Reactive Capture and Conversion of CO2 into Hydrogen over Bifunctional Structured Ce1-xCoxNiO3/Ca Perovskite-Type Oxide Monoliths

Carbon capture, utilization, and storage (CCUS) technologies are pivotal for transitioning to a net-zero economy by 2050. In particular, conversion of captured CO2 to marketable chemicals and fuels appears to be a sustainable approach to not only curb greenhouse emissions but also transform wastes like CO2 into useful products through storage of renewable energy in chemical bonds. Bifunctional materials (BFMs) composed of adsorbents and catalysts have shown promise in reactive capture and conversion of CO2 at high temperatures. In this study, we extend the application of 3D printing technology to formulate a novel set of BFMs composed of CaO and Ce1-xCoxNiO3 perovskite-type oxide catalysts for the dual-purpose use of capturing CO2 and reforming CH4 for H2 production. Three honeycomb monoliths composed of equal amounts of adsorbent and catalyst constituents with varied Ce1-xCox ratios were 3D printed to assess the role of cobalt on catalytic properties and overall performance. The samples were vigorously characterized using X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), N2 physisorption, X-ray photoelectron spectroscopy (XPS), H2-TPR, in situ CO2 adsorption/desorption XRD, and NH3-TPD. Results showed that the Ce1-xCox ratios-x = 0.25, 0.50, and 0.75-did not affect crystallinity, texture, or metal dispersion. However, a higher cobalt content reduced reducibility, CO2 adsorption/desorption reversibility, and oxygen species availability. Assessing the structured BFM monoliths via combined CO2 capture and CH4 reforming in the temperature range 500-700 °C revealed that such differences in physiochemical properties lowered H2 and CO yields at higher cobalt loading, leading to best catalytic performance in Ce0.75Co0.25NiO3/Ca sample that achieved 77% CO2 conversion, 94% CH4 conversion, 61% H2 yield, and 2.30 H2/CO ratio at 700 °C. The stability of this BFM was assessed across five adsorption/reaction cycles, showing only marginal losses in the H2/CO yield. Thus, these findings successfully expand the use of 3D printing to unexplored perovskite-based BFMs and demonstrate an important proof-of-concept for their use in combined CO2 capture and utilization in H2 production processes.

Highly Efficient and Stable Methane Dry Reforming Enabled by a Single-Site Cationic Ni Catalyst

Zeolite-supported nickel (Ni) catalysts have been extensively studied for the dry reforming of methane (DRM). It is generally believed that prior to or during the reaction, Ni is reduced to a metallic state to act as the catalytic site. Here, we employed a ligand-protected synthesis method to achieve a high degree of Ni incorporation into the framework of the MFI zeolite. The incorporated Ni species retained their cationic nature during the DRM reaction carried out at 600 °C, exhibiting higher apparent catalytic activity and significantly greater catalytic stability in comparison to supported metallic Ni particles at the same loading. From theoretical and experimental evidence, we conclude that the incorporation of Ni into the zeolite framework leads to the formation of metal-oxygen (Niδ+-O(2-ξ)-) pairs, which serve as catalytic active sites, promoting the dissociation of C-H bonds in CH4 through a mechanism distinct from that of metallic Ni. The conversion of CH4 on cationic Ni single sites follows the CHx oxidation pathway, which is characterized by the rapid transformation of partial cracking intermediates CHx*, effectively inhibiting coke formation. The presence of the CHx oxidation pathway was experimentally validated by identifying the reaction intermediates. These new mechanistic insights elucidate the exceptional performance of the developed Ni-MFI catalyst and offer guidance for designing more efficient and stable Ni-based DRM catalysts.

