Catalytic Combustion Of Lean Methane Research Articles

Catalytic combustion of lean methane over different Co3O4 nanoparticle catalysts

Three types of Co3O4 catalyst, namely Co3O4 nanoparticles (denoted as Co3O4-NPs, ∼12 nm in diameter), Co3O4 nanoparticles encapsulated in mesoporou s SiO2 (denoted as Co3O4@SiO2), and Co3O4 nanoparticles inside microporous SiO2 hollow sub-microspheres (denoted as Co3O4-in-SiO2), were explored to catalyze the combustion of lean methane. It was found that the methane conversion over the three catalysts has the order of Co3O4-NPs ≈ Co3O4@SiO2 > Co3O4-in-SiO2 due to the different catalyst structure. The comparison experiments at high temperatures indicate the Co3O4@SiO2 has a significantly improved anti-sintering performance. Combined with the TEM and BET measurements, the results prove that the presence of the mesoporous SiO2 layer can maintain the catalytical activity and significantly improve the anti-sintering performance of Co3O4@SiO2. In contrast, the microporous SiO2 layer reduces the catalytical activity of Co3O4-in-SiO2 possibly due to its less effective diffusion path of combustion product. Thus, the paper demonstrates the pore size of SiO2 layer and catalyst structure are both crucial for the catalytical activity and stability.

Design of hybrid La1-xCexCoO3-δ catalysts for lean methane combustion via creating active Co and Ce species

The catalytic activity of perovskite-typed catalysts depends on both the surface properties and bulk structure. Herein, we report a facile strategy to induce surface reconstruction and lattice distortion of the La1-xCexCoO3-δ catalysts via acid-etching pretreatment, ultimately realizing superior performance for catalytic combustion of lean methane, even in the presence of steam and hydrogen sulfide. The exsolution of small Ce and Co oxides (ca. 5 nm) from the perovskite were found on the surface of the La1-xCexCoO3-δ catalysts to form a hybrid structure after the acid-etching, which interact with the perovskite bulk to create more Co3+ and surface absorbed oxygen as active sites for methane combustion. It is also found that Ce species can be embedded in the crystal lattice and decorated on the surface of the catalysts after the acid-etching, which may enhance the formation of surface absorbed oxygen and the redox ability of Co3+/Co2+ pair. This results in high catalytic activity (T90 = 486 ℃) with a space velocity of 30,000 mL·g−1·h−1. Otherwise, the weak ability of hydroxyl species adsorbed on the surface of acid-etched catalysts restrain further adsorption of water molecules, improving the stability of methane combustion in the presence of water vapour. The increase in CeO2 content on the surface due to acid etching also contributes to the catalyst’s resistance to sulfur poisoning. The present work may provide a new strategy for the synthesis of hybrid perovskite catalysts with excellent catalytic performance, stability and resistance to impurities poisoning.

Lean methane catalytic combustion over the mesoporous MnOx-Ni/MgAl2O4 catalysts: Effects of Mn loading

In the current investigation, the textural features and catalytic efficiency of the Mn-promoted Ni/MgAl2O4 catalysts were evaluated in the catalytic combustion of lean methane. The results demonstrated that adding manganese oxide up to 5 wt.% to the catalyst improved the structural features and light-off temperatures due to the increase of the reduction degree and oxygen vacancies. The role of the Tcalcination and processing factors on the methane conversion of the 5%Mn-20%Ni/MgAl2O4 catalyst was also studied. The results indicated that the CH4 conversion decreased with the increment of O2/CH4 molar ratio and GHSV value. The stability test revealed that the prepared sample exhibited high stability during 10 h time on stream. Furthermore, the obtained results indicated that the BET area, reduction degree, oxygen mobility, and catalytic performance increased with decreasing the calcination temperature from 700 to 500 °C.

