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The reaction of methane decomposition is an endothermic process that produces hydrogen without any impurities as a gas product and carbon nanotubes/carbon nanofibers as a solid product. In this study, NiO–MgO catalysts with different nickel loadings (20, 30, 40, and 50 wt. %) were synthesized using the mechanochemical method. The Physicochemical features of the synthesized catalysts were characterized by various methods such as BET, XRD, SEM, TPO, and H2-TPR. The prepared samples were tested in the methane decomposition process at various temperatures under the GHSV value of 48,000 ml/(gcat h). Among the prepared samples, the 50wt.%NiO–MgO exhibited the best activity (40% methane conversion at 575 °C) in this process due to its higher concentration of active metal and better catalyst reducibility. Also, the effect of different parameters such as feed ratio, GHSV, and calcination temperature was studied on the activity of this catalyst. The results showed that with the increase of GHSV and feed ratio, the methane conversion decreased due to the lesser contact time and diminishing the proportion of accessible active sites per methane entrance molecules. Moreover, the results showed that with the rise of calcination temperature from 500 to 700 °C, the methane conversion decreased due to the sintering of nickel particles. The results also showed that the addition of 15 wt.% Cr2O3 to the catalyst formulation improved the catalytic performance and lifetime in the thermocatalytic decomposition of methane due to the higher reducibility and dispersion of the active species on the catalyst surface. [ABSTRACT FROM AUTHOR]

Boron-doped carbon nanotubes (BCNTs) with varying B content (0–8 at%) were prepared by thermo-catalytic decomposition of ethanol in presence of boric acid at 1073 K. It was observed that hydrogen adsorption capacity improved to a critical B content of 3.86 at% and then decreased. Maximum hydrogen adsorption was found to be 0.497 wt% at 273 K and 16 bar with 3.86 at% of boron doping in CNTs. With the help of transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy, it was found that in addition to dopant concentration, dopant bonding with carbon structures, crystallinity and defects play pivotal roles in determining the extent of hydrogen adsorption by BCNTs. The thermogravimetric studies revealed the oxidation stability of the BCNTs. The hydrogen adsorption kinetics was found to follow the pseudo-second-order model. The rate constant value was minimum for the BCNT with the highest hydrogen storage capacity. [Display omitted] • B-doped CNTs (BCNTs) with varying B at% were prepared using floating catalyst CVD method. • Hydrogen storage values were maximum for BCNTs with 3.86 at% B content. • B doping above 3.86 at% negatively affects the hydrogen storage values. • The nature of bond formation between B and C influenced the storage. • The hydrogen adsorption data followed pseudo-second-order kinetic model. [ABSTRACT FROM AUTHOR]

Thermocatalytic decomposition of methane is proposed to be an economical and green method to produce CO x -free hydrogen and carbon nanomaterials. In this work, the catalytic performance of Ni–Mn–Ru/Al 2 O 3 catalyst under different reaction parameters (such as, pre-reduction temperature, reaction temperature, space velocity, etc.) were investigated to obtain optimum reaction conditions. The catalysts were characterized by N 2 adsorption/desorption, X-ray diffraction, inductively coupled plasma optical emission spectrometer and hydrogen temperature programmed reduction. For the 60 wt% Ni-5 wt% Mn-10 wt% Ru/Al 2 O 3 catalyst using Ru(NO)(NO 3) x (OH) y (x + y = 3) as Ru precursor, the methane conversion rate obtained is high as 93.76% under optimum reaction conditions (reduction at 700 °C for 1 h, reaction at 750 °C, GSHV = 36,000 mL/g cat h). Carbon nanomaterials formed during the process of methane thermocatalytic decomposition were characterized by scanning electron microscopy, thermal gravimetric analyzer and Raman spectroscopy. Carbon nanofibers were formed over all the Ni–Mn–Ru/Al 2 O 3 catalysts. • Performance of Ni–Mn–Ru/Al 2 O 3 catalyst for TCD of CH 4 was studied. • The CH 4 conversion rate was 93.76% under optimum reaction conditions. • Carbon nanofibers were formed on all Ni–Mn–Ru/Al 2 O 3 catalysts. [ABSTRACT FROM AUTHOR]

