Insights into the roles of metallic and coordinatively unsaturated cobalt sites in efficient 1,5-pentanediol production

Herein, the conversion of tetrahydrofurfuryl alcohol (THFA) and furfuryl alcohol (FAL)—hydrogenation products of furfural (FUR)—to 1,5-pentanediol (1,5-PDO) is investigated using a mixed metal oxide catalytic system composed of CoO_x, MgO, and Al₂O₃. Different types of active sites are analyzed to establish correlations between catalyst structure and performance. Upon reduction, CoO forms the metallic species Co⁰ and coordinatively unsaturated Co²⁺ near O vacancies (OVs). These Co²⁺ Lewis acid sites adsorb ether and hydroxyl O atoms from FAL and THFA, thereby weakening or cleaving the C2–O1 bond via coordination interactions. Simultaneously, H activated at the Co⁰ sites undergoes spillover to the adsorbed intermediates, promoting hydrogenolysis and 1,5-PDO generation. At higher reduction temperatures, catalytic activities for both FAL and THFA transformations are enhanced due to the increase in the number and proximity of Co²⁺/OV sites, which favor strong dual-site adsorption via the η²-(O1, O2) coordination mode. In the case of FAL, this higher concentration of Co²⁺/OV sites also promotes higher selectivity toward 1,5-PDO. MgO provides basic sites that enhance strong reactive molecule adsorption probably via deprotonation, whereas Al₂O₃ increases surface area and thus catalytic activity. Although the use of FAL as the reactant results in significantly higher productivity as compared to the case of THFA (FAL: 30.6 mmol_1,5-PDO g_cat.⁻¹ h⁻¹ vs. THFA: 0.3 mmol_1,5-PDO g_cat.⁻¹ h⁻¹), this higher productivity is achieved with the loss of 1,5-PDO selectivity, which is considerably lower (selectivity from FAL: 45.9 % vs. selectivity from THFA: 81.8 %).