Catalytic Combustion Of Methane Research Articles

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.

Catalytic Combustion of Methane: From Mechanism and Materials Properties to Catalytic Performance

Catalytic Combustion of Methane: From Mechanism and Materials Properties to Catalytic Performance

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.

A facile approach to improve the methane catalytic performance of LaCoO3 perovskite

Some series of LaCoO3 perovskite metal oxide catalysts were modified with different molar amounts of transition metal Co and Fe, namely LaCoO3-xCo and LaCoO3-yFe. They were applied to methane catalytic combustion, and the effects of Co and Fe doping on the defect structure mechanism of LaCoO3 crystal growth and on the performance of methane catalytic combustion were investigated, respectively. The results showed that hydrothermal addition of Co and Fe could both significantly improved the performance of LaCoO3 catalyst for methane catalytic combustion, with the best catalytic methane activity at x=2 and y=7, the T50 was 425 ℃ and 397 ℃, the T90 was 480 ℃ and 457 ℃, respectively. The performance of the hydrothermally modified catalysts were investigated by characterization techniques such as BET, XRD, SEM and XPS, and it turned out that the excellent activity was mainly due to the significantly enhanced oxygen migration rate and the altered LaCoO3 crystal growth mechanism constructing surface defects during the hydrothermal process. In conclusion, this study provides an efficient and simple method for the synthesis of methane combustion catalysts.

Influence of carrier effect on Pd/Al2O3 for methane complete catalytic oxidation.

Pd/Al2O3 catalysts modified by different chemical elements (Mg, Si, Ce, and Zr) were tested for methane (CH4) catalytic combustion, and PdO nanoparticles loaded on modified Al2O3 were systematically studied. These conditions assess the carrier effects of Pd/Al2O3 and acid strength influences on CH4 combustion. We observed carrier effects on activation energy through tuning Pd 3d binding energies (BEs) and on pre-exponential factors (A) through Pd dispersion and acidity on supports. When the BE of Pd 3d5/2 is 337.3 eV, PdO nanoparticles loaded on modified Al2O3 have excellent activity in cracking the C−H bond of CH4, which leads to the lowest activation energy (E a ), regardless of the size effect of the PdO nanoparticle. Furthermore, a theoretical construction that acid sites on catalysts promote the reversible elementary step (2Pd−OH ↔ Pd−O* + Pd* + H2O) right shifts improving the A dependency on the quantity of exposed Pd* and Pd−O*. As a result, Al2O3, as the carrier, not only modifies the electronic characteristics and size of supported PdO nanoparticles but also participates in the reaction process via acid sites on the surface of Al2O3.

Recent progress of catalytic methane combustion over transition metal oxide catalysts.

Methane (CH4) is one of the cleanest fossil fuel resources and is playing an increasingly indispensable role in our way to carbon neutrality, by providing less carbon-intensive heat and electricity worldwide. On the other hand, the atmospheric concentration of CH4 has raced past 1,900 ppb in 2021, almost triple its pre-industrial levels. As a greenhouse gas at least 86 times as potent as carbon dioxide (CO2) over 20 years, CH4 is becoming a major threat to the global goal of deviating Earth temperature from the +2°C scenario. Consequently, all CH4-powered facilities must be strictly coupled with remediation plans for unburned CH4 in the exhaust to avoid further exacerbating the environmental stress, among which catalytic CH4 combustion (CMC) is one of the most effective strategies to solve this issue. Most current CMC catalysts are noble-metal-based owing to their outstanding C–H bond activation capability, while their high cost and poor thermal stability have driven the search for alternative options, among which transition metal oxide (TMO) catalysts have attracted extensive attention due to their Earth abundance, high thermal stability, variable oxidation states, rich acidic and basic sites, etc. To date, many TMO catalysts have shown comparable catalytic performance with that of noble metals, while their fundamental reaction mechanisms are explored to a much less extent and remain to be controversial, which hinders the further optimization of the TMO catalytic systems. Therefore, in this review, we provide a systematic compilation of the recent research advances in TMO-based CMC reactions, together with their detailed reaction mechanisms. We start with introducing the scientific fundamentals of the CMC reaction itself as well as the unique and desirable features of TMOs applied in CMC, followed by a detailed introduction of four different kinetic reaction models proposed for the reactions. Next, we categorize the TMOs of interests into single and hybrid systems, summarizing their specific morphology characterization, catalytic performance, kinetic properties, with special emphasis on the reaction mechanisms and interfacial properties. Finally, we conclude the review with a summary and outlook on the TMOs for practical CMC applications. In addition, we also further prospect the enormous potentials of TMOs in producing value-added chemicals beyond combustion, such as direct partial oxidation to methanol.

