CH4 Cracking Research Articles

MCM-41 from rice husk silica as a support for Ni catalyst in the emission-free production of H2 by CH4 cracking.

Selecting a sustainable source of silica from biomass waste was the research challenge that was put forth in this investigation. Herein, the MCM-41 support has been synthesized using a renewable rice husk and explored as a support for Ni-Cu catalyst in the production of zero-emission H2 through CH4 pyrolysis. The role of Cu promoter was investigated by doping different amounts of Cu loading to 30wt%Ni/R-MCM-41catalyst, which improved the catalytic performance in terms of CH4 conversion and stability. An optimum Cu loading of 3wt% addition to 30wt%Ni/R-MCM-41 catalyst demonstrated the best catalytic performance compared to all the catalysts in terms of hydrogen yield (15,218mol H2/mol Ni) and carbon formation rate. The Ni-Cu alloy formation was confirmed by X-ray diffraction, H2-temperature programmed reduction, and pulse chemisorption studies, as demonstrated by decreased H2 uptake (from 41 to 33μmol/gcat) and enhanced N2O (from 89.2 to 138.3μmol/g) uptakes, which results in a significant improvement in the availability of the surface metal species (both Cu and Ni), which in turn contributed to increase the CH4 cracking performance and stabilization of Ni species. Additionally, doping Cu results in better carbon nanotube production, as shown by the lowest ID/IG ratio from the Raman spectroscopic analysis.

Multiscale modeling of catalyst deactivation in dry methane reforming

Dry methane reforming (DRM) presents a promising strategy to convert greenhouse gases (CH4 and CO2) into syngas, a valuable precursor for the production of long-chain alkanes. However, catalyst deactivation remains a major issue, primarily caused by the deep cracking of CH4 and CO2 as well as the metal-catalyzed growth of carbon whiskers. To address this challenge, we introduce a multiscale model that analyzes DRM reactions on the Ni surface and predicts whisker formation. The multiscale modeling approach integrates microscopic kinetic Monte Carlo (kMC) simulations for surface reactions, mesoscopic pellet-scale modeling for predicting whisker growth length and macroscopic modeling to consider packed bed porosity and pressure drop across the reactor. Further, by systematically introducing time-steppers using the gap-tooth scheme, we significantly improved the computational efficiency, reducing the computational time from 17 days to 6 h at the expense of minimal accuracy loss in predicting whisker length. Based on this, we assert that such a multiscale model enables the analysis of various operating conditions affecting catalyst deactivation and kinetics of surface reaction, aiding in the design and optimization of DRM process.

Bi-reforming of model biogas to syngas over ultrasmall Ru/MgO nano-catalysts prepared via soft template-assisted mechanochemical method

The upgrading of renewable biogas into value-added fuel and chemicals via syngas is of great significance. Ru/MgO nano-catalysts were prepared via novel soft template-assisted mechanochemical method. Comprehensive characterizations (XRD, N2 physisorption, ICP-OES, CO-chemisorption, CO2-TPD, XPS, HAADF-STEM, HRTEM, CH4-TPSR/CO2-TPO, TGA and Raman spectroscopy, etc.) were conducted to deeply analyze the fresh/spent catalysts. The 0.2Ru/MgO-0.2CTAB catalyst showed high initial activity in terms of CH4/CO2 conversion (∼94 %/61 %) and maintained catalytic stability over 120 h in bi-reforming of model biogas, at 800 °C under CH4/CO2/N2/H2O molar ratio of 3:2:1:2.6 and weight hourly space velocity of 30960 mL g-1h−1. CTAB and other soft templates were effective in enhancing the dispersion of Ru nanoparticles (NPs), which contribute to the inhibition of the deep cracking of CH4 and coke accumulation. Alkaline MgO oxide was crucial in the activation of CO2 and the production of active O* species, thus promoting the removal of carbonaceous precursor and inhibiting the coke accumulation. Additionally, the strong interaction between ultrafine Ru NPs and the MgO support significantly contributed to its anti-sintering performance. The combined advantages of narrow size distribution of ultra-small Ru NPs, suitable basicity of MgO as well as the interaction between ultrafine Ru NPs and MgO over 0.2Ru/MgO-0.2CTAB catalyst led to satisfying catalytic performance in bi-reforming of model biogas.

