Catalysts For CO2 Methanation Research Articles

Insights by in-situ studies on the nature of highly-active hydrotalcite-based Ni-Fe catalysts for CO2 methanation

Designing CO2 methanation catalysts that meet industrial requirements is still challenging. We report Ni-Fe hydrotalcite-derived catalysts with a wide range of Ni and Mg loadings showing that an optimised composition with Ni0.4 gives a very high CO2 conversion rate of 0.37 mmol/gcat/s at 300 °C. This catalyst is studied by in-situ APXPS and NEXAFS spectroscopies and compared with the other synthesised samples to obtain new mechanistic insights on methanation catalysts active for low-temperature (300 °C) methanation, which is an industrial requirement. Under methanation conditions, in-situ investigations revealed the presence of metallic Ni sites and low nuclearity Ni-Fe species at xNiL (Ni loading) = 21.2 mol%. These sites are oxidised on the low Ni-loaded catalyst (xNiL= 9.2 mol%). The best CO2 conversion rate and CH4 selectivity are shown at intermediate xNiL (21.2 mol%), in the presence of Mg. These superior performances are related to the high metallic surface area, dispersion, and optimal density of basic sites. The TOFCO2(turnover frequency of CO2 conversion) increases exponentially with the fractional density of basic to metallic sites (XB) from 1.1 s-1 (xNiL= 29.2 mol%) to 9.1 s-1 (xNiL= 7.6 mol%). It follows the opposite trend of the CO2 conversion rate. In-situ DRIFTS data under methanation conditions evidence that the TOFCO2at high XB is related to the presence of a formate route which is not predominant at low XB (high xNiL). A synergistic interplay of basic and metallic sites is present. This contribution provides a rationale for designing industrially competitive CO2 methanation catalysts with high catalytic activity while maintaining low Ni loading.

Optimization of Co-Ni-Mg-Al mixed-oxides CO2 methanation catalysts with solution combustion synthesis: On the importance of Co incorporation and basicity

Hydrogenation of CO2 to methane is a promising prospect for the utilization of carbon dioxide. Ni-Mg-Al mixed oxides have been reported as a catalyst for this process. Their promotion with cobalt allows to improve Ni reducibility, enhances surface basicity, electronic and textural properties. Solution combustion synthesis was used to optimize the introduction of cobalt to the Ni-Mg-Al oxide matrix. Three synthesis strategies were applied to obtain different morphologies and study their catalytic performance. Characterization techniques (ICP-MS, XRD, low-temperature N2 sorption, H2-TPR, CO2-TPD, TEM, XAS) showed that simultaneous combustion of all the precursors (Ni, Mg, Al, and Co) led to dissociation of nickel and cobalt to the support which resulted in the reduction of catalytic activity and blockage of active centers. The separation of the synthesis into two steps increased the availability of active centers, improved surface properties, and catalytic performance. Furthermore, it led to a decrease in the coordination number of nickel, due to higher contribution of cobalt in the metal crystallites, which resulted in improved catalytic activity. Our findings showed that the addition of cobalt in the second step, in the NiCo-D catalyst, enhanced the CO2 and H2 conversions for methane production compared to the other applied synthesis strategies.

Spatially Formed Tenacious Nickel-Supported Bimetallic Catalysts for CO2 Methanation under Conventional and Induction Heating

The paper introduces spatially stable Ni-supported bimetallic catalysts for CO2 methanation. The catalysts are a combination of sintered nickel mesh or wool fibers and nanometal particles, such as Au, Pd, Re, or Ru. The preparation involves the nickel wool or mesh forming and sintering into a stable shape and then impregnating them with metal nanoparticles generated by a silica matrix digestion method. This procedure can be scaled up for commercial use. The catalyst candidates were analyzed using SEM, XRD, and EDXRF and tested in a fixed-bed flow reactor. The best results were obtained with the Ru/Ni-wool combination, which yields nearly 100% conversion at 248 °C, with the onset of reaction at 186 °C. When we tested this catalyst under inductive heating, the highest conversion was observed already at 194 °C.

