Metallic Ni nanocatalyst in situ formed from LaNi5H5 toward efficient CO2 methanation

LaNi₅ alloy can be utilized to directly store and release hydrogen in mild condition, thus it is considered as a long-term safe and stable solid-state hydrogen storage material. In this work, LaNi₅H₅ was used as the solid-state hydrogen source in the CO₂ methanation reaction. Impressively, the carbon dioxide conversion can be achieved to nearly 100% under 3 MPa mixed gas at 200 °C. The microstructure and composition analysis results reveal that the high catalytic activity may originate from the promoted elementary steps over in situ formed metallic Ni nanoparticles during the CO₂ methanation process. More importantly, as the lowered reaction temperature prevented the agglomeration of Ni nanoparticles, this catalyst exhibited durable stability with 99% conversion rate of CO₂ retained after 400 h cycling test.     

Promotion effect by Mg on the catalytic behavior of MgNi/WO3 in the CO methanation

In this study, tungsten oxide with a high specific surface area was fabricated using a nanocasting technique and used to prepare support for nickel catalysts for CO methanation. Additionally, Mg was further introduced as a promoter for tuning the catalytic performance. The 25Ni/WO₃ catalyst demonstrated a relatively high CO conversion, but a poor CH₄ selectivity; however, with the addition of 7 wt% Mg to the catalyst, the CH₄ selectivity reached 92% at a temperature of 440 °C. The improved CH₄ selectivity can be attributed to the enhanced CO dissociation, which was related to the reduced Ni particle size, as well as the enhanced Ni electron cloud density. The role of a physical barrier and electron transfer of MgO induces an enhancement of the metal–support interactions, which are conducive to decreasing the Ni particle size. Meanwhile, the electron transfer performance of MgO constitutes a crucial factor in enhancing the Ni electron cloud density. Furthermore, with benefit from the inhibition of agglomeration of the Ni particles by the MgO promoter, a significantly better catalytic stability was also observed on 7Mg25Ni/WO₃ than with the 25Ni/WO₃ catalyst.     

Low-temperature CO2 reforming of methane over Ni supported on ZnAl mixed metal oxides

Ni catalysts supported on mixed ZnOAl₂O₃ and on pure ZnO and Al₂O₃ were prepared, characterized by XRD, TPR, and XPS, and tested in long-term methane dry reforming at low temperature (400 °C). Depending on Zn/Al ratio in the supports, the catalysts varied in their physico-chemical properties and exhibited different trends in their on-stream catalytic activity. Catalysts with high alumina content consist of a mixture of alumina and zinc aluminate phases with metallic Ni particles on their surface. These samples show medium activity for reforming and high on-stream stability. The catalysts on mixed Zn-rich supports were more active than those on Al-rich supports and exhibited maxima in their activity after 30–40 h on stream, while Ni on pure ZnO possessed very low activity. Such contrast in performance of Zn-rich catalysts was explained by detected transformation of initially formed NiZn alloy to a mixture of Ni and Ni₃ZnC_0.7 particles that are assumed to have higher activity for reforming. Moreover, the size of Ni-containing particles on Zn-rich supports decreased under reaction conditions resulting in higher Ni dispersion.     

An investigation of the simultaneous presence of Cu and Zn in different Ni/Al2O3 catalyst loads using Taguchi design of experiment in steam reforming of methane

Nowadays, increasing environmental pollution as well as restrictions on the use of fossil fuels have shifted the attention toward using hydrogen as a new source of clean and effective energy. Additionally, hydrogen and syngas are employed as feedstock for the production of valuable materials in the petrochemical industry. Methane steam reforming is the main procedure for the hydrogen and syngas production. In this study, Taguchi design of experiment (L9) was used to investigate the effects of simultaneous presence of copper (Cu) and Zinc (Zn) metals on different Ni/Al₂O₃ catalyst loads. It should be noted that some of the catalysts were characterized using XRD, BET, SEM and TGA analyses. According to the Taguchi design, it was concluded that the increment of Cu content enhances the catalyst stability and increases the CO selectivity. Increasing Zn content advocated CH₄ conversion, H₂ yield, and less selectivity toward the CO production. The XRD, BET and SEM test results revealed that the addition of Cu resulted in better distribution of active support phase. The TGA results indicated that the addition of Cu and Zn stabilized the catalyst activity; in this case, Cu was more effective than Zn. The overall results demonstrated that 15% load of Ni on Al₂O₃ support, simultaneous addition of Cu and Zn loads of 1% and 5%, respectively, enhanced the catalyst stability and activity and improved the catalyst performance in the selective hydrogen production as well.     

