Molecular sieve manufacturer explains the pore structure, diffusion, and activity of molecular sieves at the subcrystalline level

One of the main challenges of molecular transfer in molecular sieves remains to match the diffusion coefficients tested through different techniques with catalyst performance data. This difficulty has two sides.
Firstly, the order of magnitude differences in diffusion coefficient values measured by different techniques (macro and micro) for the same guest host system are often reported. Therefore, it is difficult to directly integrate diffusion data into the study of catalysts. Although the quantitative value of the catalyst is still unclear, there has been no new progress in pure diffusion experiments.
The second difficulty comes from different batches of the same catalyst. In the early 1970s, researchers proposed the idea that 'your ZSM-5 is not mine'. On the basis of these recent studies, this reference can be extended to other molecular sieve topologies: previously, it was believed that single crystal molecular sieves were composed of several symbiotic building blocks. These subunit interfaces contain many diffusion boundaries because this potential does not match the positioning of the microporous network or has different pore orientations. For each crystal and batch of molecular sieves, there may be a mismatch. This fact has a significant impact on catalysts, as certain regions of the molecular sieve crystal cannot be reached by reactant molecules.
In the past few years, many excellent papers have been published on the selection of complex molecular sieve pore network orientation by distinguishing different building modules. The catalytic properties of this crystal were studied through spatiotemporal separation technology as a study of structural behavior, and the non-uniform catalytic properties of this molecular sieve crystal were demonstrated. These studies indicate a trend: the larger the molecular sieve crystal, the less perfect the pore structure.
The first literature included in the crystal growth building unit of ZSM-5 molecular sieve was published in the early 1990s. By combining Transmission electron microscopy and Scanning electron microscope, it is found that most of the ZSM-5 molecular sieve crystals are connected by rotating 90 ° around the c axis of a common continuum with the small area of the growth crystal plane as the core. On the surface of large crystals, associated with impurities, ramps are also observed. Consistent with these observations, the researchers proposed the first model for crystal growth.
In addition, a liquid-phase reaction was studied using optical microscopy, fluorescence microscopy, and polarized light, such as the acid catalyzed oligomerization of styrene derivatives in the pores of ZSM-5 zeolite crystals. Similar perspectives were obtained in the diffusion energy barrier and pore orientation of the crystals.
All of these results confirm that the studied zeolite samples exhibit spatially heterogeneous catalytic performance, with some special crystal parts difficult to contact by the reactants, and the pore orientation is different from the expected crystal orientation. Hunan Providence New Materials Co., Ltd is a professional molecular sieve manufacturer which can provide USY zeolite, NaY zeolite, REY zeolite, ZSM-5 zeolite, welcome to consult.