Acetone condensation and selective hydrogenation to MIBK on Pd and Pt hydrotalcite-derived Mg [sbnd]Al mixed oxide catalysts

Abstract

The condensation and selective hydrogenation of acetone to methyl isobutyl ketone (MIBK) was studied on a directly comparable series of 0.1–1.5 wt% Pd and Pt catalysts supported on hydrotalcite (HT)-derived Mg Al mixed-oxides in a liquid-phase batch micro-reactor at 99–153 °C and 400 psig. The support catalyzes the condensation of acetone to diacetone alcohol (DAA) and its subsequent dehydration to mesityl oxide (MO); Pd and Pt catalyze the selective hydrogenation of MO to MIBK. The net yield of MIBK is independent of metal type and loading, depending only on the wt% of exposed metal. However, the by-products are quite different-Pt/HT is more selective for the direct hydrogenation to isopropanol (IPA) while Pd/HT forms more of the intermediate diacetone alcohol (DAA). Among the Pd- and Pt-based catalysts examined, the 0.1 wt% Pd/HT gives the maximum MIBK yield of ∼32%, with an unusually low selectivity to IPA, 0.6 mol% compared to 15 mol% for the next best catalyst. This appears to be due to its higher basicity, and (to a lesser extent) to its minimal concentration of metal sites. This metal loading is sufficient to fully hydrogenate mesityl oxide to MIBK, and it also shows minimal acetone hydrogenation to isopropanol. A study of physically mixed Pd/silica + HT versus Pd/HT shows that the acid/base and hydrogenation functions need not be molecularly close.