Selective oxidation catalysts obtained by immobilization of iron(III) porphyrins on thiosalicylic acid-modified Mg-Al layered double hydroxides

Bringing Homogeneous Iron Catalysts on the Heterogeneous Side: Solutions for Immobilization

Noble metal catalysts currently dominate the landscape of chemical synthesis, but cheaper and less toxic derivatives are recently emerging as more sustainable solutions. Iron is among the possible alternative metals due to its biocompatibility and exceptional versatility. Nowadays, iron catalysts work essentially in homogeneous conditions, while heterogeneous catalysts would be better performing and more desirable systems for a broad industrial application. In this review, approaches for heterogenization of iron catalysts reported in the literature within the last two decades are summarized, and utility and critical points are discussed. The immobilization on silica of bis(arylimine)pyridyl iron complexes, good catalysts in the polymerization of olefins, is the first useful heterogeneous strategy described. Microporous molecular sieves also proved to be good iron catalyst carriers, able to provide confined geometries where olefin polymerization can occur. Same immobilizing supports (e.g., MCM-41 and MCM-48) are suitable for anchoring iron-based catalysts for styrene, cyclohexene and cyclohexane oxidation. Another excellent example is the anchoring to a Merrifield resin of an FeII-anthranilic acid complex, active in the catalytic reaction of urea with alcohols and amines for the synthesis of carbamates and N-substituted ureas, respectively. A SILP (Supported Ionic Liquid Phase) catalytic system has been successfully employed for the heterogenization of a chemoselective iron catalyst active in aldehyde hydrogenation. Finally, FeIII ions supported on polyvinylpyridine grafted chitosan made a useful heterogeneous catalytic system for C-H bond activation.

Enhanced arsenate removal from aqueous solution by Mn-doped MgAl-layered double hydroxides

In this study, Mn-doped MgAl-layered double hydroxides (LDHs) were successfully synthesized for efficient removal arsenate from aqueous solution. The structure and composition of Mn-doped MgAl-LDHs intercalated by different ions such as CO₃^2-, Cl^-, or NO₃^- were investigated. The characterizations of XRD, ATR FT-IR, SEM, TG-DTA, and N₂ adsorption-desorption presented that the Mn-doped MgAl-LDHs (donated as Mn-LDHs) have very similar physical morphologies and properties to the MgAl-Cl-LDHs (donated as Mg-LDHs). However, the Mn-LDHs exhibits more preferable arsenate adsorption than Mg-LDHs. The As(V) removal kinetics data of Mn-LDHs is followed pseudo-second-order expression. The adsorption capacity of As(V) on Mn-LDHs via Langmuir isotherm model was 166.94 mg g^-1. The results of XPS revealed that the enhanced removal mechanism can be attributed to surface complexation of As(V) with Mn on the surface of Mn-LDHs. These results prove that Mn-doped LDHs can be considered as a potential material for adsorption As(V) from wastewater.

A sandwich-type catalytic composite reassembled with a birnessite layer and metalloporphyrin as a water oxidation catalyst

Sandwich-type MnTAPP@bir was synthesized by re-assembly of exfoliated birnessite and MnTAPP, and exhibited superior OER performance.

Oxidation catalyst obtained by the immobilization of layered double hydroxide/Mn(iii) porphyrin on monodispersed silica spheres

Several functional hybrid materials have been reported as immobilized porphyrin derivatives in various organic and inorganic host materials (polymers, mineral clays, silica, etc.), with potential applications in various fields, such as photochemistry, electrochemistry and heterogeneous catalysis. Layered double hydroxides (LDHs), commonly known as hydrotalcite-like materials, have also been analyzed for use as supports for metallocomplexes. Recently, nanocomposite materials with a core-shell structure produced by combining two kinds of nanometer-size materials have received considerable attention, since the use of these materials is a promising strategy to prevent the aggregation and self-oxidation of molecules, reducing the catalytic activity. In this study, monodispersed hierarchical layered double hydroxides on silica spheres (LDH@SiO₂) with core-shell structures were developed for metalloporphyrin immobilization and the materials were used as the oxidant catalysts of different substrates.