Conversion mechanism of thermal plasma-enhanced CH4-CO2 reforming system to syngas under the non-catalytic conditions

Thermal plasma activation of CH₄-CO₂ reforming (CRM) to syngas under non-catalytic conditions is an efficient and clean technology for the large-scale utilization of hydrocarbon resources and the conversion of greenhouse gases. This study investigates the equilibrium state and transformation mechanism of a CRM reaction system activated by thermal plasma through experimental, thermodynamic, and kinetic analyses. The experimental results illustrated that the CO₂ conversion rate and H₂ selectivity showed a downward trend with an increase in the CO₂/CH₄ molar ratio, whereas the CH₄ conversion rate and CO selectivity showed the opposite trend. When CO₂/CH₄ molar ratio was 6/4, the selectivity for CO and H₂ increased to 87.0 % and 80.8 %, respectively. Excess CO₂ promotes the partial oxidation of CH₄ to eliminate carbon deposition, resulting in an H₂/CO molar ratio value closer to 1. Thermodynamic results show that the thermal-plasma-initiated CRM reaction can reach thermodynamic equilibrium more easily than the conventional catalyzed reactions, achieving much higher feedstock gas conversion without carbon deposition. The kinetic results obtained from the PSR model revealed that CH₄ and CO₂ were cleaved to form free radicals at the instant of contact with the plasma flame. O, H, and other particles generated in the form of free radicals rapidly collided with each other and transformed into CO and H₂, accelerating the reaction process. The results presented in this study will help reveal the transformation mechanism of the CRM reaction activated by thermal plasma under non-catalytic conditions and provide a new perspective for studying CRM reactions.

Effect of La on the catalytic performance of mesoporous Ni/γ-Al2O3 catalysts for dry reforming of methane

Mesoporous Ni/La2O3/γ-Al2O3 catalysts with different La contents (0, 0.5, 1.5, 2.5, 3.5, and 4.5 wt.%) were prepared by the step-by-step impregnation method. The physicochemical properties of the prepared Ni/La2O3/γ-Al2O3 catalysts were characterized by H2-TPR, XRD, BET, O2-TPO, and TG. The effect of La dosage on the catalytic performance of Ni/γ-Al2O3 catalyst for dry reforming of methane was further investigated. The results show that the La content has a significant effect on the reducibility of high-valence Ni species, specific surface area, pore size, and pore volume as well as the catalytic performances. The high-valence Ni species in the NL3.5A catalyst precursor has high reducibility. And the specific surface area, pore size and pore volume of the NL3.5A catalyst are 145.9 m2 g−1, 11.7 nm, and 0.47 cm3 g−1, respectively. The catalytic activity of the series of prepared mesoporous Ni/La2O3/γ-Al2O3 catalysts follows the order: NL3.5A > NL2.5A > NL4.5A > NL1.5A > NL0.5A > NL0A. Namely, the NL3.5A catalyst possesses the best catalytic activity. The CH4 and CO2 conversions of NL3.5A catalyst are 61.6 and 39.1% at 600 °C, respectively. Additionally, it maintains a superior recycle capability for dry reforming of methane reaction because of the high coke resistance compared with the Ni/γ-Al2O3 catalyst.

Porous Silicon Oxycarbonitride Ceramics with Palladium and Pd2Si Nanoparticles for Dry Reforming of Methane

Pd-containing precursor has been synthesized from palladium acetate and poly(vinly)silazane (Durazane 1800) in an ice bath under an argon atmosphere. The results of ATR-FTIR and NMR characterizations reveal the chemical reaction between palladium acetate and vinyl groups in poly(vinyl)silazane and the hydrolyzation reaction between –Si–H and –Si–CH=CH₂ groups in poly(vinyl)silazane. The palladium nanoparticles are in situ formed in the synthesized precursors as confirmed by XRD, XPS, and TEM. Pd- and Pd₂Si-containing SiOCN ceramic nanocomposites are obtained by pyrolysis of the synthesized precursors at 700 °C, 900 °C–1100 °C in an argon atmosphere. The pyrolyzed nanocomposites display good catalytic activity towards the dry reforming of methane. The sample pyrolyzed at 700 °C possesses the best catalytic performance, which can be attributed to the in situ formed palladium nanoparticles and high BET surface area of about 233 m² g⁻¹.

