Hydroxyapatite-supported Ru CAtalysts for the chemical STORage of H2 as AMmoniA – H2CASTORAMA

Ammonia (NH3) is a key chemical compound for the production of fertilizers, which remain of the utmost interest in the feeding of the world’s population. More recently NH3 has been identified as an energy vector which could be used as a chemical to store the hydrogen produced by water electrolysis powered by sunlight and wind renewable energies. The ever increasing annual production of NH3 amounted to be about 235 million tons in 2019, which makes this chemical as the second most produced chemical after sulfuric acid, is achieved via the well-known Haber-Bosch process industrialized as early as 1913. This process is based on the reaction of molecular dihydrogen and dinitrogen (N2 + 3 H2 = 2 NH3) and was found to be originally catalysed by Fe-based materials. This process is commonly operated at high temperatures (> 400°C) and pressures (> 20MPa), which makes it energy intensive. In addition, H2 used in the Haber-Bosch process is produced by catalytic steam reforming of natural gas (CH4 + H2O = CO + 3 H2), which is also energy intensive. The production of NH3 through these processes is therefore at the origin of large amounts of greenhouse gas, which release should be reduced in the current context of global warming. Early 70s, it was found that the NH3 synthesis could be catalysed more effectively than with the Fe-based catalyst by promoted Ru materials supported on activated carbons and later on oxides. Overall, it was found in this field that the catalytic performance of the Ru catalysts was strongly dependent on the size of the Ru nanoparticle and on the basicity of the promoters and/or support. Since hydroxyapatite (HAp), an environmental-friendly calcium phosphate material, is known to be basic in nature, this project aims at providing Ru/HAp catalysts with a fine control of both the basicity of the supporting hydroxyapatites and the size of the Ru nanoparticles to determine the most appropriate material for improving the catalytic performance in NH3 synthesis.