3D web freestanding RuO2–Co3O4 nanowires on Ni foam as highly efficient cathode catalysts for Li–O2 batteries

The mechanism of Li–O₂ batteries is based on the reactions of lithium ions and oxygen, which hold a theoretical higher energy density of approximately 3500 W h kg⁻¹. In order to improve the practical specific capacity and cycling performance of Li–O₂ batteries, a catalytically active mechanically robust air cathode is required. In this work, we synthesized a freestanding catalytic cathode with RuO₂ decorated 3D web Co₃O₄ nanowires on nickel foam. When the specific capacity was limited at 500 mA h g⁻¹, the RuO₂–Co₃O₄/NiF had a stable cycling life of up to 122 times. The outstanding performance can be primarily attributed to the robust freestanding Co₃O₄ nanowires with RuO₂ loading. The unique 3D web nanowire structure provides a large surface for Li₂O₂ growth and RuO₂ nanoparticle loading, and the RuO₂ nanoparticles help to promote the round trip deposition and decomposition of Li₂O₂, therefore enhancing the cycling behavior. This result indicates the superiority of RuO₂–Co₃O₄/NiF as a freestanding highly efficient catalytic cathode for Li–O₂ batteries.

Freestanding RuO₂–Co₃O₄ nanowires on Ni foam were synthesized and applied as a cathode in Li–O₂ battery. This cathode can deliver a high capacity of 9620 mA h g⁻¹ and stable long-term operation exceeding 122 cycles at 100 mA g⁻¹.     

Co3O4–Ag photocatalysts for the efficient degradation of methyl orange

In this paper, a series of Co₃O₄–Ag photocatalysts with different Ag loadings were synthesized by facile hydrothermal and in situ photoreduction methods and fully characterized by XRD, SEM, TEM, FTIR spectroscopy, XPS, UV-vis and PL techniques. The catalysts were used for the degradation of methyl orange (MO). Compared with the pure Co₃O₄ catalyst, the Co₃O₄–Ag catalysts showed better activity; among these, the Co₃O₄–Ag-0.3 catalyst demonstrated the most efficient activity with 96.4% degradation efficiency after 30 h UV light irradiation and high degradation efficiency of 99.1% after 6 h visible light irradiation. According to the corresponding dynamics study under UV light irradiation, the photocatalytic efficiency of Co₃O₄–Ag-0.3 was 2.72 times higher than that of Co₃O₄ under identical reaction conditions. The excellent photocatalytic activity of Co₃O₄–Ag can be attributed to the synergistic effect of strong absorption under UV and visible light, reduced photoelectron and hole recombination rate, and decreased band gap due to Ag doping. Additionally, a possible reaction mechanism over the Co₃O₄–Ag photocatalysts was proposed and explained.

A novel Co₃O₄–Ag catalyst covered on the Ni foam substrate was synthesized via facile hydrothermal and in situ photoreduction methods for the efficient degradation of methyl orange.     

Conversion of levulinic acid to γ-valerolactone over Ru/Al2O3–TiO2 catalyst under mild conditions

Novel catalytic material with high catalytic activity and hydrothermal stability plays a key role in the efficient conversion of levulinic acid (LA) to γ-valerolactone (GVL) in water. In this study, mixed oxides Al₂O₃–TiO₂, Al₂O₃–MoO₃ and Al₂O₃–Co₃O₄ were synthesized by co-precipitation using aqueous solution of NaOH as precipitant. Ru catalysts supported on mixed oxides were prepared by impregnation method and their catalytic performances were tested in the hydrogenation of LA to GVL on a fixed bed reactor. The physicochemical properties of the catalysts were characterized by XRD, H₂-TPR, NH₃-TPD, and BET techniques. The TiO₂ component significantly affected the acidity of the catalyst, and thus its catalytic activity for the GVL yield was affected. The desired product GVL with a yield of about 97% was obtained over the Ru/Al₂O₃–TiO₂ catalyst under mild conditions (WHSV = 1.8 h⁻¹, T = 80 °C). Moreover, the catalyst Ru/Al₂O₃–TiO₂ exhibited excellent thermal stability in the test period of time.

