Catalytic Properties of Molecular Sieves

Molecular sieves, often called zeolites or zeolite molecular sieves.They are classically defined as "aluminosilicates with a pore (channel) framework structure that can be occupied by many large ions and water". According to the traditional definition, molecular sieves are solid adsorbents or catalysts with a uniform structure that can separate or selectively react molecules of different sizes. In a narrow sense, molecular sieves are crystalline silicates or aluminosilicates, which are connected by silicon-oxygen tetrahedron or aluminum-oxygen tetrahedron through oxygen bridges to form a system of channels and voids, thus having the characteristics of sieving molecules. Basically, it can be divided into several types of A, X, Y, M and ZSM, and researchers often attribute it to the solid acid category.

Catalytic Properties of Molecular Sieves

(1) Activity requirements for catalytic reaction:

Large specific surface area, uniform pore distribution, adjustable pore size, good shape selection for reactants and products; stable structure, high mechanical strength, high temperature resistance (400 ~ 600 ℃), good thermal stability, after activation and regeneration reusable; non-corrosive to equipment and easy to separate from reaction products, basically no "three wastes" are generated in the production process, and the waste catalyst is easy to handle and does not pollute the environment. For example, the research system of shape-selective catalysis includes almost all the conversion and synthesis of hydrocarbons, as well as the catalytic conversion of alcohols and other nitrogen, oxygen, sulfur-containing organic compounds and biomass, which are fundamental research, applied research and industrial Development has opened up a vast field. Some transition metal-containing zeolite molecular sieves are not only used in traditional acid-base catalysis systems, but also in oxidation-reduction catalysis processes.

(2) Efficient catalysis of zeolite molecular sieves

For zeolite molecular sieves used in industrial catalysis, high performance is the basic requirement and goal. The type and number of active centers of catalytic materials and the diffusion performance of micropores are the intrinsic factors that affect their catalytic activity. Catalytic selectivity is closely related to the shape selectivity of micropores, the occurrence of side reactions, and the diffusion speed of each reaction molecule. Lifetime has always been an important indicator to measure the performance of catalytic materials. The eternal topic of the process. On the premise that the catalyst activity meets the requirements, if the deactivated catalyst is easy to regenerate and the structure can be recovered, that is, it can be regenerated repeatedly, and then with a suitable reaction process, the purpose of prolonging the life of the catalyst can be achieved. Therefore, high performance not only puts forward higher requirements for zeolite molecular sieve materials, but also requires multi-scale combination and coordination of catalytic materials, reaction processes and reaction engineering systems, and finally enables catalysts to achieve high performance in industrial applications.