Cerium oxide /Co-Co Prussian blue analogue composite catalyst for enhanced peroxymonosulfate activation for effective removal of tetracycline hydrochloride from water

In this paper, a novel CeO2/Co3[Co(CN)6]2 (CeO2/PBACo-Co) composite was prepared with co-precipitation and utilized to activate peroxymonosulfate (PMS) to eliminate tetracycline hydrochloride (TCH). Catalyst screening showed that the composite with a CeO2:PBACo-Co mass ratio of 1:5 (namely, 0.2-CeO2/PBACo-Co) had the best performance. The degradation efficiency of TCH in 0.2-CeO2/PBACo-Co/Oxone system was investigated. The experimental results illustrated that 98% of 50 mg/L TCH and 48.5% of TOC were degraded by 50 mg/L 0.2-CeO2/PBACo-Co and 400 mg/L Oxone within 120 min at 25 °C and initial pH 5.3. Recycling studies showed that the elimination rate of TCH can still achieve 85.8% after five cycles, suggesting that 0.2-CeO2/PBACo-Co composite processes good reusability. Trapping experiments and EPR tests revealed that the reaction system produced multiple active species (1O2, O2•-, SO4•-, and •OH). We proposed the catalytic mechanism of 0.2-CeO2/PBACo-Co for PMS activation, which mainly involves the promoted Co3+/Co2+ cycle by Ce3+ donated electrons. These results indicate that CeO2/PBACo-Co composite is an effective catalyst for wastewater remediation.

Heterostructured Co/CeO2-Decorating N-Doped Porous Carbon Nanocubes as Efficient Sulfur Hosts with Enhanced Rate Capability and Cycling Durability toward Room-Temperature Na-S Batteries

Room-temperature sodium-sulfur (RT Na-S) batteries have gained significant interest thanks to their satisfactory energy density and abundant earth resources. Nevertheless, practical implementations of RT Na-S batteries are still impeded by serious shuttle effects of sodium polysulfide (NaPS) intermediates, sluggish redox kinetics of cathodes, and poor electronic conductivity from S-species. To solve these problems, heterostructured Co/CeO2-decorating N-doped porous carbon nanocubes (Co/CeO2-NPC) are constructed as a S support, which integrates the strong adsorption and fast conversion of NaPSs, together with superior electronic conductivity. Consequently, the as-synthesized S@Co/CeO2-NPC cathode for RT Na-S batteries exhibits improved rate performance (1275, 561.1, and 485 mAh g-1 at 0.1, 5, and 10 C, respectively) and superior cyclic durability (capacity degeneration of 0.027% per cycle after 1000 cycles at 5 C). Such a S cathode combining a heterostructure interface, hierarchical porous carbon nanocubes, and polar compositions can considerably increase electronic conductivity and promote NaPS adsorption and conversion, achieving superior performance toward RT Na-S batteries.

Soot Combustion over Cu-Co Spinel Catalysts: The Intrinsic Effects of Precursors on Catalytic Activity

In this work, a series of CuCo₂O₄-x (x = N, A and C) catalysts were synthesized using different metal salt precursors by urea hydrothermal method for catalytic soot combustion. The effect of CuCo₂O₄-x catalysts on soot conversion and CO₂ selectivity in both loose and tight contact mode was investigated. The CuCo₂O₄-N catalyst exhibited outstanding catalytic activity with the characteristic temperatures (T₁₀, T₅₀ and T₉₀) of 451 °C, 520 °C and 558 °C, respectively, while the CO₂ selectivity reached 98.8% during the reaction. With the addition of NO, the soot combustion was further accelerated over all catalysts. Compared with the loose contact mode, the soot conversion was improved in the tight contact mode. The CuCo₂O₄-N catalysts showed better textural properties compared to the CuCo₂O₄-A and CuCo₂O₄-C, such as higher specific surface areas and pore volumes. The XRD results confirmed that the formation of a CuCo₂O₄ crystal phase in all catalysts. However, the CuO crystal phase only presented in CuCo₂O₄-N and CuCo₂O₄-A. The relative contents of Cu²⁺, Co³⁺ and O_ads on the surface of CuCo₂O₄-x (x = N, A and C) catalysts were analyzed by XPS. The CuCo₂O₄-N catalyst displayed the highest relative content of Cu²⁺, Co³⁺ and O_ads. The activity of catalytic soot combustion showed a good correlation with the order of the relative contents of Cu²⁺, Co³⁺ and O_ads. Additionally, the CuCo₂O₄-N catalyst exhibited lower reduction temperature compared to the CuCo₂O₄-A and CuCo₂O₄-C. The cycle tests clarified that the copper-cobalt spinel catalyst obtained good stability. In addition, based on the Mars-van Krevelen mechanism, the process of catalytic soot combustion was described combined with the electron transfer process and the role of oxygen species over CuCo₂O₄ spinel catalysts.

