How are Highly Efficient VOCs Catalysts Made?

Core Raw Material Selection and Pre-treatment

Unlike the procurement standards for ordinary chemical raw materials, the selection of raw materials for VOCs catalysts requires a triple layer of quality control. First is the selection of active component precursors. Depending on the treatment scenario, precious metal salts such as platinum, palladium, and rhodium, or non-precious metal oxides such as manganese, cobalt, and copper are precisely selected. All precursors must be tested by atomic absorption spectrometry to ensure a purity of ≥99.5% and impurity content below 50ppm.

The carrier, as the "supporting framework" of the active component, directly affects the number of catalytic active sites. High-purity alumina, titanium-silica molecular sieves, or cordierite honeycomb substrates are commonly used, requiring surface area testing (≥200m²/g) and pore structure analysis to ensure the pore size distribution is within the 2-50nm mesoporous range. Auxiliary additives focus on enhancing carrier stability, such as adding a small amount of cerium dioxide to improve anti-poisoning ability, and adding kaolin to optimize molding performance. All auxiliary materials must undergo compatibility testing.

The pre-treatment stage is also crucial: precious metal precursors need to be dissolved at a constant temperature and filtered to remove impurities, and the carrier needs to be dried at 120℃ and pre-calcined at 500℃ to remove residual moisture and organic impurities, ensuring the stability of subsequent processes.

Carrier Modification and Structuring

Carrier modification is a core step in improving catalyst performance. First, a nanoscale porous coating is constructed on the carrier surface using the sol-gel method.  Then, plasma treatment technology is used to etch the carrier surface, increasing the number of surface hydroxyl groups and creating more anchoring points for the active components. For honeycomb carriers, a special pore channel optimization technique is also employed to control the pore density between 300-600 cpsi, balancing permeability and specific surface area.

After carrier preparation, rigorous physical performance testing is required: the specific surface area and pore size distribution are tested using the liquid nitrogen adsorption-desorption method, and the mechanical strength is tested using a compressive strength tester (axial compressive strength of honeycomb carrier ≥ 1.5 MPa) to ensure that the carrier is not easily damaged during subsequent loading and use.

Precise Loading of Active Components

The uniform loading of active components is key to the high efficiency of the catalyst. This step requires the selection of differentiated processes depending on the type of active component. For precious metal catalysts, the "equal volume impregnation method" is used, immersing the pre-treated carrier in a precisely formulated precious metal precursor solution. Vacuum negative pressure assisted penetration ensures uniform distribution of the active components on the carrier surface and within the pores, with a loading error controlled within ±0.05%.

Non-precious metal catalysts mostly use the co-precipitation method, mixing the carrier and the active component precursor solution in proportion, stirring and precipitating at a constant pH and temperature.  This is followed by centrifugal separation and washing to remove salts, ensuring that the active component and carrier form a stable solid solution structure.

After loading, the catalyst undergoes a gradient drying process: first, drying at a low temperature of 80°C for 4 hours to remove surface moisture, then increasing the temperature to 120°C for 8 hours to remove bound water within the pores, and finally calcining in a muffle furnace at 400-600°C for 4-6 hours to convert the active components into a stable oxide form and enhance the bonding strength with the carrier.

Molding and Post-treatment

To adapt to different exhaust gas treatment equipment, the catalyst needs to be manufactured into a specific shape. Granular catalysts are manufactured using a tablet pressing process, where the calcined powder is mixed with a small amount of binder and pressed into granules under a pressure of 10-20 MPa, ensuring a compressive strength of ≥50 N/granule.  Rod-shaped catalysts are produced using an extrusion molding process, where the raw material is extruded into rods using a screw extruder, and then cut to obtain products of uniform length. Honeycomb catalysts are manufactured using an integral molding process, where the carrier slurry is mixed with the active components and binder, extruded through a honeycomb mold, and dried to obtain a complete honeycomb structure.

The molded catalysts undergo a secondary sintering treatment, sintered in a high-temperature furnace at 600-800℃ for 8-12 hours to further enhance mechanical strength and thermal stability, while eliminating internal stresses generated during the molding process. For precious metal catalysts, a reduction treatment step is also added, reducing the precious metal oxides to elemental metal active sites in a hydrogen atmosphere at 300-400℃ for 2-3 hours.

Storage

Storage should follow the principle of "low temperature, dry, light-protected, and well-ventilated." The storage temperature should be controlled at 5-30℃, with a relative humidity of ≤60%, avoiding co-storage with acidic or alkaline substances to prevent premature poisoning or deactivation of the catalyst.

author: Hazel
date: 2025-11-28