Novel catalytic material with high catalytic activity and hydrothermal stability plays a key role in the efficient conversion of levulinic acid (LA) to γ-valerolactone (GVL) in water.     

Preparation and characterization of Fe3O4@SiO2@TiO2–Co/rGO magnetic visible light photocatalyst for water treatment

In this work, Fe₃O₄@SiO₂@TiO₂–Co/rGO magnetic photocatalyst was successfully prepared by a sol–gel method and a hydrothermal method. The crystalline structure and performance of the resulting catalyst have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy and ultraviolet-visible light (UV-Vis) spectroscopy. The magnetic photocatalyst consists of Fe₃O₄@SiO₂@TiO₂–Co active particles and rGO carriers. The active particles have a double-shell core–shell structure with a size of about 500 nm and are supported on the rGO lamellae. TiO₂ doping with a small amount of metal Co and rGO can significantly improve the catalytic effect of magnetic photocatalyst, and rGO can also significantly improve the adsorption of pollutants by magnetic photocatalyst. The catalyst exhibited high photocatalytic activity in the degradation of methylene blue (MB) under visible light. 92.41% of this ability was retained after five times of repetitive use under the same conditions. The magnetic photocatalyst is easy to recover, and a recovery rate of 93.88% is still maintained after repeated use for 5 times.

With its low cost, high photocatalytic activity, high chemical stability and easy magnetic separation, Fe₃O₄@SiO₂@TiO₂–Co/rGO magnetic photocatalyst has a good application potential.     

Efficient deoxygenation of waste cooking oil over Co3O4–La2O3-doped activated carbon for the production of diesel-like fuel

Untreated waste cooking oil (WCO) with significant levels of water and fatty acids (FFAs) was deoxygenated over Co₃O₄–La₂O₃/AC_nano catalysts under an inert flow of N₂ in a micro-batch closed system for the production of green diesel. The primary reaction mechanism was found to be the decarbonylation/decarboxylation (deCOx) pathway in the Co₃O₄–La₂O₃/AC_nano-catalyzed reaction. The effect of cobalt doping, catalyst loading, different deoxygenation (DO) systems, temperature and time were investigated. The results indicated that among the various cobalt doping levels (between 5 and 25 wt%), the maximum catalytic activity was exhibited with the Co : La ratio of 20 : 20 wt/wt% DO under N₂ flow, which yielded 58% hydrocarbons with majority diesel-range (n-(C₁₅ + C₁₇)) selectivity (∼63%), using 3 wt% catalyst loading at a temperature of 350 °C within 180 min. Interestingly, 1 wt% of catalyst in the micro-batch closed system yielded 96% hydrocarbons with 93% n-(C₁₅ + C₁₇) selectivity within 60 min at 330 °C, 38.4 wt% FFA and 5% water content. An examination of the WCO under a series of FFA (0–20%) and water contents (0.5–20 wt%) indicated an enhanced yield of green diesel, and increased involvement of the deCOx mechanism. A high water content was found to increase the decomposition of triglycerides into FFAs and promote the DO reaction. The present work demonstrates that WCO with significant levels of water and FFAs generated by the food industry can provide an economical and naturally replenished raw material for the production of diesel.

Untreated waste cooking oil (WCO) with significant levels of water and fatty acids (FFAs) was deoxygenated over Co₃O₄–La₂O₃/AC_nano catalysts under an inert flow of N₂ in a micro-batch closed system for the production of green diesel.     

