Conversion refers to the percentage of the starting material – known as substrates – that is transformed into products. In chemical process engineering, conversion is a crucial parameter, as it reflects the efficiency of a process.

Conversion is strongly temperature-dependent and generally increases with rising temperature. An example of near-complete conversion, as sought in industry, is the combustion of volatile organic compounds (VOCs) at temperatures above 750 °C. In practice, however, complete conversion is often not achievable because the activation energy of many chemical reactions is too high. Furthermore, increasing the temperature leads to both increased energy consumption and the formation of undesirable byproducts, thus reducing selectivity.

To achieve this goal, catalysts are used in approximately 70–80% of all industrial processes. Catalysts lower the activation energy, increase selectivity, and allow chemical reactions to be carried out under milder conditions. This not only increases energy efficiency thanks to lower process temperatures but also reduces the formation of unwanted byproducts.