Coke-resistance enhancement of mesoporous γ-Al2O3 and MgO-supported Ni-based catalysts for sustainable hydrogen generation via steam reforming of acetic acid

Highly ordered mesoporous γ-Al₂O₃ particles and MgO materials were synthesized by evaporation induced self-assembly (EISA) and template-free hydrothermal co-precipitation routes, respectively. Ni, Ni–MgO, and Ni–La₂O₃-containing catalysts were prepared using a wet-impregnation method. The synthesized catalysts were characterized by N₂ adsorption–desorption, XRD, SEM-EDS, DRIFTS, XPS, TGA-DTA, and Raman spectroscopy analysis. The mesoporous γ-Al₂O₃ catalyst support exhibited a high surface area of 245 m²/g and average pore volume of 0.481 cm³/g. The DRIFTS results indicate the existence of large Lewis's acid regions in the pure γ-Al₂O₃ and metal-containing catalysts. Catalytic activity tests of pure materials and metal-containing catalysts were carried out at the reaction temperature of 750 °C and a feed molar ratio of AA/H₂O/Ar:1/2.5/2 over 3 h. Complete conversion of acetic acid and 81.75% hydrogen selectivity were obtained over the catalyst 5Ni@γ-Al₂O₃. The temperature and feed molar ratio had a noticeable impact on H₂ selectivity and acetic acid conversion. Increasing the water proportion in the feed composition from 2.5 to 10 considerably improved the catalytic activity by increasing hydrogen selectivity from 81.75% to 91%. Although the Ni-based γ-Al₂O₃-supported catalysts exhibited higher activity performance compared to the Ni-based MgO-supported catalysts, they were not as resistant to coke formation as were MgO-supported catalysts. The introduction of MgO and La₂O₃ into the Ni@γ-Al₂O₃ and Ni@MgO catalysts' structures played a significant role in lowering the carbon formation (from 37.15% to 17.6%–12.44% and 12.17%, respectively) and improving the thermal stability of the catalysts by decreasing the agglomeration of acidic sites and reinforcing the adsorption of CO₂ on the catalysts' surfaces. Therefore, coke deposition was reduced, and catalyst lifetime was improved.