Effect of ZnO on acid–base properties and catalytic performances of ZnO/ZrO2–SiO2 catalysts in 1,3-butadiene production from ethanol–water mixture

Abstract

The effect of ZnO and the preparation method of ZnO/ZrO₂–SiO₂ catalysts on their acid–base properties and catalytic performances in the conversion of diluted ethanol mixtures into 1,3-butadiene (BD) is presented. Based on the results of the temperature-programmed desorption (TPD) of NH₃/CO₂, near-ambient pressure X-ray photoelectron spectrometry (NAP-XPS) with O₂/ethanol + H₂O, adsorption of pyridine and deuterated chloroform followed by Fourier-transform infrared (FTIR) spectroscopy, and catalytic experiments, it has been concluded that the differences in activities and selectivities of the prepared catalysts can be attributed to the formation of different amounts of Zn-containing acidic or basic active sites. A wet-kneading procedure facilitates the preparation of a more active/selective catalyst as compared to that obtained using the incipient wetness impregnation of ZrO₂–SiO₂ with an aqueous solution of zinc salt. Dependencies between the acid–base capacity ratio of zinc oxides, calculated from the NH₃/CO₂-TPD and NAP-XPS data as well as the initial reaction rate of BD formation have been observed for ZnO/ZrO₂–SiO₂ catalysts. In the presence of a catalytic system with a predominance of acidic sites on the surface, higher ethanol conversion and BD selectivity can be achieved as opposed to systems involving a predominance of basic sites. The ZnO/ZrO₂–SiO₂ catalyst prepared by using zinc oxide nanoparticles and ZrO₂–SiO₂ provides a BD yield of ∼52.4% in the conversion of 80% ethanol–20% H₂O mixture (673 K, 1.3 g_EtOH g_cat⁻¹ h⁻¹); a BD productivity of 0.4 g_BD g_cat⁻¹ h⁻¹ can be achieved.