Boosting total oxidation of propane over CeO2@Co3O4 nanofiber catalysts prepared by multifluidic coaxial electrospinning with continuous grain boundary and fast lattice oxygen mobility

Redox-induced controllable engineering of MnO2-MnxCo3-xO4 interface to boost catalytic oxidation of ethane

Multicomponent oxides are intriguing materials in heterogeneous catalysis, and the interface between various components often plays an essential role in oxidations. However, the underlying principles of how the hetero-interface affects the catalytic process remain largely unexplored. Here we report a unique structure design of MnCoOx catalysts by chemical reduction, specifically for ethane oxidation. Part of the Mn ions incorporates with Co oxides to form spinel MnxCo3-xO4, while the rests stay as MnO2 domains to create the MnO2-MnxCo3-xO4 interface. MnCoOx with Mn/Co ratio of 0.5 exhibits an excellent activity and stability up to 1000 h under humid conditions. The synergistic effects between MnO2 and MnxCo3-xO4 are elucidated, in which the C2H6 tends to be adsorbed on the interfacial Co sites and subsequently break the C-H bonds on the reactive lattice O of MnO2 layer. Findings from this study provide valuable insights for the rational design of efficient catalysts for alkane combustion.

In Situ Reconstruction of Active Heterointerface for Hydrocarbon Combustion through Thermal Aging over Strontium-Modified Co3O4 Nanocatalyst with Good Sintering Resistance

The issue of catalyst deactivation due to sintering has gained significant attention alongside the rapid advancement of thermal catalysts. In this work, a simple Sr modification strategy was applied to achieve highly active Co3O4-based nanocatalyst for catalytic combustion of hydrocarbons with excellent antisintering feature. With the Co1Sr0.3 catalyst achieving a 90% propane conversion temperature (T90) of only 289 °C at a w8 hly space velocity of 60,000 mL·g-1·h-1, 24 °C lower than that of pure Co3O4. Moreover, the sintering resistance of Co3O4 catalysts was greatly improved by SrCO3 modification, and the T90 over Co1Sr0.3 just increased from 289 to 337 °C after thermal aging at 750 °C for 100 h, while that over pure Co3O4 catalysts increased from 313 to 412 °C. Through strontium modification, a certain amount of SrCO3 was introduced on the Co3O4 catalyst, which can serve as a physical barrier during the thermal aging process and further formation of Sr-Co perovskite nanocrystals, thus preventing the aggregation growth of Co3O4 nanocrystals and generating new active SrCoO2.52-Co3O4 heterointerface. In addition, propane durability tests of the Co1Sr0.3 catalysts showed strong water vapor resistance and stability, as well as excellent low-temperature activity and resistance to sintering in the oxidation reactions of other typical hydrocarbons such as toluene and propylene. This study provides a general strategy for achieving thermal catalysts by perfectly combining both highly low-temperature activity and sintering resistance, which will have great significance in practical applications for replacing precious materials with comparative features.

Insights into effects of grain boundary engineering in composite metal oxide catalysts for improving catalytic performance

Volatile Organic Compounds (VOCs) have long been a threat to human health. However, designing economical and efficient transition metal composite oxide catalysts for VOCs purification remains a challenge. Herein, this study demonstrates the enormous potential of grain boundary engineering in facilitating VOCs decomposition over ordered mesoporous composite oxide denoted as 3D-MnxCoy (x, y = 1, 3, 5, 7, 9). Specifically, the three-dimensional (3D) Mn7Co1 catalyst shows 100% ethyl acetate removal efficiency for a continuous airflow containing 1000 ppm ethyl acetate over 60000 h-1 space velocity at 160 °C. Mechanism study suggests that the high catalytic performance originates from the lattice distortion caused by the introduction of heteroatoms, along with the size effect of nanopore walls, which leads to the formation of various grain boundaries on the catalyst surface. The presence of grain boundaries facilitates the generation of oxygen vacancies, thus promoting the migration and activation of oxygen species. Furthermore, the near-atmospheric pressure X-ray photoelectron spectroscopy (NAP- XPS) monitoring results reveal that the bimetallic synergy enhanced by grain boundary accelerates the catalytic reaction rate of VOCs through Mn3++Co3+↔Mn4++Co2+ redox cycle. This study may shed light on the great potential of ordered mesoporous bimetallic oxide catalysts in VOCs pollution control.

