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Thermocatalytic decomposition is an efficient purification technology that is potentially applicable to degrading chemical warfare agents and industrial toxic gases. In particular, ZrO2 has attracted attention as a catalyst for the thermocatalytic decomposition of dimethyl methylphosphonate (DMMP), which is a simulant of the nerve gas sarin. However, the influence of the crystal phase and morphology on the catalytic performance of ZrO2 requires further exploration. In this study, monoclinic- and tetragonal-phase ZrO2 (m- and t-ZrO2, respectively) with nanoparticle, flower-like shape and hollow microsphere morphologies were prepared via hydrothermal and solvothermal methods, and their thermocatalytic decomposition of DMMP was systematically investigated. For a given morphology, m-ZrO2 performed better than t-ZrO2. For a given crystalline phase, the morphology of hollow microspheres resulted in the longest protection time. The exhaust gases generated by the thermocatalytic decomposition of DMMP mainly comprised H2, CO2, H2O and CH3OH, and the by-products were phosphorus oxide species. Thus, the deactivation of ZrO2 was attributed to the deposition of these phosphorous oxide species on the catalyst surface. These results are expected to help guide the development of catalysts for the safe disposal of chemical warfare agents. [ABSTRACT FROM AUTHOR]

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]

Thermo-Catalytic decomposition (TCD) of methane can be regarded as a cornerstone towards the development of greenhouse gas-free processes for pure hydrogen production. Most studies of TCD focused on process schemes where the extraction of hydrogen from the gaseous CH 4 − H 2 mixture is accomplished in a unit separated from the reaction environment. In this article, we investigate numerically a different setup that involves the use of a semi-batch annular fixed-bed membrane reactor. The permeselective membrane allows to lower the reaction temperature, overcoming equilibrium limitations. The intrinsic time-dependency of the process (induced by catalyst deactivation due to massive deposition of the solid carbon product), together with spatial concentration gradients triggered by hydrogen permeation through the membrane give rise to a non-trivial dynamical behavior of the reactor. Specifically, we observe that a localized reaction front develops near the membrane at the early stage of the process. At later times, the front moves away from the membrane zone throughout the bed as larger and larger portions of the catalyst become inactive. The front thickness and dynamics are found to have a strong influence upon the overall timescales of the reaction. A dimensionless analysis of the dependence of the reactor efficiency on the pressure and on the catalyst activity (here quantified by the Damköhler number) is carried out by assuming 550 °C as a working temperature. An optimal working pressure is found at relatively high Damköhler value. Qualitatively different operating modes of the membrane reactor in different regions of the pressure-Damköhler parameter space are identified and interpreted. • A 2d model for methane TCD in a hydrogen-permerselective membrane reactor is investigated. • Semi-batch operating conditions are enforced due to catalyst deactivation caused by carbon deposition. • The effect of pressure and catalyst activity on the conversion time is investigated. • A non-monotonic dependence of the process efficiency vs the operating pressure is found. • An optimal working pressure is identified. [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]

Abstract Thermocatalytic decomposition of methane is proposed to be an economical and green method to produce CO x -free hydrogen and carbon nanomaterial. In present work, 60 wt% Ni/Al 2 O 3 catalysts with different additives (Cu, Mn, Pd, Co, Zn, Fe, Mg) were prepared by co-impregnation method to investigate promotional effects of these metal additives on the activity and stability of 60 wt% Ni/Al 2 O 3 and find out a really effective promoter for decomposition of methane. The catalyst was characterized by N 2 adsorption/desorption, X-ray diffraction, scanning electron microscopy, inductively coupled plasma optical emission spectrometer and hydrogen temperature programmed reduction. While metal additives (5 wt%) were added into 60 wt% Ni/Al 2 O 3 , the activity stability of 60 wt% Ni/Al 2 O 3 was improved and the CH 4 conversion of 60 wt% Ni/Al 2 O 3 was also improved except Zn addition. Mn addition was found to improve the catalytic activity of 60 wt% Ni/Al 2 O 3 significantly and the CH 4 conversion of 5 wt% Mn-60 wt% Ni/Al 2 O 3 was ∼80%. Cu addition was found to remarkably improve the catalytic stability of 60 wt% Ni/Al 2 O 3 and the CH 4 conversion of 5 wt% Cu-60 wt% Ni/Al 2 O 3 decreased from 61% to 45% after 250 min of reaction time. Carbon nanomaterials formed in the thermocatalytic decomposition process were characterized by X-ray diffraction, scanning electron microscopy, thermal gravimetric analyzer and Raman spectroscopy. Carbon deposits consist of amorphous carbon and carbon nanofibers. Graphical abstract Effect of different 5 wt% M-60 wt% Ni/Al 2 O 3 catalysts on methane conversion. Image 1 Highlights • Performance of Ni/Al 2 O 3 with different metal additions for TCD of CH 4 was studied. • The catalytic activity of Ni/Al 2 O 3 was improved by adding Cu, Mn, Pd, Co, Fe, Mg. • Carbon nanofibers were formed on all Ni-based catalysts. [ABSTRACT FROM AUTHOR]