Comparative Study of the CO2 Methanation Activity of Hydrotalcite-Based Nickel Catalysts Generated by Using Different Reduction Protocols

Parameters controlling the reduction of nickel hydrotalcite-based catalysts have been investigated in order to optimize the activity of the catalyst for CO2 methanation. Beside the variation of temperature and duration in the reduction process of the catalysts with hydrogen, two different reduction modes have been explored. The first one is the direct reduction of the dried uncalcined hydrotalcite-based precursor material whereas the second one is given by the reduction of the same type of precursor material but having been subjected to a calcination step prior to reduction. The corresponding kinetic measurements for the two principally different catalyst preparation schemes reveal that omitting the calcination step can largely be beneficial. Standard characterization data (XRD, BET, TG-FTIR, XPS) for the different catalytic materials will be presented.

Graphical abstract

Promoting dry reforming of methane via bifunctional NiO/dolomite catalysts for production of hydrogen-rich syngas

Extensive effort has been focused on the advancement of an efficient catalyst for CO2 reforming of CH4 to achieve optimum catalytic activity together with cost-effectiveness and high resistance to catalyst deactivation. In this study, for the first time, a new catalytic support/catalyst system of bifunctional NiO/dolomite has been synthesized by a wet impregnation method using low-cost materials, and it shows unique performance in terms of amphoteric sites and self-reduction properties. The catalysts were loaded into a continuous micro-reactor equipped with an online GC-TCD system. The reaction was carried out with a gas mixture consisting of CH4 and CO2 in the ratio of 1 : 1 flowing 30 ml min-1 at 800 °C for 10 h. The physicochemical properties of the synthesized catalysts were determined by various methods including X-ray diffraction (XRD), N2 adsorption-desorption, H2 temperature-programmed reduction (H2-TPR), temperature-programmed desorption of CO2 (TPD-CO2), and temperature-programmed desorption of NH3 (TPD-NH3). The highest catalytic performance of the DRM reaction was shown by the 10% NiO/dolomite catalyst (CH4 & CO2 conversion, χCH4; χCO2 ∼ 98% and H2 selectivity, S H2 = 75%; H2/CO ∼ 1 : 1 respectively). Bifunctional properties of amphoteric sites on the catalyst and self-reduction behaviour of the NiO/dolomite catalyst improved dry reforming of the CH4 process by enhancing CH4 and CO2 conversion without involving a catalyst reduction step, and the catalyst was constantly active for more than 10 h.

Promotional effect of magnesium oxide for a stable nickel-based catalyst in dry reforming of methane

The generation of synthesis gas (hydrogen and carbon monoxide mixture) from two global warming gases of carbon dioxide and methane via dry reforming is environmentally crucial and for the chemical industry as well. Herein, magnesium-promoted NiO supported on mesoporous zirconia, 5Ni/xMg–ZrO₂ (x = 0, 3, 5, 7 wt%) were prepared by wet impregnation method and then were tested for syngas production via dry reforming of methane. The reaction temperature at 800 °C was found more catalytically active than that at 700 °C due to the endothermic feature of reaction which promotes efficient CH₄ catalytic decomposition over Ni and Ni–Zr interface as confirmed by CH₄–TSPR experiment. NiO–MgO solid solution interacted with ZrO₂ support was found crucial and the reason for high CH₄ and CO₂ conversions. The highest catalyst stability of the 5Ni/3Mg–ZrO₂ catalyst was explained by the ability of CO₂ to partially oxidize the carbon deposit over the surface of the catalyst. A mole ratio of hydrogen to carbon monoxide near unity (H₂/CO ~ 1) was obtained over 5Ni/ZrO₂ and 5Ni/5Mg–ZrO₂, implying the important role of basic sites. Our approach opens doors for designing cheap and stable dry reforming catalysts from two potent greenhouse gases which could be of great interest for many industrial applications, including syngas production and other value-added chemicals.

