The change of CO2 carrying capacity of CaO sorbents prepared from different precursors has been studied using thermogravimetric analysis in a long series of isothermal recarbonation−decomposition cycles in the temperature range of 750−850 °C. The residual capacity of the CaO sorbents after a large number of cycles was found to depend on the precursor type, the experimental temperature, and the duration of the recarbonation stage. The residual capacities of the CaO derived from the powdered calcium carbonates were much higher than that of the CaO produced from the crystalline CaCO3. A simple tentative model has been suggested, according to which recarbonation−decomposition cycles result in formation of the interconnected CaO network that acts as a refractory support and determines sorption properties of the material. By using a new model, a simple synthesis procedure has been suggested that produces CaO sorbents with high residual CO2 carrying capacities.

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In this work, a series of K2CO3-containing composite materials based on alumina supports with different porous structure were synthesized and studied in a direct air capture process. Alumina supports with the modified porous structure were obtained as a result of the thermal treatment of porous γ-Al2O3 at elevated temperatures. Composite materials were synthesized by impregnating the porous support (unmodified or modified alumina) with an aqueous solution of potassium carbonate. All the K2CO3/Al2O3 sorbents were tested in the process of CO2 absorption from the air with a relative humidity of 25% followed by thermal desorption as a result of heating the material to 200 °C. The composite materials were characterized by X-ray diffraction and temperature-programmed desorption methods. Among the materials studied, the composite sorbent based on the porous alumina thermally modified at T = 750 °C demonstrated the highest dynamic CO2 absorption capacity. This composite material was later tested in a direct air capture/methanation process combining CO2 capture from ambient air and methanation via the catalytic Sabatier reaction. The process was implicated using an adsorber and a catalytic reactor connected in series. To regenerate the composite sorbent after the step of CO2 absorption from ambient air, the adsorber was heated to 200 °C in an H2 flow. The desorbed CO2 was converted into methane in the preheated catalytic reactor containing the Ru/Al2O3 methanation catalyst. The optimization of the operating conditions (namely, the catalytic reactor temperature and the inlet H2 flow rate) allowed for obtaining CH4 from carbon dioxide with a yield of 98%. The thermal energy required for heating the new CO2 sorbent from 25 to 200 °C at the desorption/methanation step of the direct air capture/methanation process was estimated to be 9 MJ per 1 m3 (STP) of produced CH4.

To improve the stability of high temperature CO 2 absorbent for sorption enhanced reforming applications yttria supported CaO were synthesized using two methods: calcination of mixed salt precursors and wet impregnation of yttria support. According to XRD data, CaO does not interact with the yttria matrix. However, introduction of CaO drastically changes the morphology of primary yttria particles. Increase in CaO concentration results in gradual plugging of the smaller pores and sintering of yttria support. The CO 2 absorption uptake in recarbonation-decomposition cycles increases with increase in CaO content and reach 9.6 wt % at CaO content of 19.9 wt %. CaO recarbonation extent varies from 49 to 77%. CaO/Y 2 O 3 absorbents are extremely stable under overheating and maintain their capacity in long series of decomposition-recarbonation cycles even after calcination at 1350 °C. The novel material resists moisture and retains its strength during storage in the air. According to tests, CaO/Y 2 O 3 can be considered as a promising CO 2 absorbent for fixed bed sorption enhanced hydrocarbons reforming.

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A pair of mesoporous and hierarchical macro/mesoporous alumina-supported catalysts having distinct textural parameters have been chosen to elucidate the effect of texture on activity in hydrodesulfurization (HDS) and hydrodemetallization (HDM) of heavy tatar oil possessing extremely high viscosity and sulfur content. For monitoring catalyst properties, the samples have been investigated by XRD, XFS, XPS, EXAFS, SEM, TEM, FTIR, TPD-NH3, mercury porosimetry, and N2 adsorption methods. Among different factors such as support acidity, active component dispersion, and texture, the last one has been found to play the most significant role in this process. The hierarchical macro/mesoporous catalyst shows lower coking rate of the hydrotreated products, as well as higher HDS and HDM conversions despite its lower active component dispersion and decreased support acidity.

CoMo catalysts supported on meso/macroporous alumina have been designed for hydrotreating of heavy oil. Pellets were prepared from pseudoboehmite and polystyrene colloidal crystals with subsequent CoMo compounds supporting on alumina. Supports, fresh and spent catalysts were characterized by crushing tests, X-ray diffraction, scanning and high-resolution transmission electron microscopies, N 2 sorption and pycnometric techniques, mercury porosimetry, and different methods of elemental analyses. The hydrotreating experiments were carried out at 380−420 °C and 70 bar in the presence of CoMo catalysts supported on meso/macroporous or reference mesoporous alumina. Viscosity, desulfurization extent, microcarbon residue, and asphaltenes content were determined for the reaction products. CoMo compounds supported on meso/macroporous Al 2 O 3 had transformed to the layered sulfides under the influence of reaction medium, while no significant changes of supported compounds were observed for the reference mesoporous catalyst. The bimodal meso/macroporous catalyst had increased activity in hydrodemetallization and hydrodesulfurization reactions compared with the mesoporous analogue.

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