Special Issue "Catalytic Oxidation of Methane"

A special issue of Catalysts (ISSN 2073-4344). This special issue belongs to the section "Environmental Catalysis".

Deadline for manuscript submissions: closed (30 November 2018)

Special Issue Editor

Guest Editor
Prof. Dr. Anil Banerjee

Department of Chemistry, Columbus State University, Columbus, GA 31909, USA
Website | E-Mail
Interests: heterogeneous catalysis; low temperature catalytic oxidation of methane and carbon monoxide; kinetics and mechanism; surface science; identification of surface species by XPS; storage of hydrogen as automobile fuel

Special Issue Information

Dear Colleagues,

Catalytic oxidation of methane is an important area for both academic research and industrial applications. Methane (the major component of natural gas) is one of the main energy sources for gas-powered turbines for power generation, and transport vehicles (using compressed natural gas). Methane is 84 times more potent than carbon dioxide as a green house gas and is emitted from power generation, diesel and compressed natural gas engines, gas wells, etc. The three-way catalytic converters work well at higher temeperatures (above 600 °C) and are not very effective for lean-burn engines and during “idling”. A good amount of research has been reported in the literature on catalytic combustion of methane producing carbon dioxide and water. However, even after 40–50 years of research in this area, the search is still on for low-temperature catalysts that would oxidize methane below 350 °C and hopefully at atmospheric temperature. Some of the perenial issues like catalyst deactivation, stabilty, sintering etc., would require more research. In recent years, some advances have been made to develop low-tempearture catalysts and encapsulate catalysts to minimize deactivation by water and other sources. This special issue will focus on the science and enginnering of development of low-temperature catalysts (below 350 °C) for catalytic combustion of methane to carbon dioxde and water. Contributions on research and development in the following areas are welcome:

(a) Development of low-tempertaure catalysts and processes for methane combustion.
(b) Kinetics and mechanism of catalytic combustion of methane at low temperatures.
(c) Processes/methods to stop or minimize catalyst deactivation and sintering.
(d) Identification of surface species before/during/after catalytic combustion by XPS and other surface techniques.

Prof. Dr. Anil Banerjee
Guest Editor

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Keywords

  • low temperature catalytic combustion of methane
  • kinetics and mechanism
  • heterogeneous and homogeneous catalysis
  • automotive catalysts
  • diesel-engine catalysts
  • lab and or bench -scale process development
  • identification of surface species
  • surface science
  • deactivation
  • sintering

Published Papers (8 papers)

