Mechanistic Studies of Methanol Oxidation to Formaldehyde on Isolated Vanadate Sites Supported on High Surface Area Zirconia

The oxidation of methanol on both ZrO 2 and V/ZrO 2 was investigated using temperature-programmed experiments together with in situ infrared spectroscopy. Characterization of V/ZrO 2 after calcination by Raman spectroscopy and XANES shows that the vanadium is present as isolated VO 4 units in a distorted tetrahedral geometry. Methanol was found to adsorb dissociatively on both Zr−O−Zr and V−O−Zr species to create Zr−OCH 3 /Zr−OH and V−OCH 3 /Zr−OH pairs, respectively. Upon heating, CH 3 OH and H 2 O desorb initially from all samples. Above 423 K, surface formate species are detected while H 2 and CO are the main products formed on ZrO 2 . Upon addition of vanadium, CH 2 O production increases dramatically during temperature-programmed reaction. The absence of CH 2 O during temperature-programmed desorption and oxidation experiments on V/ZrO 2 is likely due to rapid readsorption of the product onto the ZrO 2 support, leading to the formation of formate species and H 2 . The apparent activation energy for V/ZrO 2 is 18 kcal/mol. The activities of isolated vanadate species supported on SiO 2, TiO 2, and ZrO 2 are compared and discussed.