Improvement of low-temperature NH3-SCR catalytic performance over nitrogen-doped MOx–Cr2O3–La2O3/TiO2–N (M = Cu,Fe, Ce) catalysts

A series of MO_x–Cr₂O₃–La₂O₃/TiO₂–N (M = Cu, Fe, Ce) catalysts with nitrogen doping were prepared via the impregnation method. Comparing the low-temperature NH₃-SCR activity of the catalysts, CeCrLa/Ti–N (xCeO₂–yCr₂O₃–zLa₂O₃/TiO₂–N) exhibited the best catalytic performance (NO conversion approaching 100% at 220–460 °C). The physico-chemical properties of the catalysts were characterized by XRD, BET, SEM, XPS, H₂-TPR, NH₃-TPD and in situ DRIFTS. From the XRD and SEM results, N doping affects the crystalline growth of anatase TiO₂ and MO_x (M = Cu, Fe, Ce, Cr, La) which were well dispersed over the support. Moreover, the doping of N promotes the increase of the Cr⁶⁺/Cr ratio and Ce³⁺/Ce ratio, and the surface chemical adsorption oxygen content, which suggested the improvement of the redox properties of the catalyst. And the surface acid content of the catalyst increased with the doping of N, which is related to CeCrLa/TiO₂–N having the best catalytic activity at high temperature. Therefore, the CeCrLa/TiO₂–N catalyst exhibited the best NH₃-SCR performance and the redox performance of the catalysts is the main factor affecting their activity. Furthermore, in situ DRIFTS analysis indicates that Lewis-acid sites are the main adsorption sites for ammonia onto CeCrLa/TiO₂–N and the catalyst mainly follows the L–H mechanism.

A series of MO_x–Cr₂O₃–La₂O₃/TiO₂–N (M = Cu, Fe, Ce) catalysts with nitrogen doping were prepared via the impregnation method.     

Novel mesoporous Co3O4–Sb2O3–SnO2 active material in high-performance capacitive deionization

Capacitive deionization (CDI), as an emerging eco-friendly electrochemical brackish water deionization technology, has widely benefited from carbon/metal oxide composite electrodes. However, this technique still requires further development of the electrode materials to tackle the ion removal capacity/rate issues. In the present work, we introduce a novel active carbon (AC)/Co₃O₄–Sb₂O₃–SnO₂ active material for hybrid electrode capacitive deionization (HECDI) systems. The structure and morphology of the developed electrodes were determined using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Brunauer–Emmett–Teller (BET)/Barrett–Joyner–Halenda (BJH) techniques, as well as Fourier-transform infrared (FT-IR) spectroscopy. The electrochemical properties were also investigated by cyclic voltammetry (CV) and impedance spectroscopy (EIS). The CDI active materials AC/Co₃O₄ and AC/Co₃O₄–Sb₂O₃–SnO₂ showed a high specific capacity of 96 and 124 F g⁻¹ at the scan rate of 10 mV s⁻¹, respectively. In addition, the newly-developed electrode AC/Co₃O₄–Sb₂O₃–SnO₂ showed high capacity retention of 97.2% after 2000 cycles at 100 mV s⁻¹. Moreover, the electrode displayed excellent CDI performance with an ion removal capacity of 52 mg g⁻¹ at the applied voltage of 1.6 V and in a solution of potable water with initial electrical conductivity of 950 μs cm⁻¹. The electrode displayed a high ion removal rate of 7.1 mg g⁻¹ min⁻¹ with an excellent desalination–regeneration capability while retaining about 99.5% of its ion removal capacity even after 100 CDI cycles.

Capacitive deionization (CDI), as an emerging eco-friendly electrochemical brackish water deionization technology, has widely benefited from carbon/metal oxide composite electrodes.     