Operando Spectroscopic Studies of Solid Oxide Fuel Cell Operation Using Dimethyl Ether as an Alternative Fuel

Dimethyl ether (DME) is an oxygen-containing fuel that is an attractive alternative to the reforming of light alkanes like CH4. Its higher volumetric exergy compared to CH4 yields comparable power densities to other fuels while decreasing its potential for performance degradation that results from coking. We have characterized an SOFC operating at 800 °C on DME using a suite of operando optical and ex post facto methods. Based on exhaust gas infrared spectroscopy, DME decomposes to CH4, C2H2, H2O, CO2, and CO. Electrochemical analysis indicates that under dry DME the maximum power output of an anode supported button cell Ni-YSZ SOFC is only 10% lower than under CH4 (where H content was matched in the fuel stream). FTIR analysis of the anode exhaust gas indicates an electrochemical response under galvanostatic conditions resulting in the consumption of both CH4 and C2H2 to form CO, CO2, and H2O. Operando near-infrared thermal imaging reveal more cooling at the anode surface with DME than CH4 resulting from increased endothermic cracking of CH4. Additional contributions to the cooling are possible from reforming reactions.

Machine learning aided design of single-atom alloy catalysts for methane cracking

The process of CH4 cracking into H2 and carbon has gained wide attention for hydrogen production. However, traditional catalysis methods suffer rapid deactivation due to severe carbon deposition. In this study, we discover that effective CH4 cracking can be achieved at 450 °C over a Re/Ni single-atom alloy via ball milling. To explore single-atom alloy catalysis, we construct a library of 10,950 transition metal single-atom alloy surfaces and screen candidates based on C–H dissociation energy barriers predicted by a machine learning model. Experimental validation identifies Ir/Ni and Re/Ni as top performers. Notably, the non-noble metal Re/Ni achieves a hydrogen yield of 10.7 gH2 gcat–1 h–1 with 99.9% selectivity and 7.75% CH4 conversion at 450 °C, 1 atm. Here, we show the mechanical energy boosts CH4 conversion clearly and sustained CH4 cracking over 240 h is achieved, significantly surpassing other approaches in the literature.

Surface basic site effect on CoLa/m-Al2O3 catalysts for dry reforming of methane

Dry reforming of methane (DRM) is a novel technology that enables the direct utilization of greenhouse gases (CH4 and CO2) for the production of value-added products. In the DRM reaction, the acid-base characteristics of the catalyst support play a pivotal role in determining the performance of the catalyst. In this study, a series of Co-based catalysts with different alkali earth metal-modified Al2O3 composite supports, specifically m-Al2O3 (m=Ca, Mg, and Ba), were prepared using the impregnation method. Various characterization techniques were employed to investigate the impact of alkaline site modulation on the support surface with respect to anti-sintering and anti-coking properties. The results demonstrate that the m-Al2O3 composite support catalysts, prepared with Mg and Ca modulation, exhibit an abundance of basic sites and oxygen vacancies. This promotes the adsorption and activation of CO2, enhances the rate of carbon elimination, and effectively addresses carbon deposition and metal sintering issues. Notably, the CoLa/Mg-Al2O3 catalyst shows the highest performance under reaction conditions of 750 °C, with CH4 and CO2 conversions reaching 92.3 % and 97.5 %, respectively. On the other hand, the CoLa/Ba-Al2O3 catalysts display poor performance in dry reforming. Kinetic studies indicate that CoLa/Mg-Al2O3 catalyst significantly reduce the apparent activation energy required for CH4 and CO2 cracking. Furthermore, it is demonstrated that the introduction of alkali earth metals can promote the dissociation of CH4 and CO2.