Aerosol-phase synthesis of bimetallic NiCu oxide-decorated CeO2 nanoparticle cluster for catalytic methane combustion

• Successful aerosol synthesis of NiCuOx@CeO2 for catalytic methane combustion. • Composition and crystalline of the hybrid nanostructure were tunable. • Superior catalytic activity (TOFCH4: 0.483 s −1 at 400 °C) was achievable. • Ni-preferred adsorption and dissociation of methane was rate-determining step. A raspberry-structured hybrid nanocatalyst composed of spherical NiCu bimetallic oxide nanoparticle decorated on ceria nanoparticle cluster (NiCuO x @CeO 2 ) was successfully synthesized via a gas-phase evaporation-induced self-assembly approach. Chemical composition and crystalline of the NiCuO x @CeO 2 were tunable during the gas-phase synthesis. The NiCuO x @CeO 2 demonstrates superior catalytic performance toward methane combustion, showing low light-off temperature (∼350 °C), high conversion ratio, high turnover frequency (0.483 s −1 at 400 °C) and sufficiently high 8-h operation stability were achievable by adjusting the composition of the catalysts. The results show that 1Ni0CuO x @CeO 2 (i.e., the sample without CuO) demonstrated the highest catalytic activity, implying adsorption and dissociation of CH 4 (i.e., preferably on NiO) was rate-determining step. Significant higher activity, especially under a low temperature range (<380 °C), was identified for the hybrid NiCuO x @CeO 2 samples under an oxygen-lean condition than in oxygen-rich condition, indicating the addition of CuO promoted redox ability of NiCuO x in the hybrid nanostructure. The stability was shown to be proportional to the ratio of NiO in the catalysts, indicating that increase of NiO amount was beneficial for thermal stability. The prototype study demonstrates the development of bimetallic-based hybrid nanostructured catalysts nanoparticle clusters. The mechanistic understanding developed in this study shows promise for the tuning of the abilities in methane dissociation versus its redox properties to achieve an optimal performance in methane-based energy applications.

Combined theoretical and experimental kinetic approach for methane conversion on model supported Pd/La0.7MnO3 NGV catalyst: Sensitivity to inlet gas composition and consequence on the Pd-support interface

New insights into reaction mechanism for catalytic methane combustion are provided in broad operating conditions on Pd/La0.7MnO3 as model natural gas vehicle catalyst. Under lean and dry conditions, a dual mechanism is suggested with active sites combining reactive oxygen species from La0.7MnO3 and palladium instead of single site reaction mechanism. Aging in wet atmosphere has no consequence on the kinetic behavior. On the other hand, in wet atmosphere near the stoichiometry, strong accumulation of hydroxyl groups on the support would suppress the metal-support interface. Accordingly, methane combustion would take place only on Pd particles.

Electronically Engineering Water Resistance in Methane Combustion with an Atomically Dispersed Tungsten on PdO Catalyst

Improving the low-temperature water-resistance of methane combustion catalysts is of importance for industrial applications and it is challenging. A stepwise strategy is presented for the preparation of atomically dispersed tungsten species at the catalytically active site (Pd nanoparticles). After an activation process, a Pd-O-W1 -like nanocompound is formed on the PdO surface with an atomic scale interface. The resulting supported catalyst has much better water resistance than the conventional catalysts for methane combustion. The integrated characterization results confirm that catalytic combustion of methane involves water, proceeding via a hydroperoxyl-promoted reaction mechanism on the catalyst surface. The results of density functional theory calculations indicate an upshift of the d-band center of palladium caused by electron transfer from atomically dispersed tungsten, which greatly facilitates the adsorption and activation of oxygen on the catalyst.

Electronically Engineering Water Resistance in Methane Combustion with an Atomically Dispersed Tungsten on PdO Catalyst

AbstractImproving the low‐temperature water‐resistance of methane combustion catalysts is of importance for industrial applications and it is challenging. A stepwise strategy is presented for the preparation of atomically dispersed tungsten species at the catalytically active site (Pd nanoparticles). After an activation process, a Pd−O−W1‐like nanocompound is formed on the PdO surface with an atomic scale interface. The resulting supported catalyst has much better water resistance than the conventional catalysts for methane combustion. The integrated characterization results confirm that catalytic combustion of methane involves water, proceeding via a hydroperoxyl‐promoted reaction mechanism on the catalyst surface. The results of density functional theory calculations indicate an upshift of the d‐band center of palladium caused by electron transfer from atomically dispersed tungsten, which greatly facilitates the adsorption and activation of oxygen on the catalyst.

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.

