Solid-state synthesis method for the preparation of cobalt doped Ni–Al2O3 mesoporous catalysts for CO2 methanation

In this study, a simple solid-state synthesis method was employed for the preparation of the Ni–Co–Al₂O₃ catalysts with various Co loadings, and the prepared catalysts were used in CO₂ methanation reaction. The results demonstrated that the incorporation of cobalt in nickel-based catalysts enhanced the activity of the catalyst. The results showed that the 15 wt%Ni-12.5 wt%Co–Al₂O₃ sample with a specific surface area of 129.96 m²/g possessed the highest catalytic performance in CO₂ methanation (76.2% CO₂ conversion and 96.39% CH₄ selectivity at 400 °C) and this catalyst presented high stability over 10 h time-on-stream. Also, CO methanation was investigated and the results showed a complete CO conversion at 300 °C.     

Phosphate-modified Al2O3–ZrO2 supported Ni catalysts for efficient selective methanation of CO in H2-rich reformate gas

CO selective methanation can remove the CO in H₂-rich reformate gas to prevent the poisoning of Pt anode electrode in proton exchange membrane fuel cell. However, the methanation of CO₂ in H₂-rich gas consumes a lot of hydrogen, which greatly reduces the energy efficiency. In order to inhibit CO₂ methanation, mesostructured Al₂O₃–ZrO₂ was modified by different amounts of phosphate, and then was as Ni support. The structures and surface properties of Ni/Al₂O₃–ZrO₂ catalyst modified by phosphate were studied to reveal the effect of phosphate-modification on CO conversion and selectivity for CO methanation. It was found that the phosphate-modification inhibited the adsorption of CO₂, which increased the selective for CO methanation. But the modification with excess phosphate lessened active sites of Ni and weakened the adsorption of H₂ and CO, which decreased the activity of CO methanation.     

Enhanced activity of CO2 methanation over mesoporous nanocrystalline Ni–Al2O3 catalysts prepared by ultrasound-assisted co-precipitation method

The ultrasound-assisted co-precipitation method was employed for the synthesis of the Ni–Al₂O₃ catalysts with different metal loadings for the CO₂ methanation reaction. This study indicated that increasing the Ni loading up to 25 wt.% enhanced the surface area, decreased the crystallinity and improved the reducibility of the catalysts, while further raise in Ni loading adversely influenced the surface area. Improvements in catalytic performance were obtained with the raise in Ni content because of enhancing the BET area. The results confirmed that the 25Ni–Al₂O₃ catalyst with the highest BET area (188 m² g^?1) and dispersion of Ni has the highest catalytic activity in CO₂ methanation and reached to 74% CO₂ conversion and 99% CH₄ selectivity at 350 °C. In addition, this catalyst exhibited a great stability after 10 h time-on-stream.     

Ce-promoted Co/Al2O3 catalysts for Fischer–Tropsch synthesis

The effect of ceria promotion on the performance of Co/Al₂O₃ catalyst was evaluated in a high pressure fixed bed reactor for Fischer–Tropsch (FT) synthesis at close industrial conditions. Ce–Al₂O₃ supports with a molar ratio of Al/Ce = 8 were prepared by two different methods: one by co-precipitation of cerium and aluminum precursors in water-in-oil microemulsion and the other one by aqueous impregnation of cerium nitrate on commercial alumina. These supports, together with the unmodified alumina carrier, were used to prepare four cobalt-based catalysts. These catalysts were characterized by XRD, SEM, EDX, TEM, N₂ adsorption/desorption, TPR and chemisorption techniques. The results show that the presence of CeO₂ on the surface of the support favors the reducibility of cobalt oxides with a shift down in reduction temperature of about 70 °C. The catalytic evaluation of the catalysts revealed that cerium addition by impregnation increases the activity and selectivity to C₅₊ catalyst in FTS. The catalyst synthetized by microemulsion show lower catalytic performance. Nevertheless, the catalytic property of this material can be improved by increasing the crystalline micro-domains size of CeO₂.     

