Synthesis, characterization and activation of quaternary layered double hydroxides for the one-pot synthesis of methyl isobutyl ketone

Abstract

Quaternary hydrotalcite-like precursors containing Mg(II)Pd(II)Cu(II)Al(III) with (Pd + Cu + Mg)/Al ≈ 3 and varying Pd/Cu molar ratios were prepared by coprecipitation of metal nitrates at constant pH. The precursors and their calcined products were characterized by elemental analysis, powder XRD, TG-DTA, FT-IR diffuse reflectance, TPR and N2 physisorption. Powder XRD indicated the formation of hydrotalcite of good crystallinity as the structure for all the precursors; the crystallinity decreased with increase of Pd2+ and Cu2+ in the Mg–Al brucite like layer. Thermal decomposition of HT-precursors at intermediate temperatures led to amorphous mixed oxides, PdCu/MgAl(O), which on reduction yielded a bi-functional catalyst, Pd0Cu0/MgAl(O). The resulting catalysts with acid, base and hydrogenating sites were highly effective and selective for the one-step synthesis of methyl isobutyl ketone (MIBK) from acetone and hydrogen under mild conditions. Addition of copper with Pd inhibited the formation of hydrogenated by-products, propane-2-ol (IPA) and 4-methyl-pentane-2-ol (MIBA), which resulted an increase of MIBK selectivity and also the stability of the catalysts. A proper balance between acid-base and metallic sites was paramount for high catalytic performance.