Recent Advances in Solid Catalysts Obtained by Metalloporphyrins Immobilization on Layered Anionic Exchangers: A Short Review and Some New Catalytic Results

Abstract

Layered materials are a very interesting class of compounds obtained by stacking of two-dimensional layers along the basal axis. A remarkable property of these materials is their capacity to interact with a variety of chemical species, irrespective of their charge (neutral, cationic or anionic). These species can be grafted onto the surface of the layered materials or intercalated between the layers, to expand or contract the interlayer distance. Metalloporphyrins, which are typically soluble oxidation catalysts, are examples of molecules that can interact with layered materials. This work presents a short review of the studies involving metalloporphyrin immobilization on two different anionic exchangers, Layered Double Hydroxides (LDHs) and Layered Hydroxide Salts (LHSs), published over the past year. After immobilization of anionic porphyrins, the resulting solids behave as reusable catalysts for heterogeneous oxidation processes. Although a large number of publications involving metalloporphyrin immobilization on LDHs exist, only a few papers have dealt with LHSs as supports, so metalloporphyrins immobilized on LHSs represent a new and promising research field. This work also describes new results on an anionic manganese porphyrin (MnP) immobilized on Mg/Al-LDH solids with different nominal Mg/Al molar ratios (2:1, 3:1 and 4:1) and intercalated with different anions (CO 3 2´o r NO 3´) . The influence of the support composition on the MnP immobilization rates and the catalytic performance of the resulting solid in cyclooctene oxidation reactions will be reported.

Ag Nanoparticles-Based Zinc Hydroxide-Layered Hybrids as Novel and Efficient Catalysts for Reduction of 4-Nitrophenol to 4-Aminophenol

“…[12][13][14] In this structure, the hydroxyl anions on the brucite hydroxide layer are substituted by water molecules and counter anions.…”

“…13,14 The structure of the aforementioned ZHL, Zn 5 (OH) 8 (NO 3 ) 2-.2H 2 O, can be considered a structural variation of the Zn(OH) 2 structure, where one fourth of the octahedral Zn 2+ cations are removed from the layer. 12,13 Every octahedral site occupied by a Zn 2+ cation shares edges with two empty and four occupied octahedra, producing a layer with a residual negative charge ([Zn 3 (OH) 8 ]…”

“…12 To compensate for the deficit in positive charge, tetrahedral Zn 2+ cations accommodate below and above the empty octahedra of the layer. In this way, three corners of the tetrahedra coordinate with oxygen atoms of the layer, whereas the fourth position coordinates with a water molecule.…”

“…9,12,13 In this type of materials, the guest species may be adsorbed both on the external surfaces and/or into the interlayer spacing. In this sense, layered hydroxide salts (LHS) are interesting materials as hosts in intercalation/adsorption reactions.…”

“…In this sense, layered hydroxide salts (LHS) are interesting materials as hosts in intercalation/adsorption reactions. 9,12,14 LHS have a double layered hydroxides (HDS) structure which is similar to that of brucite; [12][13][14] however, the inorganic layers are composed of only one type of metal cation such as Cu…”