Research

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17 pages, 5351 KiB

Open AccessArticle

Investigating the Effect of Ni Loading on the Performance of Yttria-Stabilised Zirconia Supported Ni Catalyst during CO₂ Methanation

by Osaze Omoregbe, Artur J. Majewski, Robert Steinberger-Wilckens and Ahmad El-kharouf

Methane 2023, 2(1), 86-102; https://doi.org/10.3390/methane2010007 - 08 Feb 2023

Viewed by 1484

Abstract

CO₂ methanation was studied on Ni-based yttria-stabilised zirconia (Ni/YSZ) catalysts. The catalysts were prepared by the wet impregnation method, where the amount of Ni content was varied from 5% to 75%. Thereafter, the prepared catalysts were analysed by BET, XRD, SEM and [...] Read more.

CO₂ methanation was studied on Ni-based yttria-stabilised zirconia (Ni/YSZ) catalysts. The catalysts were prepared by the wet impregnation method, where the amount of Ni content was varied from 5% to 75%. Thereafter, the prepared catalysts were analysed by BET, XRD, SEM and H₂-TPR. BET results showed an initial increase in the surface area with an increase in Ni loading, then a decrease after 30% Ni loading. The XRD results revealed that the Ni crystallite size increased as the Ni loading increased, while the H₂-TPR showed a shift in reduction peak temperature to a higher temperature, indicating that the reducibility of the catalysts decreased as the Ni loading increased. The activity of the synthesised catalysts for CO₂ methanation was studied by passing a mixture of H₂, CO₂ and N₂ with a total flow of 135 mL min⁻¹ and GHSV of 40,500 mL h⁻¹ g⁻¹ through a continuous flow quartz tube fixed-bed reactor (I.D. = 5.5 mm, wall thickness = 2 mm) containing 200 mg of the catalyst at a temperature range of 473 to 703 K under atmospheric pressure and a H₂:CO₂ ratio of 4. The tested Ni/YSZ catalysts showed an improvement in activity as the reaction temperature increased from 473 K to around 613 to 653 K, depending on the Ni loading. Beyond the optimum temperature, the catalyst’s activity started to decline, irrespective of the Ni loading. In particular, the 40% Ni/YSZ catalyst displayed the best performance, followed by the 30% Ni/YSZ catalyst. The improved activity at high Ni loading (40% Ni) was attributed to the increase in hydrogen coverage and improved site for both H₂ and CO₂ adsorption and activation. Full article

(This article belongs to the Special Issue Methane Conversion Technology)

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9 pages, 3020 KiB

Open AccessArticle

Efficient Performance of the Methane-Carbon Dioxide Reform Process in a Fluidized Bed Reactor

by José A. Pacífico, Nelson M. Lima Filho and Cesar A. Moraes de Abreu

Methane 2023, 2(1), 56-64; https://doi.org/10.3390/methane2010004 - 15 Jan 2023

Cited by 1 | Viewed by 1651

Abstract

The reforming of methane with CO₂ was carried out efficiently in a fluidized bed reactor at 973 K under atmospheric pressure, taking advantage of the nickel catalyst efficiency achieved with a bed of particulate fines. The fluidization operation was characterized by determining [...] Read more.

The reforming of methane with CO₂ was carried out efficiently in a fluidized bed reactor at 973 K under atmospheric pressure, taking advantage of the nickel catalyst efficiency achieved with a bed of particulate fines. The fluidization operation was characterized by determining a minimum velocity of 3.11 × 10⁻³ ms⁻¹ and higher velocities. The reactor worked with surface speeds of up to 1.84 × 10⁻² ms⁻¹, providing conversions from 45% to 51% and a syngas yield of 97%. The control base of the operation focused on the use of CO₂ was established through the reaction steps assumed for the process, including methane cracking, reverse Boudouard reaction, and RWGS (reverse reaction of water gas-shift). The reactor designed to operate in two zones was able to simultaneously process surface reactions and catalyst regeneration using feed with 50% excess CO₂ in relation to methane. Predictions indicating the production of syngas of different compositions quantified with the H₂/CO ratio from 2.30 to 0.91 decreasing with space-time were validated with the results available for process design. Full article

(This article belongs to the Special Issue Methane Conversion Technology)