Catalytic combustion of lean methane over MnCo2O4/SiC catalysts: Enhanced activity and sulfur resistance

The simultaneous control of catalytic activity and sulfur resistance is a challenging task for non-noble metal catalysts in the domain of heterogenous catalysis. Herein, by dispersing MnCo2O4 (MCO) nanoparticles on a SiC substrate, we develop a novel catalyst for methane combustion that exhibits excellent low-temperature catalytic activity as well as high sulfur resistance. Strong interactions between SiC and MCO reduce the crystallite size of MCO and increase the specific surface area of the catalyst and the concentration of the active species, namely, Co3+ and surface oxygen species. The 60%MCO/SiC sample shows the highest catalytic activity, with T10, T50, and T90 values of 335, 375, and 444 °C, respectively, at a space velocity of 45,000 mL∙g−1∙h−1. In-situ diffuse reflectance infrared spectroscopy experiments and physicochemical characterizations indicate that the enhancement of catalytic activity is mainly attributed to the abundant adsorbed oxygen and surface Co3+ species in the catalysts that accelerate the formation of carbonate and formic acid species during methane conversion. The 60%MCO/SiC sample also exhibits high sulfur resistance, which is mainly attributed to the inhibiting effect of SiC on the catalyst for bulk sulfate formation. The findings of this study provide insights for the fabrication of catalysts with high activity as well as high sulfur resistance.

CeO2-promoted BaO-MnOx catalyst for lean methane catalytic combustion at low temperatures: Improved catalytic efficiency and light-off temperature

In this research, the effect of various promoters (Zr, La, Ce, and Y) on the physicochemical features and catalytic activities of the BaO(10)-MnOx prepared by the mechanochemical preparation route was investigated in the catalytic combustion of lean methane. Incomplete methane combustion as a result of the burning of natural gas in industries is the major reason to use a catalytic system to reduce the pollutants formation (NOx, COx, etc.) and improve the combustion efficiency and proceeds towards complete combustion. In our previous study, we performed the methane combustion reaction on the mechanochemical synthesized BaO(x)-MnOx catalysts with various contents of BaO (5–20 wt%), and the results indicated that the addition of 10 wt% of BaO to MnOx could remarkably improve the catalytic efficiency due to the enhance the oxygen mobility and reduction features. In the present study, the structural properties of the synthesized catalysts were specified by XRD, BET, H2-TPR, O2-TPD, and SEM techniques. It is observed from the O2-TPD technique that the addition of promoters into the BaO-MnOx catalyst resulted in the increase in oxygen mobility, which could rise the catalytic activity. The addition of CeO2 has a more positive effect on the catalytic activity due to the higher surface area and oxygen storage capacity. The obtained results revealed that the CeO2(3)-BaO(10)-MnOx catalyst possessed the superior performance in the methane combustion. The 90% of CH4 conversion was obtained at about 350 °C over this catalyst. The effect of calcination temperature, feed ratio, GHSV, hysteresis curve, pretreatment atmospheres, and the presence of CO2 and moisture was evaluated on the catalytic efficiency. After 50 h of continuous reaction at 450 °C, the selected catalyst showed high stability and the catalyst morphology was not significantly altered. Furthermore, CO oxidation was performed over the CeO2(3)-BaO(10)-MnOx catalyst, and the results indicated that the CO conversion was reached 100% at 250 °C.

Encapsulated Co3O4/(SiAl@Al2O3) thermal storage functional catalysts for catalytic combustion of lean methane

