The role of lattice anion vacancies in the activation of CO and as the catalytic site for methanol synthesis over zirconium dioxide and yttria-doped zirconium dioxide

Abstract

The role of lattice oxygen anion vacancy sites in the activation of CO and in the synthesis of methanol was investigated over ZrO₂. The study involved a comparison of the amounts of CO and SO₃ which adsorbed, the amount of methoxide which could be titrated from zirconia, and the rate of catalytic synthesis of methane and methanol as a function of crystalline phase, calcination conditions, and Y₂O₃ levels in yttria-doped ZrO₂. Infrared and temperature-programmed desorption results established that CO adsorbed as formate and that SO₃ adsorbed as the sulfate (ZrO)₃SO. Uptake studies over yttria-doped ZrO₂ demonstrate that SO₃ interacts with anion vacancy sites to form the sulfate. A maximum in SO₃ and CO adsorption and methanol titration occurred at yttria dopant levels where ionic conductivity is highest for yttria-doped ZrO₂. The correspondence between the amount of formate or sulfate adsorbed and the amount of methanol produced form the basis for concluding that surface oxygen anion vacancies are the catalytic sites for CO activation and methanol synthesis.