ZrO Nanocrystals As Catalyst for Synthesis of Dimethylcarbonate from Methanol and Carbon Dioxide: Catalytic Activity and Elucidation of Active Sites.

The catalytic activity of zirconium oxide (ZrO) nanocrystals for the reaction of carbon dioxide (CO) with methanol to form dimethylcarbonate (DMC) was investigated. ZrO nanocrystals prepared by hydrothermal synthesis at various temperatures were compared. The size of the ZrO nanocrystals monotonically increased with the hydrothermal temperature, according to specific surface area, transmission electron microscope measurements, and their X-ray diffraction peak widths. The ZrO nanocrystals prepared by hydrothermal synthesis were found to exhibit high catalytic activity owing to their high surface area and catalytically active surfaces arising from their high crystallinity. Next, adsorbed species generated from CO on the ZrO surfaces were measured using CO temperature-programmed desorption (TPD) and in situ FT-IR spectroscopy. The results confirmed the presence of several kinds of adsorbed species including bidentate bicarbonate (b-HCO), bidentate carbonate (b-CO), and monodentate carbonate (m-CO). The relationship between the amounts of these surface species and the catalytic activity of the ZrO was investigated for the first time. The amount of the bidentate species (b-HCO and b-CO) was found to correlate well with the catalytic activity, demonstrating that the surface sites that afford these species contribute to the catalytic activity for this reaction.