Catalytic Decomposition Of Methane Reaction Research Articles

Carbon modified active pairs of Co-Co2C for CO2 hydrogenation to alcohols

The transformation process of CO2-to-alcohols can achieve the reduction in emissions of carbon dioxide and hydrogen storage, considered to be the up-and-coming way to realize the utilization of CO2. Co-based catalysts are promising, where Co0/Coδ+ is the critical active pair. The challenge is how to construct and tailor the active pair of Co0/Coδ+, to which a new scheme has been proposed in this work. Dual active sites of Co-Co2C were constructed and tailored by the carbon deposition via catalytic decomposition of methane reaction in this scheme. The formation of Co2C species promoted the non-dissociation of COx intermediates, which greatly contributed to the synthesis of alcohols. Not only the state of the Co active component changed with the addition of carbon species, but its own electron-donating effect increased the activation rate of CO2. The catalyst exhibited a CO2 turnover frequency of 7.4 × 10−3 s−1, 16.9 C-mol% and 29.5 C-mol% for ethanol and methanol selectivity at 270 °C and 3 MPa, respectively. This study provides a reference for catalyst design with the help of carbon species to modulate the state of active components.

Decarbonizing Natural Gas: A Review of Catalytic Decomposition and Carbon Formation Mechanisms

In the context of energy conservation and the reduction of CO2 emissions, inconsistencies between the inevitable emission of CO2 in traditional hydrogen production methods and eco-friendly targets have become more apparent over time. The catalytic decomposition of methane (CDM) is a novel technology capable of producing hydrogen without releasing CO2. Since hydrogen produced via CDM is neither blue nor green, the term “turquoise” is selected to describe this technology. Notably, the by-products of methane cracking are simply carbon deposits with different structures, which can offset the cost of hydrogen production cost should they be harvested. However, the encapsulation of catalysts by such carbon deposits reduces the contact area between said catalysts and methane throughout the CDM process, thereby rendering the continuous production of hydrogen impossible. This paper mainly covers the CDM reaction mechanisms of the three common metal-based catalysts (Ni, Co, Fe) from experimental and modelling approaches. The by-products of carbon modality and the key parameters that affect the carbon formation mechanisms are also discussed.

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.

Co-, Cu- and Fe-Doped Ni/Al2O3 Catalysts for the Catalytic Decomposition of Methane into Hydrogen and Carbon Nanofibers

The catalytic decomposition of methane (CDM) process produces hydrogen in a single stage and avoids CO2 emission thanks to the formation of high added value carbon nanofilaments as a by-product. In this work, Ni monometallic and Ni–Co, Ni–Cu, and Ni–Fe bimetallic catalysts are tested in the CDM reaction for the obtention of fishbone carbon nanofibers (CNF). Catalysts, in which Al2O3 is used as textural promoter in their formulation, are based on Ni as main active phase for the carbon formation and on Co, Cu, or Fe as dopants in order to obtain alloys with improved catalytic behaviour. Characterization of bimetallic catalysts showed the formation of particles of Ni alloys with a bimodal size distribution. For the doping content studied (5 mol. %), only Cu formed an alloy with a lattice constant high enough to be able to favor the carbon diffusion through the catalytic particle against surface diffusion, resulting in higher carbon formations, longer activity times, and activity at 750 °C; whereas Ni, Ni–Co, and Ni–Fe catalysts were inactive. On the other hand, Fe also improved the undoped catalyst performance presenting a higher carbon formation at 700 °C and the obtention of narrow carbon nanofilaments from active Ni3Fe crystallites.

Screening of Ni-Cu bimetallic catalysts for hydrogen and carbon nanofilaments production via catalytic decomposition of methane

The catalytic decomposition of methane (CDM) is a H2 production process in which the CO2 emission of conventional processes is avoided and from which carbon nanofilaments can be obtained as a high added value by-product. In this work, we present a thermogravimetry-based screening of catalysts according to their carbon production in the CDM reaction. Catalysts studied were based on Ni as active phase, using two textural promoters (Al2O3 or MgO) and Cu as dopant element in different proportions: 2.5, 5.0, 7.5 and 10 mol %. Cu doping resulted in an increase in both the maximum temperature of activity (>100 °C) and the carbon formation rate, which were maximum for a Cu content of 7.5 mol %, regardless of the textural promoter used. The formation of a solid solution of Ni(x)Cu(1-x), with lattice constants and particle size distribution highly dependent on the Cu content, led to the formation of fishbone carbon nanofibers with different morphological features, such as the α angle between the graphene stacks and the growth axis of the nanofilament, the diameter, the length and the formation or not of an inner hollow.

