Specific Photocatalytic\nC–C Coupling of Benzyl\nAlcohol to Deoxybenzoin or Benzoin by Precise Control of C<sub>α</sub>–H Bond Activation or O–H Bond Activation by Adjusting\nthe Adsorption Orientation of Hydrobenzoin Intermediates

Benzyl alcohol (BA) is a major biomass derivative and\ncan be further\nconverted into deoxybenzoin (DOB) and benzoin (BZ) as high-value products\nfor industrial applications through photocatalytic C–C coupling\nreaction. The photocatalytic process contains two reaction steps,\nwhich are (1) the C–C coupling of BA to hydrobenzoin (HB) intermediates\nand (2) either dehydration of HB to DOB or dehydrogenation of HB to\nBZ. We found that generation of DOB or BZ is mainly determined by\nthe activation of C<sub>α</sub>–H or O–H bonds\nin HB. In this study, phase junction CdS photocatalysts and Ni/CdS\nphotocatalysts were elaborately designed to precisely control the\nactivation of C<sub>α</sub>–H or O–H bonds in\nHB by adjusting the adsorption orientation of HB on the photocatalyst\nsurfaces. After orienting the C<sub>α</sub>–H groups\nin HB on the CdS surfaces, the C<sub>α</sub>–H bond dissociation\nenergy (BDE) at 1.39 eV is lower than the BDE of the O–H bond\nat 2.69 eV, therefore improving the selectivity of the DOB. Conversely,\non Ni/CdS photocatalysts, the O–H groups in HB orient toward\nthe photocatalyst surfaces. The BDE of the O–H bonds is 1.11\neV to form BZ, which is lower than the BDE of the C<sub>α</sub>–H bonds to the DOB (1.33 eV), thereby enhancing the selectivity\nof BZ. As a result, CdS photocatalysts can achieve complete conversion\nof BA to 80.4% of the DOB after 9 h of visible light irradiation,\nwhile 0.3% Ni/CdS photocatalysts promote complete conversion of BA\nto 81.5% of BZ after only 5 h. This work provides a promising strategy\nin selective conversion of BA to either DOB or BZ through delicate\ndesign of photocatalysts.