Generation of 3D-Intracrystalline Diffusion Structures from a 1D/12MR HZSM-12 Zeolite: Improvements in the Catalytic Stability

Abstract

Three-dimensional-intracrystalline diffusion structures were prepared from a 1D/12MR-HZSM-12 zeolite that was desilicated with NaOH solutions at different temperatures. The results showed that carefully tuned desilication preserved most of the crystalline structure and revealed that even though the strong acid sites had decreased, the hierarchical zeolites exhibited similar initial activities compared to that of the 1D-microporous precursor. Moreover, the new textural and acid properties of the desilicated zeolites strongly improved the catalytic stability during cyclohexane conversion. That stability, a key factor to be considered in the engineering scale-up of the catalyst, resulted from the decrease of the strong acid sites and more importantly from improvements in the molecular diffusion inside of the new 3D-intracrystalline porous structure that decreased the contact time, minimizing subsequent reactions that could lead to coke formation, thus avoiding deactivation. Otherwise, the presence of mesopores favored the selectivity to C6 cyclohexane isomers.

Zeolite Nanocrystals (MOR, EU-1, and ZSM-12) Synthesized Using a Versatile Diquaternary Ammonium Template as Robust Catalysts

“…The corresponding spectra in Figure are dominated by main peaks at 53 and 56 ppm for EU-1 and ZSM-12 zeolites, respectively, corresponding to tetrahedrally coordinated framework Al (Al IV ). The weak peak around 0 ppm is due to octahedrally coordinated nonframework Al (Al VI ). − Deconvolution of these spectra shows that ∼80% of Al atoms are incorporated into the framework of EU-1-Con and EU-1-Nano, while more than 90% of Al is incorporated into the framework of ZSM-12-Con and ZSM-12-Nano. The acidity of the zeolites was characterized by IR spectroscopy after pyridine adsorption and subsequent evacuation at 150, 300, and 500 °C.…”

ZSM-22 Synthesized Using Structure-Directing Agents of Different Alkyl Chain Lengths for Controlled n-Hexadecane Hydroisomerizations

“…1−4 This process is more challenging for long-chain n-paraffins compared with the isomerization of light n-paraffins because of their high affinity toward the catalyst surface, leading to increased cracking and reduced isomerized yields. 5,6 To overcome this, metal-acid bifunctional catalysts are commonly used, where metal sites are responsible for (de)hydrogenations and acid sites undertake skeletal rearrangements and cracking. 7,8 Medium-pore zeolites, such as SAPO-11, 9−11 ZSM-22, 12−14 ZSM-23, 15−17 ZSM-48, 18−20 and EU-1, 21,22 are considered the most promising acidic supports for the hydroisomerization of long-chain n-paraffins due to their exceptional shape selectivity.…”

“…The hydroisomerization of n -paraffins is one of the prime methods to enhance the quality of fuels and refined oils, and hence, it is well-established for the production of high-octane-number gasoline, low-pour-point diesel, lubricating oil, biofuels, and jet fuel. − This process is more challenging for long-chain n -paraffins compared with the isomerization of light n -paraffins because of their high affinity toward the catalyst surface, leading to increased cracking and reduced isomerized yields. , To overcome this, metal-acid bifunctional catalysts are commonly used, where metal sites are responsible for (de)­hydrogenations and acid sites undertake skeletal rearrangements and cracking. , …”