Water-tolerant catalysis by Mo–Zr mixed oxides calcined at high temperatures

Abstract

“Water-tolerant catalysis’' of Mo–Zr mixed oxides was investigated using XRD, NH₃ temperature-programmed desorption (TPD), adsorption of water and water-concerning reactions such as hydrolysis of ethyl acetate in excess water and esterification of acetic acid with ethanol in a solid–liquid reaction system. It was found that the activities of MoO₃–ZrO₂ calcined at 1073 K became higher at Mo contents [Mo/(Mo+Zr)] of around 0.2 atomic ratio. When MoO₃–ZrO₂ was calcined at 873–1073 K, the catalytic activity was greatly enhanced and became comparable to that of H-ZSM-5 (Si/Al=40). Whereas the acid strength of MoO₃–ZrO₂ measured by NH₃-TPD was unaffected by the calcination temperature, the amount of acid and the surface area decreased monotonically as the calcination temperature increased. On the other hand, the surface hydrophobicity estimated from the amount of water adsorbed on the surface was greatly enhanced with increase in the calcination temperature. Therefore, it was concluded that the high activity of MoO₃–ZrO₂ calcined at high temperatures is predominantly responsible for the enhanced surface hydrophobicity.