Catalytic Activity For Methane Combustion Research Articles

Boosting catalytic activity of Pd/LaxCe1-xMnO3 catalysts in methane combustion by a plasma-treated strategy

An innovative plasma-treated strategy was employed to prepare LaxCe1-xMnO3 (LCMO) perovskite oxides. Pd nanoparticles were loaded onto plasma-treated (P) and air-calcined (T) LCMO respectively, forming the corresponding Pd/LCMO catalysts. The results indicated that the introduction of Pd and plasma treatment largely boost the catalytic activity in methane combustion. Among these catalysts, the Pd/LCMO-P catalyst shows the best performance in CH4 oxidation, giving T90 of 425 °C. It was revealed that the morphology structure and surface defects were strongly affected by plasma treatment, further affecting the dispersion and chemical state of Pd species via surface interaction. The superior performance should be ascribed to the good redox properties (high Mn4+/Mn3+ ratio), rich surface-active oxygen species, and enhanced oxygen mobility (weakened Pd-O and Mn-O chemical bonds). Besides, the distributions of cerium in the surface and crystal lattice of LMO also improved metal-support interaction and the oxygen mobility, that boosted CH4 oxidation. This plasma-treated strategy provided an effective path to develop the efficient combustion catalyst for superior performance.

Transition Metal-Promoted LDH-Derived CoCeMgAlO Mixed Oxides as Active Catalysts for Methane Total Oxidation

A series of M(x)CoCeMgAlO mixed oxides with different transition metals (M = Cu, Fe, Mn, and Ni) with an M content x = 3 at. %, and another series of Fe(x)CoCeMgAlO mixed oxides with Fe contents x ranging from 1 to 9 at. % with respect to cations, while keeping constant in both cases 40 at. % Co, 10 at. % Ce and Mg/Al atomic ratio of 3 were prepared via thermal decomposition at 750 °C in air of their corresponding layered double hydroxide (LDH) precursors obtained by coprecipitation. They were tested in a fixed bed reactor for complete methane oxidation with a gas feed of 1 vol.% methane in air to evaluate their catalytic performance. The physico-structural properties of the mixed oxide samples were investigated with several techniques, such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), elemental mappings, inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction under hydrogen (H2-TPR) and nitrogen adsorption–desorption at −196 °C. XRD analysis revealed in all the samples the presence of Co3O4 crystallites together with periclase-like and CeO2 phases, with no separate M-based oxide phase. All the cations were distributed homogeneously, as suggested by EDX measurements and elemental mappings of the samples. The metal contents, determined by EDX and ICP-OES, were in accordance with the theoretical values set for the catalysts’ preparation. The redox properties studied by H2-TPR, along with the surface composition determined by XPS, provided information to elucidate the catalytic combustion properties of the studied mixed oxide materials. The methane combustion tests showed that all the M-promoted CoCeMgAlO mixed oxides were more active than the M-free counterpart, the highest promoting effect being observed for Fe as the doping transition metal. The Fe(x)CoCeMgAlO mixed oxide sample, with x = 3 at. % Fe displayed the highest catalytic activity for methane combustion with a temperature corresponding to 50% methane conversion, T50, of 489 °C, which is ca. 40 °C lower than that of the unpromoted catalyst. This was attributed to its superior redox properties and lowest activation energy among the studied catalysts, likely due to a Fe–Co–Ce synergistic interaction. In addition, long-term tests of Fe(3)CoCeMgAlO mixed oxide were performed, showing good stability over 60 h on-stream. On the other hand, the addition of water vapors in the feed led to textural and structural changes in the Fe(3)CoCeMgAlO system, affecting its catalytic performance in methane complete oxidation. At the same time, the catalyst showed relatively good recovery of its catalytic activity as soon as the water vapors were removed from the feed.

