Analytical review of the catalytic cracking of methane

First-Principles Microkinetic Modeling Unravelling the Performance of Edge-Decorated Nanocarbons for Hydrogen Production from Methane

“…The viability of the regeneration step can be observed by analyzing the turnover frequencies of CH 2 CH 2 formation, as shown in Figure c, from which the TOF of ethene is roughly the same order of magnitude than the H 2 TOF at the entire temperature range on N-EDNC and P-EDNC. However, the high temperatures of over 1000 K in which the CMD process is conducted make the catalyst susceptible to coke deposition, leading to the deactivation of the reactive sites. ,,,,, Therefore, we investigated the resistance to coking of the active sites on the EDNCs by evaluating the dehydrogenation from CH 2 * to CH*, as it was shown to be the rate-determining step of the methane decomposition in previous works ,, and is being applied for investigations of carbon formation on the catalysts. Furthermore, the selectivity between CH* and CH 2 * is pointed as crucial for determining the efficiency of the catalytic formation of C2 products .…”

“…Metal-based catalysts are the most commonly employed for the CMD process, with nickel- and iron-based catalysts being the most economically viable and possessing high selectivity for hydrogen production. ,,, Carbon-based materials are expected to overcome the rapid deactivation due to coke deposition, which is common among metallic catalysts. ,,, The decomposition of methane at the gas–solid interface can be largely improved by the presence of different surface configurations on the carbon catalyst, such as defects, vacancies and low-coordination sites . In fact, the amount of defects present in the carbon surface is directly correlated to the catalytic activity for CMD, especially in the initial stages of the process .…”

“…The direct conversion of methane, CH 4 , to hydrogen (so-called catalytic methane decomposition, or CMD) is an attractive process for converting natural gas into high-value chemicals, mainly due to the cleanliness of the process 1 , 2 and the large availability of natural and shale gas reserves. 3 , 4 The main challenge for thermally cracking methane is the large energy required for the C–H bond cleavage; 5 therefore, the usage of a catalyst is crucial for achieving lower temperatures for efficient conversion.…”

“…The direct conversion of methane, CH 4 , to hydrogen (so-called catalytic methane decomposition, or CMD) is an attractive process for converting natural gas into high-value chemicals, mainly due to the cleanliness of the process , and the large availability of natural and shale gas reserves. , The main challenge for thermally cracking methane is the large energy required for the C–H bond cleavage; therefore, the usage of a catalyst is crucial for achieving lower temperatures for efficient conversion . The direct catalytic conversion of methane can proceed through oxidative routes, such as oxidative coupling of methane (OCM) and partial oxidation of methane (POM), and nonoxidative routes. ,, For the former, undesirable C 2 and C 3 byproducts as well as CO 2 can be formed via reactions between methyl radicals and oxygen, making the process less sustainable. , On the other hand, the nonoxidative conversion of methane can yield high selectivity toward target products. , This process generally requires high temperatures to overcome the kinetic barrier for methane cracking and hydrogen desorption, which can result in the severe deactivation of the catalyst due to coking, thus being a major drawback of metal-based catalysts. ,,, Therefore, significant effort has been made toward the design of efficient catalysts that are expected to improve the selectivity activation of C–H bonds, while being resistant to carbon poisoning. − …”

“…Much attention has been directed to the improvement of the process of catalytic methane decomposition (CMD) into hydrogen H 2 production in the past decade. ,,,,− The benefits of the process are self-evident since the main products of CMD are pure hydrogen gas and solid carbon: CH 4 → 2H 2 + C. , Turning the CMD process into a large-scale application is a top-priority because it would allow converting CH 4 (one of the worst greenhouse gases) into hydrogen, which can be employed as a clean fuel. H 2 is becoming ever more relevant as a promising candidate to replace fossil fuels, which are rapidly depleting and cause global warming .…”