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TiO 2 supported catalysts have been widely studied for the selective catalytic reduction (SCR) of NO x ; however, comprehensive understanding of synergistic interactions in multi-component SCR catalysts is still lacking. Herein, transition metal elements (V, Cr, Mn, Fe, Co, Ni, Cu, La, and Ce) were loaded onto TiO 2 nanoarrays via ion-exchange using protonated titanate precursors. Amongst these catalysts, Mn-doped catalysts outperform the others with satisfactory NO conversion and N 2 selectivity. Cu co-doping into the Mn-based catalysts promotes their low-temperature activity by improving reducibility, enhancing surface Mn 4+ species and chemisorbed labile oxygen, and elevating the adsorption capacity of NH 3 and NO x species. While Ce co-doping with Mn prohibits the surface adsorption and formation of NH 3 and NO x derived species, it boosts the N 2 selectivity at high temperatures. By combining Cu and Ce as doping elements in the Mn-based catalysts, both the low-temperature activity and the high-temperature N 2 selectivity are enhanced, and the Langmuir–Hinshelwood reaction mechanism was proved to dominate in the trimetallic Cu–Ce–5Mn/TiO 2 catalysts due to the low energy barrier. 

Nanoarray-based monolithic catalysts have been developed for various applications, including CO oxidation, hydrocarbon combustion, lean NOx trapping, and low-pressure CO2 hydrogenation. In this work, SO2 adsorption properties have been explored and evaluated on the cordierite honeycomb monoliths grown with zinc oxide nanoarray (ZnO), zinc oxide nanoarray washcoated by BaCO3 nanoparticles (ZnO/BaCO3), and manganese oxide nanowire array with cryptomelane structure (MnOx) at a temperature range from 50 °C to 425 °C. All samples showed temperature-dependent SO2 adsorption behaviors. The adsorption results revealed the performance order: MnOx > ZnO/BaCO3 > ZnO, with ~90% SO2 adsorbed in MnOx at 425 °C. Washcoated BaCO3 contributed to the improvement of SO2 adsorption in ZnO nanoarray, and the best performance displayed in MnOx may be attributed to their high specific surface area. After regeneration, nanoarrays all exhibited good thermal stability during test-regeneration cycles. No additional phase was formed in regenerated ZnO nanoarrays (ZnO-R), while BaCO3 was converted to BaSO4 in the regenerated ZnO/BaCO3 nanoarrays (ZnO/BaCO3-R), and the sulfur species (possibly MnSO4) and Mn2O3 were found in regenerated MnOx nanoarrays (MnOx-R). It is noted that small amount of sulfur species (possibly MnSO4) may promote the SO2 adsorption of MnOx-R at a lower temperature, while the formed Mn2O3 contributed to the deactivation of MnOx-R. 

Semiconductive metal‐oxide sensors suffer from cross‐sensitivities under mixed chemical condition, specifically upon mixture of multiple oxidative or reductive gases. Herein, a single bimodular sensor is demonstrated for smart differentiation of multiple oxidative analytes by relating the resistance‐metric mode to impedance‐metric mode. The sensor construct based on ZnO nanorods readily outputs three response datasets upon exposure of oxidative‐gas mixture including O₂, SO₂, and NO₂, the resistance, real part impedance, and imaginary part impedance. The differentiative and correlated nature between these response signals allows such a single sensor platform to differentiate these oxidative gases accurately and robustly. Linear and non‐linear decision boundaries are established over a large gas‐concentration range from 2 ppm to 3% through a combination of principal component analysis and artificial neural network training. A facile user interface is demonstrated for recognition and measurement of unknown gas analytes, with the error of the predicted analyte‐concentration as low as 2%.

 

CO₂conversion into valuable chemicals and fuels, such as methanol, is one of the most practical routes for utilizing emitted CO₂and mitigating global warming. Herein, a 3D Cu‐decorated ZnO nanorod array based structured catalysts for efficient thermochemical CO₂hydrogenation to methanol at relatively low pressures (<10 atm) is successfully fabricated and demonstrated. This new type of nanorod array integrated structured catalysts has yielded a methanol formation rate of 1.9 mol h⁻¹kg⁻¹with a methanol selectivity of 56%, rivaling the state‐of‐the‐art powder‐form catalysts. The well‐dispersed copper species on the array structure as well as the array‐structure‐enhanced interfacial effect are key factors that improve the activity of the nanorod array catalysts in CO₂hydrogenation. The Cu‐ZnO nanorod array interface also suppresses reverse water‐gas shift reaction, reducing the selectivity to CO. Further improvement of the performance of the nanorod array based catalysts is demonstrated by tuning the ZnO nanorod array length. The developed nanorod array integrated monolithic catalysts also exhibit good stability during a long‐time continuous operation, demonstrating the potential and the feasibility of their practical implementation in industrial situation.