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Research

Open AccessArticle
Comparative Study of the Characteristics and Activities of Pd/γ-Al2O3 Catalysts Prepared by Vortex and Incipient Wetness Methods
Catalysts 2019, 9(4), 336; https://doi.org/10.3390/catal9040336
Received: 19 February 2019 / Revised: 30 March 2019 / Accepted: 1 April 2019 / Published: 4 April 2019
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Abstract
5 wt% Pd/γ-Al2O3 catalysts were prepared by a modified Vortex Method (5-Pd-VM) and Incipient Wetness Method (5-Pd-IWM), and characterized by various techniques (Inductively coupled plasma atomic emission spectroscopy (ICP-AES), N2-physisorption, pulse CO chemisorption, temperature programmed reduction (TPR), X-ray [...] Read more.
5 wt% Pd/γ-Al2O3 catalysts were prepared by a modified Vortex Method (5-Pd-VM) and Incipient Wetness Method (5-Pd-IWM), and characterized by various techniques (Inductively coupled plasma atomic emission spectroscopy (ICP-AES), N2-physisorption, pulse CO chemisorption, temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and X-ray diffraction (XRD)) under identical conditions. Both catalysts had similar particle sizes and dispersions; the 5-Pd-VM catalyst had 0.5 wt% more Pd loading (4.6 wt%). The surfaces of both catalysts contained PdO and PdOx with about 7% more PdOx in 5-Pd-VM. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and scanning electron microscope (SEM) images indicated presence of PdO/PdOx nanocrystals (8–10 nm) on the surface of the support. Size distribution by STEM showed presence of smaller nanoparticles (2–5 nm) in 5-Pd-VM. This catalyst was more active in the lower temperature range of 275–325 °C and converted 90% methane at 325 °C. The 5-Pd-VM catalyst was also very stable after 72-hour stability test at 350 °C showing 100% methane conversion, and was relatively resistant to steam deactivation. Hydrogen TPR of 5-Pd-VM gave a reduction peak at 325 °C indicating weaker interactions of the oxidized Pd species with the support. It is hypothesized that smaller particle sizes, uniform particle distribution, and weaker PdO/PdOx interactions with the support may contribute to the higher activity in 5-Pd-VM. Full article
(This article belongs to the Special Issue Catalytic Oxidation of Methane)
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Open AccessFeature PaperArticle
The Effect of Citric Acid Concentration on the Properties of LaMnO3 as a Catalyst for Hydrocarbon Oxidation
Catalysts 2019, 9(3), 226; https://doi.org/10.3390/catal9030226
Received: 21 December 2018 / Revised: 21 February 2019 / Accepted: 23 February 2019 / Published: 1 March 2019
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Abstract
LaMnO3 (LM) catalysts with a molar ratio of citric acid (CA) to metal (La3+ + Mn2+) nitrates ranging from 0.5 to 2 (LM0.5 to LM2) were synthesized by the citrate sol–gel method with the aim of studying the effect [...] Read more.
LaMnO3 (LM) catalysts with a molar ratio of citric acid (CA) to metal (La3+ + Mn2+) nitrates ranging from 0.5 to 2 (LM0.5 to LM2) were synthesized by the citrate sol–gel method with the aim of studying the effect of the citric acid ratio on the physicochemical properties and the catalytic performance in hydrocarbon oxidation. Structural and morphological properties of these catalysts were characterized by X-ray diffraction (XRD) and specific surface area (N2 adsorption) measurements, while the chemical composition was determined by inductively coupled plasma atomic emission spectroscopy (ICP-OES). In the selected samples, additional characterizations were carried out by thermogravimetric and differential thermal analysis (TGA/DTA), Fourier Transform Infrared Spectroscopy (FT-IR), temperature-programmed reduction by hydrogen (H2-TPR), and X-ray photoelectron spectroscopy (XPS). The results showed that the amount of citric acid used significantly influenced the TGA/DTA profile of gels along with the physicochemical properties of the catalysts. The XRD patterns are consistent with the perovskite formation as the main phase. The segregation of a small amount of Mn3O4, detected for molar ratios ranging between 0.5 and 1.5, suggested the formation of a slightly nonstoichiometric LaMn1−xO3 phase with a relatively high content of Mn4+. The catalytic performance was evaluated in the total oxidation of two selected hydrocarbons, toluene and propene, which represent typical volatile organic compounds (VOCs). Typically, three consecutive catalytic cycles were performed in order to reach steady-state performance in toluene and propene oxidation. Moreover, the stability of the catalysts under reaction conditions was investigated through 24-h experiments at 17% of toluene conversion. The catalysts LM1.2, LM1.3, and LM1.5 showed the best catalytic performance in both hydrocarbon oxidations, well comparing with the Pd/Al2O3 used as a reference. Full article
