Photocatalytic Reduction of CO₂ to Methanol Using a Copper-Zirconia Imidazolate Framework

• Main Authors: Sonam Goyal, Maizatul Shima Shaharun, Ganaga Suriya Jayabal, Chong Fai Kait, Bawadi Abdullah, Lim Jun Wei
• Format: Article
• Language: English
• Published: MDPI AG 2021-03-01
• Series: Catalysts
• Subjects: methanol; optimization; photocatalytic reduction; imidazolate framework
• Online Access: https://www.mdpi.com/2073-4344/11/3/346

A set of novel photocatalysts, i.e., copper-zirconia imidazolate (CuZrIm) frameworks, were synthesized using different zirconia molar ratios (i.e., 0.5, 1, and 1.5 mmol). The photoreduction process of CO₂ to methanol in a continuous-flow stirred photoreactor at pressure and temperature of 1 atm and 25 °C, respectively, was studied. The physicochemical properties of the synthesized catalysts were studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy. The highest methanol activity of 818.59 µmol/L.g was recorded when the CuZrIm1 catalyst with Cu/Zr/Im/NH₄OH molar ratio of 2:1:4:2 (mmol/mmol/mmol/M) was employed. The enhanced yield is attributed to the presence of Cu²⁺ oxidation state and the uniformly dispersed active metals. The response surface methodology (RSM) was used to optimize the reaction parameters. The predicted results agreed well with the experimental ones with the correlation coefficient (<i>R²</i>) of 0.99. The optimization results showed that the highest methanol activity of 1054 µmol/L.g was recorded when the optimum parameters were employed, i.e., stirring rate (540 rpm), intensity of light (275 W/m²) and photocatalyst loading (1.3 g/L). The redox potential value for the CuZrIm1 shows that the reduction potential is −1.70 V and the oxidation potential is +1.28 V for the photoreduction of CO₂ to methanol. The current work has established the potential utilization of the imidazolate framework as catalyst support for the photoreduction of CO₂ to methanol.