Precious metal loading and air velocity, is higher precious metal content better?

2021-11-09   Pageview:289

The performance of precious metal catalysts is related to the precious metal content, particle size and dispersion. Ideally, the precious metals are highly dispersed, when the precious metals are present on the carrier in very small particles (a few nanometers), and the precious metals are utilized to the maximum extent, when the processing capacity of the catalyst is positively related to the precious metal content.

However, when the precious metal content is high to a certain extent, the metal particles tend to gather and grow into larger particles, and the contact surface between the precious metal and VOCs decreases, and most of the precious metal is encapsulated in the interior, so increasing the precious metal content is not conducive to the improvement of catalyst activity.











Reactive polydimethylsiloxane R and R2 are methyl groups, and R3 is a polymer chain with an active group capable of crosslinking reaction. The active group is:
— OH (hydroxyl) — COOH (carboxyl)
One NCO (isocyanate group)-CH -CH2 (double bond)
Reactive polydimethylsiloxane must meet the following three conditions: a. The product structure can make it automatically float on the surface of the coating film; b. It must have good compatibility with the coating base material;
The C active group must chemically react with the coating base material, so that the siloxane becomes a component of the base material after the coating film is cured.

The reactive polydimethylsiloxane will make the surface of the coating film have the characteristics of silicone, permanent smoothness, pollution resistance, scratch resistance, anti-blocking, easy cleaning, outstanding hydrophobicity and oleophobicity. Recoating and other characteristics, can be used as a  wax for solvent-based anti-painting paint extension. Figure 13-3 is the cross-linked structure of reactive polydimethylsiloxane and coating base material
Cross-linked structure of reactive polydimethylsiloxane and coating base material

Among these products, the reactive type with hydroxyl group is BYK -370, BYK -310, Tego -5000. The reactive type with double bond, such as BYK -371, BYK -3500, EFKA83, can be used for radiation curing coatings. The reactive type with isocyanate groups such as EFKA-86 and EFKA-88. The reactive type with blocked isocyanate groups, such as EFKA-LP8832 (this product can release isocyanate groups above 110°C, and is especially recommended for baking paint).

8 Polydimethylsiloxane modified reactive polyacrylate
As the side chain, methyl siloxane is grafted on the polyacrylate main chain with hydroxyl at multiple points. The slip agent is added to the coating and cured, and the cross-linking reaction is carried out with the coating base material through the hydroxyl group on the main chain. The polydimethylsiloxane modified polyacrylate can also migrate and float on the surface of the coating film, and permanently fix the polydimethylsiloxane on the surface of the coating film, so that the paint film can be permanently smooth and scratch-resistant. It has the characteristics of damage, anti-adhesion, anti-pollution, easy to clean, and has the leveling properties of polyacrylate.


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