Facile synthesis of CeO2-supported gold nanoparticle catalysts for selective oxidation of glycerol into lactic acid

• We found chemical reduction with glycerol was effective for Au/nano-CeO2 synthesis.
• Glycerol-based chemical reduction enables the synthesis of larger gold particles.
• Catalyst/glycerol weight ratio affects the product distribution.
• Au/CeO2 selectively catalyzes the glycerol to lactic acid (Con. 98%, Sel. 83%).

This study explores a new synthetic route toward CeO2-supported gold nanoparticles catalysts (1, 3, and 5 wt.% Au) and their catalysis of the oxidation of glycerol at atmospheric pressure. Gold was loaded on a hydrothermally synthesized nanocrystalline CeO2 support (∼8 nm) via deposition-precipitation with urea (DPU). To obtain cerium oxide-supported gold nanoparticles, thermal reduction at 300 °C under flowing H2 is currently popular. However, this method invariably forms small gold particles (<5 nm) even with higher gold loading. In the present study, Au/CeO2 catalysts prepared by DPU were reduced via a new method: chemical reduction with glycerol (CRG). Interestingly, the reduction of a gold-urea complex supported on ceria occurs at 25 °C, and the gold nanoparticles grow slowly. The resultant chemically reduced samples were compared with their hydrogen-reduced counterparts. The CRG method primarily generated gold particles with larger average sizes than the H2 reduction method. Importantly, the CRG route enabled variation of the average gold nanoparticle size without requiring any other reagent, which is particularly advantageous for the Au/CeO2 system. The efficiency of these catalysts toward the aerobic oxidation of glycerol was tested. Accordingly, the selective oxidation of glycerol into lactate can be effectively catalyzed by Au/CeO2 catalysts at atmospheric pressure. The chemically reduced samples show increased lactate selectivity than the hydrogen-reduced samples due to the larger size of the gold particles.

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