A series of solid base catalysts, including Al2O3, MgO, MgO/Al2O3, and a Mg(Al)Ox mixed oxide (derived from a commercial hydrotalcite precursor), were prepared, characterized, and evaluated for liquid-phase transesterification of ethyl acetate with excess methanol at 55 °C. In addition, promoters (Li+, K+, and Cs+) were added to MgO via incipient wetness impregnation using various alkali metal salts. The catalysts were characterized by powder X-ray diffraction, N2 porosimetry, inductively coupled plasma-optical emission spectroscopy (ICP-OES), and CO2 temperature-programmed desorption (TPD). The order of catalytic activity was MgO &gt; Mg(Al)Ox &gt;&gt; MgO/Al2O3 &gt; Al2O3, which roughly parallels catalyst ranking by basic site density from CO2 TPD. Higher activity typically was achieved by calcination at 500°C than 600°C. CO2 TPD indicated that addition of alkali metals increases total basic sites and shifts the distribution toward strong basic sites. Alkali oxides from decomposition of LiNO3 provide strong basic sites and greatly increase catalytic activity. Compared with catalysts prepared from the hydroxides and carbonate salts, catalysts prepared from KNO3 and CsNO3 contain residual NO3- species that have a significant negative effect on catalytic activity. The benefits of alkali metal promoters in heterogeneous base-catalyzed transesterification are well known; however, the homogeneous contribution of leached alkali metal ions to total catalytic activity typically has been neglected. Herein, the homogeneous contribution was assessed by extracting metal ions from the solid catalysts using methanol and employing the filtered extract (leachate) and ethyl acetate in the catalytic reaction. The homogeneous contribution from leached alkali metals is much more significant than that of Mg2+ leached from unpromoted MgO consistent with the higher concentrations of leached alkali metal ions measured by ICP-OES.

Heterogeneous base-catalyzed transesterification

2019 Fall National Meeting

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