Insights into the roles of metallic and coordinatively unsaturated cobalt sites in efficient 1,5-pentanediol production
Asier Barredo, Nerea Viar, J. Requies, Deepak Verma, Jaehoon Kim, Iñaki Gandarias
Abstract
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 Al 2 O 3 . Different types of active sites are analyzed to establish correlations between catalyst structure and performance. Upon reduction, CoO forms the metallic species Co 0 and coordinatively unsaturated Co 2+ near O vacancies (OVs). These Co 2+ 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 Co 0 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 Co 2+ /OV sites, which favor strong dual-site adsorption via the η 2 -(O1, O2) coordination mode. In the case of FAL, this higher concentration of Co 2+ /OV sites also promotes higher selectivity toward 1,5-PDO. MgO provides basic sites that enhance strong reactive molecule adsorption probably via deprotonation, whereas Al 2 O 3 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 %).