Synthesis of Nanophased Metal Oxides in Supercritical Water: Catalysts for Biomass Conversion

Abstract

Nanoparticles of zinc oxide‐based materials (ZnO, ZnAl 2 O 4 ) with various morphologies were synthesized in supercritical water (SCW) with a flow‐type apparatus and in sub‐ and supercritical water with a batch reactor. In the flow‐type apparatus, smaller particles were obtained. Depending on the precursors, the morphology of crystallites is rod, hexagonal, or rectangular shaped. ZnAl 2 O 4 was synthesized with a high specific surface area ( S BET ) reaching 210 m 2 /g and nanocrystallite sizes ≤10 nm. The KOH concentration played a major role in the formation of ZnO and ZnAl 2 O 4 phases. Then, the synthesized materials were used as catalysts for the biomass conversion by the oxidation process to produce hydrogen.