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12 pages, 4129 KiB

Open AccessArticle

Photocatalytic Methane Conversion over Pd/ZnO Photocatalysts under Mild Conditions

by Arthur Pignataro Machado, Saulo Amaral Carminati, Eliane Ribeiro Januário, Patricia Silvaino Ferreira, Jorge Moreira Vaz and Estevam Vitorio Spinacé

Methane 2023, 2(1), 44-55; https://doi.org/10.3390/methane2010003 - 07 Jan 2023

Cited by 5 | Viewed by 1797

Abstract

Here, Pd nanoparticles supported on ZnO were prepared by the alcohol-reduction and the borohydride-reduction methods, and their efficiency towards the photocatalytic conversion of methane under mild conditions were evaluated. The resulting Pd/ZnO photocatalysts were characterized by X-ray fluorescence, X-ray diffraction, X-ray photoelectron spectroscopy, [...] Read more.

Here, Pd nanoparticles supported on ZnO were prepared by the alcohol-reduction and the borohydride-reduction methods, and their efficiency towards the photocatalytic conversion of methane under mild conditions were evaluated. The resulting Pd/ZnO photocatalysts were characterized by X-ray fluorescence, X-ray diffraction, X-ray photoelectron spectroscopy, UV–Vis, and transmission electron microscopy. The reactions were performed with the photocatalysts dispersed in water in a bubbling stream of methane under UV-light illumination. The products formed were identified and quantified by gas chromatography (GC-FID/TCD/MSD). The principal products formed were C₂H₆ and CO₂ with minor quantities of C₂H₄ and CO. No H₂ production was observed. The preparation methods influenced the size and dispersion of Pd nanoparticles on the ZnO, affecting the performance of the photocatalysts. The best performance was observed for the photocatalyst prepared by borohydride reduction with 0.5 wt% of Pd, reaching a C₂H₆ production rate of 686 µmol·h⁻¹·g⁻¹ and a C₂H₆ selectivity of 46%. Full article

(This article belongs to the Special Issue Methane Conversion Technology)

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10 pages, 1196 KiB

Open AccessArticle

Optimization of Methane Feed and N:C Ratio for Biomass and Polyhydroxybutyrate Production by the Alphaproteobacterial Methanotroph Methylocystis sp. Rockwell

by Hem K. Sharma, Dominic Sauvageau and Lisa Y. Stein

Methane 2022, 1(4), 355-364; https://doi.org/10.3390/methane1040026 - 06 Dec 2022

Viewed by 2038

Abstract

The consumption of methane and the production of biodegradable polymers using alphaproteobacterial methanotrophs offers a promising strategy to mitigate greenhouse gas emissions and reduce non-biodegradable plastic pollution. This study identified an ideal amount of added methane and N:C ratio in 100 mL batch [...] Read more.

The consumption of methane and the production of biodegradable polymers using alphaproteobacterial methanotrophs offers a promising strategy to mitigate greenhouse gas emissions and reduce non-biodegradable plastic pollution. This study identified an ideal amount of added methane and N:C ratio in 100 mL batch cultures of the alphaproteobacterial methanotroph Methylocystis sp. Rockwell growing in 1-L sealed bottles using Response Surface Methodology (RSM) to achieve both high biomass and high polyhydroxybutyrate (PHB) production. RSM analysis showed achievement of optimal biomass at 474.7 ± 10.1 mg/L in nitrate mineral salts (NMS) medium and 480.0 ± 65.5 mg/L biomass in ammonium mineral salts (AMS) medium with 8 mmol of methane and an N:C ratio of 0.022. However, optimal PHB concentration was achieved with 6 mmol methane at N:C ratios of 0.012 in NMS medium (149.7 ± 16.1 mg/L) and 0.022 in AMS medium (200.3 ± 5.1 mg/L). A multi-objective RSM analysis projected maxima in PHB production and %PHB cell content (based on dry weight) when using 4.88 mmol methane and N:C ratio of 0.016 in NMS cultures, and 6.28 mmol methane and the 0.016 N:C ratio in AMS cultures. Cultures grown under these projected conditions produced 173.7 mg PHB/L with 46.8% PHB cell content in NMS and 196.9 mg/L with 53.1% PHB cell content in AMS. Taken together, these analyses predicted the optimal conditions for growth and PHB production in batch cultures of Methylocystis sp. Rockwell and confirmed a preference for ammonium as the N-source for PHB production. This information is valuable for media formulation in industrial scale-up of Methylocystis sp. Rockwell in PHB production. Full article