The Issue of Soot-Catalyst Contact in Regeneration of Catalytic Diesel Particulate Filters: A Critical Review

Soot-catalyst contact represents the main critical issue for an effective regeneration of catalytic (i.e., catalyst-coated) diesel particulate filters (DPFs). Most of the literature reviews on this topic have mainly been focused on studies dealing with powdered soot-catalyst mixtures. Although the results obtained on powders surely provide significant indications, especially in terms of intrinsic activity of materials towards soot oxidation, they cannot be directly extended to DPFs due to completely different soot-catalyst contact conditions generated during filtration and subsequent regeneration. In this work, attention is devoted to catalytic DPFs and, more specifically, studies on both catalyst dispersion and soot distribution inside the filter are critically reviewed from the perspective of soot-catalyst contact optimization. The main conclusion drawn from the literature analysis is that, in order to fully exploit the potential of catalytic DPFs in soot abatement, both a widespread and homogeneous presence of catalyst in the macro-pores of the filter walls and a suitably low soot load are needed. Under optimal soot-catalyst contact conditions, the consequent decrease in the temperature required for soot oxidation to values within the temperature range of diesel exhausts suggests the passage to a continuous functioning mode for catalytic filters with simultaneous filtration and regeneration, thus overcoming the drawbacks of periodic regeneration performed in current applications.

Mechanism of Synergistic Effect on Electron Transfer over Co-Ce/MCM-48 during Ozonation of Pharmaceuticals in Water

The same amount of metal was deposited on the surface of three-dimensional mesoporous MCM-48 by a facile impregnation-calcination method for catalytic ozonation of pharmaceutical and personal-care products in the liquid phase. At 120 min reaction time, Co/MCM-48 and Ce/MCM-48 showed 46.6 and 63.8% mineralization for clofibric acid (CA) degradation, respectively. Less than 33% mineralization was achieved with Co/MCM-48 and Ce/MCM-48 during sulfamethazine (SMZ) ozonation. In the presence of monometallic oxides modified MCM-48 catalysts, total organic carbon (TOC) removal of diclofenac sodium (DCF) was around 80%. The composite Co-Ce/MCM-48 catalyst exhibited significantly higher activity in terms of TOC removal of CA (83.6%), SMZ (51.7%) and DCF (86.8%). Co-Ce/MCM-48 inhibited efficiently the accumulation of small molecular carboxyl acids during ozonation. A detailed research was conducted to detect the nature of material structure and mechanism of catalytic ozonation by using a series of characterizations. The main reaction pathway of CA was determined by the analysis of liquid chromatography-mass spectrometry, in line with the results of frontier electron density calculations that reactive oxygen species (ROSs) were easy to attack negative regions of pharmaceuticals. The Si-O-Si, Co···HO-Si-O-Si-OH···Ce, and O₃···Co-HO-Si-O-Si-OH···Ce-OH···O₃ basic units in catalysts were constructed to detect the orbit-energy-level difference. The results revealed that a synergistic effect existed at the interface between cobalt and cerium oxides over MCM-48, which facilitated the ROSs sequence in solution with ozone. Therefore, the multivalence redox coupling of Ce⁴⁺/Ce³⁺ and Co³⁺/Co²⁺ along with electron transfer played an important role in catalytic ozonation process.

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.

Current advances in the utility of functionalized SBA mesoporous silica for developing encapsulated nanocatalysts: state of the art

The cavities of SBA mesoporous silica materials can be used as nanoreactors for embedding catalytic species such as nanoparticles, complexes and heteropolyacids etc.

CeO2 nanowires self-inserted into porous Co3O4 frameworks as high-performance "noble metal free" hetero-catalysts

Recently, mixed metal oxides have attracted tremendous interest because of their great importance for fundamental studies and practical applications in the catalytic field to replace expensive noble metals. Herein, we report the designed synthesis of novel CeO2-Co3O4 mixed metal oxides with complex nanostructures using uniform short CeO2 nanowires self-inserted into ZIF-67 nanocrystals as precursors followed by a thermal annealing treatment. Interestingly, such a synthetic strategy can be easily extended to fabricate other CeO2 nanowires inserted into metal oxide nanoframeworks such as NiCo2O4 and ZnCo2O4. Choosing the NO reduction reaction by CO as the catalytic model, the as-obtained CeO2-Co3O4 hybrids exhibited enhanced catalytic performance, which could be attributed to the strong two-phase interaction between each component.

Screening and scale-up of cerium oxide-based binary/ternary systems as oxidation catalysts

In the present work, seven samples of cerium oxide-based binary and ternary nanoparticles were prepared by a micro emulsion technique to be used as catalysts for carbon and soot oxidations.

Effect of water vapor on sulfur poisoning of MnOx–CeO2/Al2O3 catalyst for diesel soot oxidation

Water inhibits sulfate deposition and enhances the surface acidity during the sulfation of MnO_x–CeO₂/Al₂O₃, which promotes soot oxidation.

Three-dimensionally ordered macroporous SiO2-supported transition metal oxide catalysts: facile synthesis and high catalytic activity for diesel soot combustion

Three-dimensionally ordered macroporous (3DOM) SiO₂-supported transition metal oxide catalysts were successfully synthesized, and they exhibit high catalytic activities for soot combustion.

NOx storage and soot combustion over well-dispersed mesoporous mixed oxides via hydrotalcite-like precursors

Partial substitution of Mg in hydrotalcite layers with transition metal ions leads to well-dispersed mesoporous mixed oxides exhibiting high performances on NO_x storage and soot combustion.