Impacts of metal loading in Ni/attapulgite on distribution of the alkalinity sites and reaction intermediates in CO2 methanation reaction

Both metal sites and alkaline sites are essential parameters for a catalyst used in methanation of CO₂. This study investigated the impacts of the relative abundance of metal sites and alkaline sites on the catalytic performances of nickel-based catalyst with attapulgite, a natural mineral, as the support. The results showed that the increase of nickel loading to attapulgite significantly decreased the abundance of alkaline sites, remarkably enhanced the catalytic activity, and suppressed the formation of CO. The in situ DRIFTS characterization of the CO₂ methanation indicated that the alkaline sites favored formation of the oxygen-containing reaction intermediates such as CO1, –OH, 1CO₂, formate, carbonate and bicarbonate species. In comparison, metallic nickel species promoted their further hydrogenation to form CH₄. Besides the absorption/activation of 1CO₂ was more preferable on surface of metallic nickel, but not on the alkaline sites. The availability of the alkaline sites was not as important as the metallic nickel species for preparation of an efficient catalyst for CO₂ methanation.     

CO2 valorization through direct methanation of flue gas and renewable hydrogen: A technical and economic assessment

Under the scenario of an increasing sharing of renewable energy, Power to Gas technology may offer an effective and valuable solution for surplus energy management, accounting for a large and long-term chemical storage. In the present study an innovative Power to Synthetic Natural Gas (SNG) process has been described and investigated from a techno-economic and environmental point of view. The configuration is based on a methanation process, directly applied on flue gas stream thus acting both as a CO₂ capture and sequestration technology and as renewable energy storage mechanism. Reacting hydrogen is produced via water electrolysis powered by surplus of renewable energy, normally low-priced otherwise wasted. With a reference capacity factor around 4000 h/y, the resulting SNG cost is 0.34 €/Nm³ based on a carbon tax equal to 30 €/t CO₂. The obtained results are attractive and consistent with the fact that future investment cost for water electrolysis is decreasing accordingly.     

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.     

A strategy to regenerate coked and sintered Ni/Al2O3 catalyst for methanation reaction

Supported Ni/Al₂O₃ catalysts are widely used in chemical industries. Regeneration of the deactivated Ni catalysts caused by sintering of Ni nanoparticles and carbon deposition after long-term operation is significant but still very challenging. In this work, a feasible strategy via solid-phase reaction between NiO and Al₂O₃ followed by a controlled reduction is developed which can burn out the deposited carbon and re-disperse the Ni nanoparticles well, thus regenerating the deactivated Ni catalysts. To demonstrate the feasibility of this method, Ni catalyst supported on α-Al₂O₃ (Ni/Al₂O₃) for CO methanation reaction was selected as a model system. The structure and composition of the fresh, deactivated and regenerated Ni/Al₂O₃ catalysts were comprehensively characterized by various techniques. The reduction and redistribution of Ni species as well as the interfacial interaction between Ni nanoparticles and Al₂O₃ support were investigated in detail. It is found that calcining the deactivated Ni/Al₂O₃ in air at high temperature can burn out the coke, while the sintered Ni species can combine with superficial Al₂O₃ to form a surface NiAl₂O₄ spinel phase through the solid-phase reaction. After the controlled reduction of the NiAl₂O₄ spinel, highly dispersed Ni nanoparticles on Al₂O₃ support are re-generated, thus achieving the regeneration of the deactivated Ni/Al₂O₃. Interestingly, compared with the fresh Ni/Al₂O₃ catalyst, the sizes of Ni nanoparticles became even smaller in the regenerated ones. The regenerated Ni/Al₂O₃ showed much enhanced catalytic activity in CO methanation and became more resistant to carbon deposition, due to the better dispersed Ni nanoparticles and strengthened interaction between Ni and Al₂O₃ support. Our work not only addresses the long existing catalyst regeneration issue, but also provides effective and renewable Ni-based catalysts for CO methanation.     

