Solvent-free selective oxidation of alcohols with tert-butyl hydroperoxide catalyzed by palladium(II) isatin Schiff base complex supported into three-dimensional mesoporous silica KIT-6

Computational investigation of silica-supported Pdn and Pdn(xO) nanoclusters

Silica-supported Pd nanoclusters (Pdn/SiO2) are essential catalysts in methane oxidation for pollution abatement. These catalysts operate at high temperature for long periods exposed to the exhaust gases of combustion engines. For catalyst design to ensure the required longevity, insight into the interaction between nanoclusters and the SiO2 surface is essential. Accordingly, there is a need for well-defined, computationally inexpensive, quantum mechanical models of these structures from which cluster support interactions can be understood. In this work, we have found that a strong adsorption site for a single Pd1 atom on the hydroxylated α-SiO2(101) surface can be formed when Pd adsorption is accompanied by the elimination of water. We show that this becomes a thermodynamically favourable process at the temperatures commonly used for calcination following catalyst synthesis using wet impregnation. Using this initial anchor point Pdn and Pdn(xO) nanoclusters are systematically constructed guided by the Mulliken charges of atoms at each stage. We then investigate the surface interactions of these Pdn and Pdn(xO) nanoclusters by considering the gas phase references of the same clusters. Our calculations show stability varies according to cluster size. Oxidation of the clusters leads to a weakening of cluster-surface interaction.

Cu(II) and Mn(II) Anchored on Functionalized Mesoporous Silica with Schiff Bases: Effects of Supports and Metal-Ligand Interactions on Catalytic Activity

New series of Cu(II) and Mn(II) complexes with Schiff base ligands derived from 2-furylmethylketone (Met), 2-furaldehyde (Fur), and 2-hydroxyacetopheneone (Hyd) have been synthesized in situ on SBA-15-NH₂, MCM-48-NH₂, and MCM-41-NH₂ functionalized supports. The hybrid materials were characterized by X-ray diffraction, nitrogen adsorption-desorption, SEM and TEM microscopy, TG analysis, and AAS, FTIR, EPR, and XPS spectroscopies. Catalytic performances were tested in oxidation with the hydrogen peroxide of cyclohexene and of different aromatic and aliphatic alcohols (benzyl alcohol, 2-methylpropan-1-ol, and 1-buten-3-ol). The catalytic activity was correlated with the type of mesoporous silica support, ligand, and metal-ligand interactions. The best catalytic activity of all tested hybrid materials was obtained in the oxidation of cyclohexene on SBA-15-NH₂-MetMn as a heterogeneous catalyst. No leaching was evidenced for Cu and Mn complexes, and the Cu catalysts were more stable due to a more covalent interaction of the metallic ions with the immobilized ligands.

Immobilization of Ni(ii) complex on the surface of mesoporous modified-KIT-6 as a new, reusable and highly efficient nanocatalyst for the synthesis of tetrazole and pyranopyrazole derivatives

In this paper, KIT-6@SMTU@Ni was successfully synthesized via a new method of Ni(ii) complex stabilization on modified mesoporous KIT-6, as a novel and green heterogeneous catalyst. The obtained catalyst (KIT-6@SMTU@Ni) was characterized using Fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) calculation, X-ray diffraction (XRD), atomic absorption spectroscopy (AAS), energy-dispersive X-ray spectroscopy (EDS), X-ray mapping, thermogravimetric analysis (TGA) techniques and scanning electron microscopy (SEM). After complete characterization of the catalyst, it was successfully used for the synthesis of 5-substituted 1H-tetrazoles and pyranopyrazoles. Moreover, tetrazoles were synthesized from benzonitrile derivatives and sodium azide (NaN₃). All tetrazole products were synthesized with high TON, TOF and excellent yields (88-98%) in a reasonable time (0.13-8 h), demonstrating the efficiency and practicality of the KIT-6@SMTU@Ni catalyst. Furthermore, pyranopyrazoles were prepared through the condensation reaction of benzaldehyde derivatives with malononitrile, hydrazine hydrate and ethyl acetoacetate with high TON, TOF and excellent yields (87-98%) at appropriate times (2-10.5 h). KIT-6@SMTU@Ni could be reused for five runs without any re-activation. Significantly, this plotted protocol has prominent benefits, such as applying green solvents, the use of commercially available and low-cost materials, excellent separation and reusability of the catalyst, short reaction time, high yield of products and a facile work-up.