In situ X-ray emission and high-resolution X-ray absorption spectroscopy applied to Ni-based bimetallic dry methane reforming catalysts

The promoting effect of cobalt on the catalytic activity of a NiCoO Dry Methane Reforming (DMR) catalyst was studied by a combination of in situ Kβ X-ray Emission Spectroscopy (XES) and Kβ-detected High Energy Resolution Fluorescence Detected X-ray absorption spectroscopy (HERFD XAS). Following the calcination process, Ni XES and Kβ-detected HERFD XAS data revealed that the NiO coordination in the NiCoO catalyst has a higher degree of symmetry and is different than that of pure NiO/γ-Al₂O₃. Following the reductive activation, it was found that the NiCoO/γ-Al₂O₃ catalyst required a relatively higher temperature compared to the monometallic NiO/γ-Al₂O₃ catalyst. This finding suggests that Co is hampering the reduction of Ni in the NiCoO catalyst by modulation of its electronic structure. It has also been previously shown that the addition of Co enhances the DMR activity. Further, the Kβ XES spectrum of the partly reduced catalysts at 450 °C reveals that the Ni sites in the NiCoO catalyst are electronically different from the NiO catalyst. The in situ X-ray spectroscopic study demonstrates that reduced metallic Co and Ni are the primary species present after reduction and are preserved under DMR conditions. However, the NiCo catalyst appears to always be somewhat more oxidized than the Ni-only species, suggesting that the presence of cobalt modulates the Ni electronic structure. The electronic structural modulations resulting from the presence of Co may be the key to the increased activity of the NiCo catalyst relative to the Ni-only catalyst. This study emphasizes the potential of in situ X-ray spectroscopy experiments for probing the electronic structure of catalytic materials during activation and under operating conditions.

Stable Trimetallic NiFeCu Catalysts with High Carbon Resistance for Dry Reforming of Methane

Copper has been incorporated into Ni-Fe alloys to form a series of ternary NiFeCu alloy catalysts with molar ratio of Cu/Fe varying from 0 to 1.5, which were tested in dry reforming of methane (DRM) at 923 K and atmospheric pressure with a CH₄ /CO₂ ratio of 1. XRD, TPR-H₂ and FE-TEM measurements confirm the formation of Ni-Fe-Cu alloys with particle size of 5.0-5.7 nm. The Ni₃ Fe₁ Cu₁ -Mg_x Al_y O_z (2.6 wt% Cu) shows the highest carbon resistance with only 5.0 % carbon by thermogravimetric analysis. Importantly, XPS analyses complemented with XAFS demonstrate that doping an appropriate quantity of Cu to form stable trimetallic alloy enhances the interaction between Ni and Fe, thus inhibiting Fe segregation and reducing carbon deposition. However, doping excessive Cu (3.9 wt%) weakens the Ni-Fe bond, preventing Fe from providing labile oxygen to Ni sites, which is unfavorable for carbon elimination.

Ni Single Atom Catalysts for CO2 Activation

We report on the activation of CO₂ on Ni single-atom catalysts. These catalysts were synthesized using a solid solution approach by controlled substitution of 1–10 atom % of Mg²⁺ by Ni²⁺ inside the MgO structure. The Ni atoms are preferentially located on the surface of the MgO and, as predicted by hybrid-functional calculations, favor low-coordinated sites. The isolated Ni atoms are active for CO₂ conversion through the reverse water–gas shift (rWGS) but are unable to conduct its further hydrogenation to CH₄ (or MeOH), for which Ni clusters are needed. The CO formation rates correlate linearly with the concentration of Ni on the surface evidenced by XPS and microcalorimetry. The calculations show that the substitution of Mg atoms by Ni atoms on the surface of the oxide structure reduces the strength of the CO₂ binding at low-coordinated sites and also promotes H₂ dissociation. Astonishingly, the single-atom catalysts stayed stable over 100 h on stream, after which no clusters or particle formation could be detected. Upon catalysis, a surface carbonate adsorbate-layer was formed, of which the decompositions appear to be directly linked to the aggregation of Ni. This study on atomically dispersed Ni species brings new fundamental understanding of Ni active sites for reactions involving CO₂ and clearly evidence the limits of single-atom catalysis for complex reactions.

Chemistry in supercritical fluids for the synthesis of metal nanomaterials

The supercritical flow synthesis of metal nanomaterials is sustainable and scalable for the efficient production of materials.

