Effects of Brønsted and Lewis acidities on activity and selectivity of heteropolyacid-based catalysts for hydrolysis of cellobiose and cellulose

Heteropolyacids (H3PW12O40, H4SiW12O40) and salts of metal cations (Mn+) and PW12O403- (M3/nPW12O40) act as effective homogeneous catalysts for selective hydrolysis of cellobiose and cellulose to glucose and total reducing sugars (TRS), respectively, in an aqueous phase. For Bronsted acid catalysts, including mineral acid and heteropolyacids, the activity for both reactions increases with a decrease in the deprotonation enthalpies (DPE), indicating that stronger Bronsted acidity is more favorable. For M3/nPW12O40 of 11 kinds of metal ions (Ag+, Ca2+, Co2+, Y3+, Sn4+, Sc3+, Ru3+, Fe3+, Hf4+, Ga3+ and Al3+), the rate of cellulose hydrolysis increases with Lewis acidity of the cation, while the TRS selectivity was highest for cations with moderate Lewis acidity, such as Sn4+ and Ru3+. For the hydrolysis of cellobiose, cellulose and lignocellulose, H3PW12O40 and Sn0.75PW12O40 showed higher TRS yield than H2SO4.