(This article belongs to the Special Issue Methane Conversion Technology)

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14 pages, 3681 KiB

Open AccessArticle

Shifts in Product Distribution in Microwave Plasma Methane Pyrolysis Due to Hydrogen and Nitrogen Addition

by Mateusz Wnukowski, Julia Gerber and Karolina Mróz

Methane 2022, 1(4), 286-299; https://doi.org/10.3390/methane1040022 - 15 Nov 2022

Cited by 3 | Viewed by 1769

Abstract

Methane pyrolysis can produce many valuable products besides hydrogen, e.g., C₂ compounds or carbon black. In the conditions provided by microwave plasma, the distribution of these products might be shifted by the addition of hydrogen and nitrogen. In this work, different ratios [...] Read more.

Methane pyrolysis can produce many valuable products besides hydrogen, e.g., C₂ compounds or carbon black. In the conditions provided by microwave plasma, the distribution of these products might be shifted by the addition of hydrogen and nitrogen. In this work, different ratios of H₂:CH₄, ranging from 0:1 to 4:1, were tested. The most unambiguous and promising result was obtained for the highest H₂:CH₄ ratio. For this ratio, a significant improvement in methane conversion rate was observed (from 72% to 95%) along with the increase in C₂H₂ and C₂H₄ yield and selectivity. The results support the hypothesis that the H radicals present in the plasma are responsible for improving methane conversion, while the presence of molecular hydrogen shifts the product distribution towards C₂ compounds. Based on the carbon balance, the increase in the output of C₂ compounds was obtained at the cost of solid carbon. At the same time, the addition of hydrogen resulted in the formation of bigger carbon particles. Finally, with the addition of both nitrogen and hydrogen, the formation of carbon was completely inhibited. Hydrogen cyanide was the main product formed instead of soot and some of the acetylene. Full article

(This article belongs to the Special Issue Methane Conversion Technology)

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19 pages, 3856 KiB

Open AccessArticle

An Analysis of the Methane Cracking Process for CO₂-Free Hydrogen Production Using Thermodynamic Methodologies

by Julles Mitoura dos Santos Junior, Jan Galvão Gomes, Antônio Carlos Daltro de Freitas and Reginaldo Guirardello

Methane 2022, 1(4), 243-261; https://doi.org/10.3390/methane1040020 - 07 Oct 2022

Cited by 5 | Viewed by 2881

Abstract

The thermal cracking process of methane does not present the emissions of polluting gases, forming only hydrogen with a high degree of purity and solid carbon that can be commercialized for other industrial purposes globally. Thermodynamic methodologies based on Gibbs energy minimization and [...] Read more.

The thermal cracking process of methane does not present the emissions of polluting gases, forming only hydrogen with a high degree of purity and solid carbon that can be commercialized for other industrial purposes globally. Thermodynamic methodologies based on Gibbs energy minimization and entropy maximization are used in the present study to simulate operating conditions of isothermal and adiabatic reactors, respectively. The chemical equilibrium and combined phases problem were written in a non-linear programming form and optimized with the GAMS software using the CONOPT 3 solver. The results obtained by the methodology described in this study present a good agreement with the data reported in the literature, with mean relative deviations lower than 1.08%. High temperatures and low pressures favor the decomposition of methane and the formation of products. When conditioned in an isothermal reactor, total methane conversions are obtained at temperatures above 1200 K at 1 bar. When conditioned to an adiabatic reactor, due to the lack of energy support provided by the isothermal reactor and taking into account that it is an endothermic process, high methane-conversion rates are obtained for temperatures above 1600 K at 1 bar. As an alternative, the combined effects of the addition of hydrogen to the feed combined with a system of extreme pressure variation indicate a possibility of conducting the thermal cracking process of methane in adiabatic systems. Setting the CH₄/H₂ ratio in the system feed at 1:10 at 1600 K and 50 bar, following severe depressurization through an isentropic valve, varying the pressure from 50 to 1 bar, the methane conversion varies from 0 to 94.712%, thus indicating a possible operational conformation for the process so that the amount of carbon generated is not so harmful to the process, taking into account that the formation of the same occurs only after the reaction and heating processes. Under the same operating conditions, it is possible to use about 40.57% of the generated hydrogen to provide energy for the process to occur. Full article