Ru- and Rh-Based Catalysts for CO2 Methanation Assisted by Non-Thermal Plasma

The need to reduce the concentration of CO2 in the atmosphere is becoming increasingly necessary since it is considered the main factor responsible for climate change. Carbon Capture and Utilization (CCU) technology offers the opportunity to obtain a wide range of chemicals using this molecule as a raw material. In this work, the catalytic Non-Thermal Plasma (NTP)-assisted hydrogenation of CO2 to CH4 (methanation reaction) in a Dielectric Barrier Discharge (DBD) reactor was investigated. Four different Ru- and Rh-based catalysts were prepared starting from γ-Al2O3 spheres, characterized and tested in both thermal and NTP-assisted methanation under different operating conditions. The experimental tests evidenced the very positive effect of the NTP application on the catalytic performance, highlighting that for all the catalysts the same CO2 conversion was reached at a temperature 150 °C lower with respect to the conventional thermal reaction. Among the prepared catalysts, the bimetallic ones showed the best performance, reaching a CO2 conversion of 97% at about 180 °C with a lower energy consumption with respect to similar catalysts present in the literature.

The promotional effects of Mn on Ni/SiO2 catalysts for CO methanation

The promotional effects of Mn on Ni/SiO2 catalysts for CO methanation

CO2 Methanation over Nickel Catalysts: Support Effects Investigated through Specific Activity and Operando IR Spectroscopy Measurements

Renewed interest in CO2 methanation is due to its role within the framework of the Power-to-Methane processes. While the use of nickel-based catalysts for CO2 methanation is well stablished, the support is being subjected to thorough research due to its complex effects. The objective of this work was the study of the influence of the support with a series of catalysts supported on alumina, ceria, ceria–zirconia, and titania. Catalysts’ performance has been kinetically and spectroscopically evaluated over a wide range of temperatures (150–500 °C). The main results have shown remarkable differences among the catalysts as concerns Ni dispersion, metallic precursor reducibility, basic properties, and catalytic activity. Operando infrared spectroscopy measurements have evidenced the presence of almost the same type of adsorbed species during the course of the reaction, but with different relative intensities. The results indicate that using as support of Ni a reducible metal oxide that is capable of developing the basicity associated with medium-strength basic sites and a suitable balance between metallic sites and centers linked to the support leads to high CO2 methanation activity. In addition, the results obtained by operando FTIR spectroscopy suggest that CO2 methanation follows the formate pathway over the catalysts under consideration.

Insights into the Zn Promoter for Improvement of Ni/SiO2 Catalysts Prepared by the Ammonia Evaporation Method toward CO2 Methanation

As a pure combustible gas with a high calorific value, methane has long been favored, and that is why the CO2 methanation reaction is attracting more and more attention. However, it is still challenging for this reaction due to the chemical inertness of CO2 molecules, poor reaction efficiency at low temperatures, catalyst sintering at high temperatures, and carbon monoxide toxicity. Herein, the ammonia evaporation method was utilized to synthesize a series of Zn-modified Ni/SiO2 catalysts with high surface area and high dispersity of active metals. The 80Ni-Zn/SiO2 catalyst with an appropriate Ni/Zn molar ratio of 80:1 exhibited a high-performance breakthrough with a CO2 conversion greater than 80% at 300 °C, good stability for 40 h at 310 °C, and a gas hourly space velocity of 18,000 mL·g–1·h–1. These catalysts were further characterized by using a series of methods like in situ diffuse reflectance infrared Fourier transform spectroscopy to investigate the structural properties and potential reaction pathways. The effect of the Zn promoter on the Ni/SiO2 catalyst for CO2 methanation has been well investigated, namely, improving Ni dispersion and enhancing the H2 adsorption. The findings demonstrate the broad availability, affordability, and remarkable high-performance practicability of the raw ingredients for the production of Ni-based catalysts for commercial applications.

