Photocatalytic CO₂ reduction by CH₄ over montmorillonite modified TiO₂ nanocomposites in a continuous monolith photoreactor

Highlights: • TiO₂/MMT supported monolith photo-reactor was tested for CO₂ reduction with CH₄. • MMT inhibited crystal growth and enhanced TiO₂ photo-activity in monolith reactor. • CO₂ was reduced by CH₄ to CO, CH₃OH, C₂H₆, C₃H₆ and C₃H₈ in a monolith reactor. • CO yield over TiO₂/MMT was 237.5 μmol g-catal.⁻¹ h⁻¹, a 2.52 fold than TiO₂. • Stability test revealed TiO₂/MMT partially lost photo-activity in reused cyclic runs. - Abstract: In this study, the performance of montmorillonite (MMT) modified TiO₂ nanocomposites for photocatalytic CO₂ reduction with CH₄ in a continuous monolith photoreactor has been investigated. The MMT modified TiO₂ nanocomposites were dip-coated over monolith channels and were characterized by XRD, SEM, TEM, XPS, N₂-adsorption–desorption and UV–vis spectroscopy. The MMT produced anatase phase of TiO₂ and reduced TiO₂ crystallite size from 19 nm to 13 nm. CO was the major reduction product with a yield rate of 237.5 μmol g-catal.⁻¹ h⁻¹ over 10 wt.% MMT-loaded TiO₂ at 100 °C, and CO₂/CH₄ feed ratio 1.0. The photoactivity of MMT-loaded TiO₂ monolithic catalyst was 2.52 times higher than bare TiO₂. Likewise, low concentrations of C₂H₆, CH₃OH, C₃H₆ and C₃H₈ were detected in the products mixture. These results inferred MMT modified TiO₂ and monolith photoreactor were beneficial for enhancing photocatalysis process with appreciable productivity. The stability test revealed photoactivity of MMT-loaded TiO₂ nanocomposites partially diminished in recycle runs