(This article belongs to the Special Issue Methane Conversion Technology)

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18 pages, 2951 KiB

Open AccessFeature PaperArticle

Identifying Monomeric Fe Species for Efficient Direct Methane Oxidation to C₁ Oxygenates with H₂O₂ over Fe/MOR Catalysts

by Caiyun Xu, Qian Song, Nagme Merdanoglu, Hang Liu and Elias Klemm

Methane 2022, 1(2), 107-124; https://doi.org/10.3390/methane1020010 - 01 May 2022

Cited by 4 | Viewed by 1948

Abstract

Exploring advanced catalysts and reaction systems operated at mild reaction conditions is crucial for conducting the direct methane oxidation reaction toward oxygenate products. Many efforts have been put into research on pentasil−type (MFI) zeolites based on mononuclear and/or binuclear iron sites, using H [...] Read more.

Exploring advanced catalysts and reaction systems operated at mild reaction conditions is crucial for conducting the direct methane oxidation reaction toward oxygenate products. Many efforts have been put into research on pentasil−type (MFI) zeolites based on mononuclear and/or binuclear iron sites, using H₂O₂ as the oxidant. In this work, we present a modified liquid ion−exchange method to better control Fe loading in a mordenite−type (MOR) zeolite with a Si/Al molar ratio of 9. The optimized Fe/MOR catalyst showed excellent performance in the direct methane oxidation reaction with turnover frequencies (TOFs) of 555 h⁻¹ to C₁ oxygenates, significantly better than the reported activity. Multiple comparative experiments were conducted to reveal the mechanism behind the performance. Strikingly, the active sites in the Fe/MOR catalyst were found to be mononuclear iron sites, confirmed by transmission electron microscopy (TEM), ultraviolet−visible diffuse reflectance spectroscopy (UV−vis DRS), and X-ray absorption spectroscopy (XAS). Increasing the iron loading led to the aggregation of the iron sites, which tend to trigger undesirable side reactions (i.e., H₂O₂ decomposition and over−oxidation), resulting in a significant decrease in TOFs to C₁ oxygenates. Full article

(This article belongs to the Special Issue Methane Conversion Technology)

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10 pages, 2484 KiB

Open AccessCommunication

Synthesis-Gas Production from Methane over Ni/CeO₂ Catalysts Synthesized by Co-Precipitation Method in Different Solvents

by Yvan J. O. Asencios, Kariny F. M. Elias, Andressa de Zawadzki and Elisabete M. Assaf

Methane 2022, 1(2), 72-81; https://doi.org/10.3390/methane1020007 - 23 Mar 2022

Cited by 2 | Viewed by 2520

Abstract

Ni/CeO₂ catalysts were synthesized by the coprecipitation method in a basic medium, using different solvents: water, methanol, ethanol, and isopropanol (Ni content, 10% wt.). These catalysts were tested in the production of syngas through the oxidative reforming of methane (ORM), and partial [...] Read more.

Ni/CeO₂ catalysts were synthesized by the coprecipitation method in a basic medium, using different solvents: water, methanol, ethanol, and isopropanol (Ni content, 10% wt.). These catalysts were tested in the production of syngas through the oxidative reforming of methane (ORM), and partial oxidation of methane (POM). The results of this research demonstrated that the use of alcohols (methanol, ethanol, and isopropanol) during the preparation of the Ni/CeO₂ catalysts by the coprecipitation method, improved their characteristics such as crystallite size (nm), surface area (m²·g⁻¹), and reducibility (measured by H₂-TPR) that influenced on their catalytic performance in ORM and POM reactions. The best solvent of this study was isopropanol. The use of alcohols (methanol, ethanol, isopropanol) in the co-precipitation method led to the formation of filamentous carbon on the catalyst after the reactions. The catalyst synthesized in the water proved to be inefficient in the POM and ORM reactions and led to the formation of amorphous carbon after the reactions. Full article

(This article belongs to the Special Issue Methane Conversion Technology)

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12 pages, 4248 KiB

Open AccessArticle

Expanded Reactor Engineering Calculations for the Oxidative Coupling of Methane

by Andrin Molla, Sonya Rivera, Phillip Pera, Michael Landaverde and Robert Barat

Methane 2022, 1(1), 58-69; https://doi.org/10.3390/methane1010005 - 11 Feb 2022

Viewed by 1891

Abstract

The catalytic activation of CH₄ by limited amounts of O₂ produces a mixture of synthesis gas (CO, H₂) and light hydrocarbons (C₂H_x), the relative amounts of each depending on catalyst type and process conditions. Using [...] Read more.

