Effect of ZnO on acid–base properties and catalytic performances of ZnO/ZrO2–SiO2 catalysts in 1,3-butadiene production from ethanol–water mixture†
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 gEtOH gcat−1 h−1); a BD productivity of 0.4 gBD gcat−1 h−1 can be achieved.