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The hydrotalcite-based NiAl mixed oxides were synthesized by coprecipitation and urea hydrolysis approaches and employed for SO₂ removal. The samples were well characterized by inductively coupled plasma (ICP) elemental analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and N₂ adsorption/desorption isotherm analyses. The acid-base properties were characterized by pyridine chemisorption and CO₂ temperature-programmed desorption (TPD). The calcined NiAlO from the urea method showed excellent SO₂ adsorption and its adsorption equilibrium showed a type I isotherm, which significantly improved the adsorption performance for low-concentration SO₂. Both the physical structure and the acidic-basic sites were found to play important roles in the SO₂ adsorption process. In situ Fourier transform infrared spectroscopy (FTIR) investigation revealed that adsorbed SO₂ molecules formed surface bisulfite, sulfite, and bidentate binuclear sulfate. The mechanisms for SO₂ adsorption and transformation are discussed in detail.

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Co-based catalysts have been widely applied in NO reduction by CO but still suffer from the unsatisfactory low-temperature catalytic performance. Here, a series of catalysts with a Co3O4–CoO heterointerface were in-situ-prepared and first applied into NO reduction by CO. Compared with single-phase samples, the catalysts with the Co3O4–CoO heterointerface exhibited superior catalytic performance. The best CoO x -350-7 sample showed a lowest apparent active energy (54.2 kJ·mol–1) and achieved 100% NO conversion at 150 °C (gas hourly space velocity = 50 000 h–1). The role of CoO as well as the structure–activity relationship between the interfacial effect and catalytic activity were deeply investigated. Abundant oxygen vacancies were induced due to the introduction of CoO species, and thus, the reducibility and oxygen migration of Co3O4–CoO catalysts were enhanced. The introduction of CoO not only optimized the NO adsorption but also enhanced electron donation ability from the catalyst to adsorbed NO. Moreover, the presence of CoO coupled with oxygen vacancies regulated the CO adsorption/conversion on the catalysts and thus promoted the exposure and reactivation of active sites for the reaction cycles. Accordingly, the stimulated dissociation of NO and the formation of −NCO could enhance the NO conversion to N2 at lower and higher temperatures, respectively.