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 CHCHO formation from ethanol, resulting in an increase in the rate of 1,3-butadiene formation. However, the rate of CHCHO 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 binding energy was increased by increasing the concentration of Zn, while those of both Mg and Si 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.

Recent Breakthroughs in the Conversion of Ethanol to Butadiene

“…A difference in temperature alters the thermodynamics and kinetics of the process, possibly favoring the formation of byproducts. The same is true for the contact time between the reagents and the catalyst [9,19,24]. Therefore, a careful optimization is required.…”

“…Recently, Baba et al have studied the potential of Zn-containing talc as a catalyst [19,55]. Their findings also include observations relevant to the understanding of the magnesia-silica system.…”

“…This suggests that butadiene is produced through a different route, which does not involve the aforementioned intermediate. Nevertheless, because recent kinetic studies have repeatedly supported the validity of this pathway, it cannot be ruled out [16][17][18][19].…”

“…Apart from Bhattacharyya et al, all the publications have dealt with fix-bed reactors [46]. While some researchers have investigated the effect of pressure on the catalytic activity, the reaction is generally conducted at atmospheric pressure; the reviewed literature must be therefore assumed to occur at atmospheric pressure unless otherwise noted [19]. Another parameter that influences the reaction is the catalyst pre-treatment, usually done under inert atmosphere at high temperature to activate the material.…”

“…It was recognized that characterizing the chemical properties and activity of such phases is required to confirm this hypothesis. It should be noted that synthetic talc alone has been demonstrated to be poorly active in the ETB reaction, but was highly active once ethanol dehydrogenation was promoted [19]. A comparison between mechano-chemically (MC) mixed and wet-kneaded (WK) MgO-SiO2 materials was also conducted by Kyriienko et al [28].…”