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The present study investigates the direct one step hydrothermal synthesis of three-dimensional (3D) Ti-SBA-16 (cubic, Im3m) by optimizing with ammonium fluoride (F/Si ratio ≤0.05), hydrothermal heating (40–130 °C) and aging time (24–120 h). The effective 3D mesoordering through silica condensation, in less acidic environment, co-solvent n-butanol and fluoride was observed through small angle X-ray diffraction, N2 physisorption technique (BET), 29Si-MAS NMR, transmission electron microscope and UV–visible spectroscopy. The study shows the variability of Si/Ti atomic ratios (249-9) of TiSBA-16 with improved surface area between 799 and 910 m2/g at average pore diameter of 8.7 nm. A test reaction of cyclohexene oxidation shows that TiSBA-16 (22) is more selective towards 2-cyclohexen-1-one (58%) formation.

An amorphous porous hexagonal aluminosilicate Al-ZAT was prepared using liquid crystal phase of Brij-56 and preformed MFI zeolite nanoclusters solution through bottom-up approach. The HCl concentration (0.5–2.0 M), HCl to Brij-56 ratio and zeolitic seed solution wss varied for the mesoporous system at ambient synthesis condition. The optimum Brij-56 to HCl ratio was found to be 1 Brij 56: 9–19 HCl (0.5 M) by mass. The addition of preformed zeolite seed (7–14 ml) as precursor solution instead of conventional silica source tetramethyl orthosilicate (TMOS) generate uniform mesophase and subsequently avoids formation of methanol (from TMOS hydrolysis) that affects liquid crystalline mesophase. MCM-41 (ZMCM-41) and SBA-15 (ZSBA-15) derived from similar zeolite precursor solution was synthesized for comparative study. The porous textural characteristics, and type of surface acidity were studied. The analysis showed a highly porous hexagonal structure of Al-ZAT. ZMCM-41 prepared through top-down approach, showed formation of ordered nanostructured mesoporous (disordered hexagonal). Al-ZAT and ZSBA-15 shows weaker Bronsted acid sites compared to ZMCM-41.

Oxidative dehydrogenation of n-butane was tested using carbon dioxide as a mild oxidant over bimetallic Cr–V supported catalysts (MCM-41, ZSM-5, MCM-22 and mesoZSM-5). The textural properties of the catalysts were measured by means of XRD, N2 adsorption, SEM-EDX, Raman, H2-TPR, pyridine FT-IR, NH3 and CO2-TPD techniques. The metal content of Cr and V was maintained around 1.2 and 2.8 wt% for the catalytic test in packed bed reactor at different temperatures (525–600 °C) for 180 min. 1.2Cr2.8 V/MCM-41 and 1.2Cr2.8 V/ZSM-5 exhibited maximum conversion of 14 and 13.1 %, respectively at 10 min and 600 °C. Significantly, high butenes selectivity was observed over MCM-41 (86.27 %) than ZSM-5 support (58.1 %). The mesoporosity in ZSM-5 had a negative impact on conversion level (7.1 %) but improved the butenes selectivity slightly. 1.2Cr2.8 V/M-22 showed the highest cracking ability leading to overall reduced butenes selectivity (57.9 %). The study shows that over all catalysts, n-butane conversion is independent of CO2 conversion. 1.2Cr2.8 V/M-22 showed highest CO2 conversion in the range 2.35–2.2 % between 525 and 550 °C. The apparent activation energies of dehydrogenation and cracking reaction over the four catalysts were evaluated. The ratio of conversion to coke weight per cent over the four catalysts are observed in the following order: 1.2Cr2.8 V/M-41 > 1.2Cr2.8 V/Z-5 > 1.2Cr2.8 V/mesoZ-5 > 1.2Cr2.8 V/M-22.