Experimental and computational studies of the roles of MgO and Zn in talc for the selective formation of 1,3-butadiene in the conversion of ethanol

Abstract

The one-step conversion of ethanol to 1,3-butadiene was performed using talc containing Zn (talc/Zn) as a catalyst. The influence of the MgO and Zn in the talc on the formation rate and selectivity for 1,3-butadiene were investigated. MgO as a catalyst afforded 1,3-butadiene with a selectivity that was nearly the same as talc/Zn at ∼40% ethanol conversion at 673 K, although the rate of 1,3-butadiene formation over MgO was about 40 times lower than that over the talc/Zn. The introduced Zn cations were located in octahedral sites in place of Mg cations in the talc lattice. The Zn cations accelerated the rate of CH₃CHO formation from ethanol, resulting in an increase in the rate of 1,3-butadiene formation. However, the rate of CH₃CHO consumption to form crotonaldehyde was not influenced by Zn, although the distribution of crotonaldehyde was decreased with increasing Zn concentrations. X-ray photoelectron spectra of talc/Zn showed that the O_1s binding energy was increased by increasing the concentration of Zn, while those of both Mg_2p and Si_2p were hardly influenced. DFT calculations were used to estimate the atomic charges on the O, Mg, Si, and Zn atoms when an atom of Zn per unit cell of talc was introduced into an octahedral site. On the basis of the results for the conversion of ethanol into 1,3-butadiene and the corresponding DFT calculations, the roles of the O, Zn, Mg, and Si atoms in the talc catalyst for the formation of 1,3-butadiene from ethanol were discussed.