Synthesis of Ti-EMC-2 zeolite by sonication-assisted hydrothermal method: effect on crystallinity, morphology, and formation active sites

In the present work, Ti-EMC-2 zeolite was synthesized by sonication-assisted hydrothermal treatment in the absence of SDA. The effects of Ti/Al ratio and sonication time on crystallinity, morphology, Ti content, and Ti species distribution on the zeolite were evaluated. Synthesized materials were characterized by XRD, SEM/EDS, FT-IR, photoluminescence (PL) spectroscopy, XPS, UV–Vis diffuse reflectance spectroscopy, and TEM. According to the results, the crystallinity depended on Ti content; as the Ti content increased, the crystallinity was diminished. Nevertheless, by application of ultrasound the crystallinity was improved. A synergic effect of sonication and Ti/Al ratio led to get zeolite of diverse morphologies: nanoplates, needles, and nanorods. The dispersion of Ti into zeolite was improved when sonication was employed. The formation of tetra-coordinated Ti species Ti(OSi)₄ was evidenced by photoluminescence for all cases, indicating that Ti was heterosubstituted into zeolite framework. By XPS, the presence of Ti⁴⁺ and Ti³⁺ was detected, while by UV–Vis diffuse reflectance spectroscopy tetra- and hexa-coordinated as well as framework-associated Ti species were detected. Their presence depended on the sonication time applied. These findings allow to infer that by this methodology it is possible to control of morphology, crystallinity, dispersion, kind species, and content of Ti into EMC-2 framework; therefore, it is expected that these characteristics impact on the catalytic performance of the synthesized materials.