Activated carbon as a catalyst

Activated carbon is a porous adsorption material prepared from carbon-based materials through activation treatment. It has a very high specific surface area and rich pore structure. It is widely used in fields such as environmental governance, adsorption separation, and energy storage.

 

Activated carbon is a porous adsorption material prepared from carbon-based materials through activation treatment. It has a very high specific surface area and rich pore structure. It is widely used in fields such as environmental governance, adsorption separation, and energy storage. In recent years, research on activated carbon as a catalyst or catalyst carrier has gradually increased, and it plays an important role in a variety of catalytic reactions. This article will explore the mechanism, application fields and research frontiers of activated carbon in the field of catalysis.

 

1. Basic characteristics and catalytic mechanism of activated carbon  

Activated carbon is usually prepared by carbonizing organic polymer materials (such as wood, coal, coconut shells, etc.) at high temperature in an inert atmosphere and performing activation treatment through physical or chemical methods. Its most notable feature is its rich pore structure, which usually includes micropores (pore diameter < 2 nm), mesopores (2-50 nm) and macropores (> 50 nm). These pores give activated carbon extremely high specific Surface area (up to 1000-3000 m²/g). In addition, the surface of activated carbon often contains oxygen-containing functional groups, such as carboxyl groups, hydroxyl groups, aldehyde groups, and ether groups. These functional groups have an important impact on the catalytic performance of activated carbon.  

Activated carbon can play a variety of roles in catalytic reactions, and its catalytic mechanism is mainly reflected in the following aspects:  

Activity of surface functional groups: The oxygen-containing functional groups on the surface of activated carbon can chemically interact with reactants and provide active sites. For example, functional groups such as carboxyl and hydroxyl groups can participate in catalytic processes through redox reactions.  

Electron transfer: Activated carbon has good electrical conductivity and can promote the transfer of electrons in certain electrochemical reactions, thereby increasing the reaction rate.  

Adsorption and concentration effect: The porous structure of activated carbon gives it excellent adsorption performance and can concentrate the reactants in the pores, thereby increasing the local concentration of the reactants and increasing the reaction rate. Through this "quasi-homogeneous" effect, the catalytic efficiency of activated carbon is significantly improved.  

Carrier role: Activated carbon is often used as a carrier for other active substances to stabilize and disperse catalytically active species (such as metal nanoparticles) and improve their catalytic performance. When used as a carrier, the high specific surface area of ​​activated carbon helps to evenly distribute the catalyst and improve its utilization.

2. Application of activated carbon in catalysis  

Activated carbon has shown excellent performance in a variety of catalytic oxidation reactions. For example, in wastewater treatment and air purification, activated carbon can catalyze the degradation of organic pollutants with oxygen or other oxidants.  

Catalytic wet oxidation in wastewater treatment: Activated carbon can be used as a catalyst or catalyst carrier in wet oxidation reactions to oxidize organic pollutants in water into harmless small molecular substances or carbon dioxide and water. Activated carbon not only provides high adsorption capacity, but also participates in the catalytic process through surface oxidation reactions. This technology is particularly suitable for treating high-concentration industrial wastewater, such as wastewater discharged from pharmaceutical, chemical and paper industries.  

Oxidative decomposition of VOCs: Activated carbon also has an important application in the catalytic oxidation process of volatile organic compounds (VOCs). For example, organic matter such as toluene and styrene can be oxidized by oxygen under the catalysis of activated carbon to generate carbon dioxide and water, reducing air pollution.  

Activated carbon is often used as a carrier for precious metal (such as platinum, palladium, rhodium, etc.) catalysts in hydrogenation reactions. For example, in the fields of petrochemicals and fine chemicals, activated carbon-supported palladium catalysts are often used for hydrogenation reactions of unsaturated hydrocarbons, such as the hydrogenation of styrene to produce ethylbenzene, the hydrogenation of propylene to produce propane, etc.  

The high specific surface area and good pore structure of activated carbon enable the noble metal particles to be highly dispersed, thereby providing more active sites. In addition, the adsorption and desorption process of reactants when activated carbon is used as a carrier can also effectively regulate the rate of catalytic reactions. For example, activated carbon supported palladium catalyst shows good selectivity and high efficiency in the hydrogenation reaction of chlorobenzene.  

Activated carbon is also widely used in desulfurization reactions. Traditional catalytic desulfurization methods mainly rely on transition metal oxide catalysts, but in recent years, activated carbon-supported metal catalysts have shown excellent results in the field of desulfurization. Activated carbon-loaded metal oxide catalysts such as vanadium and molybdenum can effectively remove sulfides in fuel and generate non-toxic sulfates, thereby reducing sulfur oxide emissions during the combustion process and reducing air pollution.  

The conductivity of activated carbon makes it widely used in the field of electrocatalysis, especially in electrochemical reactions such as fuel cells, electrolysis of water for hydrogen production, and supercapacitors.  

Application in fuel cells: In proton exchange membrane fuel cells (PEMFC), activated carbon is often used as a carrier for platinum catalysts. Its high specific surface area can effectively disperse platinum nanoparticles and improve the activity and efficiency of electrode reactions. In addition, the conductivity of activated carbon can improve the conductivity of the electrode, reduce resistance, and increase the overall efficiency of the fuel cell.

 Supercapacitor: Activated carbon is an ideal material for preparing supercapacitor electrodes due to its high specific surface area and good electrical conductivity. In supercapacitors, electrode materials store charges through Faradaic reactions. The porous structure of activated carbon provides more storage space, so it has higher energy density and power density.    

Activated carbon is also widely used in the field of biomass catalytic conversion. For example, activated carbon-supported metal catalysts can catalyze the conversion of biomass raw materials such as cellulose and lignin into valuable chemicals or fuels, such as bioethanol and biodiesel. This technology provides important support for the development of renewable energy.    

Activated carbon plays a vital role in the field of environmental catalysis, especially in air purification, exhaust gas treatment and water treatment. Activated carbon is often used in adsorption catalysis applications due to its excellent adsorption properties for gases and organic pollutants. For example, activated carbon can adsorb sulfur dioxide and nitrogen oxides in the environment and convert them into harmless substances through catalytic oxidation. In addition, activated carbon supported catalysts can also be used to degrade dyes, organic matter and heavy metal pollutants in industrial wastewater.