Heterogeneous Catalysts for the One-Pot Synthesis of Chemicals and Fine Chemicals

Hydrotalcite-like anionic clays (HTs; or layered double hydroxides, LDHs) can be used as precursors to mixed oxides, but their catalytic potential reaches much further. This review demonstrates that HTs can be successfully applied in a broad spectrum of organic reactions, with advantages such as improved activity, selectivity, metal dispersion, less waste production, and an improved recuperation of immobilized catalysts. HTs can be used in the as-synthesized form or after different pretreatments. The HT as such is a solid base or, depending on the elemental composition of its octahedral layers, may have redox properties. Specific metals can be incorporated either as a cation in the octahedral layer or as an anion via exchange. The anion-exchange strategy is especially successful in the context of heterogenizing homogeneous catalysts. A particular advantage for base catalysis is that the number and strength of the basic sites can be tuned precisely to a specific reaction. HTs are excellent materials to des...

Hydrotalcite-like anionic clays in catalytic organic reactions

Catalytic applications of layered double hydroxides and derivatives

Applications of Layered Double Hydroxides

Catalytic applications of Layered Double Hydroxides (LDH) or anionic clays have for a long time focused on the condensation reactions carried out with mixed oxides obtained by calcinations of Mg/Al LDH. However, the versatile character of materials prepared from these LDH exhibiting Lewis or Bronsted type basic sites has recently been underlined, and led us to contemplate extended applications in clean industrial processes. Moreover, due to their wide variety of compositions, LDH are also attractive precursors of multicomponent nanostructured catalysts. They give rise to supported metal catalysts whose metal support interaction and cooperation can be fine-tuned, as illustrated in pertinent case studies such as the hydrogenation of nitriles and the “one-pot” synthesis of methyl isobutyl ketone from acetone.

Catalysis by hydrotalcites and related materials

Calcined Mg/Al hydrotalcites (CHT) with various atomic ratios of Mg/Al were prepared and used as support. One-step synthesis of methyl isobutyl ketone (MIBK) from acetone and hydrogen at atmospheric pressure was investigated over Pd/CHT and Ni/CHT catalysts. These catalysts showed high activities and high selectivities to MIBK, reaching 60–70% selectivity at 35–40% conversion in some experiments. A temperature of ca. 140°C was sufficiently high for the calcined hydrotalcite-supported catalyst to assume basic properties and good activities in MIBK synthesis. The loading of metal (or the density of metal sites) was an important factor for product distribution in MIBK synthesis. A strong metal–support interaction was exhibited in these catalysts. A higher reduction temperature (>500°C) was needed for Ni/CHT catalysts to assume considerable reactivity and selectivities. The reduction temperature played an important role in the behavior of the Ni/CHT catalysts.

C.M Hwang

Papers

One-step synthesis of methyl isobutyl ketone from acetone with calcined Mg/Al hydrotalcite-supported palladium or nickel catalysts