Catalytic Activity For Methane Decomposition Research Articles

Enhancing Methane Removal Efficiency of ZrMnFe Alloy by Partial Replacement of Fe with Co.

High-purity hydrogen is extensively employed in chemical vapor deposition, and the existence of methane impurity significantly impacts the device performance. Therefore, it is necessary to purify hydrogen to remove methane. The ZrMnFe getter commonly used in the industry reacts with methane at a temperature as high as 700 ∘C, and the removal depth is not sufficient. To overcome these limitations, Co partially substitutes Fe in the ZrMnFe alloy. The alloy was prepared by suspension induction melting method, and was characterized by means of XRD, ICP, SEM and XPS. The concentration of methane at the outlet was detected by gas chromatography to characterize the hydrogen purification performance of the alloy. The removal effect of the alloy on methane in hydrogen increases first and then decreases with the increase in substitution amount, and increases with the increase in temperature. Specifically, the ZrMnFe0.7Co0.3 alloy reduces methane levels in hydrogen from 10 ppm to 0.215 ppm at 500 ∘C. ZrMnFe0.7Co0.3 alloy can remove 50 ppm of methane in helium to less than 0.01 ppm at 450 ∘C, demonstrating its excellent methane reactivity. Moreover, Co substitution reduces the formation energy barrier of ZrC, and Co in the electron-rich state demonstrates superior catalytic activity for methane decomposition.

Effect of coexistence of H2S on production of hydrogen and solid carbon by methane decomposition using Fe catalyst

Biogas derived from livestock manure and food residue contains CO2 and H2S as well as methane. The effect of CO2 and H2S coexistence on the production of hydrogen and solid carbon by methane decomposition over iron oxide catalysts was investigated. The catalytic activity for methane decomposition was decreased by the coexistence of H2S. Moreover, the activity decrease was aggravated by the coexistence of CO2 as well as H2S, and higher temperature was required to mitigate the activity decrease by the coexistence of CO2. By increasing the amount of catalyst, the upstream catalyst was preferentially poisoned, but the downstream catalyst developed catalytic activity thanks to its sacrifice. With 2 g of catalyst, the maximum conversion of pure methane was about 85% at 840 °C, but it was slightly less than 80% in the presence of H2S or H2S + CO2. When the catalyst amount was increased to 4 g, the conversion of pure methane was about 90% at 800 °C, but 84% in the presence of H2S and 80% in the presence of H2S + CO2. The poisoning by H2S was irreversible at low temperatures but became reversible at higher temperatures. Since H2S is adsorbed by the deposited carbon, the procedure for further removal of H2S may be omitted. The coexistence of H2S also affected the shape of the deposited carbon. Although carbon-based catalysts are known to be effective for methane decomposition in the presence of H2S, iron oxide catalysts have the advantage of superior methane conversion at low temperatures. By flowing methane with CO2 and H2S from the downstream side after the reaction flowing from the upstream side for a certain period of time, the catalytic lifetime was drastically extended and the amount of hydrogen and solid carbon produced was dramatically increased, compared to the case of flowing from upstream all the way.

Production of COx-Free Hydrogen and Few-Layer Graphene Nanoplatelets by Catalytic Decomposition of Methane over Ni-Lignin-Derived Nanoparticles.

Nickel (Ni)-lignin nanocomposites were synthesized from nickel nitrate and kraft lignin then catalytically graphitized to few-layer graphene-encapsulated nickel nanoparticles (Ni@G). Ni@G nanoparticles were used for catalytic decomposition of methane (CDM) to produce COx-free hydrogen and graphene nanoplatelets. Ni@G showed high catalytic activity for methane decomposition at temperatures of 800 to 900 °C and exhibited long-term stability of 600 min time-on-stream (TOS) without apparent deactivation. The catalytic stability may be attributed to the nickel dispersion in the Ni@G sample. During the CDM reaction process, graphene shells over Ni@G nanoparticles were cracked and peeled off the nickel cores at high temperature. Both the exposed nickel nanoparticles and the cracked graphene shells may participate the CDM reaction, making Ni@G samples highly active for CDM reaction. The vacancy defects and edges in the cracked graphene shells serve as the active sites for methane decomposition. The edges are continuously regenerated by methane molecules through CDM reaction.