Promoting effect and kinetic analysis of Fe-Co bimetallic doping on the LaMnO3 catalytic activity for methane combustion

To enhance the catalyst’s properties, a modified sol–gel method is developed in this study, and a unique perovskite catalyst, LaMnxFeyCo1-x-yO3, is successfully synthesized by doping Fe-Co into the lattice of LaMnO3. The catalytic activity of the synthesized catalysts is initially determined by applying them to methane oxidation. Then, the structural, chemical, and surface properties of these catalysts are systematically evaluated utilizing XRD, BET, O2-TPD, H2-TPR, SEM, and XPS analyses. The modified LaMn0.8Fe0.15Co0.05O3 is shown to exhibit excellent activity (T90 at 486.5 ℃) in methane catalytic combustion, comparable to several standard noble metal materials. Experimental findings indicate that such perovskite structures have a larger specific surface area, an elevated molar ratio of Mn4+, desirable low-temperature reducibility, and excellent oxygen mobility relative to the original LaMnO3. Meanwhile, more efficient electron transfer from Mn4+/Mn3+ redox cycles, as well as the emergence of oxygen defects, significantly contribute to the robust interaction between Fe-Co and LaMnO3. Further reaction kinetic analysis is conducted to determine changes in species components and identify possible catalytic pathways. Notably, Fe-Co co-doping leads to an improvement in the increase of lattice oxygen and CH4 adsorption. In addition, the MVK kinetic mechanism governs methane combustion over LaMn0.8Fe0.15Co0.05O3. This study provides new insights into enhancing energy conversion performance and efficient utilization of ventilation air methane (VAM) through the implementation of highly efficient perovskites.

Atomic-Scale 3D Structure of a Supported Pd Nanoparticle Revealed by Electron Tomography with Convolution Neural Network-Based Image Inpainting.

Electron tomography based on scanning transmission electron microscopy (STEM) is used to analyze 3D structures of metal nanoparticles on the atomic scale. However, in the case of supported metal nanoparticle catalysts, the supporting material may interfere with the 3D reconstruction of metal nanoparticles. In this study, a deep learning-based image inpainting method is applied to high-angle annular dark field (HAADF)-STEM images of a supported metal nanoparticle to predict and remove the background image of the support. The inpainting method can separate an 11nm Pd nanoparticle from the θ-Al2O3 support in HAADF-STEM images of the θ-Al2O3-supported Pd catalyst. 3D reconstruction of the extracted images of the Pd nanoparticle reveals that the Pd nanoparticle adopts a deformed structure of the cuboctahedron model particle, resulting in high index surfaces, which account for the high catalytic activity for methane combustion. Using the xyz coordinate of each Pd atom, the local Pd-Pd bond distance and its variance in a real supported Pd nanoparticle are visualized, showing large strain and disorder at the Pd-Al2O3 interface. The results demonstrate that 3D atomic-scale analysis enables atomic structure-based understanding and design of supported metal catalysts.

Comparative Study of Commercial Silica and Sol-Gel-Derived Porous Silica from Cornhusk for Low-Temperature Catalytic Methane Combustion.

The synthesis and characterization of sol-gel-derived cornhusk support for low-temperature catalytic methane combustion (LTCMC) were investigated in this study. The prepared cornhusk support was impregnated with palladium and cerium oxide (Pd/CeO2) via the classical incipient wetness method. The resulting catalyst was characterized using various techniques, including X-ray diffraction (XRD), N2 physisorption (BET), transmission electron microscopy (TEM), and hydrogen temperature-programmed reduction (H2-TPR). The catalytic performance of the Pd/CeO2/CHSiO2 catalyst was evaluated for methane combustion in the temperature range of 150-600 °C using a temperature-controlled catalytic flow reactor, and its performance was compared with a commercial catalyst. The results showed that the Pd/CeO2 dispersed on SiO2 from the cornhusk ash support (Pd/CeO2/CHSiO2) catalyst exhibited excellent catalytic activity for methane combustion, with a conversion of 50% at 394 °C compared with 593 °C for the commercial silica catalyst (Pd/CeO2/commercial). Moreover, the Pd/CeO2/CHSiO2 catalyst displayed better catalytic stability after 10 h on stream, with a 7% marginal loss in catalytic activity compared with 11% recorded for the Pd/CeO2/commercial catalyst. The N2 physisorption and H2-TPR results indicated that the cornhusk SiO2 support possessed a higher surface area and strong reducibility than the synthesized commercial catalyst, contributing to the enhanced catalytic activity of the Pd/CeO2/SiO2 catalyst. Overall, the SiO2 generated from cornhusk ash exhibited promising potential as a low-cost and environmentally friendly support for LTCMC catalysts.

