Photocatalytic conversion of CO₂ and CH₄ over immobilized titania nanoparticles coated on mesh: Optimization and kinetic study

The study on immobilized titania (TiO₂) nanoparticles semiconductor on stainless steel mesh for photocatalytic conversion of CO₂ and CH₄ has been investigated. Properties of commercial and calcinated photocatalysts on mesh surface were characterized using UV-vis spectra, BET, FESEM and XRD. The photoreduction products were identified with FTIR and GC. The process conditions was optimized using experimental design and process optimization tools to determine the maximum desired response via Response Surface Methodology (RSM) in conjunction with central composite rotatable design (CCRD). The experimental parameters were stainless steel mesh size, amount of titania nanoparticles, calcination temperature, UV light power and initial ratios of CO₂:CH₄:N₂ in feed. Calcination of coated titania nanoparticles increased the absorption of UV-vis light while uniform photocatalyst structure commensurate with decreasing agglomeration. The optimal conditions for maximum CO₂ conversion of 37.9% were determined as stainless steel mesh size of 140, coated titania nanoparticles on mesh of 4 g, calcination temperature of 600 °C, UV light power of 250 W and 10% of CO₂ in feed. Correspondingly, the selectivity of products were 4.7%, 4.3%, 3.9%, 41.4% and 45.7% for ethane, acetic acid, formic acid, methyl acetate and methyl formate, respectively. The kinetic model, based on Langmuir-Hinshelwood, incorporated photocatalytic adsorptive reduction and oxidation reactions over the catalyst surface, and fitted-well with the experimental data.