Preparation of palladium catalyst alumina

There are many methods for preparing palladium catalysts loaded on alumina. The following are several common preparation processes and key points:

I. Impregnation method

1. Principle: By impregnating the alumina carrier in a palladium-containing solution, the palladium salt is adsorbed on the surface of the carrier, and then drying, calcining and reducing steps are performed to obtain a loaded palladium catalyst.

2. Process steps

• Carrier pretreatment: Select a suitable alumina carrier (such as γ-Al₂O₃), dry and sieve to ensure uniform particle size.

• Preparation of palladium salt solution: Usually palladium chloride (PdCl₂) or palladium nitrate (Pd(NO₃)₂) solution is used to control the palladium concentration and solution pH.

• Impregnation: Immerse the alumina carrier in the palladium salt solution and let it stand for a period of time to allow the palladium salt to be fully adsorbed.

• Drying: Dry at 80-120°C to remove moisture.

• Calcination: Calcination at 400-600℃ decomposes the palladium salt into metallic palladium or its oxide, and forms a strong interaction with the carrier.

• Reduction: Reduction in a hydrogen atmosphere reduces the palladium oxide to metallic palladium to improve activity.

3. Key points

• Palladium loading: The palladium loading (usually 0.1-5 wt%) is adjusted by controlling the concentration of the palladium salt solution and the impregnation time.

• Dispersibility: The impregnation method may cause palladium particles to agglomerate, and the impregnation conditions need to be optimized or a dispersant (such as citric acid, PVP) needs to be added.

• Reduction conditions: The reduction temperature and hydrogen flow rate affect the particle size and activity of palladium and need to be strictly controlled.

II. Chemical plating method

1. Principle

Use a reducing agent (such as sodium hypophosphite) to reduce palladium ions on the surface of alumina to form uniformly dispersed palladium particles.

2. Process steps

Carrier pretreatment: Sensitize and activate alumina to make its surface catalytically active.

Chemical plating solution preparation: Mix palladium salt (such as PdCl₂) with a reducing agent and a complexing agent (such as EDTA) and adjust the pH value.

Chemical plating: Immerse the alumina carrier in the plating solution and perform chemical reduction under stirring, and palladium particles are deposited on the carrier surface.

Post-treatment: Wash, dry and roast to improve the stability of palladium particles.

3. Key points

pH control: pH affects the reduction rate and particle size of palladium and needs to be precisely controlled.

Reducing agent selection: Sodium hypophosphite is a commonly used reducing agent with mild reducing ability, which is suitable for the preparation of nano-scale palladium particles.

Uniformity: Chemical plating can achieve uniform distribution of palladium particles, but process parameters need to be optimized to avoid agglomeration.