Self-Regenerative Ni-Doped CaTiO3/CaO for Integrated CO2 Capture and Dry Reforming of Methane

In this work, a new type of multifunctional materials (MFMs) called self-regenerative Ni-doped CaTiO3/CaO is introduced for the integrated CO2 capture and dry reforming of methane (ICCDRM). These materials consist of a catalytically active Ni-doped CaTiO3 and a CO2 sorbent, CaO. The article proposes a concept where the Ni catalyst can be regenerated in situ, which is crucial for ICCDRM. Exsolved Ni nanoparticles are evenly distributed on the surface of CaTiO3 under H2 or CH4, and are re-dispersed back into the CaTiO3 lattice under CO2. The Ni-doped CaTiO3/CaO MFMs show stable CO2 capture capacity and syngas productivity for 30 cycles of ICCDRM. The presence of CaTiO3 between CaO grains prevents CaO/CaCO3 thermal sintering during carbonation and decarbonation. Moreover, the strong interaction of CaTiO3 with exsolved Ni mitigates severe accumulation of coke deposition. This concept can be useful for developing MFMs with improved properties that can advance integrated carbon capture and conversion.

Comparative Study of Exsolved and Impregnated Ni Nanoparticles Supported on Nanoporous Perovskites for Low-Temperature CO Oxidation

This study investigated the redox exsolution of Ni nanoparticles from a nanoporous La0.52Sr0.28Ti0.94Ni0.06O3 perovskite. The characteristics of exsolved Ni nanoparticles including their size, population, and surface concentration were deeply analyzed by environmental scanning electron microscopy (ESEM), transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX) mapping, and hydrogen temperature-programmed reduction (H2-TPR). Ni exsolution was triggered in hydrogen as early as 400 °C, with the highest catalytic activity for low-temperature CO oxidation achieved after a reduction step at 500 °C, despite only a 10% fraction of Ni exsolved. The activity and stability of exsolved nanoparticles were compared with their impregnated counterparts on a perovskite material with a similar chemical composition (La0.65Sr0.35TiO3) and a comparable specific surface area and Ni loading. After an aging step at 800 °C, the catalytic activity of exsolved Ni nanoparticles at 300 °C was found to be 10 times higher than that of impregnated ones, emphasizing the thermal stability of Ni nanoparticles prepared by redox exsolution.

High activity in the dry reforming of methane using a thermally switchable double perovskite and in situ generated molecular level nanocomposite

This work emphasizes the dry reforming of methane (DRM) reaction on citrate sol-gel-synthesized double perovskite oxides. Phase pure La2NiMnO6 shows very impressive DRM activity with H2/CO = 0.9, hence revealing a high prospect of next-generation catalysts. Although the starting double perovskite phase gets degraded into mostly binary oxide phases after a few hours of DRM activity, the activity continues up to 100 h. The regeneration of the original double perovskite out of decomposed phases by annealing at near synthesis temperature, followed by the spectacular retention of activity, is rather interesting and hitherto unreported. This result unravels unique reversible thermal switching between the original double perovskite phase and decomposed phases during DRM without compromising the activity and raises challenge to understand the role of decomposed phases evolved during DRM. We have addressed this unique feature of the catalyst via structure-property relationship using the in situ generated molecular level nanocomposite.

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.

Microalgae gasification over Ni loaded perovskites for enhanced biohydrogen generation

Steam gasification of microalgae upon perovskite oxide-supported nickel (Ni) catalysts was carried out for H₂-rich gas production. Ni-perovskite oxide catalysts with partial substitution of B in perovskite structures (Ni/CaZrO₃, Ni/Ca(Zr_0.8Ti_0.2)O₃, and Ni/Ca(Zr_0.6Ti_0.4)O₃) were synthesized and compared with those of the Ni/Al₂O₃ catalyst. The perovskite oxide supports improved Ni dispersion by reducing the particle size and strengthening the Ni-support interaction. Higher gas yields and H₂ selectivity were obtained using Ni-perovskite oxide catalysts rather than Ni/Al₂O₃. In particular, Ni/Ca(Zr_0.8Ti_0.2)O₃ showed the highest activity and selectivity for H₂ production because of the synergetic effect of metallic Ni and elements present in the perovskite structures caused by high catalytic activity coupled with enhanced oxygen mobility. Moreover, increasing the temperature promoted the yield of gas and H₂ content. Overall, considering the outstanding advantages of perovskite oxides as supports for Ni catalysts is a promising prospect for H₂ production via gasification technology.