(This article belongs to the Special Issue Catalytic Oxidation of Methane)
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Open AccessCommunication
Rice Husk Derived Porous Silica as Support for Pd and CeO2 for Low Temperature Catalytic Methane Combustion
Catalysts 2019, 9(1), 26; https://doi.org/10.3390/catal9010026
Received: 30 November 2018 / Revised: 21 December 2018 / Accepted: 24 December 2018 / Published: 1 January 2019
Cited by 2 | PDF Full-text (4301 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The separation of Pd and CeO2 on the inner surface of controlled porous glass (CPG, obtained from phase-separated borosilicate glass after extraction) yields long-term stable and highly active methane combustion catalysts. However, the limited availability of the CPG makes such catalysts highly [...] Read more.
The separation of Pd and CeO2 on the inner surface of controlled porous glass (CPG, obtained from phase-separated borosilicate glass after extraction) yields long-term stable and highly active methane combustion catalysts. However, the limited availability of the CPG makes such catalysts highly expensive and limits their applicability. In this work, porous silica obtained from acid leached rice husks after calcination (RHS) was used as a sustainable, cheap and broadly available substitute for the above mentioned CPG. RHS-supported Pd-CeO2 with separated CeO2 clusters and Pd nanoparticles was fabricated via subsequent impregnation/calcination of molten cerium nitrate and different amounts of palladium nitrate solution. The Pd/CeO2/RHS catalysts were employed for the catalytic methane combustion in the temperature range of 150–500 °C under methane lean conditions (1000 ppm) in a simulated off-gas consisting of 9.0 vol% O2, and 5.5 vol% CO2 balanced with N2. Additionally, tests with 10.5 vol% H2O as co-feed were carried out. The results revealed that the RHS-supported catalysts reached the performance of the cost intensive benchmark catalyst based on CPG. The incorporation of Pd-CeO2 into RHS additionally improved water-resistance compared to solely Pd/CeO2 lowering the required temperature for methane combustion in presence of 10.5 vol% H2O to values significantly below 500 °C (T90 = 425 °C). Full article
(This article belongs to the Special Issue Catalytic Oxidation of Methane)
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Open AccessArticle
Catalytic Combustion Characteristics of Methane-Air Mixtures in Small-Scale Systems at Elevated Temperatures
Catalysts 2018, 8(10), 439; https://doi.org/10.3390/catal8100439
Received: 18 September 2018 / Revised: 3 October 2018 / Accepted: 4 October 2018 / Published: 6 October 2018
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Abstract
The catalytic combustion characteristics of methane-air mixtures in small-scale systems were investigated at elevated temperatures, with particular emphasis on identifying the main factors that affect formation and removal of combustion-generated pollutants. Computational fluid dynamics simulations were performed using detailed chemical kinetic mechanisms, and [...] Read more.
The catalytic combustion characteristics of methane-air mixtures in small-scale systems were investigated at elevated temperatures, with particular emphasis on identifying the main factors that affect formation and removal of combustion-generated pollutants. Computational fluid dynamics simulations were performed using detailed chemical kinetic mechanisms, and more insights were offered into the phenomena occurring in the temperature range where homogeneous and heterogeneous reaction pathways are both important. Reaction engineering analysis was performed to provide an in-depth understanding of how to achieve low emissions of pollutants. Spatial distributions of the major species involved were presented to gain insight into the interplay between the two competing pathways involved. The results indicated that the distribution of oxidized products depends critically on the feed composition, dimension, temperature, and pressure. Small-scale catalytic systems enable low emissions of pollutants even in a high temperature environment, along with high combustion efficiency. The interplay between the two competing pathways via radicals is strong, and the heterogeneous pathway can significantly inhibit the homogeneous pathway. The inhibiting effect also accounts for the low emissions of nitrogen oxides. Almost all of the nitrogen oxides emitted by small-scale catalytic systems are nitric oxide. Catalytic combustion technology can be used to reduce the formation of undesired products, especially pollutant nitrogen oxide gases far below what can be achieved without catalysts. Recommendations for the design of small-scale catalytic systems are provided. Full article
