Facile Microwave Synthesis of Hierarchical Porous Copper Oxide and Its Catalytic Activity and Kinetics for Carbon Monoxide Oxidation

Abstract

The synthesis of copper oxide (CuO)-based nanomaterials has received a tremendous deal of interest in recent years. Particularly, the design and development of novel CuO structures with improved physical and chemical properties have attracted immense attention, especially for catalysis applications. We report on a rational, rapid, and surfactant-free microwave synthesis (MWS) of hierarchical porous copper oxide (HP-CuO) with a three-dimensional (3D) sponge-like topology using an MWS reactor. The activity of the microwave (MW)-synthesized HP-CuO catalysts for carbon monoxide (CO) oxidation was studied and compared to CuO prepared by the conventional heating method (CHM). Results showed that HP-CuO catalysts prepared by MWS for 10 and 30 min surpassed the CuO catalyst prepared by CHM, exhibiting T80 of 98 and 115 °C, respectively, as compared to 185 °C of CuO prepared by CHM (T80 is the temperature corresponding to 80% CO conversion). In addition, the MW-synthesized HP-CuO catalysts outperformed the CHM-synthesized CuO, achieving a 100% CO conversion at 150 °C compared to 240 °C in the case of CuO prepared by CHM. Interestingly, the HP-CuO catalyst expressed workable CO conversion kinetics with a reaction rate of c.a.35 μmol s–1 g–1 at 150 °C and apparent activation energy (Ea) of 82 kJ mol–1. The HP-CuO catalyst showed excellent cycling and long-term stabilities for CO oxidation up to 4 cycles and 72 h on the stream, respectively. The enhanced catalytic activity and stability of the HP-CuO catalyst appear to result from the unique topological and structural features of HP-CuO, which were revealed by SEM, XRD, Raman, BET, TGA, XPS, and TPR techniques.