Selective oxidation of cyclic olefins over framework Ti-substituted, three-dimensional, mesoporous Ti-SBA-12 and Ti-SBA-16 molecular sieves

Recent Advances in Tetra- (Ti, Sn, Zr, Hf) and Pentavalent (Nb, V, Ta) Metal-Substituted Molecular Sieve Catalysis

Metal substitution of molecular sieve systems is a major driving force in developing novel catalytic processes to meet current demands of green chemistry concepts and to achieve sustainability in the chemical industry and in other aspects of our everyday life. The advantages of metal-substituted molecular sieves include high surface areas, molecular sieving effects, confinement effects, and active site and morphology variability and stability. The present review aims to comprehensively and critically assess recent advances in the area of tetra- (Ti, Sn, Zr, Hf) and pentavalent (V, Nb, Ta) metal-substituted molecular sieves, which are mainly characterized for their Lewis acidic active sites. Metal oxide molecular sieve materials with properties similar to those of zeolites and siliceous molecular sieve systems are also discussed, in addition to relevant studies on metal-organic frameworks (MOFs) and some composite MOF systems. In particular, this review focuses on (i) synthesis aspects determining active site accessibility and local environment; (ii) advances in active site characterization and, importantly, quantification; (iii) selective redox and isomerization reaction applications; and (iv) photoelectrocatalytic applications.

Synthesis, Characterization, and Catalytic Applications of the Ti-SBA-16 Porous Material in the Selective and Green Isomerizations of Limonene and S-Carvone

This work presents studies on the activity of the Ti-SBA-16 (SBA—Santa Barbara Amorphous) catalyst in the isomerization of limonene and S-carvone. The Ti-SBA-16 catalyst was synthesized by a two-step method: first, the SBA-16 material was produced, and then it was impregnated with the titanium source. The Ti-SBA-16 catalyst was subjected to detailed characterizations by means of instrumental methods: XRD (X-ray Diffraction), UV-Vis (Ultraviolet–Visible) spectroscopy, FTIR (Fourier-Transform Infrared) spectroscopy, SEM (Scanning Electron Microscopy) with EDX (Energy Dispersive X-ray) spectroscopy, and EDXRF (Energy Dispersive X-ray Fluorescence). Both limonene and S-carvone underwent isomerization over the Ti-SBA-16 catalyst. In the isomerization of limonene, the main product was terpinolene, and its highest yield amounted to 39 mol% after 300 min at 170 °C with a catalyst content of 15 wt%. Under these conditions, the conversion of limonene reached 78 mol%. In contrast, the highest yield of carvacrol (65 mol%) was obtained with the catalyst content of 15 wt%, at 200 °C, and with the conversion of S-carvone reaching 79 mol%.

From 3D to 2D zeolite catalytic materials

Research activities and recent developments in the area of three-dimensional zeolites and their two-dimensional analogues are reviewed. Zeolites are the most important industrial heterogeneous catalysts with numerous applications. However, they suffer from limited pore sizes not allowing penetration of sterically demanding molecules to their channel systems and to active sites. We briefly highlight here the synthesis, properties and catalytic potential of three-dimensional zeolites followed by a discussion of hierarchical zeolites combining micro- and mesoporosity. The final part is devoted to two-dimensional analogues developed recently. Novel bottom-up and top-down synthetic approaches for two-dimensional zeolites, their properties, and catalytic performances are thoroughly discussed in this review.

Recent developments in liquid-phase selective oxidation using environmentally benign oxidants and mesoporous metal silicates

This Perspective article surveys recent advances in the synthesis of mesoporous transition-metal-containing silicate materials and their use for the liquid-phase selective oxidation of organic compounds with environmentally friendly oxidants – molecular oxygen, hydrogen peroxide and organic hydroperoxides.