Activation of Co-O bond in (110) facet exposed Co3O4 by Cu doping for the boost of propane catalytic oxidation

Defects engineering in metal oxide is an important avenue for the promotion of VOCs catalytic oxidation. Herein, the influence of crystal facet of Co₃O₄ is first investigated for the propane oxidation. An intelligent Cu doping is subsequently performed in the most active (110) facet exposed Co₃O₄ catalyst. The optimized Cu-Co₃O₄-110-3 catalyst exhibits a prominently enhanced activity with propane conversion rate of 1.9 μmol g^-1 s^-1 at reaction temperature of 192 °C and the propane mass space velocity of 60,000 mL g^-1 h^-1, about 2.4 times that of the pristine Co₃O₄. Systematic experimental characterizations (XAS, EPR, Raman, TPR, XPS, etc.) combined with density functional theory calculations point out that the incorporated Cu could increase the electrophilicity of nearby O atom and implant beneficial defect structures (lattice distortion, coordination unsaturation, abundant oxygen vacancies, etc.), which could significantly activate Co-O bond in Co₃O₄, leading to the facilitated generation of active oxygen species as well as promoted oxidation ability. This study could set an illuminating paradigm for the boost of the intrinsic oxidation activity by the precise defect construction in Co₃O₄ catalyst, which will help drive ahead the pursuit of non-precious metal catalyst for VOCs abatement.

Coaxial Nanofiber IrOx@SbSnOx as an Efficient Electrocatalyst for Proton Exchange Membrane Dehumidifier

Development of efficient catalysts for oxygen evolution reaction (OER) remains challenging in PEM dehumidifier or vapor electrolyzer. This study developed novel coaxial IrO_x@SbSnO_x nanofiber (NF) catalysts by electrospinning using a dual-channel needle. This method ensures the fibrous structure and the uniform loading of Ir oxide on the support of antimony tin oxide (ATO). IrO₂@SbSnO_x nanoparticles were synthesized for comparison. Characterizations showed that the active area and charge transfer resistance of NF was 1.47 times and 17.72% of that of commercial ones, respectively. The overpotential of NF at 10 mA·cm^-2 was 359 mV, much smaller than that of commercial IrO₂ (418 mV). In addition, the reaction overpotential of NF increased by only 38 mV after 1000 cyclic voltammetry cycles, indicating good electrochemical stability. To explore the enhancement mechanism, first-principles calculations were conducted for theoretically simulating the hetero-structures. Based on d-band theory, the structure formed between ATO and IrO₂ can effectively weaken the adsorption of oxygen intermediates on the catalyst surface, which reduces the OER energy barrier from 1.705 to 1.632 eV, causing an over 15% decrease of overpotential after loading on ATO. As a practical attempt, we applied the new catalysts in real PEM assembly for air dehumidification and found that the performance was improved by about 2 times compared with that using commercial catalysts. This study provides a research direction for the design of one-dimensional NF catalysts and their using in PEM applications.

Expediting Toluene Combustion by Harmonizing the Ce-O Strength over Co-Doped CeZr Oxide Catalysts

Low-temperature catalytic degradation of volatile organic compounds (VOCs) by enhancing the activity of non-precious metal catalysts has always been the focus of attention. The mineralization of aromatic VOCs requires the participation of a large number of oxygen atoms, so the activation of oxygen species is crucial in the degradation reaction. Herein, we originally adjust the Ce-O bond strength in CeZr oxide catalysts by cobalt doping to promote the activation of oxygen species, thus improving the toluene degradation performance while maintaining high stability. Subsequent characterizations and theoretical calculations demonstrate that the weakening of the Ce-O bond strength increases the oxygen vacancy content, promotes the activation of oxygen species, and enhances the redox ability of the catalysts. This strategy also promotes the activation of toluene and accelerates the depletion of intermediate species. This study will contribute a strategy to enhance the activation ability of oxygen species in non-noble metal oxide catalysts, thereby enhancing the degradation performance of VOCs.