NiGa nano-alloy for the dry reforming of methane: Influences of Ga alloying with Ni on the catalytic activity and stability

The massive emission of CO2 and CH4 has caused serious environmental and ecological problems, and dry reforming of methane reaction has received widespread attentions due to the fact that it can eliminate the two gas simultaneously. Herein, Ni60Ga40/Al2O3 (molar ratio of Ni:Ga was 60:40) catalyst was synthesized by mechanochemical synthesis method, offering 75 % CH4 conversion, 85 % CO2 conversion, and H2/CO ratio of 0.93 at 750 °C during 120 h test. Ni in Ni60Ga40/Al2O3 combines with Ga to form Ni3Ga intermetallic compound, which inhibits the sintering of Ni and rapid cracking of CH4. Moreover, the extra Ga species, existing in the form of Ga2O3-Al2O3 with abundant oxygen vacancy, boosts CO2 activation and prevents carbon development on catalyst surface. In contrast, for the pure Ni/Al2O3 and Ga/Al2O3 catalysts, the stability and catalytic activity couldn’t be obtained synchronously. This work particularly investigated the CH4 dissociation and CO2 activation for the NiGa/Al2O3 catalysts, establishing the foundation for rational design of low-cost performance catalysts for the dry reforming of methane reactions.

Dry reforming of methane over Ni/Al2O3 catalysts: Support morphological effect on the coke resistance

Flower-like (Al2O3-F), wire-like (Al2O3-W) and sphere-like (Al2O3-S) alumina supported nickel catalysts (designated as Ni/Al2O3-F, Ni/Al2O3-W and Ni/Al2O3-S) were prepared for catalytic dry reforming of methane (DRM). The resultant catalysts exhibited variable catalytic activities and coke resistance performances in the reaction, which was closely dependent on their various physicochemical properties from the morphological effect of Al2O3 supports. To be precise, Ni/Al2O3-W presented adequately high catalytic activity and promising anti-coke behavior, which was attributed to its strong metal-support interaction, the surface dispersion of small-sized Ni nanoparticles and noticeable activation ability towards CO2. Ni/Al2O3-F possessed high anti-coke performance as well in terms of its significant CO2 activation ability. However, the encapsulation effect of Al2O3-F nanostructure resulted in insufficient abundance of metallic Ni active sites on the surface of Ni/Al2O3-F, thus giving rise to poor initial catalytic activity. The weak CO2 activation ability and the large particle size of metallic Ni on Ni/Al2O3-S induced the considerable formation of filamentous carbon after long-term DRM test. With regard to in situ DRIFTs analysis, the existence of OH* as the coke precursor scavenger and its reaction with the CHx* intermediate species from CH4 cracking were demonstrated to play crucial roles in dominating the overall anti-coke performances of Ni/Al2O3 catalysts. This work provides new insights into the development of high coke-resistance Ni-based catalysts from the perspective of support morphology modulation.

Synthetic natural gas production using CO2-rich waste stream from hydrothermal carbonization of biomass: Effect of impurities on the catalytic activity

The utilization of biomass and bio-waste, particularly through hydrothermal processes, has shown promise as a technology for converting these materials into valuable products. While most research has traditionally focused on the solid and liquid byproducts of these hydrothermal treatments, the gaseous phase has often been overlooked. This study specifically investigates the conversion of off-gases produced during hydrothermal carbonation (HTC) into synthetic natural gas, offering a readily marketable product with economic potential. Although the methanation of conventional flue gases has been extensively studied, dealing with non-standard off-gases from processes like HTC presents challenges due to the presence of minor impurities like CO and CH4. This novel research seeks to experimentally evaluate the methanation of HTC off-gases using nickel-based catalysts and analyze how these impurities affect the catalytic performance. The studied catalysts include nickel supported by ceria and alumina, as well as alumina supported nickel-cobalt systems. The results demonstrate that these catalysts exhibit high CO2 conversion and CH4 selectivity under ideal gas conditions. However, when real gas compositions with impurities are considered, CO2 conversion decreases at lower temperatures (ca. 20% lower conversion for real gas vs. ideal), probably due to side reactions such as CH4 cracking. This difference becomes less pronounced at higher temperatures. Nevertheless, the catalysts perform satisfactorily, especially at temperatures exceeding 350 °C. In conclusion, this study sheds light on the methanation of HTC off-gases and underscores the significance of understanding how impurities in real gases impact the process, providing potential directions for future research.