Fabrication of highly active and stable Ni/CeO2-nanorods wash-coated on ceramic NZP structured catalysts for scaled-up CO2 methanation

The production of synthetic natural gas from CO2 methanation using green H2 produced via water electrolysis is a promising pathway regarding both the curtailment of excess power by variable renewables and the mitigation of CO2 emissions. Several catalytic systems have been employed for thermocatalytic CO2 methanation in lab-scale, with Ni-based catalysts being amongst the most cost-effective and active materials. In this regard, we have recently demonstrated the remarkable low-temperature CO2 methanation activity of a nickel catalyst supported on ceria nanorods, ascribed to the augmented metal-support synergy. Herein, we report on a scaled-up process of CO2 methanation, involving; i) fabrication of a highly porous NZP-type ceramic substrate of Ba1+xZr4P6–2xSi2xO24 in the form of extruded pellets, ii) wash-coating of Ni/CeO2-nanorods catalyst on NZP pellets, iii) design and testing of scaled-up experiments under a scaling factor of 80:1 and 65:1 in terms of mass and volume of catalysts compared to lab-scale experiments, respectively. The as-synthesized catalyst exhibited remarkable performance under variable reaction conditions and stable behavior after 75 h. Remarkably, the structured catalyst attained a methane formation rate of 277 NL gNi−1 h−1, being higher to numerous values reported in relevant works. Equally importantly, it was disclosed that increased values of space velocity led to high temperature gradient in the catalytic bed, thereby favoring the generation of CO. Intriguingly, the morphological and structural characteristics of the used catalyst remained unaltered even after various on/off reaction cycles and the stability test, which is a promising finding toward scaling-up the process at higher technology readiness levels using real feed streams.

Ni/Al2O3 catalysts for CO2 methanation: Effect of silica and nickel loading

Samples containing from 1 to 33 wt.% of NiO on silica and alumina doped with silica (1 and 20 wt.% silica in the support) have been prepared and characterized by BET, XRD, FT-IR, UV–vis–NIR, FE-SEM, EDXS, and TPR techniques. Catalysts have been pre-reduced in situ before catalytic experiments and data have been compared with Ni/Al2O3 reference sample. Characterization results showed that SiO2 support has a low Ni dispersion ability mainly producing segregated NiO particles and a small amount of dispersed Ni2+ in exchange sites. Instead, for the Si-doped alumina a “surface spinel monolayer phase” is formed by increasing Ni loading and, only when the support surface is completely covered by this layer, NiO is formed. Moreover, H2-TPR results indicated that NiO particles are more easily reduced compared to Ni species. Low loading Ni/SiO2 catalysts show high selectivity and moderate activity for RWGS (reverse Water Gas Shift) reaction, likely mainly due to nickel species dispersed in silica exchange sites, as evidenced by visible spectroscopy. High loading Ni/SiO2 catalysts show both methanation and RWGS but evident short-term deactivation for methanation, attributed to large, segregated Ni metal particles, covered by a carbon veil. Ni on alumina -rich carriers, where nickel disperses forming a surface spinel phase, show high activity and selectivity for methanation, and short-term catalyst stability as well. This activity is attributed to small nickel clusters or metal particles interacting with alumina, formed upon reaction. The addition of SiO2 in Al2O3 support decreases the activity of Ni catalysts in CO2 methanation, because it reduces the ability of the support to disperse nickel in form of the surface spinel phase, thus reducing the amount of Ni clusters in the reduced catalysts.

Facile and efficient synthesis of ordered mesoporous MIL-53(Al)-derived Ni catalysts with improved activity in CO2 methanation

