Search

Active areas of research on chemical looping technologies for the conversion of CO2 to CO are contrasted and discussed, including current performance, methods for material design, and next steps in expanding their development. Generation of CO from CO2 is of interest in sustainable chemistry and engineering to convert anthropogenic CO2 emissions into feedstock for Fischer–Tropsch (FT), methanol to gasoline (MTG), gas-to-liquid (GTL), and other synthesis pathways for fuels and materials. Chemical looping strategies have been identified which not only produce CO, but also H2 from H2O and methane sources, supplying the other key component of syngas. Configurations of these chemical looping technologies into the materials economy potentially constitute sustainable carbon loop cycles for fuels as well as carbon sequestration into industrial and commercial materials. Major areas of research in CO2 conversion by chemical looping, collectively referred to here as CO2CL, including Solar-Thermal Chemical Looping (STCL), Reverse Water Gas Shift Chemical Looping (RWGS-CL), Chemical Looping Reforming (CLR), Super Dry Reforming (SDR), Autothermal Catalyst Assisted Chemical Looping (ACACL), and Reverse Boudouard Reforming (RBR) are discussed in terms of their process characteristics, historical development of oxygen carrier (OC) material, state of the art methods for material design, and future work needed to advance the scale-up of these technologies. This perspective centers around the non-methane utilizing processes for CO2CL, focusing on the phenomena of oxygen transfer between gas molecules and the oxygen carrier (OC). [ABSTRACT FROM AUTHOR]

In this study, high yields of CO are reported from CO2 using the silica (SiO2) supported perovskite oxide, La0.75Sr0.25FeO3 (LSF), composites in the reverse water gas shift chemical looping (RWGS‐CL) process. XRD patterns of materials formed upon adding SBA‐15 to the perovskite sol‐gel precursor solution indicated successful formation of an orthorhombic perovskite oxide structure in the composites. The total surface area increased by ∼300 % with the addition of 50 % LSF to SBA‐15 by mass and surface accessibility of perovskite oxide crystallites was verified by CO2 chemisorption and XPS measurements. Composite materials achieved up to a factor of 10 increases in CO yields (∼3.5 vs 0.35 mmol CO/gLSF) compared to pure LSF through six consecutive RWGS‐CL cycles at 700 °C. Following these RWGS‐CL cycles, XRD Scherrer analyses showed that the perovskite oxide in the composite material decreased in crystallite size. This approach to synthesis of supported perovskite oxides is expected to be valuable for large‐scale CO2 conversion by RWGS‐CL. [ABSTRACT FROM AUTHOR]

Strong adsorption of ketone and diketone byproducts and their fragmentation products during the aqueous phase reforming of biomass derived oxygenates is believed to be responsible for the deactivation of supported Pt catalysts. This study involves a combined experimental and theoretical approach to demonstrate the interactions of several model di/ketone poisons with Pt/γ-Al 2 O 3 catalysts. Particular di/ketones were selected to reveal the effects of hydroxyl groups (acetone, hydroxyacetone), conjugation with C=C bonds (mesityl oxide), intramolecular distance between carbonyls in diketones (2,3-butanedione, 2,4-pentanedione), and length of terminal alkyl chains (3,4-hexanedione). The formation of adsorbed carbon monoxide (1900-2100 cm -1 ) as a decarbonylation product was probed using infrared spectroscopy and to calculate the extent of poisoning during subsequent methanol dehydrogenation based on the reduction of the ν(C≡O) band integral relative to experiments in which only methanol was dosed. Small Pt particles appeared less active in decarbonylation and were perhaps poisoned by strongly adsorbed di/ketones on undercoordinated metal sites and bulky conjugated species formed on the γ-Al 2 O 3 support from aldol self-condensation. Larger Pt particles were more resistant to di/ketone poisoning due to higher decarbonylation activity yet still fell short of the expected yield of adsorbed CO from subsequent methanol activity. Vibrational spectra acquired using inelastic neutron scattering showed evidence for strongly binding methyl and acyl groups resulting from di/ketone decarbonylation on a Pt sponge at 250 °C. Adsorption energies and molecular configurations were obtained for di/ketones on a Pt(111) slab using density functional theory, revealing potential descriptors for predicting decarbonylation activity on highly coordinated metal sites. Calculated reaction energies suggest it is energetically favorable to reform surface methyl groups into adsorbed CO and H. However, the rate of this surface reaction is limited by a high activation barrier indicating that either improved APR catalyst designs or regeneration procedures may be necessary., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)