Abstract
AbstractMgO−SiO2 samples, having the composition of natural talc (NT), were obtained by co‐precipitation (CP) and wet kneading (WK) methods. The materials were used as catalysts of the ethanol‐to‐1,3‐butadiene reaction. ZnO, Ga2O3 and In2O3 were tested as promoters. The catalyst WK gave the highest 1,3‐Butadiene (BD) yield among the non‐promoted catalysts because of the high specific surface area and strong basicity. Results suggested that over the neat WK catalyst the acetaldehyde coupling to crotonaldehyde was the rate‐determining process step. Formation of crotyl alcohol intermediate was substantiated to proceed by the hydrogen transfer reaction between crotonaldehyde and ethanol. The crotyl alcohol intermediate becomes dehydrated to BD or, in a disproportionation side reaction, it forms crotonaldehyde and butanol. The promoter was found to increase the surface concentration of the reactant and reaction intermediates, thereby increases the rates of conversion and BD formation. The order of promoting efficiency was Zn>In>Ga.
Highlights
The reaction goes through dehydrogenation of ethanol to acetaldehyde, followed aldol coupling to crotonaldehyde that has to become hydrogenated to crotyl alcohol
Sample (43.0° and 62.5°), whereas the CP sample shows broad line centered at 35.3° and 61.0° indicating the presence of an amorphous magnesium silicate phase.[11]
Figure 6shows that the conversion of ethanol and the selectivity of BD formation were significantly increased by all three applied metal oxide additives
Summary
1.54 Si-to-Mg weight ratio in the chemical formula of natural talc (Mg3Si4O10(OH)). Comparison of the bulk and surface compositions indicate a slight surface enrichment of Mg for the natural talc and for the co-precipitated material. Both samples show Type IV isotherm with H2 type hysteresis loop and another hysteresis loop at p/po > 0.9 due to pores among agglomerated particles. Reflections of MgO having periclase structure is present in the XRD pattern of the WK sample (43.0° and 62.5°), whereas the CP sample shows broad line centered at 35.3° and 61.0° indicating the presence of an amorphous magnesium silicate phase.[11] These results suggest that the CP sample is a more homogeneous mixture of Mg2 +. Oxide dopants could not be identified in the images, the results of quantitative analysis is similar to the values determined by other methods.
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