Two-Dimensional Layered Double Hydroxides for Reactions of Methanation and Methane Reforming in C1 Chemistry

CH₄ as the paramount ingredient of natural gas plays an eminent role in C1 chemistry. CH₄ catalytically converted to syngas is a significant route to transmute methane into high value-added chemicals. Moreover, the CO/CO₂ methanation reaction is one of the potent technologies for CO₂ valorization and the coal-derived natural gas production process. Due to the high thermal stability and high extent of dispersion of metallic particles, two-dimensional mixed metal oxides through calcined layered double hydroxides (LDHs) precursors are considered as the suitable supports or catalysts for both the reaction of methanation and methane reforming. The LDHs displayed compositional flexibility, small crystal sizes, high surface area and excellent basic properties. In this paper, we review previous works of LDHs applied in the reaction of both methanation and methane reforming, focus on the LDH-derived catalysts, which exhibit better catalytic performance and thermal stability than conventional catalysts prepared by impregnation method and also discuss the anti-coke ability and anti-sintering ability of LDH-derived catalysts. We believe that LDH-derived catalysts are promising materials in the heterogeneous catalytic field and provide new insight for the design of advance LDH-derived catalysts worthy of future research.

Hydrotalcite based Ni–Fe/(Mg, Al)Ox catalysts for CO2 methanation – tailoring Fe content for improved CO dissociation, basicity, and particle size

Advantages of hydrotalcite-like precursors and the synergistic effect of bimetallic Ni–Fe alloys are combined and the most appropriate amount of Fe identified with respect to activity, selectivity and stability.

Comparative study on La-promoted Ni/γ-Al2O3 for methane dry reforming – spray drying for enhanced nickel dispersion and strong metal–support interactions

Dry reforming of methane (DRM) enables an efficient utilization of two abundant greenhouse gases by converting them into syngas, a versatile feedstock for chemical synthesis. Aiming for high catalyst performance and enhanced coke resistance, different preparation techniques of La-promoted Ni/γ-Al₂O₃ catalysts for DRM were compared facilitating structure–performance correlations. The studied synthesis techniques comprehend incipient wetness impregnation and co-precipitation as well as alternative techniques such as spray drying. All catalysts were fully characterized before and after reaction by N₂-physisorption, XRD, H₂-TPR and STEM-EDX elemental mapping. Additionally, a thorough investigation of carbon deposits has been carried out by TGA/DSC and STEM-EDX, respectively. The different preparation techniques led generally to very different physical properties, structure, chemical species and anti-coking properties of the catalyst. However, some catalysts with similar physicochemical characteristics differed in catalytic performance and coking resistance. Superior catalytic performance could be reached for catalysts prepared by spray drying and related to excellent Ni dispersion, strong metal–support interaction and very low coke formation of only 2.7% of the catalyst weight. After 6 h time on stream only minor sintering occurred, with few Ni nanoparticles up to 10 nm.

Clear structure-performance correlation for the dry reforming of methane – spray drying for excellent sintering and cocking resistivity.

Robust mesoporous bimetallic yolk–shell catalysts for chemical CO2 upgrading via dry reforming of methane

A new generation highly efficient and stable mesoporous ZnO/Ni@silica yolk–shell catalyst is designed for chemical CO₂ recycling, to solve the coking and sintering issues of traditional catalysts.

Cooperativity and Dynamics Increase the Performance of NiFe Dry Reforming Catalysts

