Immobilized CuCl 2 / TiO 2 photocatalysts for the selective oxidation of benzyl alcohol to benzaldehyde

The oxidation of alcohols to aldehydes is a key transformation in industrial chemistry, as aldehydes are vital intermediates in the synthesis of pharmaceuticals and fine chemicals. Conventional oxidation routes typically employ stoichiometric and corrosive oxidants, generating significant environmental concerns. Greener oxidants such as molecular oxygen (O₂) offer a more sustainable alternative to stoichiometric oxidants; however, their efficient utilization requires activation by catalysts (e.g., Cu-, Pd-, Au-, or Ti-based systems). Homogeneous photocatalysts such as CuCl₂ exhibit promising activity under light irradiation but are limited by challenges in separation and recycling. This study investigates the immobilization of CuCl₂ and TiO₂ (P25) within sodium alginate beads to facilitate photocatalyst recovery and minimize metal leaching. Under UV irradiation for 4 h, benzyl alcohol conversions of 54% (P25) and 49% (CuCl₂) were achieved. Catalyst encapsulation markedly reduced activity due to internal mass transport limitations, as restricted diffusion of O₂ and benzyl alcohol within the bead matrix limited access to active sites and suppressed overall reaction rates. Co-immobilization of P25 and CuCl₂ partially restored conversion (22%), while maintaining high benzaldehyde selectivity (≈1 after 4 h) across all systems. These findings highlight oxygen depletion and mass transfer resistance as key constraints in bead-based photocatalysts. To guide further optimization, a MATLAB-based reactor model incorporating species transport, interfacial mass transfer, and kinetics was developed.