Sm2O3/Co3O4 catalysts prepared by dealloying for low-temperature CO oxidation

A series of Co₃O₄ catalysts modified by Sm were prepared by a combined dealloying and calcination approach, and the catalytic activities were evaluated using CO catalytic oxidation. The Sm₂O₃/Co₃O₄ catalysts were composed of a large number of nanorods and nanosheets, and exhibited a three-dimensional supporting structure with pores. The experimental results revealed that the addition of a small amount of Sm into the precursor AlCo alloy led to a dealloyed sample with improved catalytic activity, and the dealloyed Al₉₀Co_9.5Sm_0.5 ribbons (0.5 Sm₂O₃/Co₃O₄) calcined at 300 °C showed the highest activity for CO oxidation with complete CO conversion at 135 °C, moreover, CO conversion almost no attenuation, even after 70 hours of catalytic oxidation, which is superior to that of Co₃O₄. The enhanced catalytic activity of the Sm₂O₃/Co₃O₄ catalyst can be attributed to the large specific surface area, more reactive oxygen species and Co³⁺ ion, as well as electronic interactions between Sm and Co.

A series of Co₃O₄ catalysts modified by Sm were prepared by a combined dealloying and calcination approach, and the catalytic activities were evaluated using CO catalytic oxidation.     

Nanostructured RuO2–Co3O4@RuCo-EO with low Ru loading as a high-efficiency electrochemical oxygen evolution catalyst

Electrochemical water splitting technology is considered to be the most reliable method for converting renewable energy such as wind and solar energy into hydrogen. Here, a nanostructured RuO₂/Co₃O₄–RuCo-EO electrode is designed via magnetron sputtering combined with electrochemical oxidation for the oxygen evolution reaction (OER) in an alkaline medium. The optimized RuO₂/Co₃O₄–RuCo-EO electrode with a Ru loading of 0.064 mg cm⁻² exhibits excellent electrocatalytic performance with a low overpotential of 220 mV at the current density of 10 mA cm⁻² and a low Tafel slope of 59.9 mV dec⁻¹ for the OER. Compared with RuO₂ prepared by thermal decomposition, its overpotential is reduced by 82 mV. Meanwhile, compared with RuO₂ prepared by magnetron sputtering, the overpotential is also reduced by 74 mV. Furthermore, compared with the RuO₂/Ru with core–shell structure (η = 244 mV), the overpotential is still decreased by 24 mV. Therefore, the RuO₂/Co₃O₄–RuCo-EO electrode has excellent OER activity. There are two reasons for the improvement of the OER activity. On the one hand, the core–shell structure is conducive to electron transport, and on the other hand, the addition of Co adjusts the electronic structure of Ru.

The optimized RuO₂/Co₃O₄–RuCo-EO electrode with Ru loading of 0.064 mg cm⁻² exhibits the excellent oxygen evolution activity with an overpotential of 220 mV at the current density of 10 mA cm⁻² and a Tafel slope of 59.9 mV dec⁻¹.     

VOX supported on TiO2–Ce0.9Zr0.1O2 core–shell structure catalyst for NH3-SCR of NO

In this experiment, a TiO₂–Ce_0.9Zr_0.1O₂ support with core–shell structure was successfully prepared by a precipitation method and VO_X/TiO₂–Ce_0.9Zr_0.1O₂ catalyst was prepared by an impregnation method, and the catalyst was used to catalyze the NH₃-SCR of NO. Based on the results of HRTEM, XRD, BET, H₂-TPR, NH₃-TPD, XPS, Py-IR, it was speculated that due to the interaction between TiO₂ and Ce_0.9Zr_0.1O₂, more oxygen vacancies and Ce³⁺ are generated, which are beneficial to the existence of low-valence V by electron transfer between high valence state V and Ce³⁺and increase the acidic sites on the catalyst surface. The catalytic activity (>97%) of the VO_X/TiO₂–Ce_0.9Zr_0.1O₂ catalyst is superior to the current commercial catalyst (V₂O₅–WO₃/TiO₂) and has a higher N₂ selectivity (>97.5%) at 40 000 h⁻¹ GHSV and 250–400 °C.

VO_X/TiO₂–Ce_0.9Zr_0.1O₂ catalyst exhibits high activity and selectivity in a wide temperature window.     

