Co3O4-CeO2 Catalysts Research Articles

The impact of support selection and Co loading amount on the catalytic performance for methane combustion

Methane (CH4) is a key component of natural gas and is essential for energy production and utilization. However, due to its strong greenhouse effect, efficient catalytic combustion methods are needed to convert it into CO2 and H2O. This study systematically evaluates the catalytic performance of Co, CoO, and Co3O4 in methane catalytic combustion, particularly highlighting the superior activity of Co3O4. To improve catalytic efficiency, this paper examines the effects of SiO2, Al2O3, and CeO2 as support materials using co-precipitation and impregnation methods. The results show a significant improvement in the catalytic activity of Co3O4 supported on CeO2, attributed to CeO2's unique redox properties and high oxygen storage capacity. Additionally, the study explores the impact of different loading amounts (5%, 10%, 15%, 20%) of Co3O4(x)-CeO2 catalysts on their performance. The optimal 10%wt Co3O4–CeO2 catalyst achieves methane conversion rates of 10%, 50%, and 90% at temperatures of 376 °C, 473 °C, and 578 °C, respectively, demonstrating exceptional stability during a 20-h stability test and the ability to adapt to fluctuations in CH4 concentrations in low-oxygen environments, while also exhibiting significant catalytic activity across a range of methane concentrations from 0.5% to 2.5%. These findings provide important theoretical and experimental guidance for the application of cobalt-based catalysts in CH4 combustion, paving the way for future catalyst design and optimization.

The use of 18O2 to investigate the soot oxidation process on Co3O4, Co3O4-CeO2 and CeO2 catalysts in tight contact conditions

The use of 18O2 to investigate the soot oxidation process on Co3O4, Co3O4-CeO2 and CeO2 catalysts in tight contact conditions

Investigation of Co3O4–CeO2 Composite Oxide as Catalyst for the Decomposition of N2O

Co3O4–CeO2 composite oxides with various ratios of Ce/Co were fabricated by the hydrothermal method, and their activities in N2O decomposition have been studied. Co3O4–CeO2 catalyst is more active than pristine Co3O4 and CeO2 catalysts. Over Co3O4–CeO2 catalyst the strong interaction between Co3O4 and CeO2 existed, which suppressed the crystallization of Co3O4, resulting in the large surface area. Particularly, the synergetic effect between Co3O4 and CeO2 induces the formation of more active Co3+ and enhanced redox property of Co3O4–CeO2 catalyst. The desorption of adsorbed oxygen, which is the key step in N2O decomposition, can be promoted due to the existed redox cycle (Co2+ + Ce4+ ↔ Co3+ + Ce3+). Therefore, Co3O4–CeO2 composite oxide showed high activity for N2O decomposition.

Rod-like and mushroom-like Co3O4–CeO2 catalysts derived from Ce-1,3,5-benzene tricarboxylic acid for CO preferential oxidation: effects of compositions and morphology

Rod-like and mushroom-like Co3O4–CeO2 catalysts were synthesized using CeBTC MOFs as self-sacrifice templates. The two kinds of Co3O4–CeO2 catalysts with different shapes were characterized by SEM, TEM, N2 physical-sorption, XRD, TPR, Raman, XPS. The effects of compositions and morphology on the catalytic activity were investigated. The catalytic activities of Co3O4–CeO2 are correlated with the results of SEM, TEM, N2 physical-sorption, XRD, TPR, Raman, XPS to give insights into the catalytic sites. The results indicate the obtained Co3O4–CeO2 catalysts exhibit rod-like and mushroom-like, replicating the morphology of CeBTC templates. The catalytic activities of Co3O4–CeO2 were arranged in this sequence: Co1Ce > Co6Ce > Co2Ce > Co4Ce > Co8Ce, regardless their different catalyst morphology. The mushroom-like catalysts are superior to the rod-like ones due to their high surface areas and small Co3O4 crystal sizes. The sequence of catalytic activity versus Co/Ce ratio are coincidence with the order of Co–Ce synergistic interaction and Co3+/Co deduced from results of XRD, TPR, Raman, XPS. This evidence revealed that the Co–Ce synergistic interaction and Co3+ ions are responsible for the high activity of Co3O4–CeO2 catalysts. The highest CO conversion of 99% catalyst was achieved over M-Co1Ce catalyst with 12.5% CO2 and 15% H2O at 215 °C, 20,000 mL g−1 h−1. In addition, CO conversion of M-Co1Ce catalyst maintained more than 99% for 54 h in the atmosphere of simulated reformate at 20,000 mL g−1 h−1, suggesting the M-Co1Ce catalyst demonstrates potential in practice application.