Low quantity of Pt loaded onto CeCoOx nanoboxes: Surface-rich reactive oxygen species for catalytic oxidation of toluene

An optimized oxygen activity of catalysts can facilitate oxidation of volatile organic compounds. This work shows the first construction of Ce-Co oxide thin-walled nanoboxes. Bulk-phase lattice oxygen is activated by metal-metal interactions. The subsequent uniform dispersion of low loaded Pt nanoparticles further enhances the surface-adsorbed oxygen content, and creates an oxygen-rich reaction interface. Competitive adsorption of water vapor was also inhibited, and complete catalytic oxidation of toluene was achieved at low temperature (T₉₀ =140 °C). A diffuse reflectance infrared Fourier-transform spectroscopy probe was used to investigate the adsorption-catalytic process and the possible synergistic catalytic mechanism (Langmuir-Hinshelwood and Mars-van Krevelen). This work provides a strategy for improving the catalyt Crystal structure ic oxidation performance of nanocatalysts for volatile organic compounds by increasing the catalytic oxygen activity.

The Unique CO Activation Effects for Boosting NH3 Selective Catalytic Oxidation over CuOx-CeO2

Slip NH₃ is a priority pollutant of concern to be removed in various flue gases with NO_x and CO after denitrification using NH₃-SCR or NH₃-SNCR, and the simultaneous catalytic removal of NH₃ and CO has become one of the new topics in the deep treatment of such flue gases. Synergistic catalytic oxidation of CO and NH₃ appears to be a promising method but still has many challenges. Due to the competition for active oxidizing species, CO was supposed to hinder the NH₃ selective catalytic oxidation (NH₃-SCO). However, it is first found that CO could significantly promote NH₃-SCO over the CuO_x-CeO₂ catalyst. The NH₃ conversion rates increased linearly with CO concentrations in the range of 180-300 °C. Specifically, it accelerated by 2.8 times with 10,000 ppm CO inflow at 220 °C. Mechanism studies found that the Cu-O-Ce solid solution was more active for CO oxidation, while the CuO_x species facilitated the NH₃ dehydrogenation and mitigated the competition of NH₃ and CO, further stabilizing the promotion effects. Gaseous CO boosted the generation of active isolated oxygen atoms (O_i) by actuating the Cu⁺/Cu²⁺ redox cycle. The enriched O_i facilitated oxidation of NH₃ to NO and was conducive to the NH₃-SCO via the i-SCR approach. This study tapped the potential of CO for promoting simultaneous catalytic oxidation of coexisting pollutants in the flue gas.

Pt-Co nanoparticles supported on hollow multi-shelled CeO2 as a catalyst for highly efficient toluene oxidation: Morphology control and the role of bimetal synergism

A series of hollow multi-shelled CeO₂ (HoMS-CeO₂) support materials with tunable shell numbers were fabricated and applied to the catalytic oxidation of toluene. HoMS-CeO₂ possess much higher catalytic activity (T₉₀ = 236 ℃) than hollow CeO₂ with only a single shell (h-CeO₂) (T₉₀ = 275℃). The porous multiple-shelled structure has a higher S_BET, which strongly promotes gas distribution and provides more active sites. The superiority of this kind of structure was also verified by comparing h-Co₃O₄ and HoMS-Co₃O₄. Furthermore, Pt-Co bimetallic nanoparticles were loaded onto HoMS-CeO₂. The synergistic effect between Pt and Co was verified by XPS and O₂-TPD, which was observed to allow electron transfer between Pt and Co and thus regulate the electronic state of the Pt. Compared with Pt alone, Pt-Co bimetallic nanoparticles could stronglypromotethe activation of O₂and oxygen mobility, as revealed by a much higher O_ads content and a lower oxygen desorption temperature. Of the catalysts prepared in this study, the 1 wt% PtCo₃/CeO₂ catalyst was found to be the most suitable for toluene oxidation owing to its excellent activity (T₉₀ = 158 ℃), long-term stability, and water resistance. Finally, in situ DRIFTS was employed to investigate mechanism during toluene oxidation and the possible reaction pathway was proposed.