Generation of Pure H2 through CH4 Cracking Over Ni Supported on ZrO2 Modified Al2O3 Catalyst

Clean hydrogen formation via CH4 cracking on a zirconia-modified alumina support at 550 ºC and atmospheric pressure with constant Ni loading. The increased H2 yields on 20Ni/3 wt.% ZrO2-Al2O3 are explained by the large Ni surface area. TEM and XRD confirmed the deactivated catalyst’s graphitic origin, while Raman spectroscopy helped distinguish between ordered and disordered carbon. As determined by H2 pulse chemisorption, the high H2 yields produced by 20wt%Ni/3 wt.%ZrO2-Al2O3 catalyst is typified by well- ispersed Ni particles and large Ni metal area.

Comparison of Carbon Deposition and Removal from Ni-YSZ and Ni-BCZY Composites Using Operando Optical Methods

Solid oxide fuel cells (SOFCs) are attractive devices for power generation because they can operate with a variety of fuels, including H2, hydrocarbon fuels, biogas, and syngas. Conventional SOFC anode composites comprised of Ni-YSZ (YSZ = yttria-stabilized zirconia), however, suffer from performance degradation due to surface accumulation of carbon from hydrocarbon cracking. Alternative electrolyte materials such as yttria-doped barium cerate/zirconate mixtures (BCZY) offer the promise of reduced carbon formation over the Ni-BCZY electrode and lower operating temperatures by the conduction of protons instead of oxide ions. In this study, 50%-50% Ni-8YSZ and 50%-50% Ni-BCZY27 composites were exposed to CH4 in the absence and presence of either CO2 or H2O. The degree of carbon deposition and mechanism of carbon removal in the absence of fuel was estimated in the presence of steam using operando Fourier transform infrared emission spectroscopy (FTIRES) and near-infrared thermal imaging (NIRTI) at 750 °C. Upon exposure to each fuel condition, carbon removal using steam results in more CO2 + CO product formation from Ni-8YSZ implying more carbon formation on Ni-8YSZ compared to Ni-BCZY27. Carbon removal of cells exposed to CH4 alone indicate limited formation and fast depletion of CO over Ni-BCZY27; depletion of CO2, however, happens more slowly. Depletion of CO and CO2 in the Ni-8YSZ system happens more gradually suggesting the deposition of carbon over Ni-BCZY27 occurs less readily and its removal is more facile through gasification. Interestingly, the cracking of CH4 over Ni-8YSZ is accompanied by a larger degree of cooling compared to Ni-BCZY27 whereas both dry and wet reforming result in similar cooling over Ni-8YSZ and Ni-BCZY27. The results will be discussed in the context of recent work using operando spectroscopies to characterize CH4 fuel utilization in Ni-8YSZ based SOFCs in the absence and presence of various reformers.

Efficient Zr-MCM-41 supported nickel phyllosilicate catalyst for the plasma-involved dry reforming of CH4 and CO2

Plasma can effectively lower the temperature of the dry reforming of methane (DRM) reaction. However, severe carbon deposition has hindered further development of the plasma-involved DRM reaction. In this work, an efficient Zr-MCM-41 supported nickel phyllosilicate (Ni-PS) catalyst has been developed to address the problem of carbon deposition caused by CH4 cracking. Comparing with the Ni/MCM-41 catalyst prepared by the impregnation method, XRD, TEM, and EXAFS et al. have revealed that the presence of nickel phyllosilicate species in (Ni-PS)/MCM-41 is advantageous in improving the catalyst's activity. Most importantly, adding Zr improves the stability of (Ni-PS)/Zr-MCM-41 catalyst during the 50 h time-on-stream evaluation. H2-TPR, XPS, CO2-TPD and EXAFS et al. characterizations confirm that adding Zr enhances the CO2 adsorption, and improves the metal-support interaction through the anchoring effect formed by the electron transfer between Ni2+ to Zr4+, which beneficial to enhance the ability of the catalyst to remove carbon deposition and improve the stability of the catalyst. This work provides an effective catalyst synthesis strategy for the plasma involved DRM reaction.