The catalytic activation of CH₄ by limited amounts of O₂ produces a mixture of synthesis gas (CO, H₂) and light hydrocarbons (C₂H_x), the relative amounts of each depending on catalyst type and process conditions. Using an elementary reaction mechanism for the oxidative coupling of methane (OCM) on a La₂O₃/CeO₂ catalyst derived from the literature, this study replaces the activating O₂ with moist H₂O₂ vapor to reduce synthesis gas production while improving C₂H_x yields and selectivities. As the H₂O₂ content of the activating oxidant rises, more of the CH₄ conversion occurs in the gas phase instead of with the catalytic surface. In a packed bed reactor (PBR), the use of H₂O₂ allows the PBR “light-off” to occur using a lower feed temperature. In exchange for a small decline in CH₄ conversion, C₂H_x selectivity increases while synthesis gas production drops. In a continuous stirred tank reactor (CSTR), H₂O₂ improves C₂H_x over synthesis gas across a wider range of feed temperatures than is possible with the PBR. This suggests the CSTR will likely reduce OCM preheating requirements. Full article

(This article belongs to the Special Issue Methane Conversion Technology)

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Review

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28 pages, 8919 KiB

Open AccessReview

Heterogeneous Electrocatalysis of Carbon Dioxide to Methane

by Yugang Wu, Huitong Du, Peiwen Li, Xiangyang Zhang, Yanbo Yin and Wenlei Zhu

Methane 2023, 2(2), 148-175; https://doi.org/10.3390/methane2020012 - 17 Apr 2023

Cited by 3 | Viewed by 2447

Abstract

Electrocatalytic CO₂ reduction to valued products is a promising way to mitigate the greenhouse effect, as this reaction makes use of the excess CO₂ in the atmosphere and at the same time forms valued fuels to partially fulfill the energy demand [...] Read more.

Electrocatalytic CO₂ reduction to valued products is a promising way to mitigate the greenhouse effect, as this reaction makes use of the excess CO₂ in the atmosphere and at the same time forms valued fuels to partially fulfill the energy demand for human beings. Among these valued products, methane is considered a high-value product with a high energy density. This review systematically summarizes the recently studied reaction mechanisms for CO₂ electroreduction to CH₄. It guides us in designing effective electrocatalysts with an improved electrocatalytic performance. In addition, we briefly summarize the recent progress on CO₂ electroreduction into CH₄ from the instructive catalyst design, including catalyst structure engineering and catalyst component engineering, and then briefly discuss the electrolyte effect. Furthermore, we also provide a simplified techno-economic analysis of this technology. These summaries are helpful for beginners to rapidly master the contents related to the electroreduction of carbon dioxide to methane and also help to promote the further development of this field. Full article

(This article belongs to the Special Issue Methane Conversion Technology)

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19 pages, 3879 KiB

Open AccessReview

Modification Strategies of Ni-Based Catalysts with Metal Oxides for Dry Reforming of Methane

by Xingyuan Gao, Weihao Lin, Zhiyong Ge, Hongming Ge and Sibudjing Kawi

Methane 2022, 1(3), 139-157; https://doi.org/10.3390/methane1030012 - 21 Jun 2022

Cited by 10 | Viewed by 2207

Abstract

Syngas generated from the catalytic dry reforming of methane (DRM) enables the downstream production of H₂ fuel and value-added chemicals. Ni-based catalysts with metal oxides, as both supports and promoters, are widely applied in the DRM reaction. In this review, four types [...] Read more.

Syngas generated from the catalytic dry reforming of methane (DRM) enables the downstream production of H₂ fuel and value-added chemicals. Ni-based catalysts with metal oxides, as both supports and promoters, are widely applied in the DRM reaction. In this review, four types of metal oxides with support confinement effect, metal-support interaction, oxygen defects, and surface acidity/basicity are introduced based on their impacts on the activity, selectivity, and stability of the Ni-based catalyst. Moreover, the structure–performance relationships are discussed in-depth. Finally, conclusive remarks and prospects are proposed. Full article

(This article belongs to the Special Issue Methane Conversion Technology)

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