Electron traps as a valuable criterium of iron oxide catalysts' performance in CO2 hydrogenation

The main objective of the present study is to synthesize iron oxide catalysts with engineered crystal defects and to clarify their crucial impact on the final catalytic activity in the CO2 hydrogenation process. The method used to engineer the desired crystal defects is based on changing the precipitation reaction conditions, such as the addition rate and the order of the precipitant during the primary phase of the synthesis of iron oxide catalysts. The catalyst synthesis process is based on the formation of iron oxalates in the first step, followed by thermal decomposition into iron oxides in the second step, which were subsequently tested as catalysts in CO₂ hydrogenation. The reversed double-beam photoacoustic spectroscopy used for advanced characterization of the prepared catalysts demonstrated that the observed change in catalytic activity is related to the energy and density of electron traps connected with the defects in the crystal lattice of the catalysts. These defects occur during the precipitation of oxalates, and their formation is significantly affected by changes in the precipitation conditions, i.e., the course of nucleation and growth of iron oxalate crystals. The results of the presented study thus affirmed the cardinal importance of defect engineering in heterogeneous catalysis.