Unveiling the Roles of Precursor Structure and Controlled Sintering on Ni-Phyllosilicate-Derived Catalysts for Low-Temperature Methane Decomposition

Abstract

Catalytic methane decomposition (CMD) is a promising technology for large-scale production of CO x -free H2 from natural gas that can also produce valuable carbon byproducts. Although equilibrium conversions and reaction rates of CMD generally increase with temperature, operation in a low-temperature regime with simultaneous H2 recovery could potentially lead to operating cost and energy savings. Here, we report that well-dispersed Ni–SiO2, derived from high-temperature reduction of nickel phyllosilicates, is active for CMD at temperatures below 500 °C, with initial H2 production rates of up to 5.3 mol H2/gcat·h at 25% CH4 conversion. This ability to achieve rates comparable to other well-established catalysts is contrary to expectations that small (<ca. 10 nm) Ni nanoparticles are inactive for CMD because of rapid deactivation and attributed here to an unusual mobility of nickel–silica interfaces in the presence of CH4 that leads to controlled sintering of the originally well-dispersed Ni nanoparticles. We further show that the ratio of 1:1 and 2:1 nickel phyllosilicates in the precursor, which governs catalyst reducibility and can be tuned by adding NH4F to the synthesis mixture, is a key descriptor of catalytic performance. Our findings provide valuable insight into catalyst and process design for low-temperature CMD.

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

“…For the Al 2 O 3 -containing samples (Figure a), the Al 2p peaked at 73.0 eV, and the Ni 3p 1/2 peak and Ni 3p 3/2 peak were at 69.1 eV and 64.7–66.4 eV, respectively. In the Ni 2p spectra (Figure b), peaks with a binding energy at around 851.0 eV corresponded to metallic Ni (Ni 0 ), ,,, while peaks at around 854.5 and 872.0 eV were attributed to Ni 2p 3/2 and Ni 2p 1/2 of Ni 2+ oxidation states, respectively. ,,,− In the Ce 3d spectra (Figure c; for the sample containing CeO 2 ), the peaks labeled as u (899.0 eV), u ″ (906.2 eV), and u ″′ (915.0 eV) corresponded to the 3d 3/2 of Ce 4+ oxidation states, while peaks labeled as v (878.5 eV), v ″ (887.1 eV), and v ″′ (896.5 eV) were associated with the 3d 5/2 of Ce 4+ oxidation states. ,, On the other hand, peaks labeled as u ′ (901.0 eV) and v ′ (881.0 eV) corresponded to the 3d 3/2 and 3d 5/2 of Ce 3+ oxidation states, respectively. ,, By calculation, the fraction of Ce 3+ in Ce compounds (i.e., defined as Ce 3+ /(Ce 3+ + Ce 4+ )) was found to be 17.6, 18.0, 18.3, and 17.9% for 10Ni/1Ce, 10Ni/5Ce, 10Ni–1Ce/5Al, and 15Ni–1Ce/5Al, respectively. The results indicate the formation of oxygen vacancies (i.e., for the charge balance of Ce 4+ to Ce 3+ ) during the aerosol-based synthesis .…”

“…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.…”

“…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. − …”

Production of Hydrogen and Solid Carbon by Methane Decomposition under Pressurized Conditions Using a Rotary Reactor and Purification of Yielded Hydrogen by Hydrogen Separation Membrane

“…It is well known that nickel- and cobalt-based catalysts are highly effective for the methane decomposition reaction. − These catalysts show high activity even at low temperatures, but the methane conversion is governed by equilibrium; therefore, methane conversion is inevitably low at low temperatures.…”