Enhancement of the CO2 Sensing/Capture through High Cationic Charge in M-ZrO2 (Li+, Mg2+, or Co3+): Experimental and Theoretical Studies

The capture and storage of CO₂ are of growing interest in atmospheric science since greenhouse gas emission has to be reduced considerably in the near future. The present paper deals with the doping of cations on ZrO₂, i.e., M-ZrO₂ (M = Li⁺, Mg²⁺, or Co³⁺), defecting the crystalline planes for the adsorption of carbon dioxide. The samples were prepared by the sol-gel method and characterized completely by different analytical methods. The deposition of metal ions on ZrO₂ (whose crystalline phases: monoclinic and tetragonal are transformed into a single-phase such as tetragonal for LiZrO₂ and cubic for MgZrO₂ or CoZrO₂) shows a complete disappearance of the XRD monoclinic signal, and it is consistent with HRTEM lattice fringes: 2.957 nm for ZrO₂ (101, tetragonal/monoclinic), 3.018 nm for tetragonal LiZrO₂, 2.940 nm for cubic MgZrO₂, and 1.526 nm for cubic CoZrO₂. The samples are thermally stable, resulting an average size of ∼5.0-15 nm. The surface of LiZrO₂ creates the oxygen deficiency, while for Mg²⁺ (0.089 nm), since the size of the atom is relatively greater than that of Zr⁴⁺ (0.084 nm), the replacement of Zr⁴⁺ by Mg²⁺ in sublattice is difficult; thus, a decrease of the lattice constant was noticed. Since the high band gap energy (ΔE > 5.0 eV) is suitable for CO₂ adsorption, the samples were employed for the selective detection/capture of CO₂ by using electrochemical impedance spectroscopy (EIS) and direct current resistance (DCR), showing that CoZrO₂ is capable of CO₂ capture about 75%. If M⁺ ions are deposited within the ZrO₂ matrix, then the charge imbalance allows CO₂ to interact with the oxygen species to form CO₃^2- which produces a high resistance (21.04 × 10⁶ (Ω, Ohm)). The adsorption of CO₂ with the samples was also theoretically studied showing that the interaction of CO₂ with MgZrO₂ and CoZrO₂ is more feasible than with LiZrO₂, subscribing to the experimental data. The temperature effect (273 to 573 K) for the interaction of CO₂ with CoZrO₂ was also studied by the docking method and observed the cubic structure is more stable at high temperatures as compared to the monoclinic geometry. Thus, CO₂ would preferably interact with ZrO₂^c (E_RS = -19.29 kJ/mol) than for ZrO₂^m (22.4 J/mmol (ZrO₂^c = cubic; ZrO₂^m = monoclinic).

Promotion of Ru or Ni on Alumina Catalysts with a Basic Metal for CO2 Hydrogenation: Effect of the Type of Metal (Na, K, Ba)

Ru and Ni on alumina catalysts have been promoted with a 10 wt% of alkali metal (K or Na) or alkaline earth metal (Ba) and tested in CO₂ methanation. For the catalyst consisting of Ni and Ba, the variation of Ba loading while keeping Ni loading constant was studied. The promotion in terms of enhanced CH₄ yield was found only for the addition of barium to 15 wt% Ni/Al₂O₃. In contrast, K and Na addition increased the selectivity to CO while decreasing conversion. For the Ru-based catalyst series, no enhancement in conversion or CH₄ yield was attained by any of the alkaline metals. CO₂ temperature-programed desorption (CO₂-TPD) revealed that the amount of chemisorbed CO₂ increased significantly after the addition of the base metal. The reactivity of CO_x ad-species for each catalyst was assessed by temperature-programed surface reaction (TPSR). The characterization revealed that the performance in the Sabatier reaction was a result of the interplay between the amount of chemisorbed CO₂ and the reactivity of the COx ad-species, which was maximized for the (10%Ba)15%Ni/Al₂O₃ catalyst.

