(174b) Novel Copper (II) Oxide Nanoleaf Catalyst for the Hydrogen Peroxide Assisted Oxidation of Glycerol to Dicarboxylic Acids: A Combined Theoretical and Experimental Study

Quang Thang Trinh,¹ Prince N. Amaniampong,² Jithin John Varghese,¹ François Jérôme,^2,3, Samir H. Mushrif^1,4,*

¹Cambridge Centre for Advanced Research and Education in Singapore (CARES), Nanyang Technological University, 1 Create Way, Singapore 138602, Singapore.

² INCREASE (FR CNRS 3707), Université de Poitiers, ENSIP, 1 rue Marcel Doré, TSA41105, 86073 Poitiers Cedex 9, France

³ Institut de Chimie des Milieux et Matériaux de Poitiers (IC2MP), Université de Poitiers,

CNRS, ENSIP, 1 rue Marcel Doré, TSA41105, 86073 Poitiers Cedex 9, France

⁴School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.

Corresponding author: SHMushrif@ntu.edu.sg

Abstract: The synthesis of copper (II) oxide (CuO) with leaf-like morphology has been achieved under low frequency ultrasound irradiation (19.95 kHz) within less than 30 min, without the use of any template or surfactant. The advantages of the reported synthesis route are : (i) No calcination or post catalyst treatment required. (ii) Fast, green and scalable method (iii) lesser synthesis time (< 30 min).¹ The catalyst morphology was ascertained by SEM and TEM analysis, and further characterized by XPS, XRD and BET. As-synthesized CuO nanoleaves were used in the conversion of glycerol, in the presence of H₂O₂ and oxalic acid and tartronic acid yields of 56 % and 22 %, respectively were obtained. Density Functional Theory (DFT) calculations were employed to gain insights into the mechanism of glycerol oxidation on the CuO surface. Glycerol is initially activated via the deprotonation of the terminal Hydroxyl, and subsequently undergoes C-H activation to form glyceraldehyde. These steps are facilitated by the unsaturated surface lattice O₃ site on CuO surface with barriers of 43 and 59 kJ/mol, respectively.^2-4 The oxidation of glyceraldehyde to glyceric acid requires the activation of the formyl C-H bond with barrier of 74 kJ/mol and the incorporation of the lattice oxygen into glyceric acid, similarly to our reported mechanism of glucose to gluconic acid on CuO.⁴ Due to the symmetric structure of glycerol, both terminal CH₂OH groups could be oxidized to form Tartronic acid, as observed in experiment results. C-C cleavages were also studied and the results revealed that after glyceraldehyde is formed, the C-C dissociation can occur with activation barrier of 82 kJ/mol, resulting in the forming of Oxalic acid and C₁ species. However, H atoms produced from O-H and C-H activations are strongly bound on surface lattice O₃ sites, hence block those active sites on CuO.^2-4 Secondly, Oxygen vacancy generated during the reaction, would result in the reducing CuO to Cu.^3-5 DFT calculation revealed that H₂O₂ could refill the oxygen vacancies generated during the reaction, resulting into the excellent stability of the catalyst. More interestingly, the surface adsorbed Hydroxyl originating from H₂O₂ can remove H atoms on lattice O₃ site (forming water) and regenerate active sites to increase glycerol conversion. More importantly, the presence of surface OH opens an alternate reaction pathway with lower activation barriers that does not require the incorporation of lattice Oxygen into the product.⁶ The participation of surface OH (from H₂O₂) into the reaction results in excellent glycerol conversion and high catalyst stability.

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