Role of Reduced Defects for Coupling Reactions of Acetaldehyde on Anatase TiO₂(001)-(1×4) Surface

The chemistry of acetaldehyde (CH₃CHO) adsorbed on the anatase TiO₂(001)-(1×4) surface has been investigated by temperature-programmed desorption (TPD) method. Our experimental results provide the direct evidence that the perfect lattice sites on the anatase TiO₂(001)-(1×4) surface are quite inert for the reaction of CH₃CHO, but the reduced defect sites on the surface are active for the thermally driven reductive carbon-carbon coupling reactions of CH₃CHO to produce 2-butanone and butene. We propose that the coupling reactions of CH₃CHO on the anatase TiO₂(001)-(1×4) surface should undergo through the adsorption of paired CH3CHO molecules at the reduced defect sites, since the existing reduced Ti pairs provide the suitable adsorption sites.