Catalytic reactions by thermally activated, synthetic, anionic clay minerals

The thermal decomposition of a number of anionic clay minerals belonging to the pyroaurites-jogrenite group, such as hydrotalcite (Mg6Al2(OH)16(CO2−3) · 4H2O), results in a product (approximately Mg6Al2O8(OH−)2) which is a fairly strong base (pKa ≤ 35) and a useful catalyst for vapor-phase aldol condensations. Replacement of Mg by Fe, Co, Ni, and Zn, and/or replacement of Al by Fe and Cr also results in isomorphous double hydroxides which, on heat treatment, are catalytically active. A rational method of synthesizing these materials having controlled surface areas has been devised. The effect of the thermal decomposition temperature, MgAl ratio, isomorphous metal cation substitution, and interstitial anion nature on the rate and efficiency of acetone oligomerization has been examined. These materials will also catalyze HD exchange of acetone and toluene but not of n-propylbenzene or cyclohexane (300°C, LHSV ~1). They are relatively poor catalysts for olefin isomerization as well as aromatization of 1,4-cyclohexadiene and limonene.