Catalytic stability enhancement for pollutant removal via balancing lattice oxygen mobility and VOCs adsorption

Manganese oxide supported Pt single atoms (Pt₁/MnO_x) are prepared by the molten salt method. Catalytic oxidation of toluene and iso-hexane, typical emissions from furniture paints industry, is tested. Pt₁/MnO_x shows poor and high catalytic stability for toluene and iso-hexane oxidation, respectively. Enhancement in the catalytic stability for toluene oxidation is observed after the hydrogen reduction treatment of Pt₁/MnO_x at 200 °C. The hydrogen treated catalyst possesses the weaker Mn-O bonds and lower coordination number of PtO, with superior mobility of lattice oxygen and appropriate toluene adsorption. Balancing lattice oxygen mobility and volatile organic compounds adsorption is important for the catalytic stability of Pt₁/MnO_x. For the oxidation of toluene and iso-hexane mixture, owing to the competitive adsorption, iso-hexane oxidation is greatly inhibited, while toluene oxidation is not influenced. The present Pt₁/MnO_x catalyst holds promising prospect in furniture paints industry applications because of high catalytic stability and water resistance ability.

Pd Doped Co3O4 Loaded on Carbon Nanofibers as Highly Efficient Free-Standing Electrocatalyst for Oxygen Reduction and Oxygen Evolution Reactions

Self-supporting electrodes usually show excellent electrocatalytic performance which does not require coating steps, additional polymer binders, and conductive additives. Rapid in situ growth of highly active ingredient on self-supporting electric conductors is identified as a straight forward path to prepare binder-free and integrated electrodes. Here, Pd-doped Co₃O₄ loaded on carbon nanofiber materials through electrospinning and heat treatment was efficiently synthesized, and used as a free-standing electrode. Benefiting from its abundant active sites, high surface area and effective ionic conduction capability from three-dimensional (3D) nanofiber framework, Pd-Co₃O₄@CNF works as bifunctional oxygen electrode and exhibits superior activity and stability superior to commercial catalysts.

Research Progress on the Applications of Electrospun Nanofibers in Catalysis

During the last two decades, electrospinning has become a very popular technique for the fabrication of nanofibers due to its low cost and simple handling. Nanofiber materials have found utilization in many areas such as medicine, sensors, batteries, etc. In catalysis, these materials also present important advantages, since they present a low resistance to internal diffusion and a high surface area to volume ratio. These advantages are mainly due to the diameter–length proportion. A bibliographic analysis on the applications of electrospun nanofibers in catalysis shows that there are two important groups of catalysts that are being investigated, based on TiO2 and in carbon materials. The main applications found are in photo- and in electro-catalysis. The present study contributes by reviewing these catalytic applications of electrospun nanofibers and demonstrating that they are promising materials as catalysts, underlining some works to prove the advantages and possibilities that these materials have as catalysts. On one hand, the possibilities of synthesis are almost infinite, since with coaxial electrospinning quite complex nanofibers with different layers can be prepared. On the other hand, the diameter and other properties can be controlled by monitoring the applied voltage and other parameters during the synthesis, being quite reproducible procedures. The main advantages of these materials can be grouped in two: one related to their morphology, as has been commented, relative to their low resistance and internal diffusion, that is, their fluidynamic behavior in the reactor; the second group involves advantages related to the fact that the active phases can be nanoscaled and dispersed, improving the activity and selectivity in comparison with conventional catalytic materials with the same chemical composition.