It is well known that the structural problem between the autothermal operation and the outside utilization of heat in the catalytic combustion system and the runaway on catalyst bed is hard to avoid during the combustion process. Herein, the encapsulated Co3O4/(SiAl@Al2O3) thermal storage functional catalysts which couple Co3O4 catalysts and SiAl@Al2O3 phase change materials are proposed and firstly applied for catalytic combustion of lean methane to improve the thermal environment of the catalyst bed and achieve the high efficiency of lean methane utilization. The thermal management behaviors of such thermal storage functional catalysts and the dynamic coupling effect between heat storage/release characteristics of catalysts and catalytic performance during methane combustion process are investigated in detail. It is found that the encapsulated Co3O4/(SiAl@Al2O3) thermal storage catalysts retain the high latent heat of SiAl@Al2O3 phase change material (410 J/g) and the values vary from 280 J/g to 30 J/g when the SiAl@Al2O3 content decreases from 90 wt% to 10 wt%. When applying the catalysts to catalytic combustion of lean methane, such thermal storage functional catalysts with high thermal storage density show significant efficiency of lean methane conversion than pure Co3O4, and it can also keep the methane conversion at a high level for a long time even if the external heat source disappears. This indicates that the effective heat management of Co3O4/(SiAl@Al2O3) thermal storage catalysts during methane combustion process plays a crucial role in determining the catalytic activity via improving the thermal runaway and hot spots problems in catalyst bed and reducing heat loss. However, the content of SiAl@Al2O3 needs to be carefully regulated to avoid the decrease of activity resulting from the low active Co3O4 content. Particularly, the Co3O4/(SiAl@Al2O3-30 wt%) catalyst shows a competitive activity (e.g., T10, T50 and T90 at 226, 282 and 370 °C) and it surpasses the activity of pure Co3O4 in literatures although the active Co3O4 content is significantly lower than them. After turning off the heat source for 37 min, its methane conversion can still reach 50%, which is twice that of pure Co3O4. The present approach for thermal management in catalytic methane combustion reaction will provide good references for solving the problems (e.g., temperature runaway and hot-spot) in fixed bed reactors during other complex heterogeneous chemical reactions.

Heat transfer characteristics analysis and optimization of the Micro Packed Bed Bionic Reactor

The Fixed Bed Bionic Reactor (FBBR) is a novel conceptual reactor using hierarchical flow channel networks to reduce the pressure drop in fixed beds so that fine catalysts can be used to enhance the catalyst effectiveness. The Micro Packed Bed Bionic Reactor (MPBBR) is a representative implementation of the FBBR designed for fast catalytic reactions with strong heat effect. In this work, the heat transfer behaviors of the MPBBR are qualitatively analyzed. By a typical application case, the catalytic combustion of lean methane, the influences of channel structure and geometric parameters on the heat transfer performance are quantitatively analyzed. An optimal MPBBR for such highly exothermic reaction uses porous silicon carbide ceramic monoliths as honeycomb framework. The single input channel is modified by add a back-turning channel. With the optimized channel structure and geometric parameters, the maximal temperature difference in the catalyst bed is maintained under 45 °C, and the unit catalyst mass and unit reactor volume handling capacities are doubled and tripled, respectively. The MPBBR is proved to be a flexible and economical device with high performance heat transfer.

Catalytic Combustion of Lean Methane Assisted by an Electric Field over MnxCoy Catalysts at Low Temperature

An electric field was introduced into the catalytic oxidation of lean methane at low temperature over MnxCoy catalysts. Mn1Co5 exhibited the best catalytic performance with the light off temperatur...

Catalytic Combustion of Lean Methane Assisted by Electric Field over Pd/Co3O4 Catalysts at Low Temperature

A series of Pd/Co3O4 catalysts were prepared by Self-Propagating High-Temperature Synthesis (SHS) method in this study, and electric field was applied for catalytic combustion of lean methane over Pd/Co3O4 catalysts at low temperature. When electric field was applied, the catalytic combustion performance of Pd/Co3O4 catalysts was greatly improved, and the application of electric field could reduce the load of active element Pd to some extent while maintaining the same efficiency. Based on experimental tests and the analysis results of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H2-temperature-programmed reduction (H2-TPR) and in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS), the mechanism of catalytic oxidation of CH4 over Pd/Co3O4 catalysts in electric field was proposed. The catalytic combustion of CH4 occurs only when the temperature is higher than 250 °C normally, but when electric field was applied, the whole process of CH4 oxidation was promoted significantly and the reaction temperature was reduced. Electric field could promote the reduction of the support Co3O4 to release the lattice oxygen, resulting in the increase of PdOx and the surface chemisorbed oxygen, which could provide more active sites for the low-temperature oxidation of CH4. Furthermore, electric field could accelerate the dehydroxylation of CoOOH to further enhance the activity of the catalysts.

