Mechanically Transformed ZIF-67 Phases as Catalytically Active Nanomaterials for Ammonia Borane Hydrolysis

Zeolitic imidazole frameworks (ZIFs) with tailored open metal sites hold great promise for catalysis. Ball milling of sodalite (SOD) ZIF-67 transformed a stable framework into metastable kat and dia ZIF-67 phases. These metastable phases showed catalytic activity for ammonia borane (AB) hydrolysis, transforming into a nano sheet-like cobalt–imidazolate catalyst (nano Co-Im Cat, dimensions of 40–110 nm), featuring broken Co–N bonds and exposed Lewis acidic (Co3+/Co2+) and basic (N) sites as a consequence of structural opening. The catalyst exhibited good activity; 3 equiv of H2 was released within 2 min with an activation energy of 45.48 ± 0.97 kJ/mol, whereas pristine SOD ZIF-67 showed no detectable activity under identical conditions.