Multicationic LDH-derived Co(x)CeMgAlO mixed oxide catalysts for the total oxidation of methane

Several Co(x)CeMgAlO mixed oxides with different cobalt contents x between 7 and 50 at% with respect to cations, but with fixed 10 at% Ce and Mg/Al atomic ratio of 3, were obtained by the calcination of layered double hydroxide (LDH) precursors at 750 °C. The mixed oxide catalysts were characterized by XRD, nitrogen adsorption, DRIFT, DR-UV-Vis, SEM-EDX, including elemental mapping, XPS, H2-TPR and O2-TPO techniques. XRD analysis indicated the coexistence of Co3O4 crystallites with periclase-like and ceria phases, distributed homogeneously as shown by EDX measurements. The surface composition determined by XPS and the redox properties studied by H2-TPR and O2-TPO were shown to be key factors controlling the catalytic behavior of the investigated materials. Their catalytic performance was evaluated in the total oxidation of methane, used as a volatile organic compound (VOC) model molecule. Co(40)CeMgAlO mixed oxide showed the highest catalytic activity for methane combustion with a T50 of 528 °C, associated with its greatest Co/Ce surface atomic ratio and the best redox properties in the Co(x)CeMgAlO series. In addition, the influence of the contact time on the catalytic activity of the Co(40)CeMgAlO mixed oxide has been examined and its good stability was evidenced from combustion tests with prolonged time on stream. Nevertheless, the addition of water vapors to the reaction mixture induces textural and structural changes of the mixed oxide with negative consequences on its performance.

The effect of cobalt ions doping in ZnCr2O4 spinel oxide for the catalytic activity of methane combustion

The effect of cobalt ions doping in ZnCr2O4 spinel oxide for the catalytic activity of methane combustion

Co3+–O Bond Elongation Unlocks Co3O4 for Methane Activation under Ambient Conditions

The pursuit of low-temperature methane activation is a paramount challenge for heterogeneous catalysis because of the high stability of the C–H bonds (435 kJ mol–1). Very few catalysts fulfill this through either constructing complex interfaces or using special noble metal oxides. Bond length, which is highly temperature-sensitive, has long been ignored in catalyst studies. Here, we exploit a bond-length elongation strategy to unlock a nonprecious metal oxide for dissociating methane at normal temperature and pressure. Mesoporous bubblelike Co3O4 with elongated Co3+–O bonds, synthesized through a unique “melting–foaming–solidifying” route, is found to activate methane at room temperature to form COx species on the very surface revealed by temperature-programmed reaction spectroscopy experiments. A combination of experimental and theoretical methods suggests that the elongated Co3+–O bonds contribute to the greatly enhanced methane adsorption, in contrast to the weak adsorption of methane on conventional nonprecious metal oxides. Accordingly, the activation energy for the C–H bond cleavage is smaller than that for methane desorption, which finally leads to the low-temperature methane activation. The simultaneous enhancement in intrinsic activity and mass transfer endows mesoporous bubblelike Co3O4 with excellent catalytic activity for methane combustion, where the complete conversion temperature is much below that over the conventional Co3O4 nanocatalysts.

