Selective Transfer Hydrogenation of Cinnamaldehyde with Alcohol on Amorphous TiO₂ Catalysts: Competitive Adsorption between H₂O and Carbonyl

Abstract

Reduced amorphous TiO2 (A‐TiO2), with high coverage of electrons and protons on its surface, supplies a steady‐state condition for selective hydrogenation reaction. Generally, there are some complex hydrogenation reaction products ascribed to the presence of multiple adsorption modes of cinnamaldehyde (CAL). In our work, the saturated aldehyde (∼48%) and unsaturated alcohol (52%) coexist in the products with a ratio of near 1 : 1, while the saturated alcohol is not produced in the reaction. Furthermore, the presence of H2O could suppress the adsorption of the C=O group while the C=C group could be strongly adsorbed on the surface of A‐TiO2, which results in the high selectivity of HCAL (∼84%). We explain these results by proposing a reaction mechanism with several adsorption modes of CAL affected by the solvents. This discovery also puts forward a new method for promoting the selectivity of COL by removing the H2O in the reaction system.

Applications of Sensitized Semiconductors as Heterogeneous Visible-Light Photocatalysts in Organic Synthesis

“…When heated at high temperatures (200–500 °C), this semiconductor recovers its strong Lewis acidity by removing the adsorbed water layer. Once activated, the semiconductor was brought back to rt under dry atmosphere and was found capable of undergoing weak adsorption of noncoordinating substrates such as toluene ( 34 ) on the surface through π interaction. , This interaction enables the appearance of a new LMCT band in the visible region. Upon irradiation, charge separation occurs and enables electrons to be injected in the CB of Nb 2 O 5 , which generates the aromatic radical cation 35 .…”