A study of active sites for isosynthesis over zirconium dioxid

Sulfur trioxide, CO and CO/H$sb2$ were used in adsorption, titration and steady stat experiments over undoped zirconias, yttria stabilized zirconias, and calcia stabilized zirconias to determine that surface oxygen anion vacancies are the active site for isosynthesis over zirconia. The sulfur trioxide was adsorbed as a (ZrO)$sb3$S=O sulfate and the carbon monoxide was adsorbed as a formate. CO/H$sb2$ pre-formed methoxide on the catalyst surface which was then titrated off with water to form methanol. CO/H$sb2$ were also reacted over zirconia catalysts under steady state conditions to form methanol and methane. A correlation between the amount of SO$sb3$ adsorbed and the vacancy mobility in yttria doped zirconia formed the basis for proposing that SO$sb3$ titrates the anion vacancy sites on the surface of zirconia. Correlations were also found between the amount of methoxide titrated, the amount of CO adsorbed, the steady state catalytic reaction rate, and the amount of SO$sb3$ adsorbed over zirconia in general. Another correlation was found between the amount of methoxide titrated over calcia stabilized zirconia and the vacancy mobility in that same catalyst. These correlations support the hypothesis that the active site for CO hydrogenation and isosynthesis over zirconia is an oxygen anion vacancy.;Results over undoped zirconias were used to explore the effects of calcination treatment, cooling time and pretreatment on the concentrations of active sites per unit area. Increased severity of calcination led to an increase in active site concentration but a decrease in surface area. Slow cooling (hours) versus quenching the catalyst in air led to a decrease on both active site concentration and surface area. Oxygen/hydrogen pretreatment at 600$spcirc$C was found to increase the concentration of active sites relative to oxygen pretreatment at 600$spcirc$C alone. The concentration of active sites could also be influenced via the addition of dopant molecules such as CaO and Y$sb2$O$sb3$.;The use of SO$sb3$ as a probe to titrate anion vacancies and as a technique to identify active sites for isosynthesis was also developed. The above results suggest that SO$sb3$ titration may be useful in other cases where anion vacancies are suspected of being the active site for a reaction. Since metal oxides are employed as the catalyst for reaction may be more generally applicable to other metal oxide catalyzed reactions.