Flow distribution in a novel fixed bed bionic reactor

The concept of a novel Fixed Bed Bionic Reactor (FBBR) is presented in this work. The core idea is to use distributed input and output network, compact channel structure and small scale packed beds. In the FBBR, fine catalyst particles with high effectiveness can be used while the pressure drop stays at a rather low level, which breaks through the limitations of the existing fixed-bed reactors. The flow distribution uniformity is the key to the design of the FBBR. A general mathematical model is established for the FBBR elementary unit, and concise analytic solutions are obtained to describe the profile of the distribution. Characteristic parameters are extracted from the model and uniformity criteria can be set up as theoretical instructions for the design of the FBBR. To demonstrate the practical value, two application cases are presented. A large scale multilayer radial FBBR is designed for Methanol to Propylene reaction, having the advantages of higher propylene selectivity and productivity. Then a small scale modular FBBR is designed for catalytic combustion of lean methane, having the advantages of being nearly isothermal with auto-thermal function and being miniaturized and modularized with better flexibility in satisfying different scale of productions.This work has been selected by the Editors as a Featured Cover Article for this issue.

Catalytic performance of Pd–NiCo2O4/SiO2 in lean methane combustion at low temperature

In this paper, the catalyst of Pd–NiCo2O4/SiO2 was prepared and applied to the catalytic combustion of lean methane. Pd and NiCo2O4 nanoparticles were uniformly distributed on the SiO2 support, so that every Pd or NiCo2O4 nanoparticle was separated from each other by another component. Comparing with Co3O4/SiO2, NiCo2O4/SiO2, Pd–Co3O4/SiO2 and Pd#NiCo2O4/SiO2 (catalysts without uniform distribution of Pd and NiCo2O4 nanoparticles), Pd–NiCo2O4/SiO2 had the highest catalytic activity in the catalytic combustion of lean methane, with a methane total conversion temperature at 378 °C. In addition, the high activity did not decrease during the long time reaction, which showed good thermal stability. TEM and BET results showed that the nanoparticle sizes of Pd and NiCo2O4 were very small. The XRD patterns indicated that the Pd nanoparticles were highly dispersed on the surface of SiO2. The XPS spectra demonstrated the formation of NiCO2O4, the presence of enough active oxygen species on the catalyst surface and the high ratio of PdO/Pd0. The enhanced influence of Ni introduction was also proved by comparison tests. All these results indicated that the high catalytic activity of Pd–NiCo2O4/SiO2 mainly comes from the nanoparticle distribution and the Ni cation enhancement.

Catalytic combustion of lean methane at low temperature over ZrO2-modified Co3O4 catalysts

A series of ZrO2 modified Co3O4 catalysts prepared by co-precipitation method were characterized by XRD, Raman, SEM, XPS and H2-TPR, and used in the catalytic combustion of lean methane at low temperature. XRD and Raman results demonstrate that ZrO2Co3O4 is in the form of a Zr-Co-O solid solution. XPS result indicates that the content of ZrO2 in ZrO2Co3O4 composite oxide has a significant influence on the concentration of Co2+ in tetrahedral site (ATetrahedral/AOctahedral) and the surface active oxygen species, which are correlated to the activity of methane combustion. H2-TPR result shows that the ZrO2(2)-Co3O4 composite oxide exhibits better reducibility. Compared with pure Co3O4, the ZrO2(2)-Co3O4 composite oxide presented the highest activity with T90 of 335°C. All these characterizations suggest that high activity in the lean methane combustion could be ascribed to high surface areas, ATetrahedral/AOctahedral and surface active oxygen species.