Evolution of the Ni-Cu-SiO2 catalyst for methane decomposition to prepare hydrogen

Catalytic decomposition of methane (CDM) is a simple process for the production of high-purity, COX-free hydrogen, and Ni-Cu system catalysts are widely used in the filed of hydrogen production. However, Ni-Cu catalysts easily lose their activities at higher temperatures. To study the methods for facilitating the catalytic performance with Ni-Cu-SiO2 catalysts (Ni:Cu:SiO2=65:10:25, mass fraction) during the CDM reaction, and for increasing the utilization rate of the catalyst, a series of kinetic experiments were designed to test and improve the catalytic performance, and the study of generated by-products carbon structures was also carried out. Based on the kinetic experiments, TEM images, XRD data, and Raman spectra, it is found that the introduction of methane into the reactor at lower temperatures prevented the sintering of the catalyst particles into bigger clusters and increased the catalytic activity and lifetime. Moreover, this study also proved that fragmentation process was the key factor contributing to the deactivation of Ni-Cu catalysts at higher temperature. In addition, due to the disordered carbon formed over Ni-Cu-SiO2 catalysts during methane decomposition, the deactivated catalysts exhibit recovered activity at higher temperatures. For the deactivated catalysts recovered activity, the disordered carbon and the pore of generate by-products carbon structures made a big contribution to crack methane at high temperature, and the pores blocked by the generated carbons might cause those catalysts lose activity again.

Methane decomposition over high-loaded Ni-Cu-SiO2 catalysts

The performance of Ni-SiO2 and Ni-Cu-SiO2 during repeated catalytic decomposition of methane (CDM) reactions and subsequent regeneration of the deactivated catalysts with air has been studied. The catalytic activity of the 75%Ni-25%SiO2 catalyst in the second and third CDM was lower than that during the first, while the lifetime of the catalyst did not change significantly. Both the lifetime and the catalytic activity of 65%Ni-10%Cu-25%SiO2 in the second and third CDM reactions decreased significantly. 55%Ni-20%Cu-25%SiO2 showed better performance than the other two catalysts, and its activity and lifetime did not change significantly until the third CDM reaction. The hydrogen yields of 55%Ni-20%Cu-25%SiO2 were 56.8gH2/gcat., 42.8gH2/gcat., and 2.4gH2/gcat. for the first, second, and third CDM reactions, respectively. Spherical carbon structures were observed on the catalysts following all three CDM reactions over 75%Ni-25%SiO2. However, similar carbon structures were only observed following the second and third CDM over 65%Ni-10%Cu-25%SiO2, and only following the third cycle with 55%Ni-20%Cu-25%SiO2. The formation of spherical carbon during the repeated CDM reactions strongly influenced the performance of the catalysts.

High-loaded Ni[sbnd]Cu[sbnd]SiO2 catalysts for methane decomposition to prepare hydrogen and carbon filaments

NiSiO2 and NiCuSiO2 catalysts were prepared by a hetero-phase sol–gel method. Two types of kinetic experiments (routes I, II) were designed to test the catalytic performance of the NiCuSiO2 catalysts, and the textural properties of the carbon filaments were characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD), and Raman spectroscopy. Compared to traditional method of catalytic decomposition of methane (CDM) reaction, where the reduction process and the decomposition of methane occurred at the same temperature (route I), the NiCuSiO2 catalysts exhibited superior catalytic performance at a reaction temperature of 750 °C using route II. This finding was attributable to the introduction of methane into the reactor at lower temperatures, which can prevent the NiCu particles from sintering into larger clusters during the thermal treatment processes, and the carbon filament by-product could play the role of a growing support to enhance the dispersion of the metal particles. However, when the catalyst decomposition occurred at 750 °C, NiCu alloy particles broke down, and a phase separation was observed, which might be related to the loss in catalytic activity. Due to the disordered carbon formed over the NiCuSiO2 catalysts during the CDM reaction, the generated carbon filaments might begin to crack methane at a higher temperature.

