Assessing the effect of acid and alkali treatment on a halloysite-based catalyst for dry reforming of methane

Dry reforming of methane (DRM) has recently received wide attention owing to its outstanding performance in the reduction and conversion of CH4 and CO2 to syngas (H2 and CO). From an industrial perspective, nickel (Ni)-supported catalysts have been deemed among the most suitable catalysts for DRM owing to their low cost and high activity compared to noble metals. However, a downside of nickel catalysts is their high susceptibility to deactivation due to coke formation and sintering at high temperatures. Using appropriate supports and preparation methods plays a major role in improving the activity and stability of Ni-supported catalysts. Halloysite nanotubes (HNTs) are largely utilized in catalysis as a support for Ni owing to their abundance, low cost, and ease of preparation. The treatment of HNTs (chemical or physical) prior to doping with Ni is considered a suitable method for increasing the overall performance of the catalyst. In this study, the surface of HNTs was activated with acids (HNO3 and H2SO4) and alkalis (NaOH and Na2CO3 + NaNO3) prior to Ni doping to assess the effects of support treatment on the stability, activity, and longevity of the catalyst. Nickel catalysts on raw HNT, acid-treated HNT, and alkali-treated HNT supports were prepared via wet impregnation. A detailed characterization of the catalysts was conducted using X-ray diffraction (XRD), BET surface area analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), solid-state nuclear magnetic resonance (ssNMR), H2-temperature programmed reduction, (H2-TPR), CO2-temperature programmed desorption (CO2-TPD), and Ni-dispersion via H2-pulse chemisorption. Our results reveal a clear alteration in the structure of HNTs after treatment, while elemental mapping shows a uniform distribution of Ni throughout all the different supports. Moreover, the supports treated with a molten salt method resulted in the overall highest CO2 and CH4 conversion among the studied catalysts and exhibited high stability over 24 hours testing.

Recent Progresses in the Design and Fabrication of Highly Efficient Ni-Based Catalysts With Advanced Catalytic Activity and Enhanced Anti-coke Performance Toward CO2 Reforming of Methane

CO₂ reforming of methane (CRM) can effectively convert two greenhouse gases (CO₂ and CH₄) into syngas (CO + H₂). This process can achieve the efficient resource utilization of CO₂ and CH₄ and reduce greenhouse gases. Therefore, CRM has been considered as a significantly promising route to solve environmental problems caused by greenhouse effect. Ni-based catalysts have been widely investigated in CRM reactions due to their various advantages, such as high catalytic activity, low price, and abundant reserves. However, Ni-based catalysts usually suffer from rapid deactivation because of thermal sintering of metallic Ni active sites and surface coke deposition, which restricted the industrialization of Ni-based catalysts toward the CRM process. In order to address these challenges, scientists all around the world have devoted great efforts to investigating various influencing factors, such as the option of appropriate supports and promoters and the construction of strong metal-support interaction. Therefore, we carefully summarized recent development in the design and preparation of Ni-based catalysts with advanced catalytic activity and enhanced anti-coke performance toward CRM reactions in this review. Specifically, recent progresses of Ni-based catalysts with different supports, additives, preparation methods, and so on, have been summarized in detail. Furthermore, recent development of reaction mechanism studies over Ni-based catalysts was also covered by this review. Finally, it is prospected that the Ni-based catalyst supported by an ordered mesoporous framework and the combined reforming of methane will become the future development trend.

Low Temperature CO2 Reforming with Methane Reaction over CeO2-Modified Ni@SiO2 Catalysts

Developing high performance catalysts for the low temperature CO₂ reforming with methane (CRM) reaction is a challenge due to the occurrences of metal sintering and carbon deposition. In this study, we synthesized CeO₂ modified Ni@SiO₂ catalysts with excellent properties of sintering-resistance and low carbon deposition for high performance low temperature CRM. The Ni@SiO₂-CeO₂ catalysts displayed a size effect from tiny Ni nanoparticles to enhance CRM performance and a confinement effect from silica encapsulation to limit Ni sintering and exhibited oxygen storage capacity from ceria to reduce carbon deposition. Performance and characterization results revealed that the Ni@SiO₂-CeO₂-W catalyst with smaller ceria size exhibited higher performance and lower carbon deposition than the Ni@SiO₂-CeO₂-E catalyst with bigger ceria size, because the smaller ceria nanoparticles activated more CO₂. This work provided a simple strategy to deposit small sized ceria on the Ni@SiO₂ catalyst surface for the performance enhancement of low temperature CRM.

Dry reforming of methane by stable Ni-Mo nanocatalysts on single-crystalline MgO

Large-scale carbon fixation requires high-volume chemicals production from carbon dioxide. Dry reforming of methane could provide an economically feasible route if coke- and sintering-resistant catalysts were developed. Here, we report a molybdenum-doped nickel nanocatalyst that is stabilized at the edges of a single-crystalline magnesium oxide (MgO) support and show quantitative production of synthesis gas from dry reforming of methane. The catalyst runs more than 850 hours of continuous operation under 60 liters per unit mass of catalyst per hour reactive gas flow with no detectable coking. Synchrotron studies also show no sintering and reveal that during activation, 2.9 nanometers as synthesized crystallites move to combine into stable 17-nanometer grains at the edges of MgO crystals above the Tammann temperature. Our findings enable an industrially and economically viable path for carbon reclamation, and the "Nanocatalysts On Single Crystal Edges" technique could lead to stable catalyst designs for many challenging reactions.

Coking-resistant dry reforming of methane over BN–nanoceria interface-confined Ni catalysts

Coking-resistant dry reforming of methane over BN–nanoceria interface-confined Ni catalysts was demonstrated.

Effects of alumina morphology on dry reforming of methane over Ni/Al2O3 catalysts

Ni-based catalysts supported on alumina with different morphologies exhibited different properties for the dry reforming of methane due to their specific lattice planes, 3D structures, and surface functional properties.

Core–shell structured catalysts for thermocatalytic, photocatalytic, and electrocatalytic conversion of CO2

An in-depth assessment of properties of core–shell catalysts and their application in the thermocatalytic, photocatalytic, and electrocatalytic conversion of CO₂into synthesis gas and valuable hydrocarbons.

Coke-resistant defect-confined Ni-based nanosheet-like catalysts derived from halloysites for CO2 reforming of methane

In this study, halloysites, one of the most abundant clays, with hollow nanotube features were reconstructed by selectively etching silica from the outermost layer of the halloysites associated with unzipping the nanotubes to nanosheets via ball milling, and then, nickel nanoparticles were confined by the resulting defects in the nanosheets to boost charge transfer by a wet impregnation method. The obtained materials were developed as coke-resistant defect-confined Ni-based nanosheet-like catalysts for CO2 reforming of methane (CRM) for the first time. The as-prepared catalyst exhibited good coke and sintering resistance performance in CRM, and especially, there was almost no loss of activity even after a 20 h stability test due to the strong interaction between the Ni nanoparticles and the support. The present investigations may provide a new pathway for the design and application of highly coke-resistant CRM catalysts.