probe reactants. It shows that these possible key intermediates
were readily converted to lactic acid in much higher yields: 50.5%
(Table 2, Entry 3) and 93.3% (Table 2, Entry 7) from glyceraldehyde and pyruvaldhyde, respectively, than a lower yield of 40.1%
(Table 2, Entry 1) from xylose. Yet in the absence of ZrO2, much
lower amounts of lactic acid were produced with glyceraldehyde or
pyruvaldehyde as the feedstock. In addition, using glycolal dehyde
as the probe, far less than the stoichiometric amount of glycolic
acid was produced, while a large amount of formic acid was formed
and. Glycolaldehyde can be converted to glycolic acid, similar to the
conversion of acetaldehyde to acetic acid. However, glycolic acid
may be further converted into methanol and CO2 through cleavage of the C C bond. As shown in Fig. S4, the GC/MS spectra of
the aqueous products from reacting glycolaldehyde in the presence
of the ZrO2 identified a considerable amount of higher molecular