Aqueous Synthesis of Bio-Based 3-Hydroxyl Propionic Acid: Unique Substrate/Product Inhibition Effect over PtAu/TiO2 and Pt/TiO2 Catalysts

Abstract

3-Hydroxypropionic acid (HPA) is an important platform molecule in the polyester industry. However, the synthesis of biobased HPA has been largely unexplored in this field. We reported the aqueous oxidation of bioderived 1,3-propanediol (1,3-PDO) to HPA over bimetallic PtAu/TiO₂ catalysts, achieving a yield of 84.5% and a notably high turnover frequency (TOF) value of 871 h^–1 at 80 °C and 1 MPa O₂ in alkali-free medium. One of the key findings is that d-band upshifted PtAu/TiO₂ catalysts exhibit enhanced catalytic activity due to strong −OH/Pt coordination under a low concentration of 1,3-PDO (<0.3 M). However, under high 1,3-PDO concentration (>1.0 M), these catalysts show pronounced inhibition and poor activity. In sharp contrast, a monometallic Pt/TiO₂ catalyst with poor −OH/Pt coordination but strong −COOH/Pt coupling exhibits an unusual product inhibition by HPA according to experimental studies. Computational investigation has further revealed that the tunable shift of the d-band center in bimetallic PtAu clusters is the critical descriptive factor determining the coordination of −OH and −COOH with Pt sites. The mechanistic insights provide both experimental and theoretical foundation for designing industrial catalysts for polyol oxidation toward value-added commodity chemicals.