Hydrogen is an energy carrier of the future need. It could be produced from different sources and used for power generation or as a transport fuel which mainly in association with fuel cells. The primary challenge for hydrogen production is reducing the cost of production technologies to make the resulting hydrogen cost competitive with conventional fuels. Thermocatalytic decomposition (TCD) of methane is one of the most advantageous processes, which will meet the future demand, hence an attractive route for CO free environment. The present study deals with the production of hydrogen with 30 wt% of Ni impregnated in commercially available activated carbon and carbon black catalysts (samples coded as Ni/AC and Ni/CB, respectively). These combined catalysts were not attempted by previous studies. Pure form of hydrogen is produced at 850 °C and volume hourly space velocity (VHSV) of 1.62 L/h g on the activity of both the catalysts. The analysis (X-ray diffraction (XRD)) of the catalysts reveals moderately crystalline peaks of Ni, which might be responsible for the increase in catalytic life along with formation of carbon fibers. The activity of carbon black is sustainable for a longer time compared to that of activated carbon which has been confirmed by life time studies (850 °C and 54 sccm of methane). [ABSTRACT FROM AUTHOR]

Abstract: Thermocatalytic decomposition (TD) of natural gas (NG) is a promising CO2-free approach to hydrogen production, however, the practical realization of the sustainable TD process faces significant technical challenges due to rapid deactivation of existing catalysts by carbon deposits. In this work, the authors report on TD of NG and methane over a new type of carbon-based catalyst: plasma-generated carbon aerosols. The carbon aerosols were produced by non-thermal plasma-assisted decomposition of NG at near-ambient conditions. The plasma-generated carbons exhibit highest catalytic activity for methane (or NG) decomposition among known carbon-based catalysts with a comparable surface area. The nanostructure of the plasma-generated carbons was characterized and found to be consistent with highly disordered (amorphous) carbon. It is demonstrated that the combination of the carbon aerosol generator with the TD reactor provides a means for sustainable production of hydrogen and carbon from NG with a relatively high energy efficiency. [Copyright &y& Elsevier]

A fluidized bed reactor made of quartz with 0.055 m i.d. and 0.65 m in height was employed for the thermocatalytic decomposition of methane to produce CO2 free hydrogen. The fluidized bed reactor was proposed in order to overcome the reactor plugging problem due to carbon deposition, which was resulted in the shut-down of the fixed bed reactor system. Several kinds of activated carbons were employed as the catalyst to examine the reaction activity. The experimental results in this study were compared with that of fixed bed reactor. The reaction rate and deactivation of carbon catalyst were similar to that of lab scale fixed bed reactor system. The deactivation due to carbon deposition was verified with the SEM images of fresh and used carbon catalysts. The effects of gas velocity, reaction temperature and particle size on the reaction rates were also investigated. From the experimental results of this study, the optimum operating conditions for fluidized bed were also determined. [Copyright &y& Elsevier]

• TCD TOF increases with Ni(0) particle size from 4.0–19.4 nm. • TCD is a structure sensitive reaction and is independent of support composition. • Large Ni(0) nanoparticles are selective towards CNT formation. • Small Ni(0) nanoparticles are selective towards graphitic carbon layers formation. • The deactivation is caused by a decrease in Ni nanoparticle size during reaction. Thermocatalytic decomposition of methane (TCD) is a promising approach for producing CO 2 -free hydrogen and solid carbon co-product. In this study, a series of Al 2 O 3 - and MgAl 2 O 4 -based Ni catalysts, prepared with varying synthesis and pretreatment methods, were evaluated for methane TCD performance at 650 °C and characterized before and after reaction to elucidate activity-structure relationships. We found that methane TCD turnover increases with Ni particle size. Further, large Ni particle sizes (i.e., >20 nm) are selective toward the formation of carbon nanotubes (CNTs), while small Ni particle sizes (i.e., <10 nm) are selective toward the formation of graphitic carbon layers. The formation of graphitic carbon layers block access to Ni active sites, thus rendering the catalyst inactive more quickly than when CNTs are produced. Additionally, the catalyst deactivation observed with time-on-stream is due to the fragmentation of Ni particles into smaller Ni particles followed by their encapsulation with graphitic carbon layers. [ABSTRACT FROM AUTHOR]