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Nowadays, methane cracking in the presence of an efficient catalyst is one of the most investigating areas aiming hydrogen and nanocarbon synthesis. This research contribution systematically investigated the influence of methane partial pressure (PCH4), decomposition temperature, and weight of Ni/SiO2 nanocatalyst (n-Ni/SiO2) on carbon nanotube (CNT) yield. The optimum reaction condition for optimal methane cracking resulted in maximum CNT yield is derived using Design Expert Software. A series of experiments conducted to develop a quadratic polynomial model for CNT yield using response surface methodology. Surprisingly, the optimum catalyst quantity was the lowest (0.30 g) in the experimented parameter range, which exhibited the highest CNT production at 610 °C temperature and 0.8 atm PCH4. The minimal catalyst quantity for the optimum CNT production, which needs only 0.26% of the total volume of the pilot plant reactor, is a breakthrough finding in methane cracking research. It could help to overcome the reactor blockage limitation issues of the process in large scale applications. Thanks to the uniquely supported n-Ni/SiO2 catalyst prepared via co-precipitation cum modified Stober method. The fresh and used catalysts investigated using different types of characterization techniques such as XRD, BET, Raman spectra, HRTEM, and FESEM-EDX. Characterization results evidenced the presence of differently structured CNTs formed at optimum reaction conditions.

Co-precipitation cum modified Stober method was adopted to produce nano-Ni/SiO2 (n-Ni/SiO2) catalyst and conducted a series of methane decomposition kinetic experiments in a fixed bed pilot plant. Methane decomposition activity of n-Ni/SiO2 catalyst was quantified by considering thermodynamic deposition of carbon at a temperature range of 550–650 °C and methane partial pressure from 0.2 to 0.8 atm. The utmost methane conversion of 18.87 mmol/gcat min was obtained at 650 °C and methane partial pressure of 0.8 atm. The findings concluded that the enhancement occurred with carbon formation rate when increasing the methane partial pressure is very much evident at higher temperature such as 650 °C. However, the intensity in methane decomposition descending tendency was declined at lower reaction temperature. The effects of methane partial pressure and reaction temperature on the specific molar carbon formation rate were also examined. The calculated reaction order and activation energy were 1.40 and 61.1 kJ mol−1, respectively. The kinetic experiments showed the existence of an optimum reaction condition to achieve the highest performance of n-Ni/SiO2 catalyst in terms of methane decomposition rate. However, carbon accumulation ceases once complete catalyst deactivation occurred at certain reaction conditions such as high temperature and lower methane partial pressure. Virgin nanocatalyst and as-produced nanocarbons were studied with BET, XRD, and TEM.

Hydrogen, an environment-friendly energy source, is deemed to become strongly in demand over the next decades. In this work, CO x -free hydrogen was produced by the thermal catalytic decomposition (TCD) of methane by a carbon catalyst. Deactivated catalysts at four-stage of progressive were characterized by nitrogen sorption and scanning electron microscopy. TCD of methane at 820 and 940 °C was about 13- and 8-folds higher than non-catalytic decomposition, respectively. High temperatures positively affected the kinetics of hydrogen production but negatively influenced the total amount of hydrogen and carbon products. The total pore volume was a good indicator of the total amount of hydrogen product. Catalyst activity was decreased because of the changes in the catalyst's textural properties within three ranges of relative time, that is, 0 to 45, 0.45 to 0.65, and 0.65 to 1. Models for specific surface area and total pore volume as functions of catalyst deactivation kinetics were developed.

The thermo-catalytic decomposition of methane is proposed as an alternative for producing hydrogen without CO2 emissions. The present study was divided into three parts. First, a screening study of the rate of methane decomposition ( R CH 4 ) was performed using two types of activated carbons as catalysts with progressive time of methane decomposition at four different temperatures. The catalysts differed in textural properties. A full factorial design consisting of 20 experimental points for each catalyst was applied in the second part. Quadratic R CH 4 models as functions of the relative time of catalyst deactivation and decomposition temperature were developed by regression analysis of variance. The results of the R CH 4 models showed that the relative time had twice as much influence as temperature. Finally, a general R CH 4 model was then developed representing both catalysts regardless of their textural properties. All the empirical models were consistent with experimental results and were adequate for designing the methane decomposition process.

This work presents the results of a two-stage (carbon fixation and hydrogen production) experimental study for hydrogen production from microalgae using optical fiber as an internal light source. Effect of absence and presence of light on Chlamydomonas reinhardtii culture’s pH shift is also evaluated. The culture pH value is a function of light intensity; the pH in the alkaline range changes from 7.5 to 9.5 in the presence and absence of optical fiber respectively. The maximum rate of hydrogen production in the presence of exogenic glucose and optical fiber is 6 mL/Lcult/hour, which is higher than other reported values. This study has also revealed that the presence of light reduces the lag time for hydrogen production from 12 to 5 h.

