Influence of basicity on 1,3-butadiene formation from catalytic 2,3-butanediol dehydration over gamma-alumina

摘要

The direct catalytic conversion of 2,3-butanediol (BDO) to 1,3-butadiene (BD) was studied over two commercial forms of alumina (denoted as F200 and SCFa) at temperatures between 240 degrees C and 450 degrees C. Even though these two catalysts are both high surface area forms of gamma-alumina, they gave remarkably different results, with SCFa giving higher BD selectivities at all experimental conditions. The difference is attributed to the higher surface area of F200, which means a greater number of acid sites that can convert BDO to methyl ethyl ketone (MEK). NH3 and CO2-TPD results supported this conclusion by showing that the two forms of alumina had different acid/base properties. Experimental results also showed that BD selectivity was improved by increasing temperature, increasing residence time and co-feeding water. The residence time study combined with density functional theory (DFT) calculations proved that 3-buten-2-ol (3B2OL) is an important intermediate in the conversion of BDO to BD. BD selectivity decreases over sodium modified alumina SCFa. It is hypothesized that on sodium-modified alumina, 3B2OL is dehydrogenated to form methyl vinyl ketone (MVK) as opposed to dehydration to BD. Basic sites catalyzed the retro-aldol condensation of MVK, which produces acetone and formaldehyde via cleavage of the C=C bond. This is in agreement with DFT calculations showing that the proposed pathway for acetone formation is more energetically favored on Na-modified gamma-Al2O3 (110) surface compared to the pristine (110) surface. (C) 2016 Elsevier Inc. All rights reserved.