Co-production of hydrogen and carbon nanofibers from catalytic decomposition of methane over LaNi(1−x)Mx O3−α perovskite (where M = Co, Fe and X = 0, 0.2, 0.5, 0.8, 1)

In this work, LaNi(1−x)Mx O3−α (where M = Co, Fe and X = 0, 0.2, 0.5, 0.8, 1) perovskite have been successfully used as catalyst precursors for catalytic decomposition of methane (CDM). LaNi0.8Fe0.2O3−α and LaNi0.8Co0.2O3−α perovskite exhibited better catalytic performance in terms of hydrogen and carbon nanofibers yields during CDM reaction as compared to LaNiO3 perovskite, which can be attributed to the formation of the smaller and more uniform catalyst particles. Moreover, the reduced LaNi(1−x)FexO3−α perovskite also produces filamentous carbons with “chain–like structure” which is different from the filamentous carbons with “tube–like structure” produced from the reduced LaNiO3 and LaNi(1−x)CoxO3−α perovskite. This is due to the different growth mechanisms of those filamentous carbons over the different catalysts. More particularly, chain–like structure filamentous carbons were produced through “pulse–growth mechanism” over the reduced LaNi(1−x)FexO3−α perovskite, whereas tube–like structure filamentous carbons were produced through “smooth–growth mechanism” over the reduced LaNiO3 and LaNi(1−x)CoxO3−α perovskite.

Metal/activated carbon systems as catalysts of methane decomposition reaction

Catalytic decomposition of methane (CDM) is an attractive approach to COx-free production of hydrogen. This reaction is often performed with the use of metal catalysts, however, their common drawback is a fast deactivation of the metal caused by accumulation of carbonaceous deposit on the catalyst surface. The catalyst stability can be improved by the proper choice of the support of the metallic active phase. In this aspect much attention has been paid to activated carbon (AC) as it can be used in CDM reaction both as a catalyst on its own and as a support of active phase. In this study, thermo-catalytic decomposition of methane with the use of different metals (Pt, Pd, Cr) supported on activated carbon was performed. The active phase support was prepared from ash wood by chemical activation with KOH and the final catalytic systems were obtained by incipient wetness impregnation of support with salts of the above metals. The systems prepared were tested in the methane decomposition reaction carried out at three different temperatures: 750, 850 or 950°C. The most effective catalysts among the tested ones were Pd/AC systems, whereas Cr supported on AC showed even worse catalytic performance than unloaded activated carbon used as a catalyst.

Hydrogen production by propylene-assisted decomposition of methane over activated carbon catalysts

Catalytic decomposition of methane (CDM) permits obtaining hydrogen in high yields and – what is essential – it does not lead to release of CO 2. Unfortunately, most of the catalysts used in this process undergo fast deactivation. Their possible regeneration, consisting in the removal of pore blocking carbonaceous deposit of low catalytic activity, leads to generation of undesirable carbon dioxide. An alternative solution for maintaining high catalyst activity in the CDM reaction can be generation of the catalytically active carbonaceous deposit on its surface. Such a deposit can be obtained by decomposition of different organic substances. This paper reports on methane decomposition carried out in the presence of propylene (used in the concentration of 10 or 20%). The reaction was performed at three temperatures of 750 °C, 850 °C or 950 °C. Three types of activated carbon were tested as catalysts: the first one was obtained by activation of pine wood biomass with Na 2CO 3, whereas the second and third ones were commercial carbons (WG-12 and Norit RX3 Extra). According to the results, the addition of propylene to the CDM system effectively reduces deactivation of the activated carbon catalysts and permits fast stabilisation of their catalytic activity at a high level.

Preparation and evaluation of Co/Al 2O 3 catalysts in the production of hydrogen from thermo-catalytic decomposition of methane: Influence of operating conditions on catalyst performance

This paper presents the synthesis of Co-doped Al 2O 3 catalysts, developed by our group, with porous structures and high surface areas. The catalytic activity of the materials obtained was evaluated in the catalytic decomposition of methane, which is an attractive method for CO/CO 2-free production of hydrogen, particularly for fuel cell applications. The catalysts were shown to be active and stable in relation to the catalytic decomposition of methane reaction. It was observed that the catalytic performance is dependent on the catalyst characteristics and on the operational conditions employed. The conversion of methane increased with metal loading, reaction temperature and N 2:CH 4 molar ratio.

Preparation and evaluation of porous nickel-alumina spheres as catalyst in the production of hydrogen from decomposition of methane

This paper presents the synthesis of Al 2O 3 and Ni-doped Al 2O 3 spherical catalysts, developed by our group, with porous structures and high surface areas. The catalytic activity of the materials obtained was evaluated in the catalytic decomposition of methane, which is an attractive method for CO/CO 2-free production of hydrogen, particularly for fuel cell applications. The catalysts were shown to be active and stable in relation to the catalytic decomposition of methane reaction. After the catalytic tests, characterization of the deposited carbon was carried out by transmission electron microscopy, scanning electron microscopy and Raman spectroscopy. The analyses indicated the presence of single-walled nanotubes (SWNTs) and multiwalled nanotubes (MWNTs). It was observed that the catalytic behaviour and the form of carbon produced depend on the characteristics of the sites present on the catalyst surface and on the operational conditions employed.