Natural andesite as a sustainable catalyst for green hydrogen generation via NaBH 4 methanolysis

Developing cost-effective, sustainable catalysts is vital to advancing green hydrogen production technologies. This study explores natural andesite volcanic rock for the first time as an efficient, “zero-synthesis” heterogeneous catalyst for sodium borohydride (NaBH4) methanolysis. Comprehensive compositional analyses confirmed a robust multi-mineral framework dominated by quartz, plagioclase, clay minerals, and trace pyrite. Systematic evaluation of operating parameters revealed distinct performance trends: hydrogen generation rates (HGR) increased with temperature due to enhanced thermal activation and collision dynamics, and scaled with reactant concentration up to an optimum threshold dictated by active-site availability. Conversely, excessive solvent volumes or catalyst loadings introduced mass-transfer constraints and particle agglomeration. Under optimized conditions (5 mg catalyst, 125 mg NaBH4, 4 mL methanol, 30 °C), natural andesite delivered an impressive HGR of 46.60 L.min-1.gcat-1 with a remarkably low activation energy of 18.33 kJ/mol, outperforming numerous engineered counterparts. Kinetic modeling supported a Langmuir-Hinshelwood, surface-assisted mechanism in which native mineral synergy facilitated methanol activation and hydride release. Despite moderate cyclic stability, retaining over 66% activity after five cycles due to minor surface passivation by methoxyborate residues, andesite stands as a robust, low-cost material for sustainable on-demand hydrogen generation.