Ordered mesoporous Ni/Silica-carbon as an efficient and stable catalyst for CO2 reforming of methane

Ordered mesoporous silica-carbon (MSC) were used as supports of Ni based catalysts for dry reforming of methane (DRM) reaction. The effects of preparation method and precipitant on the catalysts are investigated. The physical and chemical properties are discussed based on the H₂-TPR, FTIR, XRD, TEM, H₂-TPD and N₂ adsorption/desorption characterization. It is found that the preparation method and choice of precipitants affect the catalysts significantly in terms of the properties and catalytic performance in DRM reaction. In detail, the catalysts prepared by the precipitation method show more highly dispersed Ni particles and further better catalytic activity than the impregnated catalyst. That is attributed to the forming Ni₃Si₂O₅(OH)₄ nanoflakes in the catalyst precursors with the existence of alkaline precipitants. And this Ni₃Si₂O₅(OH)₄ species bind the support more tightly than NiO in the impregnated Ni/MSC catalyst. Moreover, the choice of precipitants also influences the form of Ni₃Si₂O₅(OH)₄ species in the catalysts. Specially, the strong electrolytic capacity of NaOH gives the most Ni₃Si₂O₅(OH)₄ nanoflakes formed in Ni-MSC-1 catalyst, which results in the most highly Ni dispersity and further highest catalytic activity. Besides, the strong interaction between the Ni₃Si₂O₅(OH)₄ species and support are also advantageous to the resist sintering and formation of carbon deposition, that is related to the good catalytic stability of catalysts.     

Lanthanoid-containing Ni-based catalysts for dry reforming of methane: A review

Dry reforming of methane (DRM) is known to produce synthesis gas through the utilization of greenhouse gases to ensure environmentally benign process and rational use of natural resources. Many catalyst formulations operating at “ideal” conditions were proposed for DRM reaction, including those based on noble (Pt, Rh) and non-noble (Ni, Co) metals supported on various oxides. This review is focused on the recent advances in lanthanoid-containing Ni-based DRM catalysts. We consider the performance of Ni-based catalysts supported on LnO_x oxides (La₂O₃, CeO₂, etc.), promotion of the said composites by noble or transition metals, organization of pristine and promoted Ni–LnO_x interfaces on the surfaces of various supports, including ordered materials. Analysis of features of the high-performance DRM catalysts is provided. The outlook of the existing challenges and opportunities in the rational design of a new generation of lanthanoid-containing Ni-based catalysts for dry reforming of methane and other hydrocarbons is provided.     

CO2 methanation over Ni and Rh based catalysts: Process optimization at moderate temperature

H₂ was produced from aluminum/water reaction and reacted with CO₂ over Ni and Rh based catalysts to optimize the process conditions for CO₂ methanation at moderate temperature. Monometallic catalysts were prepared by incorporating Ni and Rh using nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O) and rhodium(III) chloride trihydrate (RhCl₃·3H₂O)as a precursor chemical. The preliminary study of the catalysts revealed higher activity and CH₄ selectivity for Rh based catalyst compared to that of Ni based catalyst. Further, Rh based catalyst was investigated using response surface methodology (RSM) involving central composite design. The quadratic model was employed to correlate the effects of variable parameters including methanation temperature, %humidity, and catalyst weight with the %CO₂ conversion, %CH₄ selectivity, and CH₄ production capacity. Analysis of variance revealed that methanation temperature and humidity play an important role in CO₂ methanation. Higher response values of CO₂ conversion (54.4%), CH₄ selectivity (73.5%) and CH₄ production capacity (8.4 μmol g^?1 min^?1) were noted at optimum conditions of 206.7°C of methanation temperature, 12.5% humidity and 100 mg of the catalyst. The results demonstrated the ability of Rh catalyst supported on palm shell activated carbon (PSAC) for CO₂ methanation at low temperature and atmospheric pressure.     

Enhanced performance of Ni catalysts supported on ZrO2 nanosheets for CO2 methanation: Effects of support morphology and chelating ligands

A series of Ni/ZrO₂ catalysts was prepared by the impregnation method with modification of the morphology of ZrO₂ support as well as the impregnation procedure and tested for CO₂ methanation. The catalysts supported on the ZrO₂ nanosheets displayed superior catalytic performance as compared with that on ZrO₂ nanoparticles, which could be mainly attributed to the abundant oxygen vacancies promoting the adsorption and dissociation of CO₂ molecules as well as the high dispersion of Ni species. With the introduction of ethylenediamine (En) in the impregnation procedure, the resulting Ni-15En/ZrO₂-1.5 catalyst showed the optimal activity with CO₂ conversion of 86% significantly higher than Ni/ZrO₂-0 of 44% and Ni/ZrO₂-1.5 of 79% at 0.5 MPa and 300 °C. The excellent performance was attributed to increased moderately basic sites for CO₂ adsorption in ZrO₂ nanosheets, as well as the enhanced dispersion of nickel caused by the complexation of Ni ions with En, which inhibited the aggregation of nickel particles in the subsequent thermal treatments. In conclusion, the synergistic effects of the morphology of ZrO₂ nanosheets as well as the chelating behavior of En contributed to the enhanced performance of Ni-15En/ZrO₂-1.5 in the CO₂ methanation reaction. The strategy shows good prospects for controlling the size of active metals, especially those that were dispersed on the surface of the two-dimensional (2D) metal oxide materials.     