H2 generation from steam gasification of swine manure over nickel-loaded perovskite oxides catalysts

In this study, nickel-loaded perovskite oxides catalysts were synthesized via the impregnation of 10%Ni on XTiO₃ (X = Ce, Sr, La, Ba, Ca, and Fe) supports and employed in the catalytic steam gasification of swine manure to produce H₂-rich syngas for the first time. The synthesized catalysts were characterized using BET, H₂-TPR, XRD, HR-TEM, and EDX analysis. Briefly, using perovskite supports resulted in the production of ultrafine catalyst nanoparticles with a uniform dispersion of Ni particles. According to the catalytic activity test, the gas yield showed the increment as 10% Ni/LaTiO₃ < 10% Ni/FeTiO₃ < 10% Ni/CeTiO₃ < 10% Ni/BaTiO₃ < 10% Ni/SrTiO₃ < 10% Ni/CaTiO₃. Meanwhile, zero coke formation was achieved due to the oxygen mobility of prepared catalysts. Also, the increase in the H₂ production for the applied catalysts was in the sequence as 10% Ni/CeTiO₃ < 10% Ni/FeTiO₃ < 10% Ni/LaTiO₃ < 10% Ni/BaTiO₃ < 10% Ni/SrTiO₃ < 10% Ni/CaTiO₃. The maximum H₂ selectivity (∼48 vol%) obtained by10% Ni/CaTiO₃ was probably due to the synergistic effect of Ni and Ti on enhancing the water-gas shift reaction, and Ca on creating the maximum oxygen mobility compared to other alkaline earth metals doped at the A place of perovskite. Overall, this study provides a suitable solution for enhanced H₂ production through steam gasification of swine manure along with suggesting the appropriate supports to prevent Ni deactivation by lowering coke formation at the same time.

Atomic-Scale Insights into Nickel Exsolution on LaNiO3 Catalysts via In Situ Electron Microscopy

Using a combination of in situ bulk and surface characterization techniques, we provide atomic-scale insight into the complex surface and bulk dynamics of a LaNiO₃ perovskite material during heating in vacuo. Driven by the outstanding activity LaNiO₃ in the methane dry reforming reaction (DRM), attributable to the decomposition of LaNiO₃ during DRM operation into a Ni//La₂O₃ composite, we reveal the Ni exsolution dynamics both on a local and global scale by in situ electron microscopy, in situ X-ray diffraction and in situ X-ray photoelectron spectroscopy. To reduce the complexity and disentangle thermal from self-activation and reaction-induced effects, we embarked on a heating experiment in vacuo under comparable experimental conditions in all methods. Associated with the Ni exsolution, the remaining perovskite grains suffer a drastic shrinkage of the grain volume and compression of the structure. Ni particles mainly evolve at grain boundaries and stacking faults. Sophisticated structure analysis of the elemental composition by electron-energy loss mapping allows us to disentangle the distribution of the different structures resulting from LaNiO₃ decomposition on a local scale. Important for explaining the DRM activity, our results indicate that most of the Ni moieties are oxidized and that the formation of NiO occurs preferentially at grain edges, resulting from the reaction of the exsolved Ni particles with oxygen released from the perovskite lattice during decomposition via a spillover process from the perovskite to the Ni particles. Correlating electron microscopy and X-ray diffraction data allows us to establish a sequential two-step process in the decomposition of LaNiO₃ via a Ruddlesden-Popper La₂NiO₄ intermediate structure. Exemplified for the archetypical LaNiO₃ perovskite material, our results underscore the importance of focusing on both surface and bulk characterization for a thorough understanding of the catalyst dynamics and set the stage for a generalized concept in the understanding of state-of-the art catalyst materials on an atomic level.