Phase-separated Ce–Co–O catalysts for CO oxidation

As a major gas pollutant, the control of CO gas emission from chemical industry and vehicle exhausts has aroused global attention in the past years and it is extremely essential to develop efficient, low-cost and environmental friendly catalysts for CO conversion and removal. In this work, we report the facile synthesis of Ce–Co–O catalysts through a simple ultrasonic spray pyrolysis process and investigate their application for low-temperature CO oxidation. The Ce–Co–O catalysts comprising of separated CeO₂ and Co₃O₄ phases show superior CO oxidation capability below 473 K (200 °C) without the assistance of any other co-catalyst or noble metal. With the increase of Co₃O₄ concentration, the CO oxidation temperature of Ce–Co–O catalysts decreases quickly and reaches a complete conversion temperature of 410 K (137 °C) in the case of the optimized Co content. Microstructure analysis using high-resolution transmission electron microscope reveals that the tiny CeO₂ and Co₃O₄ phases assembled into porous particles are well crystallized and show high chemical purity. The porous feature of Ce–Co–O catalysts synthesized from feasible ultrasonic spray pyrolysis makes them more competitive and promising towards gaseous environmental pollution processing including CO oxidation, TWCs, SCR, etc.     

W-doped ordered mesoporous Ni–Al2O3 catalyst for methanation of carbon monoxide

In order to simultaneously inhibit the Ni sintering and coke formation as well as investigate the effects of WO₃ promoter on catalytic performance, the ordered mesoporous Ni–WO₃/Al₂O₃ catalysts were synthesized by a facile one-pot evaporation-induced self-assembly method for CO methanation reaction to produce synthetic natural gas. Addition of WO₃ species could significantly promote the catalytic activity due to the enhancement of the Ni reducibility and the increase of active centers, and the optimal N10W5/OMA catalyst with NiO of 10 wt% and WO₃ of 5 wt% achieved the maximum CH₄ yield 80% at 425 °C, 0.1 MPa and a weight hourly space velocity of 60000 mL g⁻¹ h⁻¹. Besides, the reference catalyst N10W5/OMA-Im prepared by the conventional co-impregnation method was also evaluated. Compared with N10W5/OMA, N10W5/OMA-Im showed lower catalytic activity due to the partial block of channels by Ni and WO₃ nanoparticles, which reduced active centers and restrict the mass transfer during the reaction. In addition, the N10W5/OMA catalyst showed superior anti-sintering and anti-coking properties in a 425^oC-100 h-lifetime test, mainly because of confinement effect of ordered mesoporous structure to anchor the Ni particle in the alumina matrix.     

Ni–Re alloy catalysts on Al2O3 for methane dry reforming

Methane reforming with CO₂ is still of great interest due to growing demand creating a continuous need for new hydrogen sources. The main difficulty in this reaction is the deactivation of the catalyst due to the formation of carbon deposits on its surface. Herein, a series of commercial nickel catalysts supported on α-Al₂O₃ and modified with different amounts of rhenium (up to 4 wt%) was investigated. It was revealed that Re addition causes the formation of Ni–Re alloy during high temperature reduction, which was confirmed in deep XRD and STEM studies. The addition of Re positively influences not only the stability of the catalyst, but also increases its activity in the DRM reaction carried out in a Tapered Element Oscillating Microbalance (TEOM). The formation of Ni–Re alloy played a significant role in enhancing the properties of the catalyst.     

Synthesis of Cr2O3–Al2O3 powders with various Cr2O3/Al2O3 molar ratios and their applications as support for the preparation of nickel catalysts in CO2 methanation reaction

The Methanation of CO₂ to CH₄ is a significant route to save energy and reduce CO₂ emission. In this work, a series of Cr₂O₃–Al₂O₃ powders were synthesized by a novel and simple solid-state method and considered as the carrier for the nickel catalysts in CO₂ methanation. The BET area and pore volume of the supports decreased with the decrease in Al₂O₃/Cr₂O₃ molar ratio. The results indicated that the increase in Cr₂O₃ content improved the catalytic performance and 15 wt%Ni/Cr₂O₃ catalyst exhibited the highest CO₂ conversion of 80.51%, and 100% CH₄ selectivity at 350 °C. The results indicated that the CO₂ conversion improved with the increment in H₂/CO₂ molar ratio from 2 to 5. The improvement in CO₂ conversion was also observed with decreasing GHSV due to the longer residence time of the reactants on the catalyst surface. Also, the results showed that increasing calcination temperature led to a decrease in CO₂ conversion. The 15 wt%Ni/Cr₂O₃ catalyst exhibited high stability in carbon dioxide methanation reaction.     