A novel and feasible way to obtain MIL-53(Al)-derived Ni catalysts for CO2 methanation is presented. The sacrificial MIL-53(Al) was obtained by a less time and energy-consuming hydrothermal synthesis, at 190 °C, 12 h (compared to 220 °C, 72 h), at no expense on the structural and textural properties. The as-synthesized (as) and activated (lt) forms of MIL-53(Al) were derived at 600 °C to give amorphous mesoporous MIL-53(Al)-derived alumina, AlMIL-53(as) and AlMIL-53(lt), respectively. The subsequent Ni(10 wt%) catalysts obtained by impregnation were investigated by XRD, N2 physisorption, TPR, TEM, H2-TPD, and CO2-TPD. It was found that Ni/AlMIL-53 catalysts have an ordered mesoporous structure (5–10 nm), uniform distribution of round-shaped Ni nanoparticles (4–5 nm), aligned within the pores of the MIL-53(Al)-derived alumina, and an enhanced H2 and CO2 adsorption capacity compared to Ni/Al(com). Thus, Ni/AlMIL-53(as) reveals a H2 adsorption capacity 2 times larger than Ni/AlMIL-53(lt), and 4 times larger than for Ni/Al(com). This was explained by the largest dispersion of small Ni nanoparticles (∼4.2 nm), but also by an additional amount of H2 available on the catalyst, as revealed by control TPD tests. Also, Ni/AlMIL-53(as) showed a judicious distribution among weak and medium basic sites. These features made Ni/AlMIL-53(as) the best performing catalyst in CO2 methanation (200–500 °C, CO2/H2/Ar=1/4/1, 36 Lg-1h-1), with 70% CO2 conversion and 95% CH4 selectivity, at 400 °C. All catalysts showed stable CO2 conversion and CH4 selectivity over 24 h time on stream, with no evident deactivation due to Ni sintering or C deposition, the catalytic performance decreasing in the series Ni/AlMIL-53(as)>Ni/AlMIL-53(lt)>Ni/Al(com).

Investigating the Effect of Ni Loading on the Performance of Yttria-Stabilised Zirconia Supported Ni Catalyst during CO2 Methanation

CO2 methanation was studied on Ni-based yttria-stabilised zirconia (Ni/YSZ) catalysts. The catalysts were prepared by the wet impregnation method, where the amount of Ni content was varied from 5% to 75%. Thereafter, the prepared catalysts were analysed by BET, XRD, SEM and H2-TPR. BET results showed an initial increase in the surface area with an increase in Ni loading, then a decrease after 30% Ni loading. The XRD results revealed that the Ni crystallite size increased as the Ni loading increased, while the H2-TPR showed a shift in reduction peak temperature to a higher temperature, indicating that the reducibility of the catalysts decreased as the Ni loading increased. The activity of the synthesised catalysts for CO2 methanation was studied by passing a mixture of H2, CO2 and N2 with a total flow of 135 mL min−1 and GHSV of 40,500 mL h−1 g−1 through a continuous flow quartz tube fixed-bed reactor (I.D. = 5.5 mm, wall thickness = 2 mm) containing 200 mg of the catalyst at a temperature range of 473 to 703 K under atmospheric pressure and a H2:CO2 ratio of 4. The tested Ni/YSZ catalysts showed an improvement in activity as the reaction temperature increased from 473 K to around 613 to 653 K, depending on the Ni loading. Beyond the optimum temperature, the catalyst’s activity started to decline, irrespective of the Ni loading. In particular, the 40% Ni/YSZ catalyst displayed the best performance, followed by the 30% Ni/YSZ catalyst. The improved activity at high Ni loading (40% Ni) was attributed to the increase in hydrogen coverage and improved site for both H2 and CO2 adsorption and activation.

Lowering risk of methanation of carbon support in Ru/carbon catalysts for CO methanation by adding lanthanum

Two series of Ru/C catalysts doped with lanthanum ions are prepared and studied in CO methanation in the H2-rich gas. The samples are characterized by N2 physisorption, TG-MS studies, XRD, XPS, TEM/STEM and CO chemisorption. Two graphitized carbons differing in surface area (115 and 80.6 m2/g) are used as supports. The average sizes of ruthenium crystallites deposited on their surfaces are 4.33 and 5.95 nm, respectively. The addition of the proper amount of La to the Ru/carbon catalysts leads to an above 20% increase in the catalytic activity along with stable CH4 selectivity higher than 99% at all temperatures. Simultaneously, lanthanum acts as the inhibitor of methanation of the carbon support under conditions of high temperature and hydrogen atmosphere. Such positive effects are achieved at a very low concentration of La in the prepared samples, a maximum 0.04 La/Ru (molar ratio). 0.01 mmol La introduced to the Ru/C system leads to 98% CO conversion at 270 °C.

