Selective Photooxidation of Benzyl Alcohol to Benzaldehyde via H-Abstraction by Bi_2.15WO₆ under Alkaline Conditions

Abstract

In this study, Bi2.15WO6 with different morphologies was successfully synthesized and used for the selective photooxidation of benzyl alcohol to benzaldehyde in aqueous solutions. High conversion (85%) and selectivity (85%) can be simultaneously achieved under alkaline conditions by adding ethylenediamine to protect the produced benzaldehyde from overoxidation. In the oxidation process, Bi–OO• and Bi–OOH on Bi2.15WO6, instead of OH• and O2 •–, are the primary oxidizing species to sequentially abstract two H (H+ + e–) from benzyl alcohol, accompanied by the formation of H2O2. Meanwhile, h+ and OH– also minorly contribute to the selective oxidation of benzyl alcohol via the H-abstraction pathway. This study enriches our understanding of the oxidizing species involved in the selective photooxidation of benzyl alcohol to benzaldehyde.

Highly Selective Photooxidation of Benzyl Alcohol to Benzaldehyde by Bi–Mo/g-C3N4 in Aqueous Solution

“…In addition, the significant decrease in the conversion of benzyl alcohol to 20% in the presence of CAT also indicates the important contribution of the peroxo species (Figure 9a). Considering that oxidation of benzyl alcohol to benzaldehyde by Bi 2.15 WO 6 is a H-abstraction reaction, which is accompanied by the production of H 2 O 2 , 19 the DPD colorimetric method was therefore used to determine variations of H 2 O 2 in the reaction system. 27,67 Figure 10a shows that the concentrations of H 2 O 2 increase from 46 to 230 μM with increasing concentrations of benzyl alcohol (0−80 mM) after 150 min of reaction, confirming that the H-abstraction pathway is also involved in the photooxidation of benzyl alcohol by Bi−Mo/ CN-2.…”

“…Actually, our recent work also revealed the importance of surface �Bi−OO• and �Bi−OOH in selective photooxidation of benzyl alcohol to benzaldehyde on Bi 2.15 WO 6 under alkaline conditions. 19,20 Variations of surface peroxo species on various photocatalysts were also investigated by the DPD method. 67 Figure 10c shows that the doped Bi or Mo apparently improves the production of surface peroxo species in the absence of benzyl alcohol, and the significantly higher amount of surface peroxo species on Bi−Mo/CN-2 (7.2 times that of CN, 2.0 times that of Bi/CN and 1.6 times that of Mo/ CN) indicates that the decreased recombination efficiencies of photogenerated carriers and the synergistic interactions between Bi and Mo facilitate the production of surface peroxo species under visible light illumination.…”

“…The slight shift of the Bi−O band position from 300 to 310 cm −1 , accompanied by the formation of the new band at 891 cm −1 , can be attributed to the vibration of O−O bands of the �Bi−OOH peroxo species (Figure 12). 19,20 3.4. Corresponding Mechanisms Involved in Selective Photooxidation of Benzyl Alcohol to Benzaldehyde.…”

“…Likewise, Lyu et al suggested that the surface Ti–OOH peroxo on Pd@HTS-1 achieved 46.4% conversion of benzyl alcohol with high selectivity of 100% toward benzaldehyde. Although the surface Bi–OOH peroxo has been proved to greatly improve the selectivity of benzaldehyde by adding ethylenediamine at pH 13.0, the low selectivity of only 53% in the absence of ethylenediamine indicates the poor oxidation selectivity of Bi–OO• superoxo and Bi–OOH peroxo. How to ensure the high photooxidation selectivity of benzyl alcohol toward benzaldehyde without introducing additives is therefore an interesting topic.…”

Unveiling dual catalysis enhancement of a pyridinium-containing Zn(ii) coordination polymer in aerobic photooxidation of organic substrates and selective photoreduction of CO2

“…1–4 Among them, photooxidation of organic substrates and photoreduction of CO 2 have gained a lot of attention in the past decade, as these reactions not only provide a fundamental understanding of photocatalysis but also show promising practical applications. 5–11 For example, oxidative coupling of amines to imines, oxygenation of sulfides to sulfoxides, oxidation of alcohols to carbonyl compounds, and dehydrogenation of N-heterocycles are several basic reactions in organic synthesis, which are also of significant importance in the production of pharmaceuticals and fine chemicals. 12–16 Using light energy to drive these oxidation reactions is believed to be green, sustainable, and economical, especially with earth-abundant catalysts and molecular O 2 as an oxidant in air under mild conditions.…”