Design of structured reactor for biogas exhaust abatement

The post-combustion of methane from stationary sources such as powerplants at biogas installations is an important issue for scientists to address due to the quantities of methane released into the atmosphere. Methane is one of the greenhouse gases, thus its emission should be reduced. Here is shown a converter module designed for methane combustion for use independently or in a two-module reactor together with a deNOx module. The reactor unit is based on short-channel structures in the form of metallic wires immobilised with a mixed CoPd catalyst supported on gamma alumina. The structured reactor packing was characterised by spectroscopic and spectrometric methods in terms of qualitative and quantitative composition (UV–Vis, EDX, AAS), and the morphology by SEM microscopic techniques was determined. The reactor has been successfully investigated in the catalytic reaction of methane combustion from exhaust gas in the one-step methane removal and in the presence of NH3 used in the deNOx process. The results revealed high catalytic activity of methane combustion in both cases, with the catalyst’s mechanical resistance maintained. Therefore, the presented catalytic reactor is a good candidate for methane combustion in cogeneration with nitrogen oxide reduction in installations of stationary sources such as small powerplants.

Superior catalytic activity of Pd-based catalysts upon tuning the structure of the ceria-zirconia support for methane combustion

Pd-based catalysts supported on CeO2-ZrO2 (CZ) mixed oxides have been universally applied toward the oxidation of methane, a strong greenhouse gas. Herein, CZ supports of different structures were prepared using hydrothermal (ST-CZ), co-precipitation (CP-CZ), and physical mixing (Mix-CZ) methods. Subsequently, the effects of the CZ support structure on the catalytic activity of the resulting Pd/CZ catalysts toward methane combustion were evaluated. ST-CZ shows the presence of cubic and tetragonal phases of CZ solid solutions, while CP-CZ is a pure tetragonal-phase solid solution and Mix-CZ is a mixture of CeO2 and ZrO2. The CZ solid solution improved the Pd dispersion and Pd2+/Pd ratio on the catalyst surface. Furthermore, CZ oxides with a two-phase composite structure resulted in higher oxygen storage capacity and oxygen mobility in the Pd/CZ catalysts than in the pure solid solution phase. Therefore, the Pd/ST-CZ catalyst shows superior catalytic activity for methane combustion than the other two catalysts.

Enhanced Catalytic Activity for Methane Combustion through in Situ Water Sorption

Although palladium-based materials are efficient catalysts for methane combustion, H2O-poisoning remains a significant problem at low operating temperatures (<450 °C). It is a significant research ...

A facile synthesis of CuCe and CuCeFe mixed-oxide catalysts by solution combustion method for catalytic methane combustion

In this research, the solution combustion method was used to synthesize non-noble catalysts including copper-cerium (CuCe) and copper-cerium-iron (CuCeFe) mixed-oxides for catalytic combustion of methane. The effects of Cu contents (5, 10 and 15 wt%) and Fe addition were investigated. The synthesized catalysts were characterized by XRD, N2-physisorption, and H2-TPR. The results showed that increasing Cu content exceeds 10 wt% for a series of CuCe catalyst, leading to a collapse textural structure and formation of larger CuO phase. It resulted in the substantial drop of the catalytic activity for methane combustion. Furthermore, incorporation of Fe into Cu-Ce mixed oxides causes the formation of Fe2O3 and Ce-Fe-O solid solution, stabilizing the textural properties, enhancing the oxygen vacancies and oxygen mobility. The superior catalyst was 15CuCeFe because it revealed the highest methane conversion at 500 °C and relatively high conversion at a lower temperature. It can be seen that solution combustion is a facile method to prepare the mixed-oxide catalysts and incorporating the metal promoters. The Cu, Ce and Fe metals play a significant role in catalytic methane combustion not only enhancing reactants (methane and oxygen) activation but also improving the physical properties.

