Conversion Of Cellobiose Into Gluconic Acid And Sorbitol Over Carbon Nanotube-Supported Gold And Ruthenium Catalysts

The development of novel routes for the transformation of renewable biomass or biomass-derived resources into useful chemicals is of great importance for establishing sustainable chemical processes.This thesis focuses on the studies of selective oxidation and hydrogenation of cellobiose over CNT-supported gold and ruthenium catalysts,respectively.For the selective oxidation of cellobiose to gluconic acid,activity for the cellobiose hydrolysis as well as the conversion of gluconic acid over various supports has been investigated.Among various supports,CNT exhibits good activity for the cellobiose hydrolysis and is inert toward the conversion of gluconic acid.The catalytic performances of CNT-supported various metal catalysts and Au catalysts loaded on some typical supports are also investigated.It is found that 0.5 wt% Au/CNT prepared by incipient wetness impregnation followed by H₂ reduction at 250℃is the most effective catalyst for cellobiose oxidation.Gluconic acid yield of 80% could be attained at 145℃.The kinetic studies suggest that the cellobiose is hydrolyzed to glucose and subsequently the glucose was oxidized to gluconic acid by oxigen.Further studies suggest that the defects formed over the CNT surfaces may favor the adsorption of cellobiose and thus enhance its conversion.For the hydrogenation of cellobiose,carbon nanotube supported ruthenium is the most effective catalyst.The sorbitol yield of 87%can be obtained over Ru/CNT catalyst under the following conditions:c(cellobiose) = 24 mmol/L,V= 20 ml,P(H₂) = 5 MPa,w(cat) = 0.05 g,T = 185℃,t = 3 h.The mechanism of cellobiose conversion over Ru/CNT catalyst is proposed through detailed kinetics studies.Firtly, cellobiose is converted through hydrolysis and partial hydrogenation to form glucose and 3-β-D-glucopyranosyl-glucitol,respectively.The 3-β-D-glucopyranosyl-glucitol is hydrolyzed to sorbitol and glucose,after which the glucose either from cellobiose or 3-β-D-glucopyranosyl-glucitol is transformed to sorbitol and some other by products.The sorbitol further undergoes isomerization and degredation to mannitol and degradation products,respectively.