Formation kinetics of Sr0.25Ba0.75Nb2O6 and Li2B4O7 crystals from 0.25SrO–0.75BaO–Nb2O5–Li2O–2B2O3 glass

We have investigated the transition kinetics of Sr_0.25Ba_0.75Nb₂O₆ (SBN) and Li₂B₄O₇ (LBO) crystals from 0.25SrO–0.75BaO–Nb₂O₅–Li₂O–2B₂O₃ (SBNLBO) glass under isothermal and non-isothermal processes. With increasing temperature, there are two consecutive steps of crystallization of SBN and LBO from the glass. The Johnson–Mehl–Avrami function indicates that the crystallization mechanism of SBN belongs to an increasing nucleation rate with diffusion-controlled growth. The crystallite size of SBN ranges from 40 to 140 nm but it is confined to within 30–45 nm for LBO during the whole crystallization process. The relationship between the nano size and strain of SBN based on the Williamson–Hall method, and the change of activation energies of SBN and LBO crystallization analyzed by using the isoconversional model are discussed. A comparison of phonon modes between as-quenched glass and fully transformed crystals clearly shows that the low dimensional vibration modes in the structurally disordered glass change to highly dimensional network units with the formation of crystals.

We have investigated the transition kinetics of Sr_0.25Ba_0.75Nb₂O₆ (SBN) and Li₂B₄O₇ (LBO) crystals from 0.25SrO–0.75BaO–Nb₂O₅–Li₂O–2B₂O₃ (SBNLBO) glass under isothermal and non-isothermal processes.     

Activation of peroxymonosulfate by metal (Fe,Mn, Cu and Ni) doping ordered mesoporous Co3O4 for the degradation of enrofloxacin

Various transition metals (Fe, Mn, Cu and Ni) were doped into ordered mesoporous Co₃O₄ to synthesize Co₃O₄-composite spinels. Their formation was evidenced by transmission electronic microscopy (TEM), X-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) analysis. It was found that Co₃O₄-composite spinels could efficiently activate peroxymonosulfate (PMS) to remove enrofloxacin (ENR) and the catalytic activity followed the order Co₃O₄–CuCo₂O₄ > Co₃O₄–CoMn₂O₄ > Co₃O₄–CoFe₂O₄ > Co₃O₄–NiCo₂O₄. Moreover, through the calculation of the specific apparent rate constant (k_sapp), it can be proved that the Co and Cu ions had the best synergistic effect for PMS activation. The Co₃O₄-composite spinels presented a wide pH range for the activation of PMS, but strong acidic and alkaline conditions were detrimental to ENR removal. Higher reaction temperature could promote the PMS activation process. Sulfate radical was identified as the dominating reactive species in Co₃O₄-composite spinel/PMS systems through radical quenching experiments. Meanwhile, the probable mechanisms concerning Co₃O₄-composite spinel activated PMS were proposed.

Various transition metals (Fe, Mn, Cu and Ni) were doped into ordered mesoporous Co₃O₄ to synthesize Co₃O₄-composite spinels.     

Enhanced catalytic degradation of amoxicillin with TiO2–Fe3O4 composites via a submerged magnetic separation membrane photocatalytic reactor (SMSMPR)

A novel photo-Fenton catalytic system for the removal of organic pollutants was presented, including the use of photo-Fenton process and a submerged magnetic separation membrane photocatalytic reactor (SMSMPR). We synthesized TiO₂–Fe₃O₄ composites as the photocatalyst and made full use of the magnetism of the photocatalyst to realize the recollection of the catalyst from the medium, which is critical to the commercialization of photocatalytic technology for wastewater treatment. The photo-Fenton performance of TiO₂–Fe₃O₄ is evaluated with amoxicillin trihydrate (AMX) as a target pollutant. The results indicate that the TiO₂–Fe₃O₄/H₂O₂ oxidation system shows efficient degradation of AMX. Fe₃O₄ could not only enhance the heterogeneous Fenton degradation of organic compounds but also allow the photocatalyst to be magnetically separated from treated water. After four reaction cycles, the TiO₂–Fe₃O₄ composites still exhibit 85.2% removal efficiency of AMX and show excellent recovery properties. Accordingly, the SMSMPR with the TiO₂–Fe₃O₄ composite is a promising way for removing organic pollutants.