Dry Reforming of Methane with Ni Supported on Mechanically Mixed Yttria-Zirconia Support

This study focuses on CH4 reforming with CO2 over Ni supported on yttria mixed with zirconia support. Different loading of yttria was used to enhance the performance of Ni towards achieving the optimum activity. The physicochemical properties of both fresh calcined and used catalysts were studied using a range of characterization techniques. The specific surface area measurement by the BET method showed a progressive increase in the area with an increase in yttria loading. The monoclinic (m- ZrO2) and tetragonal (t- ZrO2) phases were identified on all the samples by the XRD analysis. A reduction in the intensity of m- ZrO2 was observed on adding Ni to the catalysts while the diffraction pattern of crystalline yttria was not identified. The reducibility analysis showed the influence of yttria. It induces the formation of NiYO3 species with stronger active metal-support interaction. From the catalytic test, 5Ni/10Y-Z-3215 had the highest feed conversion of about 68 and 88% for CH4 and CO2 respectively. The TEM analysis showed a uniform dispersion of NiO particles over the mixed yttria-zirconia support with no agglomeration of the active metal particles after the reaction. The measurement of the quantity of carbon deposits by the TGA revealed that the increase in yttria loading enhanced the gasification of carbon deposits with 5Ni/20Y-Z-3215 recording the lowest weight loss of about 28%.

Graphical Abstract

Effect of Mg Contents on Catalytic Activity and Coke Formation of Mesoporous Ni/Mg-Aluminate Spinel Catalyst for Steam Methane Reforming

Ni catalysts are most suitable for a steam methane reforming (SMR) reaction considering the activity and the cost, although coke formation remains the main problem. Here, Ni-based spinel catalysts with various Mg contents were developed through the synthesis of mesoporous Mg-aluminate supports by evaporation-induced self-assembly followed by Ni loading via incipient wetness impregnation. The mesoporous Ni/Mg-aluminate spinel catalysts showed high coke resistance under accelerated reaction conditions (0.0014 gcoke/gcat·h for Ni/Mg30, 0.0050 gcoke/gcat·h for a commercial catalyst). The coke resistance of the developed catalyst showed a clear trend: the higher the Mg content, the lower the coke deposition. The Ni catalysts with the lower Mg content showed a higher surface area and smaller Ni particle size, which originated from the difference of the sintering resistance and the exsolution of Ni particles. Despite these advantageous attributes of Ni catalysts, the coke resistance was higher for the catalysts with the higher Mg content while the catalytic activity was dependent on the reaction conditions. This reveals that the enhanced basicity of the catalyst could be the major parameter for the reduction of coke deposition in the SMR reaction.

The Role of Alkali and Alkaline Earth Metals in the CO2 Methanation Reaction and the Combined Capture and Methanation of CO2

CO2 methanation has great potential for the better utilization of existing carbon resources via the transformation of spent carbon (CO2) to synthetic natural gas (CH4). Alkali and alkaline earth metals can serve both as promoters for methanation catalysts and as adsorbent phases upon the combined capture and methanation of CO2. Their promotion effect during methanation of carbon dioxide mainly relies on their ability to generate new basic sites on the surface of metal oxide supports that favour CO2 chemisorption and activation. However, suppression of methanation activity can also occur under certain conditions. Regarding the combined CO2 capture and methanation process, the development of novel dual-function materials (DFMs) that incorporate both adsorption and methanation functions has opened a new pathway towards the utilization of carbon dioxide emitted from point sources. The sorption and catalytically active phases on these types of materials are crucial parameters influencing their performance and stability and thus, great efforts have been undertaken for their optimization. In this review, we present some of the most recent works on the development of alkali and alkaline earth metal promoted CO2 methanation catalysts, as well as DFMs for the combined capture and methanation of CO2.

