Heterogeneous catalysis for the novel energies - Toward renewable fuels

A catalyst is a substance that accelerates a chemical reaction without itself being consumed. In chemical catalysis, a distinction is made between homogeneous catalysis (dissolved catalyst) and heterogeneous catalysis (solid catalyst). In addition, the source of activation for the catalytic process can be thermal, electrical, photonic, etc. Present in most industrial processes today, thermal heterogeneous catalysis revolutionized agrochemicals (fertilizers) with the Haber-Bosch process for ammonia production, and is essential in refining (fuels), petrochemicals (plastics and other products) and pollution control (catalytic converters). Catalyst efficiency depends on numerous parameters such as intrinsic activity, quantity and accessibility of active sites, which can be optimized through the choice of materials and preparation method, notably in the form of metal nanoparticles supported on a porous solid.

Catalysis is set to play a major role in the energy transition. Energy comes in many different forms (mechanical, thermal, chemical, etc.). A distinction is made between primary – natural sources, such as the sun and fossil fuels –, and secondary – transformed sources, such as heat and electricity. Catalysis is necessarily involved in the conversion of primary sources into the chemical energy carriers that are fuels. To reduce dependence on fossil fuels, new catalytic solutions have emerged: valorization of CO ₂ and biomass, production of green hydrogen and e-fuels, hydrogen storage in organic liquids and ammonia, and devices such as electrolyzers and fuel cells. These innovations are essential for sustainable access to energy and require the development of ever more efficient and resistant catalysts, for example to reinvent refining (biorefining) and propose industrializable routes from non-fossil resources.

The article begins with an introduction to key concepts, then is organized into three sections, each corresponding to a type of chemical catalysis: thermocatalysis for the conversion of small molecules – with a reminder of historic processes currently being adapted to new inputs such as CO ₂ –, thermocatalysis for the conversion of large molecules and complex mixtures such as biomass and waste, and electrocatalysis applied to the valorization of the preceding molecules as well as to electricity production and storage. Sidebars highlight several aspects, including industrial and environmental implications.