Extracting Kinetic Information from Complex Gas–Solid Reaction Data

Abstract

We develop an approach for extracting gas−solid kinetic information from convoluted experimental data and demonstrate it on isothermal carbon dioxide splitting at high-temperature using CoFe 2 O 4 /Al 2 O 3 (i.e., a "hercynite" cycle based on Co-doped FeAl 2 O 4 ) active material. The reaction kinetics equations we derive account for competing side reactions, namely catalytic CO 2 splitting on and O 2 oxidation of doped hercynite, in addition to CO 2 splitting driven by the oxidation of oxygendeficient doped hercynite. The model also accounts for experimental effects, such as detector dead time and gas mixing downstream of the reaction chamber, which obscure the intrinsic chemical processes in the raw signal. A second-order surface reaction model in relation to the extent of unreacted material and a 2.4th-order model in relation to CO 2 concentration were found to best describe the CO generation of the doped hercynite. Overall, the CO production capacity was found to increase with increasing reduction temperature and CO 2 partial pressure, in accordance with previously predicted behavior. The method outlined in this paper is generally applicable to the analysis of other convoluted gas−solid kinetics experiments.

Differences in the Nature of Reaction Process for Thermochemical CO2 Splitting over NiFe2O4‐Based Materials

“…The CO generation reactions of NiFe 2 O 4 /SiO 2 and NiFe 2 O 4 /ZrO 2 are in agreement with the first‐order surface reaction regime (F1) in the entire set of splitting time, indicating that their CO 2 splitting reactions are controlled by the surface reaction. The similar conclusion of CO 2 splitting has also been reported on CoFe 2 O 4 /Al 2 O 3 and H 2 O splitting on LaFe 0.8 Co 0.2 O 3 /SiO 2 . As for NiFe 2 O 4 /MgO, the CO generation reaction shows an intermediate behavior between R2 and F1 models when α < 0.5.…”

Modifying La0.6Sr0.4MnO3 Perovskites with Cr Incorporation for Fast Isothermal CO2‐Splitting Kinetics in Solar‐Driven Thermochemical Cycles

“…For example, we only found a similar work for hercynite, which exhibited faster CO 2 -splitting rates with increased isothermal temperature, [56] ascribed to a higher reduction extent with increased temperature. Most of current literature investigates perovskite oxides only in temperatureswing cycling operation.…”

Chemical looping syngas from CO2 and H2O over manganese oxide minerals

“…However, the model was unable to characterize the solid conversion for over‐reduced pyrolusite, nor for the short 30 s cycles. The F3 model relates the rate of solid conversion to the third power of the remaining unconverted solid, and is restricted to surface phenomena . We included a reaction order with respect to the concentration to account for gas phase chemistry as outlined by the following: …”