Modelling the hydrodynamics and kinetics of methane decomposition in catalytic liquid metal bubble reactors for hydrogen production

Bubble reactors using molten metal alloys (e.g, nickel-bismuth and copper-bismuth) with strong catalytic activity for methane decomposition are an emerging technology to lower the carbon intensity of hydrogen production. Methane decomposition occurs non-catalytically inside the bubbles and catalytically at the gas-liquid interface. The reactor performance is therefore affected by the hydrodynamics of bubble flow in molten metal, which determines the evolution of the bubble size distribution and of the gas holdup along the reactor height. A reactor model is first developed to rigorously account for the coupling of hydrodynamics with catalytic and non-catalytic reaction kinetics. The model is then validated with previously reported experimental data on methane decomposition at several temperatures in bubble columns containing a molten nickel-bismuth alloy. Next, the model is applied to optimize the design of multitubular catalytic bubble reactors at industrial scales. This involves minimizing the total liquid metal volume for various tube diameters, melt temperatures, and percent methane conversions at a specified hydrogen production rate. For example, an optimized reactor consisting of 891 tubes, each measuring 0.10 m in diameter and 2.11 m in height, filled with molten Ni0·27Bi0.73 at 1050 °C and fed with pure methane at 17.8 bar, may produce 10,000 Nm3.h−1 of hydrogen with a methane conversion of 80% and a pressure drop of 1.6 bar. The tubes could be heated in a fired heater by burning either a fraction of the produced hydrogen, which would prevent CO2 generation, or other less expensive fuels.

Mesoporous Ni/MeOx (Me = Al, Mg, Ti, and Si): Highly efficient catalysts in the decomposition of methane for hydrogen production

The concurrent production of COx-free hydrogen and multi-walled carbon filaments by thermocatalytic decomposition of methane is advantageous in the environmental and energy catalysis. In the present work, a facile “one-pot” evaporation-induced self-assembly strategy was effectively adopted to fabricate the nickel catalysts supported on mesoporous Al2O3, SiO2, TiO2, and MgO, and their catalytic activities for methane decomposition were evaluated for the first time. The structural, textural, and redox properties of the as-obtained materials were characterized using a number of analytical techniques. The nitrogen sorption analysis indicated the presence of a mesoporous structure due to homogeneous aggregation of the catalyst particles with a high specific surface area of 32–236 m2/g. Among all of the catalysts, Ni/MgO exhibited the best catalytic activity for methane decomposition (65% methane conversion at 600 °C and GHSV of 48,000 mL/(g h)). The activity increased when Ni loading increased from 25 to 55 wt%. The investigation on the correlation between catalytic performance and promoter doping effect suggests that incorporating copper into the MgO support considerably enhanced the catalytic activity and stability at high temperatures. The XPS results reveal that doping of Cu to Ni/MgO enhanced the adsorption and activation of oxygen molecules. In addition, the disordered crystalline carbon filaments with different diameters and good crystallinity were generated on the surface of the Cu-doped Ni/MgO catalysts.

Catalytic activity of several carbons with different structures for methane decomposition and by-produced carbons

Since methane decomposition has no CO2 emissions, it is attracting attention as a hydrogen production method with a low environmental burden. Understanding the structure of the produced carbon is important for long-term stable production of hydrogen. In this study, methane decomposition was carried out on carbons with several different structures (activated carbon (AC), carbon black (CB), meso-porous carbon (MC), and carbon nanofiber (CNF)). We have found that the carbon produced by methane decomposition decreases activity by covering the catalyst, but itself also acts as a catalyst irrespective of the original carbon catalysts. All of the catalysts continued to maintain a methane conversion ratio of about 17% by catalyzing the produced carbon even after the activity was lowered. By analysis of the catalysts before and after the experiment, it was shown that the produced carbon covered the catalyst surface and resulted in a specific surface area of about 10 m2/g and the intensity ratio of the D band to the G band in the Raman spectra (ID/IG) of around 1.55 irrespective of the original carbons structures. We proposed that Raman spectroscopy is an effective method for evaluating initial catalytic activity for methane decomposition because ID/IG of the catalysts before the experiment have a linear relationship with the methane conversion ratio per unit surface area in the early stage of the reaction.

