Sonochemically Prepared Ni-Based Perovskites as Active and Stable Catalysts for Production of CO_x-Free Hydrogen and Structured Carbon

Abstract

A sonochemical method is employed to synthesize LaNiO3 perovskites as catalysts for methane decomposition to produce clean CO x -free hydrogen and structured carbon. The catalytic activities of perovskites prepared under various sonochemical conditions (different power densities and exposure times) are contrasted with those of LaNiO3 prepared by a conventional sol–gel method. The results show that a sonochemically prepared catalyst presents a methane conversion of up to 60% after 16 h of reaction, while the conventional sol–gel LaNiO3 catalyst deactivates quickly, reaching 1% methane conversion after 30 min of reaction. Structural characterization of the as-prepared materials indicates that under certain sonochemical conditions (low-intensity sonication for 8 h) it is possible to obtain NiO inclusions in the LaNiO3 perovskite structure, which are not present when employing the conventional synthesis technique. Upon activation of these materials under reducing conditions, it is found that the presence of the sonochemically formed NiO inclusions facilitates exsolution of the reduced Ni species to the surface of the catalyst particles, improving the catalyst activity in methane decomposition. The sonochemically synthesized catalysts, which exhibit coexistence of LaNiO3 phase and NiO inclusions, also seem to exhibit autocatalytic properties as they steer the methane decomposition reaction toward formation of non-encapsulating carbon nanotubes, which not only enhance catalyst stability but also increase the catalyst activity over long reaction times.

Combined Methane Cracking for H2 Production with CO2 Utilization for Catalyst Regeneration Using Dual Functional Nanostructured Particles

“…At present, fossil fuels such as coal, oil, and natural gas continue to serve as our primary source of energy, and the carbon emissions associated with their extraction require critical attention. − Compared to these traditional fossil fuels, hydrogen energy is an attractive alternative energy source, and it possesses a carbon-free characteristic and has a high heat value (140 kJ/g) . In addition to being directly used as an alternative to fossil fuels for energy purposes, hydrogen also serves as an important chemical feedstock for the production of various high-value chemicals. , This versatility makes hydrogen (i.e., acquired from a sustainable, low-pollution source) an appealing choice in terms of both environmental friendliness and economic benefits.…”

“…Methane reforming is a crucial industrial process for converting methane into hydrogen and other valuable products, playing a significant role in various chemical industries and clean energy applications. − Currently, the main process for producing hydrogen is steam reforming of natural gas, primarily methane (SRM). ,,, While SRM possesses high energy efficiency, the significant CO 2 emission necessitates the implementation of an additional carbon capture and storage process, which further increases the cost of utility. ,− The main difference between methane reforming and methane decomposition is that methane reforming requires an extra downstream process to separate H 2 from the syngas (i.e., a mixture of H 2 and CO), whereas methane decomposition directly produces pure H 2 without the need for separation.…”

“…On the other hand, methane decomposition has garnered significant attention for a clean, sustainable route for high-purity hydrogen production. − It involves thermal decomposition of methane into carbon and hydrogen (i.e., CH 4 → C + 2H 2 ) without the formation of CO 2. ,,, A high-purity hydrogen gas stream (up to 99%) can then be achieved by utilizing a tandem gas separation unit (i.e., to distinguish unreacted methane and H 2 ) . The hydrogen generated through this method reflects the combination of blue and green characteristics owing to its carbon capture capacity (blue) and its lack of CO 2 emissions (green) .…”

“…The hydrogen generated through this method reflects the combination of blue and green characteristics owing to its carbon capture capacity (blue) and its lack of CO 2 emissions (green) . Knowing that uncatalyzed methane decomposition exhibits very slow kinetics at temperatures below 1000 °C, utilization of a solid catalyst is essential, allowing this reaction to be initiated efficiently at a relatively lower temperature. , Among the transition metal-based catalysts, nickel is recognized as one of the most efficient in hydrocarbon cracking. ,,− Considering that unsupported nickel is prone to sintering at high temperatures, the use of a support material is necessary. , Significant efforts have been dedicated to developing straightforward and effective synthesis methods for producing suitable Ni-based supported catalysts to facilitate methane decomposition. The maximum H 2 yield (in terms of CH 4 conversion; TOF CH 4 ) ranging from 6.02 to 38.15 h –1 was achievable in a temperature range of 550–900 °C by using Ni-based catalysts. − …”

“…While methane decomposition effectively produces hydrogen, the nature of continuous coke formation causes catalyst deactivation and reactor clogging. , Conventionally, oxygen or air is employed to incinerate coke in the catalyst regeneration process. However, the highly exothermic nature of carbon oxidation (i.e., −393.5 kJ/mol) results in potential severe catalyst sintering .…”