A comparative study of Ni catalysts supported on Al2O3, MgO–CaO–Al2O3 and La2O3–Al2O3 for the dry reforming of ethane

CO₂ utilization through the activation of ethane, the second largest component of natural and shale gas, to produce syngas, has garnered significant attention in recent years. This work provides a comparative study of Ni catalysts supported on alumina, alumina modified with CaO and MgO, as well as alumina modified with La₂O₃ for the reaction of dry ethane reforming. The calcined, reduced and spent catalysts were characterized employing XRD, N₂ physisorption, H₂-TPR, CO₂-TPD, TEM, XPS and TPO. The modification of the alumina support with alkaline earth oxides (MgO and CaO) and lanthanide oxides (La₂O₃), as promoters, is found to improve the dispersion of Ni, enhance the catalyst's basicity and metal-support interaction, as well as influence the nature of carbon deposition. The Ni catalyst supported on modified alumina with La₂O₃ exhibits a relatively stable syngas yield during 8 h of operation, while H₂ and CO yields decrease substantially for Ni/Al₂O₃.     

Nickel–magnesium-modified cenospheres for CO2 methanation

Coal combustion for power generation is a source of CO₂ emission into the atmosphere. During that process, waste materials are formed such as cenospheres, which are a fraction of fly ashes. These cenospheres were applied as a catalyst support for the CO₂ methanation reaction, which is a promising process for carbon dioxide utilization. Two series of catalysts were compared, a reference one based on the unmodified cenospheres, and a second based on the cenospheres modified by perforation. Nickel supported on Cenospheres nickel, or else nickel with Mg–Al mixed oxides, were prepared by solution combustion synthesis. Perforated cenospheres supporting Mg–Al mixed oxides led to a catalyst with significantly improved catalytic performance (88% at 300 °C) and selectivity to methane (>99% at 300 °C). In this work we evidence better development of the specific surface area, increased surface basicity, improved dispersion of nickel crystallites thanks to the presence of Mg–Al and enlarged number of basic centers at the surface.     

Ru–Ni/GA-MMO composites as highly active catalysts for CO selective methanation in H2-rich gases

CO selective methanation (CO-SMET) is as an ideal H₂-rich gases purification measurement for proton exchange membrane fuel cell system. Herein, the graphene aerogel-mixed metal oxide (GA-MMO) supported Ru–Ni bimetallic catalysts are exploited for CO-SMET in H₂-rich gases. The results reveal that a three-dimensional network structure GA-MMO aerogel with higher specific surface area, better thermal stability and more defects or structural disorders is formed when MMO:GO mass ratio is in the range of 1–4. After loading of Ru, more NiO are reduced to metallic Ni by hydrogen spillover effect, and thus obviously enhances the reactivity. The GA-MMO supported Ru–Ni catalyst exhibits more excellent metal dispersion, reducibility, stronger CO adsorption and activation than the MMO supported Ru–Ni catalyst, thereby resulting in better catalytic performance and stability. This work offers new insights into the construction of highly active catalyst for the efficient generation of high-quality H₂ from H₂-rich gases.     

Hydrogen generation from alkaline NaBH4 solution using nanostructured Co–Ni–P catalysts

In the present study, nanostructured Co–Ni–P catalysts have been successfully prepared on Cu sheet by electroless plating method. The morphologies of Co–Ni–P catalysts are composed of football-like, granular, mockstrawberry-like and shuttle-like shapes by tuning the depositional pH value. The as-deposited mockstrawberry-like Co–Ni–P catalyst exhibits an enhanced catalytic activity in the hydrolysis of NaBH₄ solution. The hydrogen generation rate and activation energy are 2172.4 mL min⁻¹ g⁻¹ and 53.5 kJ mol⁻¹, respectively. It can be inferred that the activity of catalysts is the result of the synergistic effects of the surface roughness, the particle size and microscopic architectures. Furthermore, the stability of mockstrawberry-like Co–Ni–P catalyst has been discussed, and the hydrogen generation rate remains about 81.4% of the initial value after 5 cycles.     

Effect of MgO/Al2O3 ratio in the support of mesoporous Ni/MgO–Al2O3 catalysts for CO2 utilization via reverse water gas shift reaction

