Design of 3D MnO2/Carbon sphere composite for the catalytic oxidation and adsorption of elemental mercury

Three-dimensional (3D) MnO₂/Carbon Sphere (MnO₂/CS) composite was synthesized from zero-dimensional carbon spheres and one-dimensional α-MnO₂ using hydrothermal method. The hierarchical MnO₂/CS composite was applied for the catalytic oxidation and adsorption of elemental mercury (Hg⁰) from coal-fired flue gas. The characterization results indicated that this composite exhibits a 3D urchin morphology. Carbon spheres act as the core and α-MnO₂ nano-rods grew on the surface of carbon spheres. This 3D hierarchical structure benefits the enlargement of surface areas and pore volumes. Hg⁰ removal experimental results indicated that the MnO₂/CS composite has an outstanding Hg⁰ removal performance due to the higher catalytic oxidation and adsorption performance. MnO₂/CS composite had higher than 99% Hg⁰ removal efficiency even after 600min reaction. In addition, the nano-sized MnO₂/CS composite exhibited better SO₂ resistance than pure α-MnO₂. Moreover, the Hg-TPD results indicated that the adsorbed mercury can release from the surface of MnO₂/CS using a thermal decomposition method.

Support effect of Mn-based catalysts for gaseous elemental mercury oxidation and adsorption

Mn-Based catalysts with a Mn loading of 4 wt% were prepared using an impregnation method.

Nanowire Morphology of Mono- and Bidoped α-MnO2 Catalysts for Remarkable Enhancement in Soot Oxidation

In the present work, nanowire morphologies of α-MnO₂, cobalt monodoped α-MnO₂, Cu and Co bidoped α-MnO₂, and Ni and Co bidoped α-MnO₂ samples were prepared by a facile hydrothermal synthesis. The structural, morphological, surface, and redox properties of all the as-prepared samples were investigated by various characterization techniques, namely, scanning electron microscopy (SEM), transmission and high resolution electron microscopy (TEM and HR-TEM), powder X-ray diffraction (XRD), N₂ sorption surface area measurements, X-ray photoelectron spectroscopy (XPS), hydrogen-temperature-programmed reduction (H₂-TPR), and oxygen-temperature-programmed desorption (O₂-TPD). The soot oxidation performance was found to be significantly improved via metal mono- and bidoping. In particular, Cu and Co bidoped α-MnO₂ nanowires showed a remarkable improvement in soot oxidation performance, with its T₅₀ (50% soot conversion) values of 279 and 431 °C under tight and loose contact conditions, respectively. The soot combustion activation energy for the Cu and Co bidoped MnO₂ nanowires is 121 kJ/mol. The increased oxygen vacancies, greater number of active sites, facile redox behavior, and strong synergistic interaction were the key factors for the excellent catalytic activity. The longevity of Cu and Co bidoped α-MnO₂ nanowires was analyzed, and it was found that the Cu/Co bidoped α-MnO₂ nanowires were highly stable after five successive cycles and showed an insignificant decrease in soot oxidation activity. Furthermore, the HR-TEM analysis of a spent catalyst after five cycles indicated that the (310) crystal plane of α-MnO₂ interacts with the soot particles; therefore, we can assume that more-reactive exposed surfaces positively affect the reaction of soot oxidation. Thus, the Cu and Co bidoped α-MnO₂ nanowires provide promise as a highly effective alternative to precious metal based automotive catalysts.

Gaseous Heterogeneous Catalytic Reactions over Mn-Based Oxides for Environmental Applications: A Critical Review

Manganese oxide has been recognized as one of the most promising gaseous heterogeneous catalysts due to its low cost, environmental friendliness, and high catalytic oxidation performance. Mn-based oxides can be classified into four types: (1) single manganese oxide (MnOx), (2) supported manganese oxide (MnOx/support), (3) composite manganese oxides (MnOx-X), and (4) special crystalline manganese oxides (S-MnOx). These Mn-based oxides have been widely used as catalysts for the elimination of gaseous pollutants. This review aims to describe the environmental applications of these manganese oxides and provide perspectives. It gives detailed descriptions of environmental applications of the selective catalytic reduction of NOx with NH₃, the catalytic combustion of volatile organic compounds, Hg⁰ oxidation and adsorption, and soot oxidation, in addition to some other environmental applications. Furthermore, this review mainly focuses on the effects of structure, morphology, and modified elements and on the role of catalyst supports in gaseous heterogeneous catalytic reactions. Finally, future research directions for developing manganese oxide catalysts are proposed.