Recent Progresses in Constructing the Highly Efficient Ni Based Catalysts With Advanced Low-Temperature Activity Toward CO2 Methanation

With the development and prosperity of the global economy, the emission of carbon dioxide (CO2) has become an increasing concern. Its greenhouse effect will cause serious environmental problems, such as the global warming and climate change. Therefore, the worldwide scientists have devoted great efforts to control CO2 emissions through various strategies, such as capture, resource utilization, sequestration, etc. Among these, the catalytic conversion of CO2 to methane is considered as one of the most efficient routes for resource utilization of CO2 owing to the mild reaction conditions and simple reaction device. Pioneer thermodynamic studies have revealed that low reaction temperature is beneficial to the high catalytic activity and CH4 selectivity. However, the low temperature will be adverse to the enhancement of the reaction rate due to kinetic barrier for the activation of CO2. Therefore, the invention of highly efficient catalysts with promising low temperature activities toward CO2 methanation reaction is the key solution. The Ni based catalysts have been widely investigated as the catalysts toward CO2 methanation due to their low cost and excellent catalytic performances. However, the Ni based catalysts usually perform poor low-temperature activities and stabilities. Therefore, the development of highly efficient Ni based catalysts with excellent low-temperature catalytic performances has become the research focus as well as challenge in this field. Therefore, we summarized the recent research progresses of constructing highly efficient Ni based catalysts toward CO2 methanation in this review. Specifically, the strategies on how to enhance the catalytic performances of the Ni based catalysts have been carefully reviewed, which include various influencing factors, such as catalytic supports, catalytic auxiliaries and dopants, the fabrication methods, reaction conditions, etc. Finally, the future development trend of the Ni based catalysts is also prospected, which will be helpful to the design and fabrication of the Ni catalysts with high efficiency toward CO2 methanation process.

Preparation of Ni based mesoporous Al2O3 catalyst with enhanced CO2 methanation performance

A Ni based mesoporous γ-Al₂O₃ (MA) catalyst was prepared via partial hydrolysis without organic surfactants and employed in the carbon dioxide methanation reaction. The obtained catalysts were characterized by N₂ adsorption–desorption, H₂-TPR, XRD, XPS, TG, SEM and TEM-EDS techniques. CO₂ methanation was performed in a fixed-bed reactor. A high surface area of MA with excellent hydrothermal stability was obtained, which promoted the dispersion of nickel species, producing a better catalytic performance. Incorporation of more NiO species into the Ni/MA catalyst increased the amount of active metallic Ni sties, further improving the catalytic activity and CH₄ selectivity. Moreover, the monolithic skeleton of MA with fabric-like walls suppressed the aggregation of active metallic Ni sites and carbon deposition, enhancing the catalyst's stability, which provides a new insight for potential industrial applications.

A Ni based mesoporous γ-Al₂O₃ (MA) catalyst was prepared via partial hydrolysis without organic surfactants and employed in the carbon dioxide methanation reaction.

Designing and Fabricating Ordered Mesoporous Metal Oxides for CO₂ Catalytic Conversion: A Review and Prospect

In the past two decades, great progress has been made in the aspects of fabrication and application of ordered mesoporous metal oxides. Ordered mesoporous metal oxides have attracted more and more attention due to their large surface areas and pore volumes, unblocked pore structure, and good thermal stabilities. Compared with non-porous metal oxides, the most prominent feature is their ability to interact with molecules not only on their outer surface but also on the large internal surfaces of the material, providing more accessible active sites for the reactants. This review carefully describes the characteristics, classification and synthesis of ordered mesoporous metal oxides in detail. Besides, it also summarizes the catalytic application of ordered mesoporous metal oxides in the field of carbon dioxide conversion and resource utilization, which provides prospective viewpoints to reduce the emission of greenhouse gas and the inhibition of global warming. Although the scope of current review is mainly limited to the ordered mesoporous metal oxides and their application in the field of CO₂ catalytic conversion via heterogeneous catalysis processes, we believe that it will provide new insights and viewpoints to the further development of heterogeneous catalytic materials.

From CO2methanation to ambitious long-chain hydrocarbons: alternative fuels paving the path to sustainability

Comprehensive insight into the thermochemical, photochemical and electrochemical reduction of CO₂to methane and long-chain hydrocarbons as alternative fuels.