With a TiO₂–Fe₃O₄ composite as the catalyst, amoxicillin was degraded via a photo-Fenton process using a submerged magnetic separation membrane photocatalytic reactor.     

Comparison on the immersion corrosion and electrochemical corrosion resistance of WC–Al2O3 composites and WC–Co cemented carbide in NaCl solution

WC–15 wt% Al₂O₃ composites were prepared via hot pressing sintering technology. The corrosion behaviors of WC–Al₂O₃ composites and traditional WC–Co cemented carbide in NaCl solution were studied by immersion corrosion and electrochemical technique. The impedance value of the WC–Al₂O₃ composite increased more rapidly than WC–Co cemented carbide during the 24 hours, which indicated that WC–Al₂O₃ composites had a more compact passivation film than WC–Co cemented carbide. The results confirmed that the corrosion resistance of WC–Al₂O₃ composites was higher than that of WC–Co cemented carbide in NaCl solution. The corrosion mechanisms of WC–Al₂O₃ composites and WC–Co cemented carbide in NaCl solution were also revealed by SEM, EDS, XPS and Raman. The corrosion products of WC–Al₂O₃ composites mainly contain WO₃, while for WC–Co cemented carbide they are Co(OH)₂, Co₃O₄ and WO₃. The different corrosion mechanism of the two materials is attributed to the Al₂O₃ phase instead of the Co binder, which avoids the galvanic corrosion between the WC phase and the Co binder.

WC–Al₂O₃ composites possess higher corrosion resistance compared with WC–Co cemented carbide. The main corrosion mechanism for WC–Al₂O₃ composites is the oxidation of the WC phase.     

Low temperature CO oxidation catalysed by flower-like Ni–Co–O: how physicochemical properties influence catalytic performance

In this work, mesoporous Ni–Co composite oxides were synthesized by a facile liquid-precipitation method without the addition of surfactant, and their ability to catalyse a low temperature CO oxidation reaction was investigated. To explore the effect of the synergetic interaction between Ni and Co on the physicochemical properties and catalytic performance of these catalysts, the as-prepared samples were characterized using XRF, XRD, LRS, N₂-physisorption (BET), SEM, TEM, XPS, H₂-TPR, O₂-TPD and in situ DRIFTS characterization techniques. The results are as follows: (1) the doping of cobalt can reduces the size of NiO, thus massive amorphous NiO have formed and highly dispersed on the catalyst surface, resulting in the formation of abundant surface Ni²⁺ ions; (2) Ni²⁺ ions partially substitute Co³⁺ ions to form a Ni–Co spinel solid solution, generating an abundance of surface oxygen vacancies, which are vital for CO oxidation; (3) the Ni_0.8Co_0.2 catalyst exhibits the highest catalytic activity and a satisfactory stability for CO oxidation, whereas a larger cobalt content results in a decrease in activity, suggesting that the amorphous NiO phase is the dominant active phase instead of Co₃O₄ for CO oxidation; (4) the introduction of Co can alter the morphology of catalyst from plate-like to flower-like and then to dense granules. This morphological variation is related to the textural properties and catalytic performance of the catalysts. Lastly, a possible mechanism for CO oxidation reaction is tentatively proposed.

The flower-like catalyst possesses highly dispersed amorphous NiO and a high concentration of surface oxygen vacancies which are the central points for CO oxidation.     