Mechanistic understanding of methane combustion over H-SSZ-13 zeolite encapsulated palladium nanocluster catalysts

Catalytic methane (CH4) combustion to CO2 and H2O is of great practical significance and an important prototype catalytic reaction. Extensive experimental studies have suggested that zeolite supported palladium (Pd) catalysts are very active for catalytic CH4 oxidation, while the structure-performance relationship is still not clear. Herein, using H-SSZ-13 zeolite encapsulated Pd nanoclusters as a demonstration case, reaction mechanisms and kinetics of complete CH4 combustion were systematically investigated using first-principles density functional theory (DFT) calculations combined with atomistic thermodynamic analysis and the energetic span model (ESM). Four H-SSZ-13 zeolite encapsulated PdⅡxOmHn model catalysts, i.e., PdⅡ/H-SSZ-13, PdⅡO/H-SSZ-13, PdⅡ2O/H-SSZ-13, and PdⅡ3O3H/H-SSZ-13 were studied. The encapsulated [PdⅡ2O]2+ and [PdⅡ3O3H]+ nanoclusters were identified as the most stable binuclear and trinuclear Pd structures under experimental oxidative conditions. DFT calculations indicated that the most kinetically relevant step in the complete CH4 oxidation reaction over four Pd model catalysts is different. The first, third, third, and fourth C–H bond cleavage were identified as the most kinetically relevant steps over PdⅡ/H-SSZ-13, PdⅡO/H-SSZ-13, PdⅡ2O/H-SSZ-13, and PdⅡ3O3H/H-SSZ-13, respectively. Using the energetic span model, the relative turnover frequencies of CH4 oxidation over four PdⅡxOmHn/H-SSZ-13 model catalysts were calculated. Consistent with recent experimental observation, the encapsulated PdⅡ3O3H/H-SSZ-13 nanocluster was found to be the most active catalyst for complete CH4 oxidation. On the basis of DFT results and the ESM model analysis, it is noted that the reaction rate of complete CH4 oxidation over the PdⅡxOmHn/H-SSZ-13 catalysts is not completely dependent on one “highest” activation barrier, i.e., the barrier for the most kinetically relevant step. Neither one specific transition state nor one reaction step carried all the kinetics information that determines the catalytic performance of the PdⅡxOmHn/H-SSZ-13 catalysts. The present work sheds light on the structure-performance relationship for CH4 combustion over the zeolite supported noble metal catalysts.

Nickel Hydroxide Nanosheets Prepared by a Direct Manual Grinding Strategy for High-Efficiency Catalytic Combustion of Methane.

Nickel hydroxide nanosheets were prepared by a very simple direct manual grinding strategy and then calcined at 200, 300, 400, and 500°. The synthesized samples were tested in lean methane (1.0% CH4, air balanced) catalytic combustion and subjected to a series of physical and chemical characterizations. The sample calcined at 200 °C (Ni(OH)2-200) presented a typical nanosheet structure and the best methane catalytic activity in all the samples, which can completely catalyze methane at 400 °C. The crystal structure changed from β-Ni(OH)2 to NiO at a calcination temperature of 300 °C. The β-Ni(OH)2 nanosheets began to partially agglomerate into nanoparticles at 400 °C and almost transformed into nanoparticles at 500 °C. Interestingly, the original nanosheet samples Ni(OH)2-200 and NiO-300 still maintained their morphology and structure although they all went through an activity test at 500 °C in a 1.0% CH4 atmosphere, which proves that the calcination of nanosheets in a CH4 atmosphere tended to maintain their nanosheet morphology compared with calcination in the air. Furthermore, through the activity test, X-ray photoelectron spectroscopy results, TPx, and in situ DRIFTS characterization, it was proved that the hydroxyl groups on the Ni(OH)2-200 and NiO nanosheets were beneficial to the dissociation of methane on the catalyst surface, and the nanosheet structure was also prone to generating more active adsorbed oxygen, so the activation energy of methane was lowered. A methane catalytic mechanism on the Ni(OH)2 nanosheets and NiO nanoparticles was proposed, which further proved the key role of hydroxyl groups in methane combustion.

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.

Effects of deep eutectic solvent on Cu-Mn-C-O composite catalysts: Surface species, physical and chemical properties in methane combustion

A series of Cu-Mn-C-O composite catalysts for low-temperature catalytic combustion of methane were successfully prepared by synthetic induction of CuMn2O4 precursors via hydrothermal method which used deep eutectic solvent (DES) as an inducer. The structure and properties of the catalyst were investigated by XRD, BET, XPS and SEM characterizations to investigate the effect of DES addition on the crystal growth of the catalyst. The results showed that the Cu-Mn-C-O composite catalyst produced a new phase of MnCO3, which changed the number and distribution of acid-base sites on the catalyst surface and effectively promoted the desorption of catalytic reaction products. The catalytic activity test showed that the methane catalytic activity of the Cu-Mn-C-O composite catalyst was significantly enhanced at Mn/C molar ratio of 1:2.5, with T50 and T90 values of 365 °C and 425 °C, respectively. This can be attributed to the high proportional distribution of high-valent manganese in the internal electronic structure of the composite catalyst system, which generated a large number of surface adsorbed oxygen species and thus facilitated the oxidation of methane at lower temperatures. Thermal analysis of composite catalysts revealed relatively high activation energy and thermal stability in the combustion process of composite catalysts. This study will lead to innovative insights into the design of composite catalysts for methane oxidation.

