The oxidative degradation rates of a CO 2 sorbent composed of a mesoporous alumina impregnated with poly-(ethylenimine) (PEI) are measured under systematically varied conditions and a reaction rate law is created. Good agreement is shown between the rate of oxidation obtained via in situ calorimetric heat measurement during oxidative degradation reactions and the loss of CO 2 capture performance presented as amine efficiency (mol CO 2 /mol amine). PEI mass loss and elemental composition are tracked over the course of the reaction and used in conjunction with the oxidation rate measurements to shed insight into the oxidation reaction(s). These data, in combination with measurements of the heat of reaction, suggest a common reaction set across the range of temperatures, oxygen concentrations, and sorbent compositions tested. The data are consistent with the basic autoxidation scheme (BAS), the accepted mechanism of autoxidation of aliphatic polymers. We propose a lumped kinetic model to describe the oxidation reaction set and estimate an activation energy of 105 kJ/mol and an oxygen reaction order of 0.5−0.7 from the data accordingly. These parameters can be incorporated into process cycle models to estimate the material lifetime, a critical uncertainty in the deployment of DAC technologies.

The transformation of Co, Cu, and mixed Co/ Cu MOF-74 crystals into bimetallic, carbon-supported Co− Cu catalysts is investigated via high-temperature pyrolysis. Mixed-metal MOFs prepared via a one-step solvothermal synthesis of MOF-74 are transformed into high metal content (48−63 wt %) catalysts by pyrolysis in N 2 at atmospheric pressure and elevated temperatures (300−900 °C). Comprehensive catalysis and structural characterization studies (temperature-programmed reduction, N 2 physisorption, transmission electron microscopy, scanning transmission electron microscopy, X-ray photoelectron spectroscopy, and in situ X-ray absorption spectroscopy) are reported using a range of Co x Cu 1−x (0.33 < x < 0.95) catalyst compositions. The data suggest MOF precursor restructuring occurs to increasingly favor, at higher pyrolysis temperatures, formation of bimetallic nanoparticles with a Co-rich core and Cu-rich shell (Co@Cu core−shell) and suggest a metallic active site in furfural hydrogenation. For differential furfural conversion reactions of the bimetallic catalysts, furfuryl alcohol selectivities between 66 and 89% and 2-methylfuran selectivities of 10−25% are obtained at 180 °C and a W/F of 3.6 g cat /(mol•h) (specific rates of 50− 530 μmol/(g cat •min)). Higher Co:Cu ratios tend to increase activity and shift selectivity toward production of 2-methylfuran. Catalysts formed at elevated pyrolysis temperatures (≥600 °C) display more complete Cu-shells, while at lower pyrolysis temperatures some Co atoms are still present on the nanoparticle surface, resulting in lower furfuryl alcohol selectivity and higher conversion.

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5 wt% Pd/γ-Al2O3 catalysts were prepared by a modified Vortex Method (5-Pd-VM) and Incipient Wetness Method (5-Pd-IWM), and characterized by various techniques (Inductively coupled plasma atomic emission spectroscopy (ICP-AES), N2-physisorption, pulse CO chemisorption, temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and X-ray diffraction (XRD)) under identical conditions. Both catalysts had similar particle sizes and dispersions; the 5-Pd-VM catalyst had 0.5 wt% more Pd loading (4.6 wt%). The surfaces of both catalysts contained PdO and PdOx with about 7% more PdOx in 5-Pd-VM. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and scanning electron microscope (SEM) images indicated presence of PdO/PdOx nanocrystals (8–10 nm) on the surface of the support. Size distribution by STEM showed presence of smaller nanoparticles (2–5 nm) in 5-Pd-VM. This catalyst was more active in the lower temperature range of 275–325 °C and converted 90% methane at 325 °C. The 5-Pd-VM catalyst was also very stable after 72-hour stability test at 350 °C showing 100% methane conversion, and was relatively resistant to steam deactivation. Hydrogen TPR of 5-Pd-VM gave a reduction peak at 325 °C indicating weaker interactions of the oxidized Pd species with the support. It is hypothesized that smaller particle sizes, uniform particle distribution, and weaker PdO/PdOx interactions with the support may contribute to the higher activity in 5-Pd-VM.

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