(This article belongs to the Special Issue Catalytic Oxidation of Methane)
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Open AccessFeature PaperArticle
Low-Temperature Activity and PdO-PdOx Transition in Methane Combustion by a PdO-PdOx/γ-Al2O3 Catalyst
Catalysts 2018, 8(7), 266; https://doi.org/10.3390/catal8070266
Received: 21 May 2018 / Revised: 18 June 2018 / Accepted: 28 June 2018 / Published: 29 June 2018
Cited by 2 | PDF Full-text (5434 KB) | HTML Full-text | XML Full-text
Abstract
The search to discover a suitable catalyst for complete combustion of methane at low temperature continues to be an active area of research. We prepared a 5 wt % PdO-PdOx/γ-Al2O3 catalyst by a modified Vortex-assisted Incipient Wetness Method. [...] Read more.
The search to discover a suitable catalyst for complete combustion of methane at low temperature continues to be an active area of research. We prepared a 5 wt % PdO-PdOx/γ-Al2O3 catalyst by a modified Vortex-assisted Incipient Wetness Method. X-ray Photoelectron Spectroscopy showed that the original catalyst contained PdO (38%) and PdOx (62%) on the surface and indicated that PdOx originated from the interaction of PdO with the support. Scanning Transmission Electron Microscopy confirmed the catalyst had an average particle size of 10 nm and was well-dispersed in the support. The catalyst exhibited exceptional low-temperature activities with 90–94% methane conversion at 300–320 °C. The catalyst was active and stable after several catalytic runs with no signs of deactivation by steam in this narrow temperature range. However, the conversion decreased in the temperature range 325–400 °C. The surface composition changed to some extent after the reaction at 325 °C. A tentative mechanism proposes PdOx (Pd native oxide) as the active phase and migration of oxide ions from the support to PdO and then to PdOx during the catalytic oxidation. The high methane conversion at low temperature is attributed to the vortex method providing better dispersion, and to catalyst–support interaction producing the active phase of PdOx. Full article
(This article belongs to the Special Issue Catalytic Oxidation of Methane)
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Open AccessArticle
Numerical Investigations of the Influencing Factors on a Rotary Regenerator-Type Catalytic Combustion Reactor
Catalysts 2018, 8(5), 173; https://doi.org/10.3390/catal8050173
Received: 13 March 2018 / Revised: 8 April 2018 / Accepted: 10 April 2018 / Published: 24 April 2018
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Abstract
Ultra-low calorific value gas (ULCVG) not only poses a problem for environmental pollution, but also createsa waste of energy resources if not utilized. A novel reactor, a rotary regenerator-type catalytic combustion reactor (RRCCR), which integrates the functions of a regenerator and combustor into [...] Read more.
Ultra-low calorific value gas (ULCVG) not only poses a problem for environmental pollution, but also createsa waste of energy resources if not utilized. A novel reactor, a rotary regenerator-type catalytic combustion reactor (RRCCR), which integrates the functions of a regenerator and combustor into one component, is proposed for the elimination and utilization of ULCVG. Compared to reversal-flow reactor, the operation of the RRCCR is achieved by incremental rotation rather than by valve control, and it has many outstanding characteristics, such as a compact structure, flexible application, and limited energy for circulation. Due to the effects of the variation of the gas flow and concentration on the performance of the reactor, different inlet velocities and concentrations are analyzed by numerical investigations. The results reveal that the two factors have a major impact on the performance of the reactor. The performance of the reactor is more sensitive to the increase of velocity and the decrease of methane concentration. When the inlet concentration (2%vol.) is reduced by 50%, to maintain the methane conversion over 90%, the inlet velocity can be reduced by more than three times. Finally, the highly-efficient and stable operating envelope of the reactor is drawn. Full article
(This article belongs to the Special Issue Catalytic Oxidation of Methane)
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Open AccessArticle
Active Component Migration and Catalytic Properties of Nitrogen Modified Composite Catalytic Materials
