Co3O4–CeO2 mixed oxide-based catalytic materials for diesel soot oxidation

Co3 O4 -CeO2 Nanocomposites for Low-Temperature CO Oxidation

In an effort to combine the favorable catalytic properties of Co₃ O₄ and CeO₂ , nanocomposites with different phase distribution and Co₃ O₄ loading were prepared and employed for CO oxidation. Synthesizing Co₃ O₄ -modified CeO₂ via three different sol-gel based routes, each with 10.4 wt % Co₃ O₄ loading, yielded three different nanocomposite morphologies: CeO₂ -supported Co₃ O₄ layers, intermixed oxides, and homogeneously dispersed Co. The reactivity of the resulting surface oxygen species towards CO were examined by temperature programmed reduction (CO-TPR) and flow reactor kinetic tests. The first morphology exhibited the best performance due to its active Co₃ O₄ surface layer, reducing the light-off temperature of CeO₂ by about 200 °C. In contrast, intermixed oxides and Co-doped CeO₂ suffered from lower dispersion and organic residues, respectively. The performance of Co₃ O₄ -CeO₂ nanocomposites was optimized by varying the Co₃ O₄ loading, characterized by X-ray diffraction (XRD) and N₂ sorption (BET). The 16-65 wt % Co₃ O₄ -CeO₂ catalysts approached the conversion of 1 wt % Pt/CeO₂ , rendering them interesting candidates for low-temperature CO oxidation.

CoOx-decorated CeO2 heterostructures: effects of morphology on their catalytic properties in diesel soot combustion

The effect of the morphology, which exposes different crystal planes, on the physicochemical properties and catalytic activity in diesel carbon soot oxidation was studied using CoOx-decorated CeO2 (CoCeO2) heterostructured catalysts, such as nanorods (NRs), nanocubes (NCs), and nanoparticles (NPs). The CoOx/CeO2 nanorods (CoCeO2-NR) showed superior carbon soot combustion activity at lower temperatures to CoCeO2-NCs and CoCeO2-NPs under both tight and loose contact modes with soot combustion temperatures (T50) of 321 and 494 °C, respectively. A comprehensive analysis by means of X-ray diffraction, Raman spectroscopy, high-angle annular dark-field scanning transmission electron microscopy, in situ X-ray absorption fine structure, temperature-programmed reduction, oxygen storage/release measurements, and density functional theory calculations revealed that the improved activity of CoCeO2-NRs is mainly ascribed to the high oxygen release rate and strong redox capability of the supported Co species, with complete reversibility. This originates from the high reactivity of oxygen atoms on (110) surfaces, compared to (100) and (111) surfaces over CeO2. Additionally, CoCeO2-NRs displayed durability and recyclability without any significant loss of catalytic activity or structural change. These insights will aid in the rational design of practical catalysts for the purification of diesel exhaust and other important transformations.

Synthesis of a CeO2/Co3O4 catalyst with a remarkable performance for the soot oxidation reaction

A highly active catalyst based on CeO₂/Co₃O₄ for soot oxidation at low temperatures with complete selectivity toward CO₂.

Highly enhanced soot oxidation activity over 3DOM Co3O4-CeO2 catalysts by synergistic promoting effect

Three-dimensionally ordered macroporous (3DOM) Co₃O₄-CeO₂ catalysts with controllable Co/Ce molar ratios synthesized by colloidal crystal template method were developed to catalyze the NO_x-assisted soot oxidation for the first time, and the obtained 3DOM Co₃O₄-CeO₂ catalysts exhibited highly enhanced soot oxidation activity. Detailed characterizations of 3DOM Co₃O₄-CeO₂ catalysts revealed that the highly enhanced soot oxidation activity was originated from the synergistic promoting effect by combining the macroporous effect resulted from the unique 3DOM framework, the chemical nature associated with more Co³⁺ reactive sites, the surface enrichment of Ce species and the improved redox properties. Meanwhile, the high NO_x storage and oxidation capacity resulted from the integrated respective merits of Co₃O₄ and CeO₂ also accounted for the enhanced soot oxidation activity via NO_x-assisted mechanism. Furthermore, the 3DOM Co₃O₄-CeO₂ catalysts demonstrated strong stability because of the surface enrichment of Ce species improving the thermal stability and the robust 3DOM framework inhibiting the structural collapse, showing their potential applications under practical conditions.

A versatile CeO2/Co3O4 coated mesh for food wastewater treatment: Simultaneous oil removal and UV catalysis of food additives

Food waste water is one of the most urgent environmental problems for the close connection between food and our daily life. Herein, we use a simple hydrothermal method to prepare a highly efficient catalyst-CeO₂/Co₃O₄ compound on the stainless steel mesh, aiming for food waste water treatment. Possessing the superhydrophilic property and catalytic ability under ultraviolet light, CeO₂/Co₃O₄ coated mesh has successfully processed three representative contaminants in food wastewater, which are soybean oil (food oil), AR (food dye) and VA (food flavor) simultaneously with an one-step filtration. Besides, the mesh is stable in a wide pH range and performs well in reusability. Therefore, such a multifunctional material with simple preparation method, high processing efficiency and facile operation shows a promising prospect for practical production and application for food wastewater treatment.

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.

Design structure for CePr mixed oxide catalysts in soot combustion

A “molten state” appeared during heat treatment of CePr synthesized by a solid-phase grinding method with nitrates as precursors, which rapidly dispersed Ce and Pr. Therefore, CePr catalysts with different structures can be prepared, with catalytic activities independent of grinding time.