Combined steam and CO2 reforming of methane over one-pot prepared Ni/La-Si catalysts

The highly dispersed mNi/xLa−Si catalysts with varied weight percentages of Ni and La were synthesized via one-pot sol-gel process and subsequently applied to combined carbon dioxide and steam reforming of methane (CSDRM) for syngas production. The addition of La improved the catalytic activity and stability as well as the coke resistance of the mNi/xLa−Si catalysts. The effects of preparation routes, Ni contents and CO₂/steam (C/S) ratios on the performances of the Ni/LaSi catalysts were studied in detail for the CSDRM. The 17.5Ni/3.0LaSi catalyst synthesized with the assistance of poly (ethylene glycol) and ethylene glycol exhibited the most excellent catalytic activity, stability and coke resistance. In addition, the H₂/CO ratios in the product gas could be tuned by changing the C/S ratios in the feed. When the C/S ratio was 0.5, the H₂/CO ratio of about 2 was achieved for the 17.5Ni/3.0LaSi catalyst.     

Promotional effect of addition of ceria over yttria-zirconia supported Ni based catalyst system for hydrogen production through dry reforming of methane

The idea of hydrogen production through dry reforming of methane (DRM) is simply outstanding as it is related to decrease the concentration of green-house gases. Yttria-Zirconia supported Nickel catalyst has thermal stability and mobile lattice oxygen but poor oxygen replenishment by CO₂ to the reduced sites. Promotional addition of ceria adds catalytic merit as quick availability of lattice oxygen, good oxygen replenishment by CO₂ to the reduced sites, and reducing bandgap. Herein, 1-3 wt% Ce promoted yttria-zirconia supported Ni catalyst is investigated and characterized by X-ray Diffraction (XRD), Raman, Infrared and UV–vis spectroscopy, CH₄-temperature programmed surface reaction (CH₄-TPSR) and cyclic H₂TPR-CO₂TPD-H₂TPR experiment. The addition of 2 wt% ceria causes lower crystallinity of metallic nickel (than 1 wt% ceria) which facilitates wide range of CH₄ decomposition sites (confirmed by CH₄-TPSR). It additionally cultivates the mixed cerium zirconium oxide for resultant mixed potential and additional oxygen mobility. It ensures about 79% H₂ yield.     

On the effect of yttrium promotion on Ni-layered double hydroxides-derived catalysts for hydrogenation of CO2 to methane

Ni-containing mixed oxides derived from layered double hydroxides with various amounts of yttrium were synthesized by a co-precipitation method at constant pH and then obtained by thermal decomposition. The characterization techniques of XRD, elemental analysis, low-temperature N₂ sorption, H₂-TPR, CO₂-TPD, TGA and TPO were used on the studied catalysts. The catalytic activity of the catalysts was evaluated in the CO₂ methanation reaction performed at atmospheric pressure. The obtained results confirmed the formation of nano-sized mixed oxides after the thermal decomposition of hydrotalcites. The introduction of yttrium to Ni/Mg/Al layered double hydroxides led to a stronger interaction between nickel species and the matrix support and decreased nickel particle size as compared to the yttrium-free catalyst. The modification with Y (0.4 and 2 wt%) had a positive effect on the catalytic performance in the moderate temperature region (250–300 °C), with CO₂ conversion increasing from 16% for MO-0Y to 81% and 40% for MO-0.4Y and MO-2.0Y at 250 °C, respectively. The improved activity may be correlated with the increase of percentage of medium-strength basic sites, the stronger metal-support interaction, as well as decreased crystallite size of metallic nickel. High selectivity towards methane of 99% formation at 250 °C was registered for all the catalysts.     