Catalysts 2018, 8(4), 125; https://doi.org/10.3390/catal8040125
Received: 2 February 2018 / Revised: 7 March 2018 / Accepted: 16 March 2018 / Published: 21 March 2018
Cited by 2 | PDF Full-text (5959 KB) | HTML Full-text | XML Full-text
Abstract
During the catalytic combustion reaction of methane, the migration of the active species on surface facilitates the catalytic reaction, and the element doping can improve the redox performance of the catalyst. Nitrogen-modified perovskite type composite catalysts were prepared by hydrothermal method and then [...] Read more.
During the catalytic combustion reaction of methane, the migration of the active species on surface facilitates the catalytic reaction, and the element doping can improve the redox performance of the catalyst. Nitrogen-modified perovskite type composite catalysts were prepared by hydrothermal method and then characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), temperature-programmed reductions (TPR), and X-ray photoelectron spectra (XPS). The results revealed that nitrogen sources (urea, biuret, melamine, carbohydrazide, and semicarbazide hydrochloride) and nitrogen source addition changed the catalytic performance in physical and chemical properties, the migration of reactive species and the catalytic performance. When the addition amount of semicarbazide hydrochloride was three times that of LaCoO3, the composite catalysts had high Co3+/Co2+ (1.39) and Oads/Olat (15.18) and showed the best catalytic performance: the temperatures that are required for achieving methane conversion of 50% and 90% were 277 and 360 °C, which are more effective than noble metal oxides. Moreover, the in situ diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) were applied to elucidate the efficient for CH4 removal and also can further explain the surface reaction mechanism of the composite catalyst during the methane catalytic combustion. Full article
(This article belongs to the Special Issue Catalytic Oxidation of Methane)
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Open AccessArticle
Active and Stable Methane Oxidation Nano-Catalyst with Highly-Ionized Palladium Species Prepared by Solution Combustion Synthesis
Catalysts 2018, 8(2), 66; https://doi.org/10.3390/catal8020066
Received: 11 December 2017 / Revised: 26 January 2018 / Accepted: 29 January 2018 / Published: 7 February 2018
Cited by 5 | PDF Full-text (10341 KB) | HTML Full-text | XML Full-text
Abstract
We report on the synthesis and testing of active and stable nano-catalysts for methane oxidation. The nano-catalyst was palladium/ceria supported on alumina prepared via a one-step solution-combustion synthesis (SCS) method. As confirmed by X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HTEM), [...] Read more.
We report on the synthesis and testing of active and stable nano-catalysts for methane oxidation. The nano-catalyst was palladium/ceria supported on alumina prepared via a one-step solution-combustion synthesis (SCS) method. As confirmed by X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HTEM), SCS preparative methodology resulted in segregating both Pd and Ce on the surface of the Al2O3 support. Furthermore, HTEM showed that bigger Pd particles (5 nm and more) were surrounded by CeO2, resembling a core shell structure, while smaller Pd particles (1 nm and less) were not associated with CeO2. The intimate Pd-CeO2 attachment resulted in insertion of Pd ions into the ceria lattice, and associated with the reduction of Ce4+ into Ce3+ ions; consequently, the formation of oxygen vacancies. XPS showed also that Pd had three oxidation states corresponding to Pd0, Pd2+ due to PdO, and highly ionized Pd ions (Pd(2+x)+) which might originate from the insertion of Pd ions into the ceria lattice. The formation of intrinsic Ce3+ ions, highly ionized (Pd2+ species inserted into the lattice of CeO2) Pd ions (Pd(2+x)+) and oxygen vacancies is suggested to play a major role in the unique catalytic activity. The results indicated that the Pd-SCS nano-catalysts were exceptionally more active and stable than conventional catalysts. Under similar reaction conditions, the methane combustion rate over the SCS catalyst was ~18 times greater than that of conventional catalysts. Full methane conversions over the SCS catalysts occurred at around 400 °C but were not shown at all with conventional catalysts. In addition, contrary to the conventional catalysts, the SCS catalysts exhibited superior activity with no sign of deactivation in the temperature range between ~400 and 800 °C. Full article
(This article belongs to the Special Issue Catalytic Oxidation of Methane)
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