Selective conversion of cellulose into bulk chemicals over Brønsted acid-promoted ruthenium catalyst: one-pot vs. sequential process

Abstract

Acid hydrolysis and hydrogenation/hydrogenolysis reactions can be combined for catalytic conversion of cellulose into renewable biorefinery feedstocks by using two heterogeneous catalysts: sulfonic acid (–SO₃H) functionalized mesoporous silica (MCM-41) and Ru/C. The combination is suitable for a one-pot tandem process to convert cellulose into alkanediols (mainly propylene glycol and ethylene glycol), yet deactivation of the sulfonic acid (–SO₃H) functionalized mesoporous silica occurred rapidly after only one reaction cycle because of an irreversible change in the mesoporous structure and loss of acid groups. However, much better selectivity of hexitol or γ-valerolactone (GVL) can be obtained in a sequential tandem process by hydrogenating the hydrolysis products, glucose and levulinic acid (LA). A similar irreversible deactivation of acid catalyst also occurred when it involved the hydrogenolysis of glucose into alkanediols. When the sulfonic acid-functionalized mesoporous silica is filtered, and the hydrolysis products of cellulose are directly used in the hydrogenation reaction without further purification, a better selectivity and stability of hexitol production can be obtained. Under such conditions, the lifetime of the catalyst system can be significantly extended, up to 6 times the original durability of the acid-functionalized silica.