Amination of methanol for selective production of acetonitrile over Zn-Al mixed oxide catalysts synthesized at different pH

Abstract

Zn–Al mixed oxides with different acidic and basic natures were synthesized under different pH (8.0–9.5) conditions and applied to the amination of methanol (MeOH). The physical and chemical properties of the samples were characterized using X-ray diffraction (XRD), N2 sorption, and X-ray photoelectron spectroscopy (XPS), as well as temperature-programmed desorption (TPD) with different probe molecules, such as NH3, CO2, iso-propanol (IPA), and MeOH. The conversion of MeOH and selectivity to acetonitrile (ACN) increased as the pH of the synthetic mixture increased to 9.5. The activity of the catalysts was in good accordance with the desorption temperatures of propylene in IPA-TPD and dimethyl ether in MeOH-TPD, while their selectivity to ACN was well correlated with the proportion of the weak base sites on the surface of the catalyst. Particularly, the changes in the acidity and basicity of the catalysts with the synthesis pH were mainly influenced by the degree of disorder of the ZnAl2O4 spinel structure. During the amination of MeOH, the catalytic activity, product selectivity, and deactivation behavior of the catalysts were affected by the reaction parameters. The Zn–Al mixed oxide catalyst was readily regenerated by via simple calcination, which removed the carbonitride and coke that were formed during the reaction.