Influence of cobalt on performance of Cu–CeO2 catalysts for preferential oxidation of CO

Copper and cobalt oxides supported on CeO2 were investigated for preferential oxidation of carbon monoxide (CO-PROX) in the presence of excess hydrogen and CO2. (CuO)1−x(Co3O4)x/3−(CeO2)2.5 (x = 0, 0.25, 0.50, 0.75, 0.85 and 1) catalysts were prepared by coprecipitation method. These mixed oxide catalysts were characterized by several physicochemical techniques, such as BET surface area (SBET), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). XRD studies show the peaks related to CuO and Co3O4 phases in copper and cobalt containing CeO2 catalysts. The average particle size of the CeO2 crystallites is in the range of 8–10 nm as evaluated from HRTEM studies. XPS studies demonstrate that Cu, Co and Ce in (CuO)1−x(Co3O4)x/3−(CeO2)2.5 catalysts are presented in +2 and +1, +3 and +2 and +4 and +3 oxidation states, respectively. The catalyst with x = 0.75 shows better activity and selectivity towards CO-PROX. Though the catalyst with only copper (CuO–CeO2, x = 0) shows good activity but reverse water gas shift (RWGS) reaction is noticed at high temperature. On the other hand, RWGS reaction is suppressed on the cobalt containing CuO–CeO2 catalyst. Cobalt on CeO2 with x = 1 shows hardly any activity for PROX reaction at low temperatures. No methanation activity is observed on CuO–CeO2 or Co3O4–CeO2 catalysts. In contrast, combination of copper and cobalt on CeO2 shows methanation of CO where enhanced activity is observed with increasing in cobalt content.

Role of rubidium promotion on the nitrous oxide decomposition activity of nanocrystalline Co3O4-CeO2 catalyst

Rb-promoted nanocrystalline Co3O4-CeO2 catalysts were prepared by the impregnation of the Co3O4-CeO2, previously prepared using the solution combustion route, with an aqueous solution of Rb2CO3 (Rb/Co ratios 0.0125–0.20) and subsequent calcination at 500 °C. The obtained catalysts and the un-promoted Co3O4 and Co3O4-CeO2 catalysts have been characterized using XRD, FT-IR, SEM, TEM, XPS, H2-TPR and N2 physisorption techniques. The activity of the various catalysts was tested for N2O direct decomposition. All the Rb-promoted catalysts exhibited better performance than the bare Co3O4-CeO2 catalyst, where the highest activity was obtained using the catalyst with Rb/Co ratio of 0.025. The activity performance of the various catalysts was discussed in terms of the electronic properties modification accompanying the Rb-doping. For the optimum catalyst, further experiments were conducted in the presence of O2 and NO in the reactor feed.

Heterogeneous activation of persulfate by Co3O4-CeO2 catalyst for diclofenac removal

A series of Co3O4-CeO2 mixed metal oxides were synthesized by co-precipitation method and successfully used to activate persulfate for diclofenac removal. The effects of Co:Ce mole ratio, calcination temperature and calcination time on the catalytic activities were investigated. Results showed that the activity of Co3O4-CeO2 catalysts increased with Co:Ce mole ratio from 1:9 to 7:3, and decreased with the calcination temperature from 300 to 800 °C. 90% diclofenac was removed with Co7Ce3-300-1 catalyst (Co:Ce = 7:3, calcinated at 300 °C for 1 h) after 15 min. Moreover, short calcination time and low temperature resulted in smaller crystallite size, more structural defects, more active crystal surfaces and larger surface area of the catalyst, which led to higher removal efficiency of diclofenac. The high ratios of Co2+/Co3+, Ce3+/Ce4+ and Oads/Olatt were very important to enhance the catalytic activity. Finally, a potential reaction mechanism was proposed based on characterization of the fresh and spent catalysts.

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 NOx-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 NOx storage and oxidation capacity resulted from the integrated respective merits of Co3O4 and CeO2 also accounted for the enhanced soot oxidation activity via NOx-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.

Effect of Calcination Temperature on the Catalytic Oxidation of Formaldehyde Over Co3O4–CeO2 Catalysts

The effect of calcination temperature (350–650 °C) on the structure and catalytic activity of Co3O4–CeO2 mixed oxides prepared by sol–gel method was investigated by XRD, H2-TPR, O2-TPD and formaldehyde (HCHO) oxidation. The Co3O4–CeO2 calcined at 450 °C (Co3O4–CeO2-450) exhibited the best performance, showing that the complete oxidation of HCHO was achieved at temperature as low as 80 °C. The results of characterizations revealed that the Co3O4–CeO2-450 had excellent catalytic activity due to the larger specific surface area, the best reducibility and more abundant surface active oxygen species.