Solution combustion synthesis of Ni/La2O3 for dry reforming of methane: tuning the basicity via alkali and alkaline earth metal oxide promoters

The production of syngas via dry reforming of methane (DRM) has drawn tremendous research interest, ascribed to its remarkable economic and environmental impacts. Herein, we report the synthesis of K, Na, Cs, Li, and Mg-promoted Ni/La₂O₃ using solution combustion synthesis (SCS). The properties of the catalysts were determined by N₂ physisorption experiments, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS), and H₂-TPR (temperature programmed reduction). In addition, their catalytic performance towards DRM was evaluated at 700 °C. The results demonstrated that all catalysts exhibited porous structures with high specific surface area, in particular, Mg-promoted Ni/La₂O₃ (Mg–Ni–La₂O₃) which depicted the highest surface area and highest pore volume (54.2 m² g⁻¹, 0.36 cm³ g⁻¹). Furthermore, Mg–Ni–La₂O₃ exhibited outstanding catalytic performance in terms of activity and chemical stability compared to its counterparts. For instance, at a gas hourly space velocity (GHSV) of 30 000 mL g⁻¹ h⁻¹, it afforded 83.2% methane conversion and 90.8% CO₂ conversion at 700 °C with no detectable carbon deposition over an operating period of 100 h. The superb DRM catalytic performance of Mg–Ni–La₂O₃ was attributed to the high specific surface area/porosity, strong metal-support interaction (MSI), and enhanced basicity, in particular the strong basic sites compared to other promoted catalysts. These factors remarkably enhance the catalytic performance and foster resistance to coke deposition.

Alkali and alkaline earth metal oxides-promoted Ni/La₂O₃ catalysts synthesized by solution combustion synthesis revealed enhanced catalytic performance towards dry reforming of methane.

Nanoparticle Ex-solution for Supported Catalysts: Materials Design, Mechanism and Future Perspectives

Supported metal catalysts represent one of the major milestones in heterogeneous catalysis. Such catalytic systems are feasible for use in a broad range of applications, including renewable energy devices, sensors, automotive emission control systems, and chemical reformers. The lifetimes of these catalytic platforms depend strongly on the stability of the supported nanoparticles. With this regard, nanoparticles synthesized via ex-solution process emphasize exceptional robustness as they are socketed in the host oxide. Ex-solution refers to a phenomenon which yields selective growth of fine and uniformly distributed metal nanocatalysts on oxide supports upon partial reduction. This type of advanced structural engineering is a game-changer in the field of heterogeneous catalysis with numerous studies showing the benefits of ex-solution process. In this review, we highlight the latest research efforts regarding the origin of the ex-solution phenomenon and the mechanism underpinning particle formation. We also propose research directions to expand the utility and functionality of the current ex-solution techniques.

A Thermodynamic Investigation of Ni on Thin-Film Titanates (ATiO3)

Thin, ~1-nm films of CaTiO3, SrTiO3, and BaTiO3 were deposited onto MgAl2O4 by Atomic Layer Deposition (ALD) and then studied as catalyst supports for ~5 wt % of Ni that was added to the perovskite thin films by Atomic Layer Deposition. Scanning Transmission Electron Microscopy demonstrated that both the Ni and the perovskites uniformly covered the surface of the support following oxidation at 1073 K, even after redox cycling, but large Ni particles formed following a reduction at 1073 K. When compared to Ni/MgAl2O4, the perovskite-containing catalysts required significantly higher temperatures for Ni reduction. Equilibrium constants for Ni oxidation, as determined from Coulometric Titration, indicated that the oxidation of Ni shifted to lower PO2 on the perovskite-containing materials. Based on Ni equilibrium constants, Ni interactions are strongest with CaTiO3, followed by SrTiO3 and BaTiO3. The shift in the equilibrium constant was shown to cause reversible deactivation of the Ni/CaTiO3/MgAl2O4 catalyst for CO2 reforming of CH4 at high CO2 pressures, due to the oxidation of the Ni.