Syngas methanation with municipal solid waste char supported Ni catalyst: Choice of key parameters and catalyst's response

The low quality municipal solid wastes (MSW) derived char has a potential to be used as a methanation catalyst to achieve low-cost methanation of the syngas derived from MSW, and its performance with varying reaction parameters should be explored for better application. In this study, a MSW char supported Ni-based catalyst (Ni-MSWC) was prepared by impregnation; the influences of CO₂ and CH₄ impurities in the raw syngas on methanation and the feasibility of conducting methanation in a low-pressure condition were investigated, then the catalyst's response to the changing parameters was identified. The results showed that the presence of low concentration CO₂ in the H₂-rich syngas is favorable to the gasification of the char carrier and activates Ni-MSWC catalyst. However, it also promotes F–T synthesis reaction and leads to a decrease in the methane yield (Y_CH4). The decrease in reaction pressure causes a decrease in Y_CH4 and results in coke formation; but inhibits F–T synthesis reaction and increases methane selectivity (S_CH4). A higher reaction pressure increases system complexity and accelerates char carrier consumption. Moreover, presence of methane by 2.8% (vol.) promotes the methanation of CO₂ through the methane dry reforming reaction, but it inevitably causes coke formation and affects the catalyst's stability. Based on Y_CH4 and Ni-MSWC's responses, CO:CO₂ ≥ 3:2 and reaction pressure of 1 MPa (gauge pressure) are recommended, which help to inhibit the side reactions and maintain a high Y_CH4 (>95%).     

The evaluation of autothermal methane reforming for hydrogen production over Ni/CeO2 catalysts

Nanocrystalline Ni/CeO₂ catalysts with various loadings of Ni (10, 15, 20, and 25%) were synthesised by a facile solvent deficient precipitation method for methane autothermal reforming process. The characterisation techniques such as XRD, BET, TPH, H₂-TPR were carried out on fresh and spent samples to investigate the catalytic properties of the Ni/CeO₂. On the basis of characterisation results, the 20% Ni/CeO₂ performs the best activity among the catalysts with different Ni contents. The optimal reaction conditions for autothermal methane reforming has been investigated by evaluating the effect of reaction parameters including the reactivity temperature, the gas hourly space velocity (GHSV) and H₂O/CH₄ (S/C) and O₂/CH₄ (O/C) molar ratios. The stability of 20 wt% Ni/CeO₂ catalyst at 700 °C is examined for 20 h on-stream reaction. It reveals that the methane conversion starts a graduate decrease trend from the second 10 h, which is found to be because of the sintering of Ni nanoparticles by TPH and BET analysis.     

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.     

The influence of nickel content on the performance of hydrotalcite-derived catalysts in CO2 methanation reaction

A series of mixed oxides obtained by thermal decomposition of hydrotalcites containing different amounts of Ni and constant M^II+/M^III+ molar ratio were characterized by XRD, XANES, XES, H₂-TPR, CO₂-TPD, elemental analysis and low temperature nitrogen sorption technique. The results confirm the formation of periclase-like structured materials after thermal treatment, with nickel present as NiO in octahedral coordination environment. As proven by H₂-TPR with increasing Ni content the interaction between Ni and hydrotalcite matrix weakens, which has a positive influence on the catalytic performance. The catalysts containing different amounts of nickel (10.3, 16.2, 27.3, 36.8, 42.5 wt.%) showed at 300 °C a very good catalytic performance in carbon dioxide methanation, with CO₂ conversion of 36 (Ni10.3)–82% (Ni42.5) and CH₄ selectivity of 98–99%.     

On the influence of the preparation routes of NiMgAl-mixed oxides derived from hydrotalcite on their CO2 methanation catalytic activities

In this work, a series of NiMgAl oxides (NMA) derived from hydrotalcite catalysts were prepared via co-precipitation (NMA-CP), urea hydrolysis (NMA-UH), and impregnation (NMA-IMP) techniques, then subsequently tested for CO₂ methanation. The well-defined synthesis of derived hydrotalcite mixed oxides was confirmed by physicochemical characterizations including XRD, SEM, BET, H₂-TPR and CO₂-TPD. The preparation methods showed a substantial influence on the structure and thermal activity of catalysts. Indeed, the NMA-UH catalyst demonstrated a high and stable catalytic activity in terms of CO₂ conversion and CH₄ selectivity, with ca. 82.3% and 99.8% (GHSV = 12,000 h^?1, H₂/CO₂ = 4/1) respectively, at 300 °C. This is mainly due to its large specific surface area, small Ni-particle size, and higher basicity.