Experimental Study about Shale Acceleration on Methane Cracking

The temperature or maturity limit of methane (CH4) cracking is very useful for the determination of the most depth or the highest maturity in natural gas exploration owing to the composition of over mature gas. In this work, three series of CH4 cracking experiments were conducted under different conditions of N2 + CH4, N2 + CH4 + montmorillonite and N2 + CH4 + shale, respectively, in a gold tube system. The experimental results show that some heavy gas with negative carbon isotope composition could be generated in the three series experiments and that shale has more intense catalysis for CH4 cracking than montmorillonite. The catalysis of metal elements distributed in the minerals of shale is attributed to CH4 cracking acceleration. The shale catalysis makes the maturity threshold of CH4 substantial cracking decrease from 6.0%Ro under no catalysis, to 4.5%Ro under a shale system in a geological setting. Nevertheless, we suggest not to lightly practice natural gas exploration in shale with the maturity range of 3.5–4.5%Ro, as the maturity threshold of gas generation from oil prone organic matter distributed extensively in shale is 3.5%Ro.

The atomic-level adjacent NiFe bimetallic catalyst significantly improves the activity and stability for plasma-involved dry reforming reaction of CH4 and CO2

The plasma technology can effectively reduce the high temperature (≥700 °C) reaction condition of dry reforming of methane (DRM) reaction. But the inevitable carbon deposition problem seriously hinders the progress of plasma-involved DRM reaction. In order to promote the carbon elimination reaction between the adsorbed CO2 and carbon deposition produced by CH4 cracking, we have developed an effective atomic-level adjacent NiFe bimetallic catalyst. Compared to the Ni-based monometallic catalyst, the atomic-level adjacent NiFe bimetallic catalyst shows high activity and excellent stability in the plasma-involved DRM reaction. The conversions of CO2 and CH4 are 80.5% and 73.8%, respectively. Meanwhile, the catalytic performance remains well stable during the 100 h time-on-stream evaluation. The atomic-level adjacent NiFe bimetals were characterized by XRD, TEM and EXAFS et al., which are responsible for the improved activities. Most importantly, the addition of Fe can increase the surface oxygen and enhance CO2 adsorption confirmed by XPS and CO2-TPD, which beneficial to improve the ability to convert carbon deposition and improve the stability of catalyst. This work provides a feasible synthetic strategy for designing the high activity and well stability catalyst for the plasma-involved DRM reaction.

Effect of biochar support on the catalytic performance of Fe-based catalysts for CH4 cracking

In the context of carbon neutrality, the decarbonization utilization of fossil energy has gradually become a research hotspot. The focus of this paper is on the use of loaded Fe-based catalysts for typical catalytic methane decomposition (CMD) hydrogen production technologies. The temperature response and product characteristics of rice husk-based biochar-Fe catalysts for CMD technology were investigated, with a focus on the effect of functional ‘supports’ on the reaction and product. The results show that the CH4 conversion, H2 yield and carbon yield are significantly higher at 850 °C than the reaction at 750 °C, reaching 24.39%, 739.26 mmol/gFe and 3.05 g/gFe. The solid phase characterization shows that the active metal existed in the form of Fe0 before the reaction and is converted to Fe3C after the reaction, and the average particle size of the metal in the mesopores is only 21.09 nm under the influence of the biochar pore size. The solid phase products are mainly highly graphitized “Coke” due to the negative effect of the biochar support on the dispersion of the active metal; the biochar also enhances the reduction of Fe2O3, which in turn affects the shaping of the active components and products.