2 and 5 wt.% nickel was supported on different MgO to Al₂O₃ (M/A) ratios (0.5, 1 and 1.5) and evaluated in reverse water gas shift (RWGS) reaction. The catalysts were prepared by impregnation method and the nanocrystalline supports were synthesized by simple surfactant (CTAB) assisted precipitation technique. The following catalytic activity was observed for 2% & 5% Ni supported on different M/A ratios; M/A = 1 > M/A = 1.5 > M/A = 0.5. The perceived order was related to difference in the structural properties of supports and catalysts. The BET results revealed decrease of specific surface area with increase in M/A ratio, mesoporous structure for M/A = 0.5 and 1 and meso-macroporous structure for M/A = 1.5. The effect of nickel loading on the support with M/A = 1 was also investigated. 1.5% Ni showed high CO₂ conversion of 39.2% at 700 °C and CO selectivity higher than 90% at all temperatures. Increase of nickel loading higher than 1.5% was in favor of CH₄ formation. The TEM images of 1.5% Ni on M/A = 1 revealed uniform distribution of Ni particles with average size of 4.9 nm. The H₂-TPR analysis displayed shifting of maximum temperature of the main peak (γ) to higher temperatures with increase of M/A ratio in the support, indicating harder reducibility of catalysts with higher MgO content. The 1.5% Ni supported on M/A = 1 (MgAl₂O₄) showed great catalytic stability and CO selectivity (>98%) after 15 h on stream.     

Catalytic performance of Samarium-modified Ni catalysts over Al2O3–CaO support for dry reforming of methane

Mesoporous calcina-modified alumina (Al₂O₃–CaO) support was produced through the simple and economical co-precipitation method, then nickel (Ni, 10 wt%) and samarium (Sm, 3 wt%) ions loaded by two-solvent impregnation and one-pot strategies. The unpromoted/samarium-promoted catalysts were evaluated using X-ray Diffraction (XRD), High-Resolution Transmission Electron Microscopy (HR-TEM), nitrogen adsorption-desorption, Temperature Programmed Oxidation/Reduction (TPR/TPO), and Field Emission Electron Scanning Microscopy (FE-SEM) methods, then investigated in methane dry reforming. The results revealed that with adding samarium to Ni catalyst through impregnation method, the average Ni crystallite size and specific surface area decreased from 11.5 to 5.75 nm and from 76.08 to 30.9 m²/g, respectively; as a result, the catalytic activity increased from about 50% to 68% at 700 °C. Furthermore, the TPO and FE-SEM tests indicated the formation of carbon with nanotube nature on the catalyst surface.     

Effect of sulfur–carbon interaction on sulfur poisoning of Ni/Al2O3 catalysts for hydrogenation

The poisoning effects of two types of carbon-containing sulfides (CS₂ and CH₃SSCH₃) on Ni/Al₂O₃ catalysts for the hydrogenation of benzene and cyclohexene were systematically investigated via experiments and DFT calculations. The toxicity of CH₃SSCH₃ is two and three times greater than that of CS₂ for the hydrogenation of cyclohexene and benzene, respectively. The characterization and DFT results reveal that CH₃SSCH₃ dissociates easily during hydrogenation and releases CH₄, allowing sulfur atoms to poison the Ni sites. However, the presence of CS₂ in the hydrogenation step slows the decline in the catalytic performance, because of resistance to the direct dissociation of the strong CS bond of CS₂. The chemisorbed CS₂ molecules and their incomplete dissociation weaken the strength of NiS bond and decrease the poisoning effect of sulfur. The poisoning processes of two sulfides are also discussed following a DFT study. This work opens up promising possibilities for the industrial study of S-poisoning resistance in supported Ni catalysts.     

Ni/La2O3 and Ni/MgO–La2O3 catalysts for the decomposition of NH3 into hydrogen

The decomposition of NH₃ for hydrogen production was studied using Ni/La₂O₃ catalysts at varying compositions and temperatures prepared via surfactant-templated synthesis to elucidate the influence of catalyst active metal content, support composition and calcination temperature on the catalytic activity. The catalytic performance of all samples was studied between 300 and 600 °C under atmospheric pressure. The catalytic activity of the sample were as follows: 10Ni/La₂O₃-450 > 10Ni/La₂O₃-550 > 10Ni/La₂O₃-650 ≈ 10Ni/La₂O₃-750 ≈ 10Ni/La₂O₃-850. The excellent activity (100%) of 10Ni/La₂O₃-450 could be due to the high surface area, basicity strength and concentration of surface oxygen species of the catalyst as evidenced by BET, CO₂-TPD and XPS. In addition, to adjust the activity of the catalyst support, the molar ratios of Mg and La were varied (1:1, 3:1, 5:1, 7:1 and 9:1). The 5Ni/5MgLa (5:1 M ratio) was found to be the most active (100%) relative to other Ni/MgLa formulations. Furthermore, the Ni content in the Ni/5MgLa sample was adjusted between 10 and 40 wt%. Increasing the Ni content of the catalysts increased NH₃ conversion with the 40 wt% Ni formulation demonstrating complete NH₃ conversion at 600 °C and a high gas hourly space velocities (GHSV) (30,000 mL∙h⁻¹∙g_cat⁻¹).     

