Microporous–mesoporous ZSM-12 zeolites: Synthesis by using a soft template and textural, acid and catalytic properties

Exploring the impact of synthetic strategies on catalytic cracking in hierarchical beta zeolites via hydrothermal desilication and organosilane-templated synthesis

Hierarchical zeolites can be synthesized by different strategies, resulting in the creation of mesoporosity with different configurations (inter-crystalline or intra-crystalline) in addition to unique porous and catalytic properties.

Fabrication of the Hierarchical HZSM-5 Membrane with Tunable Mesoporosity for Catalytic Cracking of n-Dodecane

Hierarchical HZSM-5 membranes were prepared on the inner wall of stainless steel tubes, using amphiphilic organosilane (TPOAC) and mesitylene (TMB) as a meso-porogen and a swelling agent, respectively. The mesoporosity of the HZSM-5 membranes were tailored via formulating the TPOAC/Tetraethylorthosilicate (TPOAC/TEOS) ratio and TMB/TPOAC ratio, in synthesis gel, and the prepared membranes were systematically characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), N2 adsorption–desorption, N2 permeation, inductively coupled plasma (ICP), in situ fourier transform infrared (FT-IR), ammonia temperature-programmed desorption (NH3-TPD), etc. It was found that the increase of the TPOAC/TEOS ratio promoted a specific surface area and diffusivity of the HZSM-5 membranes, as well as decreased acidity; the increase of the TMB/TPOAC ratios led to an enlargement of the mesopore size and diffusivity of the membranes, but with constant acid properties. The catalytic performance of the prepared HZSM-5 membranes was tested using the catalytic cracking of supercritical n-dodecane (500 °C, 4 MPa) as a model reaction. The hierarchical membrane with the TPOAC/TEOS ratio of 0.1 and TMB/TPOAC ratio of 2, exhibited superior catalytic performances with the highest activity of up to 13% improvement and the lowest deactivation rate (nearly a half), compared with the microporous HZSM-5 membrane, due to the benefits of suitable acidity, together with enhanced diffusivity of n-dodecane and cracking products.

Synthesis of hierarchical ZSM-12 nanolayers for levulinic acid esterification with ethanol to ethyl levulinate

Hierarchical ZSM-12 nanolayers have been successfully synthesized via a one-pot hydrothermal process using dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (TPOAC) as a secondary organic structure-directing agent (OSDA). The as-synthesized ZSM-12 samples were characterized by means of XRD, SEM, TEM, N₂ physisorption, and NH₃-TPD. This clearly demonstrates that the TPOAC content and the crystallization time are crucial parameters for the formation of nanolayered structures. The presence of such a structure significantly improves the mesoporosity of ZSM-12 by generating interstitial mesopores between nanolayers, eventually resulting in enhancing external surface areas and mesopore volumes, and subsequently promoting the molecular diffusion inside a zeolite framework. To illustrate its advantages as a heterogeneous catalyst, hierarchical ZSM-12 nanolayers were applied in the catalytic application of an esterification of levulinic acid with ethanol to ethyl levulinate. Interestingly, hierarchical ZSM-12 nanolayers exhibit an improvement of catalytic activity in terms of levulinic acid conversion (78.5%) and ethyl levulinate selectivity (98.7%) compared with other frameworks of hierarchical zeolite nanosheets, such as ZSM-5 and FAU. The example reported herein demonstrates an efficient way to synthesize a unidimensional pore zeolite with hierarchical nanolayered structure via a dual template method and also opens up perspectives for the application of different hierarchical porous systems of zeolites in the bulky-molecule reactions such as in the case of levulinic acid esterification with ethanol.

Hierarchical ZSM-12 nanolayers were successfully synthesized via a dual template approach as an efficient catalyst for levulinic acid esterification.

In Situ Fabrication of Hierarchical MTW Zeolite via Nanoparticle Assembly by a Tailored Simple Organic Molecule

Amphiphilic surfactants are widely used as templates to synthesize hierarchically structured zeolites due to their multiple functions; however, piloting such new dual-functional templates is limited by their time-consuming nature and high cost. Herein, a simple organic molecule, without a long hydrophobic alkyl chain, was tailored from a gemini-type, poly-quaternary ammonium surfactant, and effectively used as a dual-porogenic template to synthesize hierarchical MTW zeolite. Upon a range of synthesis parameter optimizations, our detailed characterization suggested that the hierarchical MTW zeolite would completely crystallize within 36 hours from the surface to the inside of quasi-spherical particles through in situ consumption of amorphous silicon and aluminum species; much faster than most of the hierarchical MTW zeolites generated by conventional methods. Moreover, the as-prepared hierarchical MTW zeolite exhibited 4 times higher catalytic performance and lifetime of benzene-propene alkylation compared to conventional MTW zeolite, while the introduced crystalline mesopores are of benefit to diffuse reactants, products, and coke depositions. Our strategy broadens the design of new templates in more effective ways to facilely synthesize versatile hierarchical zeolites for diverse applications, especially for those in which macromolecules are involved.

Seed-induced synthesis of multilamellar ZSM-5 nanosheets directed by amphiphilic organosilane

Multilamellar ZSM-5 nanosheets formed by the transformation of ordered MCM-41-like mesophases.