Deactivation

The deactivation of catalysts is a central aspect in the development and optimization of chemical processes. It describes the irreversible or reversible reduction of catalytic activity and selectivity over time. The causes of deactivation are diverse and depend strongly on the process conditions and the materials used. The most important mechanisms include poisoning, coking, sintering and mechanical processes.

Poisoning

Poisoning occurs when certain substances, called poisons, block the active centers of the catalyst. These substances bind irreversibly or strongly to the active surfaces, making them inaccessible to the actual reactants. Typical poisons are sulfur compounds, halogens, phosphorus or carbon monoxide, depending on the nature of the catalyst.

Coking

The formation of coke, i.e. carbon-containing deposits, is particularly relevant in processes that process hydrocarbons or aromatic compounds. Coke deposits block the active centers and pores of the catalyst, which leads to a significant reduction in reactivity. Regeneration often occurs by oxidation of the deposits at high temperatures.

sintering

Sintering describes the thermally induced loss of active surface area due to the coalescence of small metal or metal oxide particles to form larger agglomerates. This leads to a reduction in the surface-to-volume ratio and thus to a decrease in catalytic activity. This process occurs particularly at high operating temperatures.

Mechanical degradation

Mechanical degradation involves physical damage to the catalyst, such as abrasion, breakage or clogging of the pore structure by particles from the feed stream. This form of deactivation often occurs in fluidized bed reactors or under high gas flow conditions.

Understanding the underlying mechanisms is essential to develop targeted strategies to avoid deactivation or regeneration and thus extend the lifetime of the catalysts.