Catalytic decomposition of methane over rare earth metal (Ce and La) oxides supported iron catalysts

The concurrent production of carbon oxides-free hydrogen and crystalline carbon by the thermocatalytic decomposition of methane is advantageous for environmental and energy catalysis. In the present work, rare earth metal oxide-supported iron catalysts were effectively prepared via a simple co-precipitation method, and their catalytic activity for methane decomposition was evaluated for the first time. The structural, textural and redox properties of the prepared catalysts were characterized using different analytical methods. The powder X-ray diffraction patterns of the catalysts indicated the presence of CeO2 and Fe2O3 as different phases in the fresh Fe/CeO2 catalyst and La(OH)3, Fe2O3, and LaFeO3 as different phases in the fresh Fe/La2O3 catalysts. However, large amounts of cerium and lanthanum orthoferrites were identified in the reduced samples. The nitrogen sorption analysis indicated the presence of a mesoporous texture due to the homogeneous aggregation of catalyst particles. The catalysts showed high catalytic activity and stability for methane decomposition, and no deactivation was observed for a period of 360 min of time on stream. A maximum hydrogen yield of 66 ± 1% was observed for both of the catalysts at 800 °C. However, the Fe/CeO2 catalyst showed high catalytic stability, where the highest initial and final hydrogen yield was found to be almost constant for the Fe/CeO2 catalyst. However, a substantial drop in the hydrogen yield was noticed for the Fe/La2O3 catalyst during the course of the reaction. The improved surface stabilization and fine dispersion of iron nanocrystals on the ceria matrix made it highly active and stable compared to the lanthanum-based catalyst for the methane decomposition reaction. The encapsulation of metallic iron by carbon deposited on the Fe/La2O3 catalyst could be responsible for the low catalytic stability. Multi-walled carbon nanotubes with different shapes were deposited on the catalysts with respect to the support material. A set of spiral-shaped multi-walled carbon nanotubes with a double helical-shaped chain-like structure were deposited on the Fe/La2O3 catalyst, that is rarely formed in methane decomposition. The nanocarbon deposited on the Fe/CeO2 catalyst exhibited a high degree of crystallinity and graphitization, as shown by the Raman spectroscopy.

Catalytic decomposition of undiluted methane into hydrogen and carbon nanotubes over Pt promoted Ni/CeO2 catalysts

A series of Pt promoted Ni/CeO2 catalysts were prepared and characterized, and their catalytic activity for methane decomposition was reported.

Stabilization of Ni, Fe, and Co nanoparticles through modified Stöber method to obtain excellent catalytic performance: Preparation, characterization, and catalytic activity for methane decomposition

Nanoparticle formation from their respective precursors through bottom-up method is a very fascinating practice in nanotechnology. This research contribution discusses two promising bottom-up methods: (i) controlled precipitation of Ni, Fe, and Co nanoparticles and reinforcement with silicate through modified Stöber method and (ii) chemical vapor deposition of nanocarbon from methane. Experimental results reveal that metal oxide particles were formed as single-crystal nanoparticles after silicate addition and exhibited catalytic activity enhancing features, such as low particle size and high surface area and porosity. The single-point surface area increased from 62.22 m2/g to 91.50 m2/g, 35.13 m2/g to 97.31 m2/g, and 14.29 m2/g to 48.96 m2/g for n-NiO, n-FeO, and n-CoO nanoparticles, respectively, after silicate incorporation. Preliminary catalytic activity was also analyzed in a fixed-bed pilot plant. n-NiO/SiO2 nanoparticles were found to be the most efficient catalyst for thermocatalytic methane decomposition and generated 57.28% hydrogen at 730 °C. Physical and chemical characteristics of the fabricated nanocatalysts were determined using N2 adsorption–desorption measurement (Brunauer–Emmett–Teller method), X-ray diffraction (XRD), transmission electron microscopy (TEM), hydrogen temperature-programmed reduction (H2-TPR), and field-emission scanning electron microscopy (FESEM) analyses. Produced nano-carbon was inspected with TEM, FESEM and XRD.

