(555g) Silica As a Redox Support for Enhanced CO2 to CO By Perovskite Oxides in the Reverse Water Gas Shift Chemical Looping Process

Conversion of CO₂ is crucial for realigning the carbon cycle and essentially providing the means for renewable fuel production. Perovskite oxides, more notably La_0.75Sr_0.25FeO₃ (LSF), have exhibited promising CO₂ to CO conversion capabilities through high temperature redox applications such as the reverse water gas shift chemical looping process (RWGS-CL). In this work, LSF was combined with SiO₂ (25% w/w) thus resulting in CO production of 2850 µmoles/g LSF, 150% greater than the unsupported control. Silica also increased the reduction rate of LSF in isothermal RWGS-CL which has been the limiting reaction step. X-ray diffraction patterns revealed the minor presence of inevitable secondary phases FeSiO₃ and La₂SiO₅ along with a minute tridymite phase. These were all proven have no direct contribution to the activity enhancement through energy of vacancy formation calculations done by DFT accompanied by experiments with different LSF loading (25, 50, and 75% w/w). Crystallite size estimations by Scherrer analyses of post experimental samples showed that silica is capable of reversing the coalescence of perovskite grains, from high temperature syntheses, throughout redox applications. The increased surface area alleviates the transport resistance of bulk oxygen to establish a greater degree of vacancy formation for an improved CO formation yield.