CO2 methanation using metals nanoparticles supported on high surface area MgO

This work shows that Ru nanoparticles supported on high surface area nano MgO is a highly active and selective catalyst for CO2 methanation, which is a promising method to store renewable energy and limit the emission of greenhouse gasses. We studied the effect of the Ru loading on MgO supports with different surface areas and compared the results to the corresponding Ni-based catalyst. Our results show that high surface area MgO containing 5 wt % Ru has the highest activity. This catalyst was stable for more than 50 h and resulted in 54 % conversion at 375 °C, which, under the given reaction conditions, corresponds to a site time yield of 520 molCH4 molRu−1 h−1. For comparison, the Ni-based catalyst only resulted in 45 % conversion at 450 °C with a low selectivity to CH4 (STY=263 molCH4 molNi−1 h−1). Furthermore, Ru on high surface area MgO catalyst was already active at low temperature of 250 °C due to chemisorption and activation of CO2 on the MgO support, which is promising for low-temperature CO2 methanation.

TiH2-supported Ru catalyst with unusual electron transfer behaviour for highly efficient carbon dioxide methanation at low temperature

TiH2-supported Ru catalysts are developed for CO2 methanation, in which the usual support-to-metal electron transfer behaviour and hydrogen spillover effect are regulated to balance CO intermediate activation, H2 activation and catalyst hydration.

Progress in reaction mechanisms and catalyst development of ceria-based catalysts for low-temperature CO2methanation

We present a detailed review on the mechanistic understanding and catalyst development of CeO2-based CO2methanation catalysts. Current challenges for deeper investigations and future perspectives are presented as well.

Cerium-promoted nickel catalysts supported on yttrium-doped γ-alumina for carbon dioxide methanation

The catalytic performance of the Ni/Al, Y-doped Ni/Al-xY, and Ce-promoted Ni-yCe/Al-15Y catalysts for CO2 methanation was examined. The CO2 conversion and CH4 yield increased in the order of Ni/Al < Ni/Al-5Y < Ni/Al-25Y < Ni/Al-15Y at temperatures below 350 °C. The reduction degree, H2 uptake, and total CO2 adsorption uptake increased in this order for the Ni/Al-xY catalysts, suggesting that doping γ-Al2O3 with a moderate amount of Y improved the interaction between the nickel and the support. When the Ni/Al-15Y catalyst was promoted by Ce with different contents (0–5 wt%), the catalyst with 2 wt% Ce exhibited the highest CO2 conversion (92.5%) and CH4 yield (92.2%) at ≤ 350 °C. As evidenced by catalyst characterization, cerium promoter results in a synergetic Ni–Ce interaction over the combined Al-15Y support, leading to the formation of finely dispersed metal species and numerous active sites for splitting of the stable C–O bond.

Highly Stable Bimetal Ni–Co on Alumina-Covered Spinel Oxide Derived from High Entropy Oxide for CO2 Methanation

Inhibiting the sintering of supported metal catalysts for CO2 methanation is still a great challenge, especially at high temperature. Herein, the novel catalyst was prepared by using high entropy spinel oxide (Co0.2Ni0.2Mg0.2Zn0.2Mn0.2)Al2O4 (HEO) as precursor, which was reduced in a hydrogen atmosphere to obtain Ni–Co alloys supported on Al2O3-covered (Mg0.2Zn0.2Mn0.2)Al1.2O2.4 spinel oxide with a core–shell structure. This catalyst exhibited excellent stability at 550 °C for 320 h. Characterization results showed that the formation of the core–shell structure due to uniform element dispersion of the HEO precursor led to a larger interface, closer contact, and stronger interaction between the core and shell, which ensured the stability of the shell Al2O3 and further stabilized Ni–Co alloys. However, the catalyst derived from the mixed spinel oxide precursor was unable to achieve the core–shell structure support due to uneven element dispersion, which exhibited inferior stability. This study has successful extended the application of high entropy oxides.

