Recently, N-substituted anilines have been the object of increasing research interest in the field of organic chemistry due to their role as key intermediates for the synthesis of important compounds such as polymers, dyes, drugs, agrochemicals and pharmaceutical products. Among the various methods reported in literature for the formation of C–N bonds to access secondary anilines, the one-pot reductive amination of aldehydes with nitroarenes is the most interesting procedure, because it allows to obtain diverse N-substituted aryl amines by simple reduction of nitro compounds followed by condensation with aldehydes and subsequent reduction of the imine intermediates. These kinds of tandem reactions are generally catalyzed by transition metal-based catalysts, mainly potentially reusable metal nanoparticles. The rapid growth in the last years in the field of metal-based heterogeneous catalysts for the one-pot reductive amination of aldehydes with nitroarenes demands for a review on the state of the art with a special emphasis on the different kinds of metals used as catalysts and their recyclability features.

Weakly magnetic hematite (α‐Fe₂O₃) nanoparticles were synthesized by heating an amorphous polymer supported iron(III) complex (Fe_POL) at 400 °C for 4 h in air. The growth of nanoparticles (NPs) was studied by PXRD, heating the polymer from 150 °C to 400 °C at 25 °C intervals, revealing that, at all temperatures, the only crystalline phase detected is hematite. Conversely, annealing of Fe_POL at 400 °C for 4 h under nitrogen, yielded a material containing wüstite (FeO) as the only crystalline phase, supported onto pyrolised acrylamidic polymer. The synthesized materials were characterized by TXRF, PXRD, SEM‐EDS, XPS, Raman and FTIR spectroscopy as well as by magnetic analysis. Differently from natural micrometric hematite, synthesised nano‐hematite turned out to be an efficient and recyclable catalyst for the hydrogenation of nitroarenes to the corresponding anilines.

Rhodium nanoparticles (Rh NPs) embedded in different amphiphilic core-crosslinked micelle (CCM) latexes (RhNP@CCM) have been synthesized by [RhCl(COD)(TPP@CCM)] reduction with H₂ (TPP@CCM = core-anchored triphenylphosphine). The reduction rate depends on temperature, on the presence of base (NEt₃) and on the P/Rh ratio. For CCMs with outer shells made of neutral P(MAA-co-PEOMA) copolymer chains (RhNP@CCM-N), the core-generated Rh NPs tend to migrate toward the hydrophilic shell and to agglomerate depending on the P/Rh ratio and core TPP density, whereas the MAA protonation state has a negligible effect. Conversely, CCMs with outer shells made of polycationic P(4VPMe⁺I⁻) chains (RhNP@CCM-C) maintain core-confined and well dispersed Rh NPs. All RhNP@CCMs were used as catalytic nanoreactors under aqueous biphasic conditions for acetophenone, styrene and 1-octene hydrogenation. Styrene was efficiently hydrogenated by all systems with high selectivity for vinyl reduction. For acetophenone, competition between benzene ring and carbonyl reduction was observed as well as a limited access to the catalytic sites when using CCM-C. Neat 1-octene was also converted, but the activity increased when the substrate was diluted in 1-nonanol, which is a better core-swelling solvent. Whereas the molecular Rh^I center was more active than the Rh⁰ NPs in 1-octene hydrogenation, the opposite trend was observed for styrene hydrogenation. Although Rh NP migration and agglomeration occurred for RhNP@CCM-N, even at high P/Rh, the NPs remained core-confined for RhNP@CCM-C, but only when toluene rather than diethyl ether was used for product extraction before recycling.

Biodiesel obtained through the transesterification in methanol of vegetable oils, such as soybean oil (SO) and waste cooking oil (WCO), cannot be used as a biofuel for automotive applications due to the presence of polyunsaturated fatty esters, which have a detrimental effect on oxidation stability (OS). A method of upgrading this material is the catalytic partial hydrogenation of the fatty acid methyl ester (FAME) mixture. The target molecule of the partial hydrogenation reaction is monounsaturated methyl oleate (C18:1), which represents a good compromise between OS and the cold filter plugging point (CFPP) value, which becomes too high if the biodiesel consists of unsaturated fatty esters only. In the present work, polymer-supported palladium (Pd-pol) and nickel (Ni-pol) nanoparticles were separately tested as catalysts for upgrading SO and WCO biodiesels under mild conditions (room temperature for Pd-pol and T = 100 °C for Ni-pol) using dihydrogen (p = 10 bar) as the reductant. Both catalysts were obtained through co-polymerization of the metal containing monomer M(AAEMA)₂ (M = Pd, Ni; AEEMA⁻ = deprotonated form of 2-(acetoacetoxy)ethyl methacrylate)) with co-monomers (ethyl methacrylate for Pd and N,N-dimethylacrilamide for Ni) and cross-linkers (ethylene glycol dimethacrylate for Pd and N,N’-methylene bis-acrylamide for Ni), followed by reduction. The Pd-pol system became very active in the hydrogenation of C=C double bonds, but poorly selective towards the desirable C18:1 product. The Ni-pol catalyst was less active than Pd-pol, but very selective towards the mono-unsaturated product. Recyclability tests demonstrated that the Ni-based system retained its activity and selectivity with both the SO and WCO substrates for at least five subsequent runs, thus representing an opportunity for waste biomass valorization.

Kaolin from the Donigazza deposit (NW Sardinia, Italy) was used to investigate the mechanisms of zeolite crystallization under alkaline hydrothermal conditions. The starting material, composed mainly of kaolinite and opal-CT with minor quartz and low iron content, was reacted with NaOH solutions (1–5 mol L⁻¹) at 100 °C for 12–168 h. XRD analyses revealed the formation of zeolitic and related phases, including NaP1, NaP2, analcime, sodalite, and cancrinite, with zeolite contents reaching up to 100%. The extent of kaolinite dissolution varied with both NaOH concentration and reaction time, with complete transformation occurring at ≥3 mol L⁻¹ and ≥48 h. SEM imaging showed idiomorphic crystals (100 nm–10 μm) and globular nanoparticles (<50 nm), likely Na-Al-Si gels. Phase distribution reflected evolving solution chemistry, particularly changes in the Si/Al ratio due to differential dissolution of opal-CT and kaolinite. Crystallization proceeded via both classical (monomer addition) and non-classical (particle attachment) pathways, influenced by supersaturation, gel composition, and reaction kinetics. The transition from NaP1 to NaP2, and the development of metastable phases, indicate kinetic control consistent with Ostwald’s step rule. These results provide insights into the complex dynamics of zeolite formation from natural aluminosilicate precursors in alkaline environments.

A sustainable and energy‐efficient protocol for the Pd‐catalyzed Sonogashira cross‐coupling reaction is reported, which is promoted by infrared (IR) irradiation in aqueous media with a recyclable Pd/C catalyst. The methodology enables C(sp ² )─C(sp) bond formation under mild conditions with low catalyst loading (1 mol% Pd), affording the coupling products in good to excellent yields from a broad range of aryl iodides, including substrates bearing electron‐donating and electron‐withdrawing groups, and various terminal alkynes. The use of water as a benign reaction medium, combined with IR irradiation as an alternative energy input, contributes to improved sustainability and shorter reaction times compared to conventional thermal heating, while minimizing the formation of undesired by‐products. Notably, the heterogeneous Pd/C catalyst can be easily recovered and reused over several cycles, showing only a slight loss of activity, thus enhancing the overall process sustainability, after the second cycle.