Low Temperature Complete Combustion of Lean Methane over Cobalt–Nickel Mixed‐Oxide Catalysts

AbstractCobalt–nickel mixed oxides with different Co/Ni molar ratios were prepared by co‐precipitation and used for the catalytic combustion of lean methane. The catalytic performances for methane combustion were evaluated at steady‐state conditions at temperatures ranging from 250 to 500 °C, which were increased in step sizes of 25 °C. Among the catalysts, the cobalt–nickel mixed‐oxide catalysts with an appropriate Co/Ni ratio exhibit a high catalytic performance for the lean methane combustion, with the catalyst having a Co/Ni molar ratio of 1:4 showing the highest catalytic activity (methane conversion reached 100 % at 425 °C). On the basis of TEM and XRD results, the nanoparticles of the catalysts have a suitable interparticle spacing and more crystal defects. X‐ray photoelectron spectroscopy (XPS) results reveal a high number of surface‐active oxygen species and appropriate aliovalent cobalt ion numbers in the catalysts for high catalytic activity. All these effects contribute to the outstanding performance of these catalysts in the combustion of lean methane at low temperatures.

Highly Active and Thermally Stable Supported Pd@SiO2 Core–Shell Catalyst for Catalytic Methane Combustion

AbstractA series of Pd‐based core–shell catalysts (Pd@SiO2, Pd@CeO2, and Pd@ZrO2) supported on Si‐modified Al2O3 were prepared for the catalytic combustion of lean methane. Pd@SiO2 exhibited slightly lower catalytic activity than Pd@CeO2 and higher catalytic activity than Pd@ZrO2 in dry conditions; however, Pd@SiO2 had the highest catalytic activity among the three catalysts in the presence of high concentrations of water vapor. Furthermore, the Pd@SiO2 catalyst showed good thermal stability and resistivity to water poisoning. CO chemisorption and TEM results demonstrated that the core–shell structure could help in the stabilization of the active phase compared to the uncoated Pd/Si‐Al2O3 catalyst. XRD and X‐ray photoelectron spectroscopy results indicated that a balanced mixed phase of PdOx/Pd0 is the main active phase of these Pd‐based catalysts.

Catalytic Combustion of Lean Methane at Low Temperature Over Palladium on a CoO x –SiO2 Composite Support

A composite support of CoO x –SiO2 was obtained through modifying silica with cobalt of different loadings; with CoO x –SiO2 as the support, a series of Pd/CoO x –SiO2 catalysts were prepared for the combustion of lean methane at low temperature. The effects of CoO loading and palladium precursor on the catalytic performance of Pd/CoO x –SiO2 were investigated. The Pd/CoO x –SiO2 catalyst containing 20 wt% CoO and 1 wt% Pd with acetate as palladium precursor performs excellently in lean methane combustion; over it a complete conversion of methane can be achieved at 420 °C and the activity does not show any decline in a long-term test of 120 h. Various characterizations suggested that cobalt species are highly dispersed on the silica of high surface area and there exists a synergetic interaction between palladium and cobalt species, which improves the redox properties of Pd/CoO x –SiO2 and contributes to the excellent catalytic performance in lean methane combustion. Silica modified with cobalt (CoO x –SiO2) is an idea support to prepare Pd/CoO x –SiO2 catalyst of high activity in lean methane combustion; over it a complete conversion of methane can be achieved at 420 °C and the conversion does not show any decline in a long-term test of 120 h.

Catalytic performance of MnOx–NiO composite oxide in lean methane combustion at low temperature

A series of MnOx–NiO composite oxide catalysts were prepared by co-precipitation method and used in the catalytic combustion of lean methane at low temperature. Compared with the corresponding single NiO and MnOx oxides, the MnOx–NiO composite oxide with proper composition exhibits much higher catalytic performance in the lean methane oxidation. XRD and HRTEM results demonstrate that MnOx–NiO is in the form of a Ni–Mn–O solid solution. XAFS and XPS results indicate that the content of manganese in MnOx–NiO has a significant influence on the oxidation state of manganese and the crystal defect of nickel oxide. MnOx–NiO catalyst with an atomic Mn/(Mn+Ni) ratio of 0.13 is provided with abundant highly dispersed manganese species of higher valence (Mn4+) and higher coordination number as well as certain nickel vacancies, due to the strong interaction between Ni and Mn species. H2-TPR and O2-TPD results show that the MnOx–NiO composite oxide exhibits better reducibility and oxygen mobility than NiO. All these characterizations suggest a prominent synergism between NiO and MnOx in the MnOx–NiO composite oxide, which contributes to its high performance in the lean methane combustion.