Pore structure effects on the kinetics of methanol oxidation over nanocast mesoporous perovskites

Mesoporous LaMnO3 perovskite catalysts with high surface area were synthesized by using the recently developed hard templating method designated as “nanocasting”. Ordered mesoporous silica designated as SBA-15 was used as the hard template. It was found that the surface area of the nanocast perovskites can be tuned (80–190 m2/g) by varying the aging temperature of the SBA-15 template. Nanocast LaMnO3 catalysts showed high conversion efficiencies for the total oxidation of methanol under steady state conditions, the one with the highest value of surface area being the best catalysts, as expected. Kinetic studies were performed for all of the synthesized catalysts. Rate constants were found to vary in accordance with the specific surface area of the nanocast catalyst which depends on the aging temperature of the parent template. From the rate constants obtained from experimental conversions at various space velocities (19500 to 78200 h−1), values of activation energy and pre-exponential factor for the three nanocast LaMnO3 catalysts were determined by the linear regression of the Arrhenius plot. It is observed that the activation energy for all the catalysts remain constant irrespective of the variation in specific surface area. Further, a linear relationship was found to exist between the pre-exponential factor and specific surface areas of the catalysts indicating that the rates per unit surface area remains the same for all the catalysts.

Changing SBA-15 template aging temperature which affects the pore structure of the mesoporous perovskite does not change activation energy. Only preexponential factor is changed proportionally to specific surface area.Figure optionsDownload as PowerPoint slide