Overturning lactic acid hydrogenation regioselectivity via Ru-stabilized MoO3-x overlayers

Controlling regioselectivity in lactic acid conversion is a key for production of bio-based chemicals due to bio-lactic acid molecule containing active bifunctional groups such as hydroxyl (–OH) and carboxyl (–COOH). Here, we report that the Ru-stabilized MoO_3-x overlayers with rich oxygen vacancies overturn lactic acid hydrogenation regioselectivity to propionic acid (PA) via C-OH hydrodeoxygenation, achieving a high PA selectivity of 95.9%, which is completely different from the catalytic feature of the Ru particle surfaces with dominating 1,2-propanediol selectivity through hydrogenation of –COOH. Furthermore, the activity on the encapsulating oxide layers can be extended to other hydroxy acids such as glycolic acid, 3-hydroxypropionic acid, and DL-2-hydroxybutylic acid to generate their corresponding carboxylic acids, displaying a unique ability for hydrodeoxygenation of –OH group. The encapsulating oxide layers with rich oxygen vacancies can be dynamically generated in the presence of the reductive atmosphere such as H₂-Ar mixture, and efficiently stabilized by Ru nanoparticles, thus endowing more excellent activity of Ru-MoO_3-x than that of MoO₃, MoO_3-x and Ru-MoO₃. Encouragingly, lactic acid conversion and propionic acid selectivity have hardly decayed during running 5 cycles due to Ru-stabilized MoO_3-x overlayers. This work provides an efficient strategy for constructing the defective encapsulation oxide layers with rich oxygen vacancies, which helps to produce the desired bio-based chemical of PA from bio-lactic acid.