Tailoring intermediates in steam reforming of acetic acid via porosity-confined acid sites on Ni/SiO2 for enhanced catalytic activity

Abstract

Although non-noble Ni-based catalysts exhibit high activity in the steam reforming for hydrogen production, their rapid deactivation caused by sintering of active sites and carbon deposition remains a major obstacle. This study investigated the effects of SiO₂ support synthesis methods-hydrothermal (SiO₂-H), Stöber (SiO₂-S), and commercial (SiO₂-C) on the catalytic performance and coke resistance of Ni/SiO₂ catalysts in steam reforming of acetic acid. Catalytic activity tests revealed that hydrothermally synthesized Ni/SiO₂-H achieved exceptional H₂ yields of 91.3 % and near-complete acetic acid conversion (99.4 %) at 600 °C, outperforming Ni/SiO₂-S (73.3 % H₂ yield) and Ni/SiO₂-C (71.2 % H₂ yield). In-situ DRIFT measurement identified transient surface intermediates and indicated that Ni/SiO₂-H exhibited rapid intermediate turnover frequency, attributable to its dendritic mesopores, abundant acid sites, and hydroxyl-rich surface. These characteristics promoted efficient gasification of reactive fragments, thereby minimizing carbon retention. Thermogravimetric analysis revealed superior coke resistance for Ni/SiO₂-H (51.3 wt% coke vs. 65.9–66.9 wt% for Ni/SiO₂-S and Ni/SiO₂-C) and higher oxidation temperature of coke (621 °C), indicative of more graphitic carbon with enhanced stability in resulting carbon deposit. Transmission electron microscopy elucidated coke morphology disparities: smooth-walled carbon nanotubes formed via controlled growth mechanisms over Ni/SiO₂-H, while Ni/SiO₂-S and Ni/SiO₂-C as the catalysts generated defective carbon nanotubes and amorphous carbon due to pore confinement and impurity-driven nucleation. The synthesis-dependent structural properties of SiO₂-hierarchical mesoporous (Ni/SiO₂-H), layered mesopores (Ni/SiO₂-S), and blocky mesopores (Ni/SiO₂-C)-were conclusively linked to catalytic activity and carbon resistance.