amount. To confirm the identification of the major aqueous-phase compounds, electron spray ionization mass spectrometry (ESI-MS),nuclear magnetic resonance (NMR), and gas chromatography coupled with mass spectrometry (GC/MS) were used. Fig. S1 displayed an ESI-MS total ion chromatogram in the regions of m/z 30–160 and
the signals of lactic acid, glycolic acid, formic acid, and acetic acid were observed. As shown in Fig. S2, the 13C NMR spectra of lactic acid in the reaction products matched well with the standards. The GC/MS spectra also confirm the major aqueous phase products, as shown in Fig. S3. Overall, a relatively high yield of lactic acid from xylose can be achieved under mild reaction conditions when using a ZrO2 as the heterogeneous catalyst