The effects of adding Cr3+, Mn2+, Fe3+, Co2+ Ni2+, Cu2+, Zn2+ and La3+ chlorides as co-catalysts to 1-(1-propylsulfonic)-3-methylimidazolium chloride acidic ionic liquid catalyzed saccharification of corn stover in aqueous medium was studied at 140-170 degrees C, by measuring the total reducing sugar (TRS) and glucose yields. The samples with Mn2+, Fe3+, Co2+ as co-catalysts produced higher TRS yields compared to the sample without the metal ions. The Mn2+ produced the highest catalytic effect enhancements and produced TRS yields of 68.0%, 72.9%, 90.2% and 87.9% at 140, 150, 160 and 170 degrees C respectively; whereas the corn stover samples without the Mn2+ produced TRS yields of 42.9%, 52.3%, 54.4% and 53.5% at the same four temperatures. At higher temperatures of 160 and 170 degrees C, all metal ions studied produced significant enhancements in glucose yields, except Cr3+. The addition of La3+ as a co-catalyst produced the highest glucose yield improvement. (C) 2015 Elsevier Ltd. All rights reserved.