Ni–Pd/Al 2 O 3 catalysts were prepared and employed for the simultaneous production of CO x -free hydrogen and carbon nanofibers via methane thermocatalytic decomposition. The results showed that the palladium addition to nickel catalyst improved the degree of reducibility and catalytic performance. Addition of palladium to nickel creates Ni–Pd alloy, which has the high activity for methane dissociation and increases the catalytic activity. The carbon diffusion in palladium is very faster than the diffusion in nickel. This leads to enhancing the rate of carbon diffusion and preventing the formation of encapsulating carbon, which increases the catalyst lifetime. Moreover, during the methane decomposition over Ni–Pd alloy, carbon nanofibers grow from several facets and form branched structure, which increases the rate of carbon migration and prevents the coverage of active sites. Scanning electron microscopy (SEM) analysis of the spent catalysts showed the formation of the intertwined filaments form carbon. [ABSTRACT FROM AUTHOR]

Ni/Al 2 O 3 catalysts with nickel loadings from 10 to 40 wt.% prepared by wet impregnation have been tested for the thermocatalytic decomposition of propane in the temperature range from 700 to 1100 °C in a fixed bed reactor. Full conversion of propane was observed in all cases. The hydrogen yield was found to increase at higher reaction temperature, at lower temperatures significant quantities of CH 4 were observed in the product gas. The Ni loading determined stability of the catalyst. After performing the catalytic decomposition reaction for a certain time, the carbon formed on the catalyst surface was removed by combustion with air. During this regeneration process carbon monoxide was always the main product. Repeated cycles of decomposition and regeneration were carried out. By using an automated control device, it was possible to ensure a continuous operation of the reactor for 65 h. For this period, stable H 2 yield was observed with a catalyst containing 40 wt.% Ni supported by Al 2 O 3 . Fresh and spent catalysts were analyzed by BET, X-ray fluorescence (XRF), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Carbon formed by the decomposition reaction was analyzed by thermogravimetric analysis (TGA) and SEM. [ABSTRACT FROM AUTHOR]

Abstract: The direct cracking of methane can be used to produce COx and NOx-free hydrogen for proton exchange membrane fuel cells. Recent studies have been focused on enhancing the hydrogen production using the direct thermocatalytic decomposition of methane as an attractive alternative to the conventional steam reforming process. We present the results of a systematic study of methane direct decomposition using a mixed conducting oxide, Y-doped BaCeO3, membrane. A dense disk-shaped BaCe0.85Y0.15O3 membrane was successfully prepared and covered with Pd film, as the catalyst for the methane decomposition. For the methane thermocatalytic decomposition, the methane gas was employed as reactant on the membrane side with a pressure of 102 kPa and rate of 70 ml/min at the reaction temperatures of 600, 700, and 800 °C. The hydrogen was selectively transported through the mixed conducting oxide membrane to the outer side. In addition, the carbon, which is a by-product after methane decomposition, showed the morphologies of sphere-shaped nanoparticles and the transparent sheets. [Copyright &y& Elsevier]

Abstract: Chemical kinetics of hydrogen production from the thermocatalytic decomposition (TCD) of methane at the early reaction stage and the steady state is modeled in this study. Numerical simulations are also carried out to figure out the detailed reaction phenomena in a catalyst bed which is packed with activated carbon. The effects of reaction (wall) temperature, catalyst mass, and reactant flow rate on the performance of methane TCD are evaluated. The predictions suggest that the CH4 conversion is linearly proportional to the reaction temperature at the early stage; the reaction is more sensitive to the reaction temperature at the steady state. Hydrogen formation from the reaction is also affected by the flow rate to a certain extent. In contrast, the performance of methane TCD is relatively insensitive to the catalyst mass, regardless of which reaction stage is. When the temperature distribution, reaction rate, and H2 concentration in the catalyst bed are examined, two-dimensional contours of reaction rate are exhibited, whereas the isothermal and concentration contours are almost one-dimensional. The simulated results are able to aid in recognizing the reaction behavior in the reactor, thereby providing more detailed information to experimental measurements and practical design of reactor. [Copyright &y& Elsevier]

Abstract: Hydrogen has been produced by decomposing methane thermocatalytically at 1123 K in the presence of activated carbon supported Pd catalysts (Samples coded as Pd5 and Pd10 respectively) procured from SRL Chemicals, India. The studies indicated that the Pd10 catalyst has higher catalytic activity and life for methane decomposition reaction at 1123 K and volume hourly space velocity (VHSV) of 1.62 L/hr∙g. An average methane conversion of 50 mol % has been obtained for Pd10 catalyst at the above reaction conditions. SEM and TEM-EDXA images of Pd10 catalyst after methane decomposition showed formation of carbon nanofibers. XRD of the above catalyst revealed, moderately crystalline peaks of Pd which may be responsible for the increase in the catalytic life and the formation of carbon nanofibers. [Copyright &y& Elsevier]

Abstract: In view of impending depletion of hydrocarbon fuel resources and their negative environmental impact, it is imperative to significantly increase the energy conversion efficiency of hydrocarbon-based power generation systems. The combination of a hydrocarbon decomposition reactor with a direct carbon and hydrogen fuel cells (FC) as a means for a significant increase in chemical-to-electrical energy conversion efficiency is discussed in this paper. The data on development and operation of a thermocatalytic hydrocarbon decomposition reactor and its coupling with a proton exchange membrane FC are presented. The analysis of the integrated power generating system including a hydrocarbon decomposition reactor, direct carbon and hydrogen FC using natural gas and propane as fuels is conducted. It was estimated that overall chemical-to-electrical energy conversion efficiency of the integrated system varied in the range of 49.4–82.5%, depending on the type of fuel and FC used, and CO2 emission per kWelh produced is less than half of that from conventional power generation sources. [Copyright &y& Elsevier]

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]