Molecular sieve manufacturer: The influence of diffusion of zeolite molecular sieves on catalytic activity

Molecular sieve adsorbents and catalysts are widely used in industry. In 1948, commercial adsorbents were used to synthesize aluminosilicate A-type and X-type molecular sieves, as well as FCC catalyst Z-type molecular sieves.
Aluminum containing molecular sieves are inherently catalytic in various aspects. The framework of molecular sieves with isomorphic substitution of aluminum atoms contains a negative electrode, which is neutralized by a counter ion. When this counter ion is a proton, a B acid center is generated. In addition, the oxygen atoms of the framework can generate L-acid activity. After preparation, precious metal ions can be introduced through ion exchange with cations. Adding Ti, V, Fe, and Cr metals into the framework can enhance the catalytic activity of molecular sieves for oxidation-reduction reactions. A good example of the latter catalyst is titanium silicon molecular sieve, which is an oxidation-reduction molecular sieve catalyst.
It is not only catalytic activity that has attracted special attention from various aspects to molecular sieves, but also the position of the active center of molecular sieves has a clear geometric interface. Based on the geometric constraints of molecular sieves, the selectivity of molecular sieve chemical reactions can be improved through three mechanisms: reactant selectivity, product selectivity, and intermediate selectivity. Considering the selectivity of reactants, components with large volumes in the feed cannot enter the molecular sieve and will not undergo the reaction. When many reaction products are generated in the molecular sieve, only some can leave the molecular sieve or some can leave the molecular sieve faster, this process is called product selectivity. The geometric constraints of the active centers in molecular sieve reactions prevent the generation of products or the generation of specific products by intermediates, which is the selectivity of intermediates.
The importance of molecular sieve catalyst diffusion is because reactants need to reach the center of catalytic activity, and products need to leave this active point. According to the usual application in catalysts, the macroporous particles (d-pores>2nm) at the height of the packed bed contain smaller particulate particles, which are generally mesopores (2nm<d-pores<50nm) or smaller pores (d-pores<2nm). For optimizing catalytic action, external resistance comes from the film layer near the particles, which can lead to external heat and mass transfer obstacles. In addition, the large pores in granular particles and small and medium-sized particles or small and medium-sized pores in crystals will lead to external mass transfer limitations. Furthermore, external heat transfer limitations may be due to poor particle heat export.
The limitation of most transfer and the difficulty of related catalytic performance lies in the reaction diffusion problem in catalytic particles. The transformation of the difference equation is controlled to generate a dimensionless parameter and a Thiel modulus, which represents the dynamic ratio and diffusion coefficient of particles. 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.