Defect engineering over Co3O4 catalyst for surface lattice oxygen activation and boosted propane total oxidation

Engineering oxygen vacancies in acid-etched MgMn2O4 for efficiently catalytic benzene combustion: Synergistic activation of gaseous oxygen and surface lattice oxygen

The synergistic activation of gaseous oxygen and surface lattice oxygen is essential for designing highly efficient catalysts to eliminate VOCs. Herein, an effective acid treatment was carried out to create more oxygen vacancies by modulating the electronic structure of MgMn2O4 spinels and MgMnOx mixed oxides. The acid-treated MgMn2O4 exhibited outstanding catalytic performance, with the reaction rate of benzene rising by 8.55 times at 200 °C. After acid treatment, MgMn2O4 partially retained its spinel structure, while Mn2O3 in situ grew on the surface due to the selective removal of Mg2+. The transformation of Mn-O-Mg into Mn-O weakened the strength of adjacent Mn-O bonds, thereby promoting the release of surface lattice oxygen and the regeneration of oxygen vacancies. In addition, acid-treated MgMn2O4 facilitated the adsorption and activation of gaseous oxygen. In situ DRIFTS analysis proved that the synergistic activation of gaseous oxygen and surface lattice oxygen accelerated the conversion of intermediates, thus contributing to the efficient degradation of benzene.

Spinel-Based Catalysts That Enable Catalytic Oxidation of Volatile Organic Compounds

Volatile organic compounds (VOCs) have caused serious harm to human health and ecological environment, and have received much attention in recent years. Despite the successful applications of catalytic combustion of VOCs as the core technology of VOCs removal in industry, the development of efficient catalysts that can mineralize VOCs into nontoxic CO2 and H2O at low temperatures remains a great challenge. Recent studies show that spinel-based materials as efficient catalysts were extensively used in the catalytic oxidation VOCs field due to their synergistic effect, manifold compositions, and electron configurations. However, most of the pollutants are complex, consisting of multiple VOCs, water vapor, CO2, SO2 and other substances, which presents a significant challenge in constructing highly active and stable catalysts. To meet the future demand for efficient catalysts capable of removing various types of VOCs, it is urgent to rationally design and scientifically prepare spinel catalysts based on existing knowledge. This work reviews the research and development of various spinel catalysts with an emphasis on their catalytic performance in VOCs oxidation. The catalytic performance of spinel-based catalysts for different sorts of VOCs was summarized and compared. Moreover, the effects of the reaction conditions on the catalytic performance of spinel-based catalysts were examined to accommodate complicated operating conditions. Subsequently, the regulation of spinel oxides in structure and defect was coherently reviewed to guide the development and design of efficient catalysts. Especially, the research techniques for the reaction mechanism over spinel catalysts were displayed to better deepen the understanding of catalytic oxidation of VOCs. Finally, the current development and challenges were proposed and put forward for future research. This review provided a systematic understanding of the VOCs oxidation over spinel-based catalysts and offered guidance for the development of high-performance catalysts for VOCs elimination.

The influence of crystal facet on the catalytic performance of MOFs-derived NiO with different morphologies for the total oxidation of propane: The defect engineering dominated by solvent regulation effect

Crystal facet and defect engineering are crucial for designing heterogeneous catalysts. In this study, different solvents were utilized to generate NiO with distinct shapes (hexagonal layers, rods, and spheres) using nickel-based metal-organic frameworks (MOFs) as precursors. It was shown that the exposed crystal facets of NiO with different morphologies differed from each other. Various characterization techniques and density functional theory (DFT) calculations revealed that hexagonal-layered NiO (NiO-L) possessed excellent low-temperature reducibility and oxygen migration ability. The (111) crystal plane of NiO-L contained more lattice defects and oxygen vacancies, resulting in enhanced propane oxidation due to its highest O2 adsorption energy. Furthermore, the higher the surface active oxygen species and surface oxygen vacancy concentrations, the lower the C-H activation energy of the NiO catalyst and hence the better the catalytic activity for the oxidation of propane. Consequently, NiO-L exhibited remarkable catalytic activity and good stability for propane oxidation. This study provided a simple strategy for controlling NiO crystal facets, and demonstrated that the oxygen defects could be more easily formed on NiO(111) facets, thus would be beneficial for the activation of C-H bonds in propane. In addition, the results of this work can be extended to the other fields, such as propane oxidation to propene, fuel cells, and photocatalysis.

Engineering Co3O4@3DOM LaCoO3 multistage-pore nanoreactor with superior SO2 resistance for toluene catalytic combustion

Sulfur dioxide poisoning is a significant factor in catalyst deactivation during the catalytic combustion of volatile organic compounds. In this study, we prepared the LaCoO3 and Co3O4 composite catalysts using both the Ship-in-Bottle and Building-Bottle-Around-Ship approaches. Three-dimensionally ordered macropores (3DOM LaCoO3) were utilized as nanoreactors to protect the active sites during the catalytic combustion of toluene, preventing SO2 poisoning. Additionally, we grew ZIF-67 confined in the nanoreactor to create a multistage-pore structure. The Co3O4@3DOM LaCoO3 catalysts exhibited excellent activity in the complete catalytic oxidation of toluene. Various characterization studies confirmed the presence of a significant number of Co3+ species and an abundance of surface weak acid sites in the Co3O4@3DOM LaCoO3 catalysts, which synergistically enhanced the conversion of VOCs at low temperatures. Notably, the multistage pore structure provided a favorable reaction environment, accelerating the adsorption and diffusion of toluene and intermediates, resulting in excellent sulfur resistance of the catalysts. Moreover, XPS analysis confirmed a strong interaction between Co3O4 and LaCoO3, promoting rapid electron transfer and increasing the activation of O2-. In situ DRIFTS experiments verified that toluene mainly follows the MvK mechanism over Co3O4@3DOM LaCoO3 catalysts, indicating the following reaction pathway: toluene adsorption → benzyl alcohol → benzaldehyde → benzoate → anhydride → CO2 and H2O.

