Investigation of AFeO3 (A=Ba, Sr) Perovskites for the Oxidative Dehydrogenation of Light Alkanes under Chemical Looping Conditions.

Oxidative dehydrogenation (ODH) of light alkanes to produce C2-C3 olefins is a promising alternative to conventional steam cracking. Perovskite oxides are emerging as efficient catalysts for this process due to their unique properties such as high oxygen storage capacity (OSC), reversible redox behavior, and tunability. Here, we explore AFeO3 (A=Ba, Sr) bulk perovskites for the ODH of ethane and propane under chemical looping conditions (CL-ODH). The higher OSC and oxygen mobility of SrFeO3 perovskite contributed to its higher activity but lower olefin selectivity than its Ba counterpart. However, SrFeO3 perovskite is superior in terms of cyclic stability over multiple redox cycles. Transformations of the perovskite to reduced phases including brownmillerite A2Fe2O5 were identified by X-ray diffraction (XRD) as a cause of performance degradation, which was fully reversible upon air regeneration. A pre-desorption step was utilized to selectively tune the amount of lattice oxygen as a function of temperature and dwell time to enhance olefin selectivity while suppressing CO2 formation from the deep oxidation of propane. Overall, SrFeO3 exhibits promising potential for the CL-ODH of light alkanes, and optimization through surface and structural modifications may further engineer well-regulated lattice oxygen for maximizing olefin yield.

Investigation of Sr0.7 Ca0.3 FeO3 Oxygen Carriers with Variable Cobalt B-Site Substitution.

A-site and B-site substitutions are effective methods towards improving well-studied oxygen carrier materials that are vital for emerging gasification technologies. Such materials include SrFeO3 , which greatly benefits from the inclusion of calcium and/or cobalt, and Sr0.8 Ca0.2 Fe0.4 Co0.6 O3 has been regarded as the best-performing composition. In this study, systems with higher calcium and lower cobalt contents are investigated with a view to lessening the societal and economic burdens of these dual-doped carriers. Density functional theory calculations are performed to illustrate the Fe-O bonding and relaxation contributions to the oxygen vacancy formation energy in Sr1-x Cax Fe1-y Coy O3 systems (x=0.1875, 0.25, 0.3125; y=0.125, 0.25, 0.375, 0.5) and determine that increased calcium A-site substitution requires the use of less cobalt B-site doping to reach the same oxygen vacancy formation. These findings are experimentally validated in situ and ex situ characterization of bulk Sr0.7 Ca0.3 Fe1-y Coy O3 materials. Sr0.7 Ca0.3 Fe0.7 Co0.3 O3 is found to have similar O2 adsorption/desorption rates and storage capacity to Sr0.8 Ca0.2 Fe0.4 Co0.6 O3 in air/N2 cycling experiments. Additionally, both materials are outperformed by Sr0.7 Ca0.3 Fe1-y Coy O3 systems with y=0-0.10 at 400-500 °C, which cycle 1.5 wt% O2 in under ten minutes.

Performance Loss of Activated Carbon Electrodes in Capacitive Deionization: Mechanisms and Material Property Predictors.

Understanding the material property origins of performance decay in carbon electrodes is critical to maximizing the longevity of capacitive deionization (CDI) systems. This study investigates the cycling stability of electrodes fabricated from six commercial and two post-processed activated carbons. We find that the capacity decay rate of electrodes in half cells is positively correlated with the specific surface area and total surface acidity of the activated carbons. We also demonstrate that half-cell cycling stability is consistent with full cell desalination performance durability. Additionally, our results suggest that increase in internal resistance and physical pore blockage resulting from extensive cycling may be important mechanisms for the specific capacitance decay of activated carbon electrodes in this study. Our findings provide crucial guidelines for selecting activated carbon electrodes for stable CDI performance over long-term operation and insight into appropriate parameters for electrode performance and longevity in models assessing the techno-economic viability of CDI. Finally, our half-cell cycling protocol also offers a method for evaluating the stability of new electrode materials without preparing large, freestanding electrodes.

