Adsorption performance of SO2 over ZnAl2O4 nanospheres

Zinc-aluminum layered double hydroxide and double oxide for room-temperature oxidation of sulfur dioxide gas

Sulfur dioxide (SO2) gas at trace levels challenges the consumption of fuel gases and cleaning of flue gases originating from diverse anthropogenic sources. We have demonstrated Zn-Al layered double hydroxide (LDH) and layered double oxide (LDO) as low-cost and effective adsorbents in removing lowly concentrated SO2 gas at room temperature. Water in the adsorbent bed significantly improved the performance, where the maximum adsorption capacity of 38.0 mg g-1 was achieved for LDO. Based on the spectroscopic findings, the adsorbed gas molecules were oxidized to surface-bound sulfate/bisulfate species, showing complete mineralization of SO2 molecules. By employing an inexpensive NaOH-H2O2 solution-based regeneration strategy, we successfully regenerated the spent LDO, significantly restoring its gas uptake capacity. The regenerated oxide exhibited an increased gas uptake capacity ranging from 38.0 to 98.5 mg g-1, highlighting the practicality and economic feasibility of our approach. LDH/LDO materials are promising regenerable adsorbents for removing low concentrations of SO2 gas in ambient conditions.

Insight into the potential application of CuOx/CeO2 catalysts for NO removal by CO: a perspective from the morphology and crystal-plane of CeO2

A series of CuOx/CeO2-X were fabricated and employed as the NO + CO reaction catalysts.

Mechanochemical synthesis of ZnO.Al2O3 powders with various Zn/Al molar ratios and their applications in reverse water-gas shift reaction

ZnO.Al₂O₃ powders with various Zn/Al molar ratios were prepared via a solid-state reaction using a mechanochemical synthesis method, and the selected powder with a ZnO/Al₂O₃ molar ratio of 1 was used as support for the preparation of 15% Ni/ZnO.Al₂O₃ catalyst. The activity of the prepared catalyst was studied in the reverse water-gas shift (RWGS) reaction. The synthesized samples were characterized by XRD, BET, TGA/DTA, TPR, FTIR, and SEM techniques. The results indicated that the prepared powders possessed mesoporous structure with pores having small diameters with crystallite sizes in the nanometer range (6.35-12.08 nm). The results showed that the increment in Zn/Al molar ratio reduced the BET area and the pure Al₂O₃ powder possessed the highest BET area (235.4 m² g^-1). The results also indicated that the rise of calcination temperature remarkably decreased the BET area. The prepared nickel-based catalyst also exhibited a high activity in RWGS reaction.

Sulfur dioxide removal: An overview of regenerative flue gas desulfurization and factors affecting desulfurization capacity and sorbent regeneration

Numerous mitigation techniques have been incorporated to capture or remove SO₂ with flue gas desulfurization (FGD) being the most common method. Regenerative FGD method is advantageous over other methods due to high desulfurization efficiency, sorbent regenerability, and reduction in waste handling. The capital costs of regenerative methods are higher than those of commonly used once-through methods simply due to the inclusion of sorbent regeneration while operational and management costs depend on the operating hours and fuel composition. Regenerable sorbents like ionic liquids, deep eutectic solvents, ammonium halide solutions, alkyl-aniline solutions, amino acid solutions, activated carbons, mesoporous silica, zeolite, and metal-organic frameworks have been reported to successfully achieve high SO₂ removal. The presence of other gases in flue gas, e.g., O₂, CO₂, NOx, and water vapor, and the reaction temperature critically affect the sorption capacity and sorbent regenerability. To obtain optimal SO₂ removal performance, other parameters such as pH, inlet SO₂ concentration, and additives need to be adequately governed. Due to its high removal capacity, easy preparation, non-toxicity, and low regeneration temperature, the use of deep eutectic solvents is highly feasible for upscale utilization. Metal-organic frameworks demonstrated highest reported SO₂ removal capacity; however, it is not yet applicable at industrial level due to its high price, weak stability, and robust formulation.

Ni–Zn–Al-Based Oxide/Spinel Nanostructures for High Performance, Methane-Selective CO2 Hydrogenation Reactions

Abstract

In the present study, NiO modified ZnAl2O4 and ZnO modified NiAl2O4 spinel along with pure Al2O3, ZnAl2O4 and NiAl2O4 for comparison in the CO2 hydrogenation reaction have been investigated. It was found that NiAl2O4, NiO/ZnAl2O4 and ZnO/NiAl2O4 catalysts exhibited outstanding activity and selectivity towards methane even at high temperature compared to similar spinel structures reported in the literature. NiO/ZnAl2O4 catalyst showed CO2 consumption rate of ~ 19 μmol/g·s at 600 °C and ~ 85% as well as ~ 50% of methane selectivity at 450 °C and 600 °C, respectively. The high activity and selectivity of methane can be attributed to the presence of metallic Ni and Ni/NiO/ZnAl2O4 interface under the reaction conditions as evidenced by the XRD results.

Graphic Abstract

High performance Ni–Zn–Al-based oxide/spinel nanostructures is synthesized and NiO/ZnAl2O4 catalyst exhibited higher catalytic activity in the CO2 hydrogenation reaction due to the presence of metal support interaction between Ni and ZnAl2O4 support.