A novel ethanol gas sensor based on α-Bi2Mo3O12/Co3O4 nanotube-decorated particles

A novel composite based on α-Bi₂Mo₃O₁₂/Co₃O₄ nanotube-decorated particles was successfully synthesized using a highly efficient and facile two step system using electrospinning and hydrothermal techniques. The small size Co₃O₄ nanoparticles were uniformly and hydrothermally developed on the electrospun α-Bi₂Mo₃O₁₂ nanotubes. The pure α-Bi₂Mo₃O₁₂ nanofibers and composite based on α-Bi₂Mo₃O₁₂/Co₃O₄ were examined using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) analyses. From the BET measurements, the composite based on α-Bi₂Mo₃O₁₂/Co₃O₄ exhibits a large specific surface area of 54 m² g⁻¹ with mesopore diameter ranges of 2–10 nm, which is mainly attributed to the remarkable and dominant enhancement in gas sensing as compared to that of the pure α-Bi₂Mo₃O₁₂ nanofibers (38 m² g⁻¹) and Co₃O₄ nanoparticles (32 m² g⁻¹), respectively. In this work, the novel composite based on α-Bi₂Mo₃O₁₂/Co₃O₄ presented a high sensitivity of 30.25 with a quick response/recovery speed towards 100 ppm ethanol at an optimal working temperature of 170 °C, as compared to the pure α-Bi₂Mo₃O₁₂ nanofibers and Co₃O₄ nanoparticles, which display a sensitivity of 13.10 and 2.99 at an optimal working temperature of 220 °C and 280 °C. The sensing performance of the composite based on the α-Bi₂Mo₃O₁₂/Co₃O₄ sensor exhibits a superior sensing performance towards ethanol, which might be owed to the enormous number of superficial oxygen species, the small size catalytic effect of the Co₃O₄ nanoparticles and the interfacial effect formed between the n-type α-Bi₂Mo₃O₁₂ and p-type Co₃O₄ leading to a high charge carrier concentration. This is a novel investigation of a composite based on an α-Bi₂Mo₃O₁₂/Co₃O₄ sensor in the gas sensing era, which might be of vital importance in applications in the advanced gas sensing field.

A novel composite based on α-Bi₂Mo₃O₁₂/Co₃O₄ nanotube-decorated particles was successfully synthesized using a highly efficient and facile two step system using electrospinning and hydrothermal techniques.     

Integral structured Co–Mn composite oxides grown on interconnected Ni foam for catalytic toluene oxidation

Considering the three-dimensional ordered network of Ni foam-supported catalysts and the toxicity effects of volatile organic compounds (VOCs), the design of proper active materials for the highly efficient elimination of VOCs is of vital importance in the environmental field. In this study, a series of Co–Mn composite oxides with different Co/Mn molar ratios grown on interconnected Ni foam are prepared as monolithic catalysts for total toluene oxidation, in which Co_1.5Mn_1.5O₄ with a molar ratio of 1 : 1 achieves the highest catalytic activity with complete toluene oxidation at 270 °C. The Co–Mn monolithic catalysts are characterized by XRD, SEM, TEM, H₂-TPR and XPS. It is observed that a moderate ratio of Mn/Co plays significant effects on the textural properties and catalytic activities. From the XPS and H₂-TPR characterization results, the obtained Co_1.5Mn_1.5O₄ (Co/Mn = 1/1) favors the excellent low-temperature reducibility, high concentration of surface Mn³⁺ and Co³⁺ species, and rich surface oxygen vacancies, resulting in superior oxidation performance due to the formation of a solid solution between the Co and Mn species. It is deduced that the existence of the synergistic effect between Co and Mn species results in a redox reaction: Co³⁺–Mn³⁺ ↔ Co²⁺–Mn⁴⁺, and enhances the catalytic activity for total toluene oxidation.

A series of Co–Mn oxides with different Co/Mn molar ratios grown on interconnected Ni foam were prepared as monolithic catalysts for total toluene oxidation.     