Highly dispersed Fe-decorated Ni nanoparticles prepared by atomic layer deposition for dry reforming of methane

Dry reforming of methane (DRM) is a sustainable chemical process that can simultaneously transform methane and carbon dioxide, which are generally considered greenhouse gases, into syngas with H2/CO ratio close to 1. The deposition of carbon on the active sites during long-period DRM tests will lead to severe deactivation of Ni-based catalysts. Thus, in this work, we proposed a series of uniformly dispersed Fe-decorated Ni/Al2O3 catalysts via atomic layer deposition (ALD) to solve this key issue. Modification with trace amounts of Fe (0.3–0.6%) had multiple effects on facilitating the CH4 dissociation on Ni0, improving the low-temperature catalytic activity, moderating the carbon species and accelerating coke oxidation. The sample denoted as 0.3%Fe/Ni/Al2O3 exhibited almost no activity loss in the 72 h test at 650 °C. The Fe-decorated Ni/Al2O3 structure achieved a balance between the enhancement of CH4 cracking and the elimination of coke. Furthermore, this advanced ALD approach of preparing uniform secondary metal nanoparticle-decorated catalysts provided guidance to other bimetallic systems, such as Pt/Ni, Mn/Ni, and Cu/Ni.

Unraveling the Unique Promotion Effects of a Triple Interface in Ni Catalysts for Methane Dry Reforming

Methane dry reforming (MDR) is of great interest for its efficient consumption of greenhouse gases and the production of valuable syngas. The interfaces of metal and boron nitride (BN) are expected to enhance the catalytic activity and inhibit coke formation. Herein, the composite of layered metal oxides (NiMgAlOx) and BN was constructed to form the interface-confined NiMgAlOx/BN (Ni-MAO/BN) catalysts, and the unique promotion effects of a triple interface in Ni catalysts were unraveled. The triple interface among the Ni, BN, and MgAlOx oxides enhances the sintering resistance of the developed catalysts, which endows the developed catalysts with excellent adsorption/activation capacity of CH4 and CO2 as well as superb stability during a long-term MDR activity test. The abundant bicarbonate (HCO3*) species in the Ni-MAO/BN catalysts demonstrates that the triple interface significantly enhances gas activation. Meanwhile, the dynamic variation of HCO3* and CO3* species further proves the inhibition of deep CH4 cracking and the fast reaction rate over the Ni-MAO/BN catalysts. The negligible graphitic carbon observed in the operando Raman spectra and the produced large amount of H2/CO demonstrate not only the excellent coke resistance but also the strengthened activation capability of CO2 and CH4. This work elucidates the role of interfacial effects on gas activation and provides innovative insights into the design of highly efficient Ni catalysts for MDR.

Process Gas Detection of C2H2 Preparation by CH4 Cracking Based on Hollow Core Fiber Enhanced Raman Spectroscopy

Process Gas Detection of C2H2 Preparation by CH4 Cracking Based on Hollow Core Fiber Enhanced Raman Spectroscopy

Rice Husk Ash Derived SiO2 for Template Free Synthesis of H-ZSM-5 Support for Ni Catalyst: Investigation on Non-Oxidative CH4 Cracking for Clean H2 Production

Rice Husk Ash Derived SiO2 for Template Free Synthesis of H-ZSM-5 Support for Ni Catalyst: Investigation on Non-Oxidative CH4 Cracking for Clean H2 Production

Anti-coking NiCex/HAP catalyst with well-balanced carbon formation and gasification in methane dry reforming

Methane dry reforming (MDR) is a promising process to convert two major greenhouse gases into syngas. However, the major drawback of the process is the deactivation of Ni-based catalysts due to carbon deposition and metal sintering. Herein, we prepared hydroxyapatite (HAP) supported Ni catalysts modified by CeO2, which can efficiently promote MDR reaction with the excellent anti-coking property. The strong interaction between Ni and HAP guarantees the stability of highly dispersed Ni particles during the MDR reaction. The neighboring CeO2 over Ni particles could facilitate the mobility of oxygen, which assists the activation of CH4 to CH3O and in some extent hinders the deep cracking of CH4 into deposited carbon. Meanwhile, the kinetic studies indicate that the existence of reactive oxygen species is beneficial for enhancing carbon gasification. Accordingly, the addition of CeO2 balanced the carbon formation and gasification over Ni and therefore efficiently prevented coke accumulation. The exploration of NiCex/HAP catalysts would provide inspiration for future MDR catalyst design.