Nickel-Based Structured Catalysts for Indirect Internal Reforming of Methane

A structured catalyst for the dry reforming of methane (DRM) was investigated as a biogas pre-reformer for indirect internal reforming solid oxide fuel cell (IIR-SOFC). For this purpose, a NiCrAl open-cell foam was chosen as support and Ni-based samarium doped ceria (Ni-SmDC) as catalyst. Ni-SmDC powder is a highly performing catalyst showing a remarkable carbon resistance due to the presence of oxygen vacancies that promote coke gasification by CO2 activation. Ni-SmDC powder was deposited on the metallic support by wash-coating method. The metallic foam, the powder, and the structured catalyst were characterized by several techniques such as: N2 adsorption-desorption technique, X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), focused ion beam (FIB), temperature programmed reduction (H2-TPR), and Raman spectroscopy. Catalytic tests were performed on structured catalysts to evaluate activity, selectivity, and stability at SOFC operating conditions.

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.

Ni-Based catalysts supported on natural clay of attapulgite applied in the dry reforming of methane reaction

With the increase of the global average temperature year after year, dry reforming of methane to synthetic gas as a way to deal with reaction between greenhouse gases CO₂ and CH₄, therefore, has become a research focus.

Encapsulated Ni@La2O3/SiO2 Catalyst with a One-Pot Method for the Dry Reforming of Methane

Ni nanoparticles encapsulated within La2O3 porous system (Ni@La2O3), the latter supported on SiO2 (Ni@La2O3)/SiO2), effectively inhibit carbon deposition for the dry reforming of methane. In this study, Ni@La2O3/SiO2 catalyst was prepared using a one-pot colloidal solution combustion method. Catalyst characterization demonstrates that the amorphous La2O3 layer was coated on SiO2, and small Ni nanoparticles were encapsulated within the layer of amorphous La2O3. During 50 h of dry reforming of methane at 700 °C and using a weight hourly space velocity (WHSV) of 120,000 mL gcat−1 h−1, the CH4 conversion obtained was maintained at 80%, which is near the equilibrium value, while that of impregnated Ni–La2O3/SiO2 catalyst decreased from 63% to 49%. The Ni@La2O3/SiO2 catalyst exhibited very good resistance to carbon deposition, and only 1.6 wt% carbon was formed on the Ni@La2O3/SiO2 catalyst after 50 h of reaction, far lower than that of 11.5 wt% deposited on the Ni–La2O3/SiO2 catalyst. This was mainly attributed to the encapsulated Ni nanoparticles in the amorphous La2O3 layer. In addition, after reaction at 700 °C for 80 h with a high WHSV of 600,000 mL gcat−1 h−1, the Ni@La2O3/SiO2 catalyst exhibited high CH4 conversion rate, ca. 10.10 mmol gNi−1 s−1. These findings outline a simple synthesis method to prepare supported encapsulated Ni within a metal oxide porous structure catalyst for the dry reforming of methane reaction.

Large Specific Surface Area Macroporous Nanocast LaFe1−xNixO3: A Stable Catalyst for Catalytic Methane Dry Reforming

Macroporous nanocast perovskites, LaFe1−xNixO3 (x = 0.3, 0.5, and 0.7), were synthesized by using a nanocasting technique with SBA-15 as a template and applied to methane dry reforming (MDR). The prepared catalysts were characterized by X-ray diffraction, transmission electron microscopy, specific-surface-area analysis, hydrogen temperature-programmed reduction, and thermogravimetric analysis. LaFe1−xNixO3 revealed a large specific surface area, which could enhance its catalytic activity. The catalysts were reduced to Ni/LaFeO3-La2O3 in the MDR reaction. The alkaline additive, La2O3, and perovskite oxide, LaFeO3, strongly interacted with the active component to reduce the surface energy of metal particles and prevent aggregation of active Ni. The results showed that LaFe0.5Ni0.5O3 and LaFe0.3Ni0.7O3 perform better than LaFe0.7Ni0.3O3. More importantly, LaFe0.5Ni0.5O3 had a very long lifetime (>80 h) in the MDR reaction. The LaFe0.5Ni0.5O3 catalyst showed excellent stability in the MDR reaction and has potential use in industrial applications.

A citric acid-assisted deposition strategy to synthesize mesoporous SiO2-confined highly dispersed LaMnO3 perovskite nanoparticles for n-butylamine catalytic oxidation

A citric acid-assisted deposition strategy was applied to synthesize mesoporous SiO₂-confined highly dispersed LaMnO₃ perovskite nanoparticles with optimum catalytic performance and N₂ selectivity.