The dry reforming of methane (DRM), i.e., the reaction of methane and CO₂ to form a synthesis gas, converts two major greenhouse gases into a useful chemical feedstock. In this work, we probe the effect and role of Fe in bimetallic NiFe dry reforming catalysts. To this end, monometallic Ni, Fe, and bimetallic Ni-Fe catalysts supported on a Mg_xAl_yO_z matrix derived via a hydrotalcite-like precursor were synthesized. Importantly, the textural features of the catalysts, i.e., the specific surface area (172-178 m²/g_cat), pore volume (0.51-0.66 cm³/g_cat), and particle size (5.4-5.8 nm) were kept constant. Bimetallic, Ni₄Fe₁ with Ni/(Ni + Fe) = 0.8, showed the highest activity and stability, whereas rapid deactivation and a low catalytic activity were observed for monometallic Ni and Fe catalysts, respectively. XRD, Raman, TPO, and TEM analysis confirmed that the deactivation of monometallic Ni catalysts was in large due to the formation of graphitic carbon. The promoting effect of Fe in bimetallic Ni-Fe was elucidated by combining operando XRD and XAS analyses and energy-dispersive X-ray spectroscopy complemented with density functional theory calculations. Under dry reforming conditions, Fe is oxidized partially to FeO leading to a partial dealloying and formation of a Ni-richer NiFe alloy. Fe migrates leading to the formation of FeO preferentially at the surface. Experiments in an inert helium atmosphere confirm that FeO reacts via a redox mechanism with carbon deposits forming CO, whereby the reduced Fe restores the original Ni-Fe alloy. Owing to the high activity of the material and the absence of any XRD signature of FeO, it is very likely that FeO is formed as small domains of a few atom layer thickness covering a fraction of the surface of the Ni-rich particles, ensuring a close proximity of the carbon removal (FeO) and methane activation (Ni) sites.

Dry Reforming of Methane on a Highly-Active Ni-CeO2 Catalyst: Effects of Metal-Support Interactions on C-H Bond Breaking

Ni-CeO2 is a highly efficient, stable and non-expensive catalyst for methane dry reforming at relative low temperatures (700 K). The active phase of the catalyst consists of small nanoparticles of nickel dispersed on partially reduced ceria. Experiments of ambient pressure XPS indicate that methane dissociates on Ni/CeO2 at temperatures as low as 300 K, generating CHx and COx species on the surface of the catalyst. Strong metal-support interactions activate Ni for the dissociation of methane. The results of density-functional calculations show a drop in the effective barrier for methane activation from 0.9 eV on Ni(111) to only 0.15 eV on Ni/CeO2-x (111). At 700 K, under methane dry reforming conditions, no signals for adsorbed CHx or C species are detected in the C 1s XPS region. The reforming of methane proceeds in a clean and efficient way.

A Single-Source Precursor Approach to Self-Supported Nickel-Manganese-Based Catalysts with Improved Stability for Effective Low-Temperature Dry Reforming of Methane

Self-supported nickel-manganese-based catalysts were synthesized from heterobimetallic nickel manganese oxalate precursors via a versatile reverse micelle approach. The precursors were subjected to thermal degradation (400 °C) in the presence of synthetic air to form respective metal oxides, which were treated under hydrogen (500 °C) to form Ni₂ MnO₄ -O₂ -H₂ , Ni₆ MnO₈ -O₂ -H₂ and NiO-O₂ -H₂ . Similarly, the precursors were also treated directly under hydrogen at the same temperature to form Ni₂ MnO₄ -H₂ and Ni₆ MnO₈ -H₂ . The catalysts were extensively investigated by PXRD, SEM, TEM, XPS and BET analyses. The resulting catalysts were applied for dry reforming of methane (DRM) and exhibit better stability and resistance to coking than coprecipitated catalysts. Further, we show that addition of manganese, which is not an active catalyst for DRM alone, to nickel has a significant promotion effect on both the activity and stability of DRM catalysts, and a Ni/Mn ratio lower than 6:1 enables optimized activity for this system.

Hierarchically structured tetragonal zirconia as a promising support for robust Ni based catalysts for dry reforming of methane

This work presents a facile approach for preparing nanosheet-accumulating Laminaria japonica-like hierarchically structured ZrO₂ with tetragonal phase, which acts as excellent support for robust supported Ni catalyst towards dry reforming of methane.

Methane dry reforming over hydrotalcite-derived Ni–Mg–Al mixed oxides: the influence of Ni content on catalytic activity, selectivity and stability

Ni-containing hydrotalcite-derived catalysts were prepared using different Ni loadings (from ca. 4 to 60 wt%) at the same M^II/M^III ratio equal to 3.

The reducibility of highly stable Ni-containing species in catalysts derived from hydrotalcite-type precursors

A study was conducted on the speciation and reducibility of Ni in catalysts derived from hydrotalcite-type precursors intercalated by silicates.