BASIC PROPERTIES OF MG1-X(2+)ALX(3+) LAYERED DOUBLE HYDROXIDES INTERCALATED BY CARBONATE, HYDROXIDE CHLORIDE AND SULFATE ANIONS

摘要

A series of layered double hydroxide (LDH) intercalation compounds of the type [M((I-x)(II))M(x)(III)(OH)(2)][A(n-)](x).zH(2)O have been prepared with (1 - x)/x = 2.2-2.5 and A(n-) = CO32-, OH-, Cl-, and SO42- in order to establish the relationship between composition and the basic properties of the LDH structures. The base-catalyzed disproportionation of 2-methyl-3-butyn-2-o1 (MBOH) to acetylene and acetone was used to judge basic reactivity. Structural characterization was achieved by thermogravimetric analysis, X-ray diffraction patterns, and BET-N-2 surface area measurements after thermal treatment of the intercalates at the temperatures employed in the catalytic reaction. The crystalline LDH intercalates are more reactive toward MBOH transformation than the amorphous oxides formed by thermal decomposition of the LDH structures. The anion basicity influences the LDH reactivity as evidenced by the fact that the carbonate and hydroxide intercalated materials are more active than the chloride derivative. The sulfate derivative exhibits exceptionally high reactivity despite very low surface area when activated at low temperatures. All crystalline LDH intercalates displayed high basic selectivity, but the oxides obtained from the thermal decomposition of the chloride and sulfate intercalates exhibited acidic sites in addition to the basic centers. In the chloride materials the acidity may arise from the replacement of hydroxyl groups in the brucite-like layers by the halide ion. For the thermally decomposed LDH sulfate the acidity most likely originates from magnesium sulfate phase formation. [References: 22]