characterizing the Brønsted acidity and basicity of ZrO2 surface
[42–45]. The adsorbed pyridine FTIR studies also confirmed the
presence of basic sites on the surface of ZrO2 [45,46]. In this work,
the TPD of CO2 was also carried out in the temperature range from
300K to 800K to compare the basicity of ZrO2 and MgO. A large
CO2 desorption peak at 370K and two other peaks at 530K and
590K were observed on MgO while only one peak at 380K was
found on ZrO2, indicating that the existence of much stronger
basic sites on MgO. The results are in good agreement with the
literature data. However, the sole base function cannot explain
why the higher yields of lactic acid were obtained over ZrO2 than
over MgO under our test reaction conditions since MgO has a
stronger basicity based on the CO2 TPD results.