Numerical Simulation Analysis of Heating Effect of Downhole Methane Catalytic Combustion Heater under High Pressure

The hot exhaust gas generated by a downhole combustion heater directly heats the formation, which can avoid the heat loss caused by the injection of high-temperature fluid on the ground. However, if the temperature of the exhaust gas is too high, it may lead to the carbonization of organic matter in the formation, which is not conducive to oil production. This paper proposes the use of low-temperature catalytic combustion of a mixture of methane and air to produce a suitable exhaust gas temperature. The simulation studies the influence of different parameters on the catalytic combustion characteristics of methane and the influence of downhole high-pressure conditions. The results show that under high-pressure conditions, using a smaller concentration of methane (4%) for catalytic combustion can obtain a higher conversion efficiency (88.75%), and the exhaust temperature is 1097 K. It is found that the high-pressure conditions in the well can promote the catalytic combustion process of the heater, which proves the feasibility of the downhole combustion heater for in situ heating of unconventional oil and gas reservoirs.

Catalytic combustion of methane over Ni modified Pd/Al2O3 catalysts

New data on the catalytic combustion of methane on Ni modified Pd/Al2O3 catalysts were obtained. NiAl2O4 spinel phase, not well definite Ni-Al phases, reducible at lower temperatures as well as finely dispersed NiO are formed on the surface after Ni deposition. When Pd is loaded on alumina modified with up to 5% Ni, the finely divided not well stabilized PdO particles are formed. PdO strongly interacting with surface is formed in Pd + 10% Ni/Al2O3. All three oxidation states Pd0, Pd2+ and Pd4+ are registered on the surface of the studied catalysts. The observed close catalytic activity of all nickel-modified catalysts is explained by the similar surface palladium concentration, which indicates that increasing the nickel content does not lead to a significant improvement in catalytic activity.

Ultra-Lean Catalytic Combustion of Methane on Platinum Catalysts

Ultra-Lean Catalytic Combustion of Methane on Platinum Catalysts

Synergy effect of CuO on CuCo2O4 for methane catalytic combustion.

Spinel oxides (AB2O4) have been widely studied as catalysts for methane combustion. Increasing attention was focused on the catalysis properties of the [B2O3] octahedron; however, the role of the [AO] tetrahedron in the catalytic activity was seldom discussed. Herein, a series of (CuO)x–CuCo2O4 (x = 0, 0.1, 0.2) composite oxides were synthesized by a solvothermal method. The structure, morphology, and physicochemical properties of the as-synthesized samples were characterized by the XRD, SEM, BET, and XPS techniques. The results of the catalytic activity tests showed that the coexistence of CuO with CuCo2O4 can improve the catalytic activity. The XPS results demonstrated that there were remarkable Cu+ ions present in the composite oxides, which can cause increases in the number of oxygen vacancies on the surface of the catalysts. In addition, the redox of Cu+ and Cu2+ may improve the oxygen exchange capacity for methane oxidation.

Preparation and evaluation of A/ BaO‐MnO x catalysts (A: Rh, Pt, Pd, Ru) in lean methane catalytic combustion at low temperature

Lean methane catalytic combustion was studied over various noble metal catalysts supported on 10 wt% BaO-MnOx (BM), and the results demonstrated that the Rh/BM catalyst could present a dramatic change in the light-off temperature. The influence of the Rh loadings on the physicochemical features and catalytic activity and stability in CH4 combustion was evaluated in detail. The performance of the catalyst was evaluated using the temperatures (T50% and T90%) required for achieving methane conversion of 50% and 90%. The 1 wt% Rh/BM catalyst possessed the best performance with T50% = 279°C and T90% = 350°C and the light-off temperature of the 1wt%Rh/BM catalyst was about 50°C lower than that obtained for the 10wt% BaO-MnOx. The results indicated that the 1 wt% Rh/BM exhibited high stability even in the presence of various concentrations of CO2 and water vapor. Moreover, the influence of processing conditions such as pretreatment atmospheres, GHSV, and feed ratio was examined on the CH4 conversion. The 1 wt% Rh/BM catalyst was also utilized in the CO oxidation process, and the results presented a high activity at low temperature.