Shale pore alteration: Potential implications for hydrocarbon extraction and CO2 storage.

Shale unconventional reservoirs are currently and expected to remain substantial fossil fuel resources in the future. As CO2 is being considered to enhance oil recovery and for storage purposes in unconventional reservoirs, it is unclear how the shale matrix and fractures will react with CO2 and water during these efforts. Here, we examined the Utica Shale and its reactivity with CO2 and water using scanning electron microscopy, N2 and CO2 sorption isotherms, mercury intrusion porosimetry, and X-ray scattering methods. During CO2 exposure, the presence of water can inhibit CO2 migration into the shale matrix, promote carbonate dissolution, and dramatically change the pore scale variability by opening and closing pore networks over the macro- to nano-scale range. These alterations in the shale matrix could impact flow pathways and ultimately, oil recovery factors and carbon storage potential.

Individual Nanoporous Carbon Spheres with High Nitrogen Content from Polyacrylonitrile Nanoparticles with Sacrificial Protective Layers.

Functional nanoporous carbon spheres (NPC-S) are important for applications ranging from adsorption, catalysis, separation to energy storage, and biomedicine. The development of effective NPC-S materials has been hindered by the fusion of particles during the pyrolytic process that results in agglomerated materials with reduced activity. Herein, we present a process that enables the scalable synthesis of dispersed NPC-S materials by coating sacrificial protective layers around polyacrylonitrile nanoparticles (PAN NPs) to prevent interparticle cross-linking during carbonization. In a first step, PAN NPs are synthesized using miniemulsion polymerization, followed by grafting of 3-(triethoxysilyl)propyl methacrylate (TESPMA) to form well-defined core-shell structured PAN@PTESPMA nanospheres. The cross-linked PTESPMA brush layer suppresses cross-linking reactions during carbonization. Uniform NPC-S exhibiting diameters of ∼100 nm, with relatively high accessible surface area (∼424 m2/g), and high nitrogen content (14.8 wt %) was obtained. When compared to a regular nanoporous carbon monolith (NPC-M), the nitrogen-doped NPC-S demonstrated better performance for CO2 capture with a higher CO2/N2 selectivity, an increased efficiency in catalytic oxygen reduction reactions, as well as improved electrochemical capacitive behavior. This miniemulsion polymerization-based strategy for the preparation of functional PAN NPs provides a new, facile approach to prepare high-performance porous carbon spheres for diverse applications.

Visible light plasmonic heating of Au-ZnO for the catalytic reduction of CO2.

Plasmonic excitation of Au nanoparticles attached to the surface of ZnO catalysts using low power 532 nm laser illumination leads to significant heating of the catalyst and the conversion of CO2 and H2 reactants to CH4 and CO products. Temperature-calibrated Raman spectra of ZnO phonons show that intensity-dependent plasmonic excitation can controllably heat Au-ZnO from 30 to ~600 °C and simultaneously tune the CH4 : CO product ratio. The laser induced heating and resulting CH4 : CO product distribution agrees well with predictions from thermodynamic models and temperature-programmed reaction experiments indicating that the reaction is a thermally driven process resulting from the plasmonic heating of the Au-ZnO. The apparent quantum yield for CO2 conversion under continuous wave (cw) 532 nm laser illumination is 0.030%. The Au-ZnO catalysts are robust and remain active after repeated laser exposure and cycling. The light intensity required to initiate CO2 reduction is low (~2.5 × 10(5) W m(-2)) and achievable with solar concentrators. Our results illustrate the viability of plasmonic heating approaches for CO2 utilization and other practical thermal catalytic applications.

Copolymer-templated nitrogen-enriched porous nanocarbons for CO2 capture.

Nitrogen-enriched porous carbon materials made via the carbonization of polyacrylonitrile containing block copolymer act as efficient and highly selective CO(2) sorbents. Nitrogen content and surface area, which are both influenced by pyrolysis temperature and atmosphere, are crucial for CO(2) adsorption performance.