Constructing surface oxygen defects at CuO-Co3O4 interface to boost toluene oxidation over CuO/Co3O4 catalysts

As a typical heterogeneous catalytic process, the catalytic combustion of toluene over Co3O4-based catalysts is strongly depends on the surface properties of catalysts, especially the concentration of surface oxygen defects. Here, a novel way was proposed to construct chemically bonded CuO-Co3O4 interface by chemical deposition of CuO onto Co3O4 nanoflowers. The interfacial refinement effect between CuO and Co3O4 support disrupted the ordered atomic arrangement and created countless unsaturated coordination sites at CuO-Co3O4 interface, inducing a significant generation of surface oxygen defects. Surface-rich oxygen vacancies enhanced the capacity of 20%CuO/Co3O4-R to adsorb and activate oxygen species. Benefiting from this, 90 % toluene conversion was reached at 228 °C over 20%CuO/Co3O4-R, which was much lower than that over 20%CuO/Co3O4-S prepared by impregnation method and CuO/Co3O4-mix obtained by mechanically mixing way. In-situ DRIFTS analysis revealed that toluene could be directly decomposed into benzaldehyde at the highly defective CuO-Co3O4 interface, leading to toluene oxidation following the path of toluene → benzaldehyde → benzoate → maleic anhydride → water and carbon dioxide over 20%CuO/Co3O4-R, which was significantly different from decomposition mechanism over 20%CuO/Co3O4-S. Additionally, 20%CuO/Co3O4-R displayed terrific recyclability and outstanding stability, showing good application potential.

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.

Performance and mechanism analysis of sludge-based biochar loaded with Co and Mn as photothermal catalysts for simultaneous removal of acetone and NO at low temperature

Replacing NH3 in NH3-SCR with VOCs provides a new idea for the simultaneous removal of VOCs and NOx, but the technology still has urgent problems such as high cost of catalyst preparation and unsatisfactory catalytic effect in the low-temperature region. In this study, biochar obtained from sewage sludge calcined at different temperatures was used as a carrier, and different Co and Mn injection ratios were selected. Then, a series of sludge-based biochar (SBC) catalysts were prepared by a one-step hydrothermal synthesis method for the simultaneous removal of acetone and NO in a low-temperature photothermal co-catalytic system with acetone replacing NH3. The characterization results show that heat is the main driving force of the reaction system, and the abundance of Co and Mn atoms in high valence states, surface-adsorbed oxygen, and oxygen lattice defects in the catalyst are the most important factors affecting the performance of the catalyst. The performance test results showed that the optimal pyrolysis temperature of sludge was 400 °C, the optimal dosing ratio of Co and Mn was 4:1, and the catalyst achieved 42.98% and 52.41% conversion of acetone and NO, respectively, at 240 °C with UV irradiation. Compared with the pure SBC without catalytic effect, the SBC loaded with Co and Mn gained the ability of simultaneous removal of acetone and NO through the combined effect of multiple factors. The key reaction steps for the catalytic conversion of acetone and NO on the catalyst surface were investigated according to the Mars-van Krevelen (MvK) mechanism, and a possible mechanism was proposed. This study provides a new strategy for the resource utilization of sewage sludge and the preparation of photothermal catalysts for the simultaneous removal of acetone and NO at low cost.

Fabrication of highly dispersed Pd-Mn3O4 catalyst for efficient catalytic propane total oxidation

Adjusting the interaction between dual active components for enhancing volatile organic compounds (VOCs) degradation is an effective but still challenging means of air pollution control. Herein, a limited pyrolysis oxidation strategy was adopted to prepare Pd-Mn3O4 spinel catalysts with uniform morphology and active component dispersion. Among these, 1.08Pd-Mn3O4 presented the highest catalytic efficiency with a T90 value of 240 °C, which was 94 °C lower than that of Mn3O4. Characterization and density functional theory (DFT) calculation results revealed that the strong metal-support interaction (SMSI) effect between Pd and Mn3O4 promoted the redistribution of surface charges, thus strengthening the oxidation-reduction ability of the active sites. Moreover, the SMSI effect led to a better migration of surface oxygen species, and boosted the generation of active surface oxygen species. Simultaneously, the Pd catalyst further reduced the energy barrier in the initial stage of the dehydrogenation of propane. Overall, this study provided a novel design strategy for dual active components catalysts with SMSI effect and extended the application of these catalysts in the important field of VOCs elimination.

Thermally Methanol Oxidation via the Mn1@Co3O4(111) Facet: Non-CO Reaction Pathway

Co3O4, as the support of single-atom catalysts, is effective in electron-structure modulation to get distinct methanol adsorption behaviors and adjustable reaction pathways for the methanol oxidation reaction. Herein, we considered the facets that constitute a Co vacancy of the Co3O4(111) facet and a foreign metal atom M (M = Fe, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, Au, Mn) leading to single-atom catalysts. The Mn1@Co3O4(111) facet is the facet considered the most favorable among all of the possible terminations. Oxygen adsorption, decomposition, and its co-adsorption with methanol are the vital steps of methanol oxidation at the exposed Mn1@Co3O4(111) facet, giving rise to the stable configuration: two O* and one CH3OH* adsorbates. Then, the Mn1@Co3O4(111) facet activates the O-H and C-H bonds within CH3OH*, advances CH3O* → H2CO* → HCOO* → COO*, and releases the products H2, H2O, and CO2 consecutively.