Precise fabrication of surface-reconstructed LaMnO3 perovskite with enhanced catalytic performance in CH4 oxidation

In this study, MnOx/LaMnO3 catalyst (LMO) was successfully synthesized through a selectively etched method, wherein MnOx was in-situ formed on the surface of LaMnO3. The modified LMO catalysts possessed the large specific surface area, high molar ratios of Mn4+/(Mn4++Mn3+), and outstanding low-temperature reducibility. Moreover, the more efficient electron transfer from Mn3+/Mn4+ redox cycles and O2 ⇔ OL due to the generation of oxygen defects contributed to the strong interaction between MnOx and LaMnO3. Among all LMO catalysts, the LMO-4 (etched 40 min) catalyst exhibited the excellent activity (T90 at 448 °C), stability and optimum endurability in methane catalytic combustion (5 vol% water) during the steady state of 100 h, which could be greatly assigned to its larger specific surface area, superior low temperature reducibility, the highest molar ratio Mn4+ and better oxygen mobility. The lowest apparent activation energy (Ea) of LMO-4 catalyst (61.8 kJ/mol) was in good accordance with its optimum catalytic activity for methane combustion.

Ultrafine PdOx nanoparticles on spinel oxides by galvanic displacement for catalytic combustion of methane

The excellent catalytic activity of methane combustion over the Pd/NiCo2O4 is attributed to ultrafine Pd nanopariticles and a tight Pd-spinel interface obtained by galvanic displacement.

The effect of active oxygen species in nano-ZnCr2O4 spinel oxides for methane catalytic combustion

The nano-ZnCr2O4 spinel oxides was synthesized by a ethylene glycol mediated solvothermal method. Catalytic combustion of methane test showed that an excellent activity over nano-ZnCr2O4 with T10% = 300 °C and T90% = 400 °C. The results of X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption-desorption measurements (BET) indicated that a uniform nano-ZnCr2O4 spinel oxides particles with the high surface area (96.2 m2 g−1) was successfully synthesized. Oxygen temperature programmed desorption (O2-TPD) profile revealed there were two obvious desorption of oxygen species from nano-ZnCr2O4 in the range of 300–400 °C and 500–700 °C. It was clear that the desorption temperature range of the first oxygen species coincided with the methane catalytic combustion temperature. X-ray photoelectron spectroscopy (XPS) analysis exhibited that Cr6+ was present in the lattice of ZnCr2O4 apart from Cr3+. High valence cations of chromium in crystal lattice probable caused the presence of interstitial oxygen species in the structure to maintain the electroneutrality. Additionally, Raman spectra proved that there is the interstitial oxygen species in the crystal lattice of ZnCr2O4. Therefore, the excellent catalytic activity for methane combustion was contributed to the flexible interstitial oxygen in the ZnCr2O4.

The relationship between the chemical state of Pd species and the catalytic activity for methane combustion on Pd/CeO2

Three Pd/CeO2 catalysts are synthesized by reduction-deposition and an impregnation method (IMP) to clarify how the chemical state of Pd influences the catalytic performance for CH4 combustion.

Complete combustion of methane over Co3O4 catalysts: Influence of pH values

A series of Co3O4 catalysts were prepared at different pH values via a facile precipitation method and their catalytic performances were evaluated for complete methane combustion. The catalysts were characterized by various techniques such as BET, XRD, SEM, XPS, Raman, H2-TPR and NH3-TPD. It is observed that the pH values in the process of preparation significantly influenced the catalytic activity and long-term stability and the Co3O4-9.0 catalyst showed the best performance. The influence of pH values in the methane combustion activity was discussed on basis of the microstructure, surface and reduction properties of catalysts. The superior performance of Co3O4-9.0 catalyst would origin from the higher ratios of ATetrahedral/AOctahedral and Oads/Olatt, although it has the smallest surface area and biggest crystalline size. That is to say, the tetrahedral sites Co2+ concentration and surface active oxygen species play a decisive role for the catalytic activity of methane combustion.