Thermocatalytic decomposition (TCD) of methane is a promising method to produce hydrogen. A series of experiments was conducted to study the apparent kinetic, catalyst deactivation and effect of mass diffusion for methane TCD to produce hydrogen using palm-shell carbon based activated carbon (ACPS) as a catalyst in a fixed bed reactor. The experiment was carried out under atmospheric pressure at 775–850 °C, and different methane residence times calculated based on changing the ACPS weight at a constant methane flow rate or changing the methane flow rate at a constant ACPS weight. A reaction order as found substantially differs from that found in literature. A deactivation order of 0.5 and deactivation energy of 177 KJ mol−1 is obtained and the results fitted well with a simple developed model. Mass diffusion transfers are accounted for by calculating change of Weisz modulus with time on-stream using different weights of ACPS or different flow rates of methane. The result showed that Weisz modulus decrease with time and it is attributed to the deposition of carbon produced from methane decomposition. Surface properties measurements of the virgin and deactivated ACPSs indicated that methane decomposition occurs mainly within AC micropores.

Methane decomposition can be utilized to produce COX-free hydrogen for PEM fuel cells, oil refineries, ammonia and methanol production. Recent research has focused on enhancing the production of hydrogen by the direct thermocatalytic decomposition of methane to form elemental carbon and hydrogen as an attractive alternative to the conventional steam-reforming process. In this context, we review a comprehensive body of work focused on the development of metal or carbonaceous catalysts for enhanced methane conversion and on the improvement of long-term catalyst stability. This review also evaluates the roles played by various parameters, such as temperature and flow rate, on the rate of hydrogen production and the characteristics of the carbon produced. The heating source, type of reactor, operating conditions, catalyst type and its preparation, deactivation and regeneration and the formation and utilization of the carbon by-product are discussed and classified in this paper. While other hydrogen production methods, economic aspects and thermal methane decomposition methods using alternative heating sources such as solar and plasma are briefly presented in this work where relevant, the review focuses mainly on the thermocatalytic decomposition of methane using metal and carbonaceous catalysts.

A series of experiments was conducted to study the CO2 gasification of a deactivated palm-shell-based activated-carbon (ACPS) catalyst used for the thermocatalytic decomposition of methane to produce hydrogen. This catalyst becomes deactivated due to the accumulation of carbon deposits during the methane-decomposition process. The CO2 gasification was carried out at 850, 900, 950 or 1000 °C to study the deactivated ACPS, which was used at methane-decomposition temperatures of 850 or 950 °C. A series of six methane-decomposition cycles at 950 °C alternating with five gasification cycles using CO2 at 900, 950 and 1000 °C was also carried out to evaluate the stability of the catalyst. The experiments were conducted using a thermobalance by monitoring the change in mass of the catalyst with time, i.e., the mass gain during methane decomposition or the mass loss during CO2 gasification. Gasification of the virgin and deactivated ACPS showed strong temperature dependence, with the half and complete gasification times having an exponential dependence on temperature. The gasification reactivity at different conversions was higher for the virgin ACPS and increased with increases in the decomposition temperatures used for deactivation of the ACPS. The activation energies of virgin ACPS and ACPS deactivated at a decomposition temperature of 850 °C decreased with an increase in conversion, while they increased for the ACPS deactivated at a decomposition temperature of 950 °C; the activation energies varied between 81 and 163 kJ/mol. The gasification reactivity changed with methane conversion, showing maximum values for both the virgin and deactivated ACPS at a decomposition temperature of 950 °C. The initial gasification reactivity of the catalyst decreased after three gasification cycles at 1000 °C, while no significant change was observed with gasification cycles at 950 or 900 °C.

A series of experiments was conducted to study the deactivation and regeneration of activated carbon catalyst used for methane thermocatalytic decomposition to produce hydrogen. The catalyst becomes deactivated due to carbon deposition and six decomposition cycles of methane at temperatures of 850 and 950 °C, and five cycles of regeneration by using CO 2 at temperatures of 900, 950 and 1000 °C were carried out to evaluate the stability of the catalyst. The experiment was conducted by using a thermobalance by monitoring the mass gain during decomposition or the mass lost during the regeneration with time. The initial activity and the ultimate mass gain of the catalyst decreased after each regeneration cycle at both reaction temperatures of 850 and 950 °C, but the amount is smaller under the more severe regenerating conditions. For the reaction at 950 °C, comparison between the first and sixth reaction cycles shows that the initial activity decreased by 69, 51 and 42%, while the ultimate mass gain decreased by 62%, 36% and 16% when CO 2 gasification carried out at 900, 950 and 1000 °C respectively. Temperature -programmed oxidation profiles for the deactivated catalyst at reaction temperature of 950 °C and after several cycles showed two peaks which are attributed to different carbon characteristics, while one peak was obtained when the experiment was carried out at 850 °C. In conclusion, conducting methane decomposition at 950 °C and regeneration at 1000 °C showed the lowest decrease in the mass gain with reaction cycles.

Thermocatalytic decomposition of methane over activated carbon acting as a catalyst is proposed as a potential alternative for hydrogen production. However, over a certain duration catalyst becomes deactivated due to intensive carbon deposition. The main research objective is to study the catalyst deactivation kinetic and modeling of the mass gain due to carbon deposition with time. The catalyst activity was found to decrease almost linearly with the amount of carbon deposited at 800 °C, while at higher temperature the diffusion effect appeared to occur significantly, especially at the end of the process. A novel model has been developed to describe the decrease of catalyst activity with time. A deactivation order of 0.5 and deactivation energy of 194 KJ mol−1 were obtained and the mass gain fitted well with the model results based on Voorhies equation which is commonly used for reaction that involves hydrocarbon cracking. Comparison between activated carbon (AC) from palm shell carbon-based and commercial based AC shows almost similar deactivation kinetic and validity of Voorhies correlation.