The effect of crystal size was explored in this work aiming at enhancing p-xylene selectivity through toluene disproportionation over ZSM-5 zeolite. The different physicochemical properties of ZSM-5 were investigated using various characterization techniques including X-ray diffraction (XRD), pyridine adsorption, Fourier transform infra-red (FTIR), BET surface area by N2 adsorption, inductively coupled plasma (ICP) and scanning electron microscopy (SEM). Each catalyst was tested in a fixed bed reactor at a temperature 475 °C, weight hourly space velocity (WHSV) 3-83 h -1 and two different pressures (1 and 10 bar). ZSM-5 zeolites with crystal sizes 5, 50 and 100 µm were synthesized in house and compared with the commercially obtained ZSM-5 having a crystal size of 0.5 µm. As a result of increasing the crystal size the p-xylene selectivity was improved. This was attributed to the longer diffusion path lengths of the large crystals which imposed more diffusion constraints on the other xylene isomers. ZSM-5 zeolite with the largest crystal size 100 µm achieved the highest p-xylene selectivity (58 %) at the highest WHSV 83 h -1 . However, this was accompanied by a low conversion (2 wt. %). The best combination of p-xylene selectivity (40%) alongside 15 wt. % toluene conversion were achieved over ZSM-5 having 5 µm crystal sized.

This study emphasizes tuning the synthesis conditions of MFI zeolites to achieve better catalytic properties by optimizing the mesoporosity, the balance between Brønsted and Lewis sites, and the zeolite particle sizes. The MFI zeolites were hydrothermally synthesized at various temperatures employing different silica sources. The synthesis temperature was varied between 110 to 180 °C at constant synthesis time (15 h). Different silicon sources led to variations in structure, morphology, and size of the MFI zeolite along with tuned Lewis and Brønsted acid sites in parallel correlation with shape selectivity of the reaction. The catalytic activities of synthesized zeolites were investigated in the catalytic cracking of n -dodecane to produce value-added chemicals. The zeolite synthesized at 180 °C using fumed silica presented the highest catalytic conversion (96.6%), while maximum light olefin gaseous products (73.1%) were obtained for the sample synthesized at 140 °C using tetraethyl orthosilicate as the silica source. The MFI zeolite synthesized at 180 °C employing tetraethyl orthosilicate as a silica source facilitated the formation of both naphthenes and aromatics (71.3%) as major liquid products.

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Nano BEA zeolite catalysts were synthesized and modified by desilication and then ion-exchanged with Co. The desilication was carried out using 0.1 M of NaOH.

The zirconia-titania based catalyst was synthesized by a co-participation method to study the catalytic cracking of heavy naphtha (dodecane) into high added-value chemical to olefins. The nanocrystal size catalysts were...

Catalytic conversion of heavy naphtha to reformate product over the phosphorus-ZSM-5 catalyst at a lower reforming temperature.

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