Development of low cost mixed metal oxide based diesel oxidation catalysts and their comparative performance evaluation

A four cylinder diesel engine was used to evaluate the performance of two non-noble metal based diesel oxidation catalysts for emission parameters such as particulate mass, elemental/organic carbon (EC/OC), and trace-metal content in particulates.

Oxidation of diesel soot on binary oxide CuCr(Co)-based monoliths

Binary oxide systems (CuCr2O4, CuCo2O4), deposited onto cordierite monoliths of honeycomb structure with a second support (finely dispersed Al2O3), were prepared as filters for catalytic combustion of diesel soot using internal combustion engine's gas exhausts (O2, NOx, H2O, CO2) and O3 as oxidizing agents. It is shown that the second support increases soot capacity of aforementioned filters, and causes dispersion of the particles of spinel phases as active components enhancing thereby catalyst activity and selectivity of soot combustion to CO2. Oxidants used can be arranged with reference to decreasing their activity in a following series: O3≫NO2>H2O>NO>O2>CO2. Ozone proved to be the most efficient oxidizing agent: the diesel soot combustion by O3 occurs intensively (in the presence of copper chromite based catalyst) even at closing to ambient temperatures. Results obtained give a basis for the conclusion that using a catalytic coating on soot filters in the form of aforementioned binary oxide systems and ozone as the initiator of the oxidation processes is a promising approach in solving the problem of comprehensive purification of automotive exhaust gases at relatively low temperatures, known as the "cold start" problem.

Different synthesis protocols for Co3O4 -CeO2 catalysts--part 1: influence on the morphology on the nanoscale

Co₃O₄-modified CeO₂ (Co/Ce 1:4) was prepared by a combination of sol–gel processing and solvothermal treatment. The distribution of Co was controlled by means of the synthesis protocol to yield three different morphologies, namely, Co₃O₄ nanoparticles located on the surface of CeO₂ particles, coexistent Co₃O₄ and CeO₂ nanoparticles, or Co oxide structures homogeneously distributed within CeO₂. The effect of the different morphologies on the properties of Co₃O₄–CeO₂ was investigated with regard to the crystallite phase(s), particle size, surface area, and catalytic activity for CO oxidation. The material with Co₃O₄ nanoparticles finely dispersed on the surface of CeO₂ particles had the highest catalytic activity.

The synergistic effect in Co–Ce oxides for catalytic oxidation of diesel soot

O_act: active oxygen species. C*[O]: carbon–oxygen intermediate. The synergistic effect in Co–Ce catalyst leads to more oxygen vacancies and enhanced redox ability, thus assisting soot combustion.

Co3O4Catalysts on CeO2-ZrO2Supports and Co3O4-CeO2Catalysts on Al2O3/SiO2Supports for the Oxidation of Propylene

Different compositions of Co3O4catalysts on CeO2-ZrO2solid solution (Ce0.9Zr0.1O2and Ce0.8Zr0.2O2) have been studied for the oxidation of propylene. The optional amount of Co3O4active phase on CeO2-ZrO2support of 30 wt% was found. The mixed Co3O4-CeO2-ZrO2with the same composition of the optimal supported ones showed approximately the same activity, which was not higher than the activity of the mixed Co3O4-CeO2catalyst. Catalytic activities of mixed Co3O4-CeO2with different loading contents supported on high surface area supports (Al2O3, SiO2) were then measured. The optimal composition of active phase was still 30 wt% but the minimum temperature of the highest activity increased to above 300°C due to the inert nature influence of the support.

Three-dimensionally ordered macroporous (3DOM) SiOC on a cordierite monolith inner wall and its properties for soot combustion

Three-dimensionally ordered macroporous (3DOM) SiOC was successfully fabricated on a cordierite monolith, and LaCoO₃ was coated onto the 3DOM SiOC/cordierite. The 3DOM structure produced a positive effect on soot combustion.

A Co3O4–CeO2 functionalized SBA-15 monolith with a three-dimensional framework improves NOx-assisted soot combustion

Co₃O₄–CeO₂/SBA-15 monolith can efficiently filter and catalyze the soot particles. The optimized one exhibited a low T₁₀ (293 °C) and T₉₀ (378 °C).

Co3O4 particles grown over nanocrystalline CeO2: influence of precipitation agents and calcination temperature on the catalytic activity for methane oxidation

Crystalline cobalt oxides were prepared by a precipitation method using three different precipitation agents, (NH₄)₂CO₃, Na₂CO₃ and CO(NH₂)₂.

Low-cost catalysts for the control of indoor CO and PM emissions from solid fuel combustion

Cu-Mn based mixed oxide type low-cost catalysts have been prepared in supported form using mesoporous Al(2)O(3), TiO(2) and ZrO(2) supports. These supports have been prepared by templating method using a natural biopolymer, chitosan. The synthesized catalysts have been characterized by XRD, BET-SA, SEM, O(2)-TPD and TG investigations. The catalytic activity for CO as well as PM oxidation was studied, in a view of their possible applications in the control of emissions from solid fuel combustion of rural cook-stoves. The trend observed for the catalytic activity of the synthesized catalysts for CO oxidation was ZrO(2)>TiO(2)>Al(2)O(3) while for PM oxidation it was observed to be TiO(2)>ZrO(2)>Al(2)O(3). The effect of CO(2), SO(2) and H(2)O on CO oxidation activity was also investigated, and despite partial deactivation, the catalysts show good CO oxidation activity. An effective regeneration treatment was attempted by heating the partially deactivated catalysts in presence of oxygen. Redox properties of TiO(2) and ZrO(2) and their structure appeared to be responsible for their promotional activity for CO and PM oxidation reactions. These unordered mesoporous materials could be useful for such reactions where mass transfer is more important than shape and size selectivity.