Nanoscale Cobalt-Manganese Oxide Catalyst Supported on Shape-Controlled Cerium Oxide: Effect of Nanointerface Configuration on Structural, Redox, and Catalytic Properties

Understanding the role of nanointerface structures in supported bimetallic nanoparticles is vital for the rational design of novel high-performance catalysts. This study reports the synthesis, characterization, and the catalytic application of Co-Mn oxide nanoparticles supported on CeO₂ nanocubes with the specific aim of investigating the effect of nanointerfaces in tuning structure-activity properties. High-resolution transmission electron microscopy analysis reveals the formation of different types of Co-Mn nanoalloys with a range of 6 ± 0.5 to 14 ± 0.5 nm on the surface of CeO₂ nanocubes, which are in the range of 15 ± 1.5 to 25 ± 1.5 nm. High concentration of Ce³⁺ species are found in Co-Mn/CeO₂ (23.34%) compared with that in Mn/CeO₂ (21.41%), Co/CeO₂ (15.63%), and CeO₂ (11.06%), as evidenced by X-ray photoelectron spectroscopy (XPS) analysis. Nanoscale electron energy loss spectroscopy analysis in combination with XPS studies shows the transformation of Co²⁺ to Co³⁺ and simultaneously Mn^4+/3+ to Mn²⁺. The Co-Mn/CeO₂ catalyst exhibits the best performance in solvent-free oxidation of benzylamine (89.7% benzylamine conversion) compared with the Co/CeO₂ (29.2% benzylamine conversion) and Mn/CeO₂ (82.6% benzylamine conversion) catalysts for 3 h at 120 °C using air as the oxidant. Irrespective of the catalysts employed, a high selectivity toward the dibenzylimine product (97-98%) was found compared with the benzonitrile product (2-3%). The interplay of redox chemistry of Mn and Co at the nanointerface sites between Co-Mn nanoparticles and CeO₂ nanocubes as well as the abundant structural defects in cerium oxide plays a key role in the efficiency of the Co-Mn/CeO₂ catalyst for the aerobic oxidation of benzylamine.

Co3O4@CeO2 hybrid flower-like microspheres: a strong synergistic peroxidase-mimicking artificial enzyme with high sensitivity for glucose detection

In recent years, the development of artificial nanostructured enzymes has received enormous interest in nanobiotechnology due to their advantages over natural enzymes. In the present work, different amounts (5, 10, and 20 wt%) of Co₃O₄ nanoparticle decorated CeO₂ hybrid flower-like microspheres (Co₃O₄@CeO₂) have been investigated for peroxidase-like activity and it was found that 10 wt% of Co₃O₄@CeO₂ exhibited excellent peroxidase-like activity for the catalytic oxidation of the 3,3',5,5'-tetramethylbenzidine (TMB) substrate in the presence of H₂O₂. The formation of more Ce³⁺ ions associated with the oxygen vacancies and a strong synergistic interaction between CeO₂ and Co₃O₄ may be responsible for the enhanced peroxidase-like activity. Based on their peroxidase activity, Co₃O₄@CeO₂ hybrid microspheres were used for the colourimetric detection of glucose. It was found that Co₃O₄@CeO₂ hybrid microspheres showed a substantial enhancement in the detection selectivity. The limit of detection (LOD) was also improved with a limit as low as 1.9 μM. Thus, we believe that Co₃O₄@CeO₂ hybrid flower-like microspheres with high peroxidase-like activity can be exploited for biosensing applications.

Fe-doped CeO2 nanorods for enhanced peroxidase-like activity and their application towards glucose detection

Surface defects of Fe-doped CeO₂ nanorods were found to be active sites for increasing peroxidase mimetic activity.

Low-temperature CO oxidation over manganese, cobalt, and nickel doped CeO2 nanorods

Transition metal doped ceria nanorods exhibit a better CO oxidation activity at lower temperatures.

The adsorption and catalytic oxidation of the element mercury over cobalt modified Ce–ZrO2 catalyst

Co modification dramatically enhances Hg⁰ removal efficiency because of the increased surface active oxygen species.