Selective hydrodeoxygenation of tartaric acid to succinic acid
A novel one-step process for catalytic production of succinic acid from tartaric acid, which is largely available in the waste streams of wine making, is developed. A liquid-phase system comprised of a molybdenum oxide catalyst supported on carbon black (MoOx/BC) and hydrobromic acid in acetic acid under a H2 atmosphere is effective for selective cleavage of the C–O bonds of tartaric acid and selective hydrogenation of the resulting unsaturated carbons. Temperature, hydrogen pressure, and catalyst pre-treatment are optimized to understand their impact on catalytic activity and product distribution, leading to an 87% yield of succinic acid at 170 °C. Importantly, reduction of the carboxyl groups and C–C bond cleavage are retarded. Pre-reduction and characterization studies (TPR, XRD, XPS, and XAS) reveal that the high catalyst activity of MoOx/BC is correlated with the lower Mo oxidation states (+4 to 0) formed during pre-reduction that promote cleavage of the C–O bonds of tartaric acid and hydrogenation of the CC bond of the intermediate fumaric acid. Recyclability studies and structural characterization of the recovered catalyst indicate that MoOx/BC remains active upon reuse.