@article{tian_luongo_donat_müller_larring_westmoreland_li_2022, title={Oxygen Nonstoichiometry and Defect Models of Brownmillerite-Structured Ca<sub>2</sub>MnAlO<sub>5+δ</sub> for Chemical Looping Air Separation}, volume={10}, ISSN={2168-0485 2168-0485}, url={http://dx.doi.org/10.1021/acssuschemeng.2c03485}, DOI={10.1021/acssuschemeng.2c03485}, abstractNote={Brownmillerite-structured Ca2MnAlO5+δ has demonstrated excellent oxygen storage capacity that can be used for chemical looping air separation (CLAS), a potentially efficient approach to produce high-purity oxygen from air. To effectively utilize this material as an oxygen sorbent in CLAS, it is necessary to comprehensively understand its thermodynamic properties and the structure–performance relationships in the operating range of interest. In this work, the oxygen nonstoichiometry (δ) of Ca2MnAlO5+δ was systematically measured by thermogravimetric analysis (TGA) in the temperature ranging from 440 to 660 °C and under an oxygen partial pressure ranging from 0.01 to 0.8 atm. The partial molar enthalpy and entropy for the oxygen-releasing reaction were calculated using the van't Hoff equation with an average value of 146.5 ± 4.7 kJ/mol O2 and 162.7 ± 5.1 J/K mol O2, respectively. The experimentally measured nonstoichiometry (δ) was well fitted by a point defect model applied in two regions divided by the predicted equilibrium P–T curve. The equilibrium constants for appropriate defect reactions were also determined. The thermochemical parameters, molar enthalpy and entropy for the main reaction, obtained from the defect model were 136.9 kJ/mol O2 and 225.3 J/K mol O2, respectively, showing reasonable agreement with the aforementioned values. The applicability of the defect model was also verified at a higher oxygen partial-pressure environment of up to 4 atm and exhibited reasonable prediction of the trend. The experimental studies on oxygen nonstoichiometry combined with the defect modeling provide useful insights into oxygen sorbents' redox performances and helpful information for the design and optimization of oxygen sorbents in CLAS.}, number={31}, journal={ACS Sustainable Chemistry & Engineering}, publisher={American Chemical Society (ACS)}, author={Tian, Yuan and Luongo, Giancarlo and Donat, Felix and Müller, Christoph R. and Larring, Yngve and Westmoreland, Phillip R. and Li, Fanxing}, year={2022}, month={Jul}, pages={10393–10402} }
 @article{tian_dudek_westmoreland_li_2020, title={Effect of Sodium Tungstate Promoter on the Reduction Kinetics of CaMn0.9Fe0.1O3 for Chemical Looping - Oxidative Dehydrogenation of Ethane}, volume={398}, ISSN={["1873-3212"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85085392858&partnerID=MN8TOARS}, DOI={10.1016/j.cej.2020.125583}, abstractNote={Reduction kinetics of unpromoted and Na2WO4-promoted CaMn0.9Fe0.1O3 redox catalysts are measured in the context of chemical looping-oxidative dehydrogenation (CL-ODH). CL-ODH is a promising alternative for ethylene production compared to steam cracking, as it reduces the energy demand and increases the single-pass ethane conversion. The ability of a redox catalyst for selective hydrogen combustion (SHC), i.e. selectively oxidizing hydrogen co-product from ethane dehydrogenation, represents an effective strategy for CL-ODH because it can shift the reaction equilibrium and facilitate exothermic overall reaction. In this work, kinetic models and parameters of unpromoted and Na2WO4-promoted, Fe-doped CaMnO3 (CaMn0.9Fe0.1O3) under H2 and C2H4 were investigated. The reduction of unpromoted CaMn0.9Fe0.1O3 follows reaction-order models. C2H4 reduction has a higher energy barrier and a greater dependence on active lattice oxygen concentration, resulting in an order-of-magnitude decrease in the reduction rate. In comparison, the reduction of Na2WO4-promoted CaMn0.9Fe0.1O3 follows an Avrami-Erofe’ev nucleation and nuclei growth model. The addition of Na2WO4 more significantly suppressed C2H4 combustion relative to H2 oxidation. As a result, the reduction rate of Na2WO4-promoted CaMn0.9Fe0.1O3 under H2 was three orders of magnitude greater than that under C2H4, demonstrating its excellent SHC properties. The resulting redox catalyst was shown to be effective for ethane CL-ODH with measured 90.5% ethylene selectivity and 41.6% ethylene yield at 750 °C. The kinetics models and parameters provide useful information for CL-ODH reactor design and further development of the redox catalyst.}, journal={CHEMICAL ENGINEERING JOURNAL}, author={Tian, Yuan and Dudek, Ryan B. and Westmoreland, Phillip R. and Li, Fanxing}, year={2020}, month={Oct} }
 @article{dudek_tian_jin_blivin_li_2020, title={Reduction Kinetics of Perovskite Oxides for Selective Hydrogen Combustion in the Context of Olefin Production}, volume={8}, ISSN={["2194-4296"]}, url={https://doi.org/10.1002/ente.201900738}, DOI={10.1002/ente.201900738}, abstractNote={Chemical looping represents a novel approach for generating light olefins in which thermal cracking or catalytic dehydrogenation is coupled with selective hydrogen combustion (SHC) by a metal oxide redox catalyst, which enables autothermal operation, increased per‐pass conversion, and greater‐than‐equilibrium yields. Recent studies indicate that Na2WO4‐promoted perovskite oxides are effective redox catalysts with high olefin selectivity. Herein, kinetic parameters, rates, and reaction models for the reduction of unpromoted and Na2WO4‐promoted CaMnO3 redox catalysts by H2, C2H4, and C2H6, is reported. Reduction rates of CaMnO3 under ethylene and ethane are significantly lower than under H2. Model fitting of reduction kinetics show good agreement with reaction order–controlled models for CaMnO3 reduction and predict greater oxygen site dependence and higher activation energy for CaMnO3 reduction by C2H4 as compared with H2. Avrami–Erofe'ev nucleation and growth models provide the best fit to the reduction of Na2WO4/CaMnO3 in H2 and in C2H4. After Na2WO4 promotion, the reduction rate of CaMnO3 is three orders of magnitude lower in ethylene in comparison to hydrogen, consistent with its superior selectivity to hydrogen combustion. The models developed can be applied toward reactor design and optimization in the context of enhanced olefin production via SHC under a cyclic redox scheme.}, number={8}, journal={ENERGY TECHNOLOGY}, publisher={Wiley}, author={Dudek, Ryan B. and Tian, Yuan and Jin, Gaochen and Blivin, Millicent and Li, Fanxing}, year={2020}, month={Aug} }