In situ investigation of ethylene epoxidation on silver supported nanoparticles: from catalytic process to chemical looping

Ethylene epoxidation leads to the production of ethylene oxide, a commodity used to synthesize plastics, pharmaceuticals, detergents, etc. with a yearly increasing production. The industrial catalyst consists of promoted silver nanoparticles supported on alumina, and its catalytic performances have been thoroughly tested. Although several research efforts have been spent to spectroscopically characterize the system, many of them focused on model systems mimicking the actual catalyst, fundamental research questions remain. Recently, a new approach based on chemical looping has been proposed as an alternative to the catalytic reaction. By means of chemical looping, a process is split into multiple steps, within which a specific reaction intermediate forms and is stabilized. In the case of epoxidation, it avoids the dosing of a potentially explosive mixture of ethylene and oxygen, allows an easier separation of the ethylene oxide product, and enables to control the conditions of each of the reaction steps. Although some chemical looping tests have been carried out, the reaction mechanism and the relevant materials structures still need to be understood. Ambient pressure x-ray photoelectron spectroscopy and electron yield near edge x-ray absorption fine structure spectroscopy are suitable techniques to investigate in situ the solid-gas interface under relevant reaction conditions (gas environment and temperature). Combining such techniques with a complete pre-characterization and testing of the catalytic/chemical looping performances of powder samples and with theoretical calculations, the main goals of this project are:i) to investigate and characterize active sites involved in the catalytic reaction on actual samples;ii) to detect reaction intermediate/s formed during the catalytic reaction in the absence/presence of promoters on actual samples;iii) to investigate in situ the chemical looping epoxidation, characterizing the active sites, the role of the oxygen carrier supports and understanding the reaction mechanism, comparing it to the catalytic one.The project is ambitious and fills the pressure and material gaps that typically divide catalysis and surface science, to provide a complete understanding of a fundamental process. Theoretical calculations will help to combine the spectroscopic findings with the reactivity tests, so that the results will be of potential interest to develop new materials and to understand how chemical looping works and under what conditions it may be a valid alternative to the catalytic process.