Multidisciplinary green approaches (ultrasonic, co-precipitation, hydrothermal, and microwave) for fabrication and characterization of Erbium-promoted Ni-Al2O3 catalyst for CO2 methanation

The dispersion of nickel catalysts is crucial for the catalytic ability of CO2 methanation, which can be influenced by the fabrication method and the operation process of the catalysts. Therefore, a series of fabrication methods, including ultrasonic, hydrothermal, microwave, and co-precipitation, have been applied to prepare 25Ni-5Er-Al2O3 catalysts. The fabrication method can partially influence the structural and catalytic activity of the nickel aluminate catalysts. Among the catalysts modified by Erbium prepared with various methods, the catalyst fabricated by ultrasonic pathway exhibited better catalytic performance and CH4 selectivity especially, at a temperature (400 ℃). The impact of the temperature of the reaction (200–500 °C) was examined under a stoichiometric precursor ratio of (H2:CO2) = 4: 1, atmospheric pressure, and space velocity (GHSV) of 25000 mL/gcath. The results demonstrate that the ultrasonic method is strongly efficient for fabricating Ni-based catalysts with a high BET surface area of about 190.33 m2g−1. The catalyst composed via the ultrasonic technique has 69.38 % carbon dioxide conversion and 100 % methane selectivity at 400 °C for excellent catalytic performance in CO2 methanation reactions. The fabrication effect can be associated with its high surface area, which is achieved via the hot spot mechanism. Besides, the addition of Erbium promotes the Ni dispersion on the supports and stimulates the positive reaction because of the erbium oxygen vacancies.

Clay exfoliation method as a route to obtain mesoporous catalysts for CO2 methanation

A unique method for obtaining a mesoporous catalytic support through the exfoliation of a montmorillonite is reported. This method consisted of the intercalation of Na-clay with Al-Keggin species and polyvinyl alcohol followed by microwave irradiation. The mesoporous support was employed to prepare Ni-catalysts which were used in the natural gas synthesis through CO2 methanation. The synthesis method was validated confirming the clay exfoliation and the main formation of mesopores. Also, the Ni-catalysts have mainly weak basic surface properties lower than 38 µmol.g−1, and containing Ni0 nanoparticles with sizes between 9 and 12 nm which were thermally stable after reduction and methanation reaction. The catalyst with 5% Ni wt. gave conversions between 50 and 80% with temperatures ranging from 200 to 300 °C and selectivities of 100% towards the formation of CH4 without coke formation. The (3 and 5% Ni) Ni-catalysts are stable up to 8 h at 400 °C in the methanation reaction maintaining 100% of selectivity.•Mesoporous catalytic supports are obtained through a unique clay exfoliation method (Al-keggin, PVA, and microwaves).•(3% and 5% wt.) Ni-mesoporous catalysts are thermally stable and Ni0 nanoparticles between 9 and 12 nm are achieved.•5%wt. Ni-catalyst have no deactivation up to 8 h at 400 °C and displays unprecedented performance at low temperatures in CO2-methanation with 100% of selectivity.

Unveiling the promotion effect of Zr species on SBA-15 supported nickel catalysts for CO2 methanation

Introducing promoters on Ni-based catalysts for CO2 methanation have been proved to be positive for enhancing their performance. And the correlation of the promotion mechanism and the reaction pathway is significant for designing efficient catalysts. In this contribution, series of Zr species promoted SBA-15 supported Ni catalysts were prepared by citric acid complexation method under a range of Zr/Ni atomic ratios from 0 to 2.5. In situ and ex situ characterizations were carried out. It was found that the addition of citric acid was conductive to improve CH4 selectivity due to the higher concentrations of Ni0 confined in SBA-15, harvesting sufficient H atoms for CH4 formation following formate pathway via a formyl intermediate. Furthermore, a coverage layer of Zr species was found on the support at Zr/Ni = 1.7, which interacted with the Ni particles, providing higher concentrations of medium basic sites for CO2 activation. Accordingly, the optimum catalytic performance was obtained on ZrNi-1.7(CI), achieving CO2 conversion as high as 78.1% and nearly 100% CH4 selectivity at 400 °C, following the formate hydrogenation pathway. In addition, the ZrNi-1.7(CI) showed good stability owing to the confinement effect of SBA-15 and the Ni–Zr interaction, no carbon deposits were detected after 50 h test.