Formic Acid Modified Co3O4-CeO2 Catalysts for CO Oxidation

A formic acid modified catalyst, Co3O4-CeO2, was prepared via facile urea-hydrothermal method and applied in CO oxidation. The Co3O4-CeO2-0.5 catalyst, treated by formic acid at 0.5 mol/L, performed better in CO oxidation with T50 obtained at 69.5 °C and T100 obtained at 150 °C, respectively. The characterization results indicate that after treating with formic acid, there is a more porous structure within the Co3O4-CeO2 catalyst; meanwhile, despite of the slightly decreased content of Co, there are more adsorption sites exposed by acid treatment, as suggested by CO-TPD and H2-TPD, which explains the improvement of catalytic performance.

Freeze-dried Co3O4–CeO2 catalysts for the preferential oxidation of CO with the presence of CO2 and H2O in the feed

A synthesis method in two steps was used to obtain Co3O4–CeO2 (COCE) catalysts. Firstly, freeze-drying precursors to obtain a submicrometric ceria powders support were calcined at a temperature as low as 400°C. Then, the support was impregnated with a Co(II) acetate solution by incipient wetness impregnation, varying the loading of Co between 5 and 20wt%, and calcined again at 400°C. xCOCE samples were tested for the preferential oxidation of CO in a H2-rich stream (CO-PROX). All samples showed catalytic activity and high selectivity towards CO2 at low reaction temperatures, being 15COCE the most active catalyst. Moreover, simulating a CO-PROX unit operation, the influence of the presence of CO2 and H2O in the feed was tested, showing a high activity and selectivity mainly to CO2.

CeO2 and Co3O4–CeO2 nanoparticles: effect of the synthesis method on the structure and catalytic properties in COPrOx and methanation reactions

CeO2 and Co3O4–CeO2 nanoparticles were synthesized, thoroughly characterized, and evaluated in the COPrOx reaction. The CeO2 nanoparticles were synthesized by the diffusion-controlled precipitation method with ethylene glycol. A notably higher yield was obtained when H2O2 was used in the synthesis procedure. For comparison, two commercial samples of CeO2 nanoparticles (Nyacol®)—one calcined and the other sintered—were also studied. Catalytic results of bare CeO2 calcined at 500 °C showed a strong influence of the method of synthesis. Despite having similar BET area values, the CeO2 synthesized without H2O2 was the most active sample. Co3O4–CeO2 catalysts with three different Co/(Co + Ce) atomic ratios, 0.1, 0.3, and 0.5, were prepared by the wet impregnation of the CeO2 nanoparticles. TEM and STEM observations showed that impregnation produced mixed oxides composed of small CeO2 nanoparticles located both over the surface and inside the Co3O4 crystals. The mixed oxide catalysts prepared with a cobalt atomic ratio of 0.5 showed methane formation, which started at 200 °C due to the reaction between CO2 and H2. However, above 250 °C, the reaction between CO and H2 became important, thus contributing to CO elimination with a small H2 loss. As a result, CO could be totally eliminated in a wide temperature range, from 200 to 400 °C. The methanation reaction was favored by the reduction of the cobalt oxide, as suggested by the TPR experiments. This result is probably originated in Ce–Co interactions, related to the method of synthesis and the surface area of the mixed oxides obtained.

The effect of accessible oxygen over Co3O4–CeO2 catalysts on the steam reforming of ethanol

The effect of accessible oxygen on the steam reforming of ethanol (SRE) over Co3O4–CeO2 catalysts was investigated. Both equal molar ratio of Co3O4–CeO2 catalysts were prepared by hydrothermal co-precipitation (H), and hydrothermal ultrasonic-assisted co-precipitation (UH) methods and characterized through X-ray diffraction (XRD), in situ temperature programmed reduction/temperature programmed oxidation (TPR/TPO), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and elemental analysis (EA) techniques at various stages of the catalyst. The results indicated that the incorporation of cobalt ion into the ceria lattice could increase the dispersion of catalyst, oxygen vacancies and promote the oxygen-storing and releasing capability of ceria, especially over the catalyst prepared by ultrasonic-assisted method. The accessible oxygen played an important role on the SRE reaction and resistant to carbon deposition. The Co–Ce (UH) catalyst was more active and selective in the SRE reaction, where ethanol was fully converted and hydrogen selectivity (SH2) was about 70% at 400 °C under H2O/EtOH molar ratio of 13.0 and gas hourly space velocity (GHSV) of 22,000 h−1. The high oxygen storage capacity (OSC) and high accessible oxygen for the Co–Ce (UH) catalyst allowed oxidation/gasification of deposited carbon as soon as it formed, and less coke was detected.

