Ethanol to 1,3‐Butadiene Conversion by using ZrZn‐Containing MgO/SiO₂ Systems Prepared by Co‐precipitation and Effect of Catalyst Acidity Modification

Abstract

Abstract:The conversion of ethanol to 1,3-butadiene (1,3-BD) has been investigated over ZrO2 and ZnO containing magnesia silica oxides prepared by co-precipitation method at different Mg-to-Si molar ratios. The effect of reaction temperature and ethanol flow rate was investigated. The catalyst acidity was modified through the addition of alkali metals (Na, K and Li) to the final materials. Catalysts were characterised by nitrogen physisorption analysis, Xray diffraction, scanning electron microscopy with energy dispersive X-ray, temperature programmed desorption of ammonia, infrared spectroscopy and 29 Si/( 7 Li) NMR spectroscopy. The catalytic results showed that the controlled reduction of catalyst acidity allows suppressing of ethanol dehydration, whilst increasing 1,3-BD selectivity. The best catalytic performance achieved 72 mol % for the combined 1,3-BD and acetaldehyde selectivity.

Recent Breakthroughs in the Conversion of Ethanol to Butadiene

“…One issue is the difference in preparation method which significantly alters many of the features of the MgO-SiO 2 catalysts, making their comparison difficult, as evidenced by the different Mg-to-Si ratios being reported as optimal. In general, it is recognizes that a predominantly basic catalyst with some degree of acidity is the preferred balance to produce active materials [7,13,25,27,29,30,51]. Weckhuysen et al have reported that sufficient amount of Lewis acid in the form of Mg-O-Si with small amounts of strong basic sites has led to the most active wet-kneaded catalysts [51].…”

“…Rather than tweaking the preparation method, the acid properties of a catalyst can be altered by a post-treatment with alkali metals [30,33,60]. Both Jones et al and Wang et al have reported the selective poisoning of the stronger acid sites on their zirconium-containing catalysts [30,33].…”

“…To understand the role of magnesia, they have compared the activity of two MgO catalysts prepared by calcination and by hydrothermal treatment. Surprisingly, hydrothermally-treated magnesia was capable of converting ethanol with a conversion of 36.6% and a selectivity of 47.1% towards butadiene at a WHSV of 0.19 h −1 at 673 K. At the same time, calcined MgO did not lead to the formation of BD, an observation that had previously led several authors to conclude that acidity provided by SiO 2 was actually necessary [12,13,27,29,30]. Based on the XPS spectra of O 1s for both samples, a correlation was drawn between the formation of butadiene and the presence of a distinct oxygen species in the MgO phase.…”

“…Jones et al have investigated the use of mixed zinc and zirconium oxides as promoters for the MgO-SiO 2 catalysts mentioned above which were prepared by wet-kneading and co-precipitation at a variety of Mg-to-Si ratios [30,44]. 1.5 wt % Zr(IV) and 0.5 wt % Zn(II) were introduced by simultaneous aqueous impregnation with the appropriate salts, followed by calcination.…”

“…Based on the XPS spectra of O 1s for both samples, a correlation was drawn between the formation of butadiene and the presence of a distinct oxygen species in the MgO phase. Baba et al suggest that this feature plays a key role in the ETB reaction by being an active site for the MPVO reduction of crotonaldehyde to crotyl alcohol and production of acetaldehyde by heterolytic dissociation involving ethanol (Equation (5) [30,44]. MgO-SiO 2 was initially prepared by wet-kneading magnesium oxide and silica in water.…”