Modification of amorphous alloy catalysts(1)


Amorphous alloy catalysts are in a thermodynamic metastable state, which always transitions to their stable state (crystalline state) to varying degrees during the reaction, resulting in a decrease in catalyst activity or selectivity. Studies have shown that for amorphous alloys with low crystallization temperature, the crystallization temperature can generally be increased by adding a 3rd or 4th component. By adding modifiers to amorphous alloys, not only their catalytic activity and selectivity, as well as their anti-sulfur and anti-amine poisoning ability can be significantly improved. Moreover, it can effectively inhibit its crystallization. The main reason is that adding atoms of larger size to amorphous alloys can change the tight packing mode, thereby reducing the free volume and diffusion coefficient and inhibiting structural changes. Commonly used modifiers include transition metals (Cr, Mo, W, Zn, etc.), rare earth metals (La, Y, Ce, Sm, etc.) and metalloids (P, B, etc.).
  
Metal additives can increase the disorder and dispersion of amorphous alloys, and also affect the activity and selectivity of catalysts by changing the electronic state of the active center. A supported Ni-M-B amorphous alloy catalyst containing metal additive M (M is zn, Cr, Cu, Mn, Mo, Co, Fe) was prepared by chemical reduction, and its structure and selective hydrogenation performance for the preparation of o-chloroaniline from o-clonitrobenzene were studied. The results show that appropriate amounts of Zn, Cr and Mo can improve the activity and selectivity of the catalyst, Mn has little effect on the activity and selectivity of the catalyst, and Fe, Co and Cu reduce the activity of the catalyst. Cu, Fe and Co are easy to form alloys with Ni because most of them appear in the catalyst in a metallic state, and because their atomic radius is also very similar to Ni, they can replace some Ni atoms dispersed in the Ni lattice, resulting in the dispersion of Ni atoms, reducing their ability to form multi-site adsorption with nitro, so the activity of the catalyst is reduced. zn, Cr, Mo and Mn appear in the catalyst in an oxidation state and do not cause changes in the Ni lattice. Although the specific surface area of the catalyst is increased, the unit Nj that can form multiple adsorption of nitro groups does not change much, so the activity of the catalyst increases after adding zn, Cr, Mo and Mn.

 

 

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Reni nickel catalyst science knowledge(1)

Physical and chemical properties: Reni nickel catalyst before activation is silver-gray amorphous powder (nickel-aluminum alloy powder), with a moderate degree of flammability, partial activation in the presence of water and the production of hydrogen easy agglomeration, long-term exposure to air is easy to weather. Nickel-aluminum alloy powder is activated into gray-black particles, accompanied by active hydrogen, extremely unstable, oxidative combustion in the air, must be immersed in water or ethanol for preservation. It was first used by American engineer Murray Rainey as a catalyst in the hydrogenation of vegetable oils. The preparation process is to treat nickel-aluminum alloy with concentrated sodium hydroxide solution, in this process, most of the aluminum will react with sodium hydroxide and dissolve, leaving a lot of micropores of different sizes. In this way, the surface of Raininickel is a fine gray powder, but from a microscopic point of view, each tiny particle in the powder is a three-dimensional porous structure, this porous structure greatly increases its surface area, and the large surface area brings high catalytic activity, which makes Raininickel widely used as a heterogeneous catalyst in organic synthesis and industrial hydrogenation reactions. Since "Rainey" is a registered trademark of Grace Chemicals, strictly speaking, only products manufactured by the company's Davidson Chemical Division can be called "Lanny Nickel". The term "metal backbone catalyst" or "sponge-metal catalyst" is used to refer to catalysts with a microporous structure and physical and chemical properties similar to Raney nickel.