Selective synthesis of carbon nanotubes by catalytic decomposition of methane using Co-Cu/cellulose derived carbon catalysts: A comprehensive kinetic study

Hydrogen and CNT Production by Methane Cracking Using Ni–Cu and Co–Cu Catalysts Supported on Argan-Derived Carbon

“…In addition, it is also interesting to note that for both catalysts, at the higher temperatures studied, the initial reaction rate, which corresponds to a fresh (not deactivated) catalyst situation, does not follow the expected trend of an activated phenomenon, and the value obtained at 950 • C for Ni-Cu, 11.22 g C /g metal •h is even lower than that obtained at 900 • C, see Table 2 and Figure 3c. This fact can be explained by a change in the catalyst selectivity towards the formation of a different type of carbon nanomaterial in these conditions, as can be seen in the characterization results section [27,30,46,47].…”

“…As regards the effect of reaction temperature, considering that both phenomena, the reaction and the deactivation, are activated processes; an increase in the temperature will augment both rates, see Figure 3c. However, the lower value carbon productivity attained at high temperatures, e.g., 950 • C for the Ni-Cu catalyst, is a consequence of the prevalence in this case of the deactivation over the main reaction, due to the higher value of the activation energy of the deactivation process [27]. This fact implies that the observed activation energy becomes apparently negative (ca.…”

“…Table 1 summarizes the textural properties of the fresh catalysts before reaction. In this Table 1, the values corresponding to the same type of metallic catalysts (Ni-Cu and Co-Cu), but supported on other carbon-based material, carbon derived from cellulose (CDC), and prepared using the same method are also included [24,27]. The main difference was found in the higher microporosity of the catalysts supported by the argan-derived carbon, especially in the case of the Ni-Cu catalyst.…”

“…The incorporation of a second metal as a catalytic promoter was reported to have positive effects on the activity and stability [23][24][25][26]. In previous studies, we demonstrated that an appropriate design of the catalyst composition and an adequate selection of the operating conditions (mainly temperature and CH 4 /H 2 feed-ratio) allows not only the control of hydrogen yield in the catalytic decomposition of methane (CDM) reaction but also of the selectivity towards the desired carbonaceous nanomaterials [27]. Thus, reaction temperatures below 800-850 • C favor the formation of CNTs [27], while temperatures above 900-950 • C are more prone to produce graphene-related materials (GRMs) [24,28], depending on the catalyst composition.…”

“…The composition of the active phases (Ni-Cu and Co-Cu) was chosen based on previous works with the aim of obtaining different materials such as carbon nanotubes [27], or even graphene-related materials (GRMs) [24]. As a means to optimize the productivity and also the quality of the carbonaceous material formed, the effect of the main operating conditions during the reaction, i.e., feed composition and reaction temperature, was investigated.…”