Supported Co3O4-CeO2 catalysts on modified activated carbon for CO preferential oxidation in H2-rich gases

CO preferential oxidation (PROX) reactions were performed over the supported Co3O4-CeO2 catalysts on modified activated carbon (AC) for eliminating the trace CO from H2-rich gases. The effects of support modification by H2O2 oxidation treatment, catalyst calcination temperature, Ce/Co atomic ratio (nCe/Co), Co3O4-CeO2 loading and reaction parameters on catalytic properties of the Co3O4-CeO2/AC catalysts were investigated. Various characterization techniques like scanning electron microscopy (SEM), X-ray diffraction (XRD) and H2 temperature-programmed reduction (H2-TPR) were employed to reveal the relationship between catalysts nature and catalytic performance. Results illustrate that the supported Co3O4-CeO2 catalyst on modified AC exhibits excellent catalytic properties, which highly depends on dispersity and reducibility of Co3O4 affected by the time of support treatment (tp), calcination temperature, nCe/Co and loading. The supported 35wt% Co3O4-CeO2 catalyst (1:8 of nCe/Co) on the modified AC with H2O2 oxidation treatment for 6h demonstrates the best catalytic properties and the almost complete CO transformation takes place in a wide temperature range of 125–190°C. Moreover, it is also found that the developed catalyst exhibits an outstanding catalytic stability, and 100% CO conversion can be maintained as the time on stream evolutes up to 1800min even in the presence of CO2 and H2O in the feed. The optimized Co3O4-CeO2/AC may be a robust and promising catalyst for eliminating trace CO from H2-rich gases.

Simple, Low-cost Preparation of High Surface Area Co3O4–CeO2 Catalysts for Total Decomposition of Toluene

Abstract High surface area Co3O4–CeO2 catalysts were prepared by the simple calcination of carbonate–precursor mixtures at 300 °C. The Co3O4–CeO2 catalyst with a Co/Ce molar ratio of 1 showed high activity for toluene decomposition, comparable to that of Pt(0.08 wt %)/zeolite catalyst. The total decomposition of toluene was achieved at degradation temperatures as low as 200 °C. The Co3O4–CeO2 catalyst was highly stable, even after two weeks of reaction.

MnOx modified Co3O4-CeO2 catalysts for the preferential oxidation of CO in H2-rich gases

In this work, MnOx modified Co3O4-CeO2 catalysts were prepared and used for preferential oxidation of CO in hydrogen-rich gases. The catalytic performance tests results showed that the catalyst with Co:Ce:Mn molar ratio of 8:1:1 exhibited the best low-temperature CO oxidation activity and higher selectivity for CO-PROX reaction among tested catalysts. 100% CO conversion could be obtained over this catalyst at 80–180°C with the feeding gas of 1vol.% CO, 1vol.% O2, 50vol.% H2 and N2 balance under the space velocity of 40,000 ml h−1 gcat−1. Adding CO2 and/or water was unfavorable for CO removal, even so complete oxidation of CO was still achieved over this catalyst with the reaction stream of 20vol.% CO2, 10vol.% H2O, 1vol.% CO, 1vol.% O2, 50vol.% H2 and N2 balance under high space velocity of 80,000 ml h−1 gcat−1 at reaction temperature range of 160–180°C. The catalysts were characterized by XRD, TEM, EDX, TPR and XPS techniques and the results showed that adding MnOx into Co3O4-CeO2 led to more uniform mixing of Co3O4 and CeO2 particles and led to finely dispersed and high valence state cobalt oxides species, which contributed to high catalytic activity of Co-Ce-Mn mixed oxides catalysts.

Preferential oxidation of CO in H2 over Co3O4-CeO2 catalysts

Co3O4-CeO2 catalysts prepared by the co-precipitation method have been studied for the preferential oxidation of carbon monoxide in hydrogen. Effects of the cobalt contents and calcination temperature on Co3O4-CeO2 were investigated, and the Co3O4-CeO2 catalyst containing 80 wt.% Co3O4 calcined at 350°C exhibited the highest activity and good selectivity. The influence of the components of the feeding gas (H2, CO2 and H2O) on the preferential oxidation of carbon monoxide had also been tested. The tested results showed that the negative effect of H2 was much weaker than that of H2O and CO2.