Three-dimensionally ordered macroporous LaMnAl11O19-supported Pd nanocatalysts highly active for methane combustion

Three-dimensionally ordered macroporous (3DOM) LaMnAl11O19 and 0.97wt% Pd/3DOM LaMnAl11O19 samples with a good-quality 3DOM structure have been prepared using the poly(methyl methacrylate) (PMMA)-templating and polyvinyl alcohol (PVA)-protected reduction methods, respectively. The Pd nanoparticles (NPs) with a size of 2–5nm were uniformly dispersed on the macropore wall surface of 3DOM LaMnAl11O19. Due to the highest adsorbed oxygen species concentration and the best low-temperature reducibility, the 0.97wt% Pd/3DOM LaMnAl11O19 sample showed the best catalytic activity for methane combustion, with the reaction temperatures (T10%, T50%, and T90%) required for achieving methane conversions of 10, 50, and 90% being 259, 308, and 343°C at SV=20,000mL/(gh), respectively. The 0.97wt% Pd/3DOM LaMnAl11O19 catalyst was catalytically stable, whereas the 0.98wt% Pd/3DOM Mn2O3 sample was partially deactivated after 50h of methane oxidation. The introduction of 3.0vol% H2O or 2.0 vol% CO2 to the reaction system resulted in the reversible deactivation of 0.97wt% Pd/3DOM LaMnAl11O19, but the addition of 100ppm SO2 led to the irreversible deactivation of the catalyst. It is concluded that the good-quality 3DOM structure, uniformly dispersed Pd NPs, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Pd NPs and 3DOM LaMnAl11O19 were accountable for the good catalytic performance of 0.97wt% Pd/3DOM LaMnAl11O19.

Catalytic performance enhancement by alloying Pd with Pt on ordered mesoporous manganese oxide for methane combustion

Ordered mesoporous Mn2O3 (meso-Mn2O3) and meso-Mn2O3-supported Pd, Pt, and Pd-Pt alloy x(PdyPt)/meso-Mn2O3; x = (0.10−1.50) wt%; Pd/Pt molar ratio (y) = 4.9−5.1 nanocatalysts were prepared using KIT-6-templated and poly(vinyl alcohol)-protected reduction methods, respectively. The meso-Mn2O3 had a high surface area, i.e., 106 m2/g, and a cubic crystal structure. Noble-metal nanoparticles (NPs) of size 2.1−2.8 nm were uniformly dispersed on the meso-Mn2O3 surfaces. Alloying Pd with Pt enhanced the catalytic activity in methane combustion; 1.41(Pd5.1Pt)/meso-Mn2O3 gave the best performance; T10%, T50%, and T90% (the temperatures required for achieving methane conversions of 10%, 50%, and 90%) were 265, 345, and 425 °C, respectively, at a space velocity of 20000 mL/(g·h). The effects of SO2, CO2, H2O, and NO on methane combustion over 1.41(Pd5.1Pt)/meso-Mn2O3 were also examined. We conclude that the good catalytic performance of 1.41(Pd5.1Pt)/meso-Mn2O3 is associated with its high-quality porous structure, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interactions between Pd-Pt alloy NPs and the meso-Mn2O3 support.

Ordered mesoporous MCo2O4 (M = Cu, Zn and Ni) spinel catalysts with high catalytic performance for methane combustion

Ordered mesoporous MCo2O4 (M=Cu, Zn and Ni) spinel catalysts were synthesized via nano-replication method using mesoporous silica KIT-6 as the hard template. They were applied to methane combustion, in comparison with bulk MCo2O4 spinel catalysts prepared by co-precipitation method. A combined N2 adsorption-desorption, XRD and TEM results clearly confirm that mesoporous MCo2O4 (m-MCo2O4) spinel catalysts contain ordered mesostructure, resulting in the higher BET surface area and pore volume than bulk ones (b-MCo2O4). Moreover, the former catalysts demonstrate the better thermal stability as indicated by larger amount of MCo2O4 phase and smaller size of crystallite domain after calcination at 550°C. Therefore, such excellent properties rationalize that the m-MCo2O4 spinel catalysts reveal higher catalytic activity for methane combustion than bulk counterparts. When it comes to the catalytic performance of the meso catalysts for methane combustion, the m-CuCo2O4 spinel catalyst has superior performance, which is related to the high normalized amount of Co3+ cations on the surface, as evidenced by XPS.