Barium promoted Ni/Sm2O3 catalysts for enhanced CO2 methanation

Low temperature CO₂ methanation is a favorable pathway to achieve high selectivity to methane while increasing the stability of the catalysts. A Ba promoted Ni/Sm₂O₃ catalyst was investigated for CO₂ methanation at atmospheric pressure with the temperature ranging from 200–450 °C. 5Ni–5Ba/Sm₂O₃ showed significant enhancement of CO₂ conversion particularly at temperatures ≤ 300 °C compared to Ni/Sm₂O₃. Incorporation of Ba into 5Ni/Sm₂O₃ improved the basicity of the catalysts and transformed the morphology of Sm₂O₃ from random structure into uniform groundnut shape nanoparticles. The uniformity of Sm₂O₃ created interparticle porosity that may be responsible for efficient heat transfer during a long catalytic reaction. Ba is also postulated to catalyze oxygen vacancy formation on Sm₂O₃ under a reducing environment presumably via isomorphic substitution. The disappearance of a high temperature (∼600 °C) reduction peak in H₂-TPR analysis revealed the reducibility of NiO following impregnation with Ba. However, further increasing the Ba loading to 15% formed BaNiO₃–BaNiO_2.36 phases which consequently reduced the activity of the Ni–Ba/Sm₂O₃ catalyst at low temperature. Ni was suggested to segregate from BaNiO₃–BaNiO_2.36 at high temperature thus exhibiting comparable activity with Ni/Sm₂O₃ at 450 °C.

Low temperature CO₂ methanation on 5Ni–5Ba/Sm₂O₃ is a favorable pathway to achieve high selectivity to methane while increasing the stability of the catalysts.     

Effects of the novel catalyst Ni–S2O82−–K2O/TiO2 on efficient lignin depolymerization

To improve the utilization of lignin, much effort has been devoted to lignin depolymerization with the aim to decrease waste and enhance profitability. Here, a dual property (acid and base) catalyst, namely S₂O₈²⁻–K₂O/TiO₂, was carefully researched. Upon loading S₂O₈²⁻ and K₂O onto TiO₂, acid and base sites emerged, and S₂O₈²⁻ and K₂O mutually enhanced the acid and base strengths of the catalyst enormously; this indeed facilitated lignin depolymerization. Under appropriate conditions, the yields of liquid product, petroleum ether soluble (PE-soluble) product and total monomer products were 83.76%, 50.4% and 28.96%, respectively. The constituents of the PE-soluble fraction, which are mainly monomers and dimers, can be used as liquid fuels or additives. In addition, after the catalyst was modified by Ni, better results were obtained. Surprisingly, it was found that the Ni enhanced not only the hydrogenation capacity but also the acidity. The highest high heating value (HHV) of the liquid product (33.6 MJ kg⁻¹) was obtained, and the yield of PE-soluble product increased from 50.4 to 56.4%. The product can be utilized as a fuel additive or be converted to bio-fuel. This catalysis system has significant potential in the conversion of lignin to bio-fuel.

To improve the utilization of lignin, much effort has been devoted to lignin depolymerization with the aim to decrease waste and enhance profitability.     

Combustion of lean methane over Co3O4 catalysts prepared with different cobalt precursors

To investigate the effect of catalyst precursors on physicochemical properties and activity of lean methane catalytic combustion, a series of Co₃O₄ catalysts were prepared via a precipitation method by using four different cobalt precursors: Co(C₂H₃O₂)₂, Co(NO₃)₂, CoCl₂, and CoSO₄. The catalysts were characterized by BET, XRD, SEM, Raman, XPS, XRF, O₂-TPD and H₂-TPR techniques. It was found that the different types of cobalt precursor had remarkable effects on the surface area, particle size, reducibility and catalytic performance. In contrast, the Co₃O₄-Ac catalyst showed a relatively small surface area, but its activity and stability were the highest. XPS, Raman, O₂-TPD and H₂-TPR results demonstrated that the superior catalytic performance of Co₃O₄-Ac was associated with its higher Co²⁺ concentration, more surface active oxygen species and better reducibility. In addition, the activity of the Co₃O₄-S catalyst reduced significantly due to the residual impurity SO₄²⁻, which could reduce the concentration of surface adsorbed active oxygen species and inhibit oxygen migration.

The effects of cobalt precursor on the microstructure, surface properties, reducibility and catalytic performance for methane combustion were investigated.