La caratterizzazione "in situ" quale strumento efficace per lo studio del meccanismo di reazione di sistemi catalitici per la conversione della CO2 a combustibili alternativi

The collaboration with Laboratories Institute of Material and Environmental Chemistry Research Centre allowed to deeply investigate Cu-based catalysts used for CO2 hydrogenation reaction to DME production. Specifically, by coupling operando and in situ spectroscopic investigations, along with traditional ex situ physio-chemical characterization techniques, it was possible to individuate the nature and the functionality of surface adsorption sites, determine the intermediate compounds formed and evaluate how the CO2 is activated on Cu-zeolite based catalysts to be then converted to DME. DRIFT operando spectroscopic investigations allowed getting a deep understanding about the multiple catalytic steps behind DME synthesis, providing crucial information for a rational design of hybrid catalysts. Experiments in steady-state and transient modes confirmed the cooperation of metallic, acid-base and redox sites at a busy gas-solid interface, where the activation of hydrogen atoms, CO and surface oxygen precedes the intermediation of carbonate, formate and methoxy species towards the formation of methanol and then its acid condensation into dimethyl ether. The adsorbed species observed confirm previous postulates of the mechanism of methanol synthesis, namely that the CO2 like adsorbs dissociatively forming CO and surface oxygen with subsequent formation of carbonate on copper, followed by hydrogenation of the carbonate to the formate and thereafter to methoxy and methanol. The methanol is then dehydrated to dimethyl ether. The study of transient species indicated that the oxidation state of Cu slight changes during the reaction and that both partially oxidized copper particles are already present on the catalyst surface. This evidence has been also confirmed by in situ-CO adsorption carried out on Cu-based and Cu-free catalysts and also by XPS and UV-Vis measurements on used catalyst (in operando DRIFT conditions).