performance. Among the catalysts studied, Cu/MgO/c-ZrO₂ showed a consistent methanol conversion and a higher hydrogen production rate. Under the optimized conditions, Cu/MgO/c-ZrO₂ exhibited a stable methanol conversion (∼70%) and a consistent hydrogen production rate (∼200 mmol/g_cat/h) even after 45 h of operation. The addition of MgO results in smaller Cu crystallites, which improves the reducibility of CuO_x, enhances the oxygen vacancy concentration, increases the (Cu⁺/Cu⁰)/Cu²⁺ ratio, and boosts methanol steam reforming activity. Moreover, MgO restricts the sintering and oxidation of the active species during the reaction and prevents the phase transformation of c-ZrO₂ into m-ZrO₂