Selective growth of single-walled carbon nanotubes over Co–MgO catalyst by chemical vapor deposition of methane

The selective synthesis of SWCNTs with narrow chirality and diameter distribution by methane decomposition over a Co–MgO catalyst is reported. Raman spectroscopy, temperature programmed oxidation (TPO), UV–Vis–NIR absorption spectroscopy, and nitrogen physisorption were used to probe SWCNTs morphology, reaction selectivity, SWCNTs chirality and diameter distribution, and carbon yield. The catalyst was examined by nitrogen physisorption, X-ray diffraction (XRD), temperature programmed reduction (TPR), and UV–Vis-diffuse reflectance spectroscopy to elucidate the structure and chemical state of the species responsible for SWCNT growth. The results established a clear link between the degree of dispersion of Co species inside the MgO lattice and the catalyst activity and selectivity for SWCNT growth. High dispersion and stabilization of Co species influenced catalytic activity for methane decomposition and the high SWCNT selectivity. The yield of carbon and SWCNT selectivity increased with an increase in temperature, however, SWCNTs diameter distribution shifts to larger diameter tubes as synthesis temperature was increased.

Methane Activation by Nonthermal Plasma Generated Carbon Aerosols

Activation of methane is one of the most challenging problems in catalysis due to the refractory nature of methane. Of particular interest is catalytic dissociation of methane as an attractive CO2-free route to production of hydrogen from natural gas. Synthesis, characterization, and evaluation of catalytic activity of plasma-generated carbon aerosols for methane decomposition reaction are reported in this work. Carbon aerosols were produced by nonthermal plasma assisted decomposition of a carbon precursor gas (methane or propane) at near-ambient conditions. Plasma-generated carbons exhibited significantly higher catalytic activity for methane decomposition than known carbon-based catalysts with a comparable surface area. The mechanism of methane activation as well as the interrelation between the nanostructure of the plasma-generated carbons and their catalytic activity are discussed. The high catalytic activity of plasma-generated carbons for methane decomposition is attributed to the increased surface concentration of high-energy sites formed during nonequilibrium plasma assisted dissociation of a carbon precursor.

AIR LIQUIDE HYDROGEN PLANT FOR BASF

Bubble reactors using molten metal alloys (e.g, nickel-bismuth and copper-bismuth) with strong catalytic activity for methane decomposition are an emerging technology to lower the carbon intensity of hydrogen production. Methane decomposition occurs non-catalytically inside the bubbles and catalytically at the gas-liquid interface. The reactor performance is therefore affected by the hydrodynamics of bubble flow in molten metal, which determines the evolution of the bubble size distribution and of the gas holdup along the reactor height. A reactor model is first developed to rigorously account for the coupling of hydrodynamics with catalytic and non-catalytic reaction kinetics. The model is then validated with previously reported experimental data on methane decomposition at several temperatures in bubble columns containing a molten nickel-bismuth alloy. Next, the model is applied to optimize the design of multitubular catalytic bubble reactors at industrial scales. This involves minimizing the total liquid metal volume for various tube diameters, melt temperatures, and percent methane conversions at a specified hydrogen production rate. For example, an optimized reactor consisting of 891 tubes, each measuring 0.10 m in diameter and 2.11 m in height, filled with molten Ni0·27Bi0.73 at 1050 °C and fed with pure methane at 17.8 bar, may produce 10,000 Nm3.h−1 of hydrogen with a methane conversion of 80% and a pressure drop of 1.6 bar. The tubes could be heated in a fired heater by burning either a fraction of the produced hydrogen, which would prevent CO2 generation, or other less expensive fuels.