Ordered mesoporous Ni–Mg–Al2O3 as an effective catalyst for CO2 reforming of CH4

The Ni based catalysts have been considered as promising candidates for the CO₂ reforming of CH₄ (CRM). However, they have suffered from two challenging issues of sintering and carbon accumulation. In order to overcome these drawbacks, a series of ordered mesoporous Ni-xMg-Al₂O₃ catalysts (x was the mole ratio of Mg/(Mg + Al)) with different Mg contents were synthesized by an improved one-pot evaporation-induced self-assembly method. The effect of Mg on the physicochemical property and catalytic performance of Ni-xMg-Al₂O₃ catalysts for CRM was investigated. The catalysts were characterized by XRD, H₂-TPR, XPS, TEM, NH₃-TPD, and N₂ adsorption-desorption at low temperature. The results showed that the introduction of Mg into the Ni–Al₂O₃ maintained well the ordered mesoporous structure and enhanced the interaction between Ni and Al₂O₃, which could effectively restrict the thermal agglomeration of Ni nanoparticles. In addition, the acid sites were decreased with the introduction of Mg, which was beneficial for resistance to carbon accumulation, and then improving the CRM performance. Among Ni-xMg-Al₂O₃ catalysts, Ni–3Mg–Al₂O₃ presented the highest catalytic activity and stability. Under the conditions of 750 °C and GHSV = 32000 mL g^?1 h^?1, the conversion of CH₄ and CO₂ could reach 81.97% and 89.11% without deactivation for 20 h.     

The effect of La2O3 and CeO2 modifiers on properties of Ni–Al catalysts for LNG prereforming

Ni/La–Al₂O₃ and Ni/Ce–Al₂O₃ catalysts with a small amount of promoters intended for prereforming of LNG were characterized by XRF, N₂ adsorption-desorption, XRD, H₂ chemisorption, HRTEM and XPS. The catalytic activity was evaluated in methane steam reforming both in the kinetic and diffusion regime, at temperatures characteristic of pre-reforming. Carbonaceous deposit was analysed by TPO-MS method. The nature and location of the coke were studied by HRTEM.La or Ce addition into Ni–Al system causes the increase of the active surface area of Ni by enhancing its dispersion. Studies at kinetic regime have shown that the promoted catalysts have almost twice the activity than reference Ni–Al catalyst. This effect was not confirmed by measurements in the diffusion regime on whole catalyst tablets. Almost identical textural properties of catalysts and diffusive limitations related to them but not the catalytic properties of the material itself appeared to be crucial factors. The presence of La (but not Ce) causes a significant increase in resistance to coking.     

Ni/Ru–Mn/Al2O3 catalysts for steam reforming of toluene as model biomass tar

The catalytic steam reforming of the major biomass tar component, toluene, was studied over two commercial Ni-based catalysts and two prepared Ru–Mn-promoted Ni-base catalysts, in the temperatures range 673–1073 K. Generally, the conversion of toluene and the H₂ content in the product gas increased with temperature. A H₂-rich gas was generated by the steam reforming of toluene, and the CO and CO₂ contents in the product gas were reduced by the reverse Boudouard reaction. A naphtha-reforming catalyst (46-5Q) exhibited better performance in the steam reforming of toluene at temperatures over 873 K than a methane-reforming catalyst (Reformax 330). Ni/Ru–Mn/Al₂O₃ catalysts showed high toluene reforming performance at temperatures over 873 K. The results indicate that the observed high stability and coking resistance may be attributed to the promotional effects of Mn on the Ni/Ru–Mn/Al₂O₃ catalyst.     

Impacts of nickel loading on properties,catalytic behaviors of Ni/γ–Al2O3 catalysts and the reaction intermediates formed in methanation of CO2

In this study, methanation of CO₂ over Ni/Al₂O₃ with varied nickel loading (from 0 to 50 wt%) was evaluated, striving to explore the effects of nickel loading on catalytic behaviors and the reaction intermediates formed. The results showed that agglomeration of nickel particles were closely related to interaction between nickel and alumina. Increasing nickel loading resulted in the increased proportion of nickel having medium strong interaction with alumina, the reduced reduction degree of NiO, the increase of medium to strong basic sites, the enhanced activity for methanation and the competition between reverse water gas shift (RWGS) reaction and methanation. Lower nickel loading promoted RWGS reaction while methanation of CO₂ dominated at higher nickel loading. The catalyst with a nickel loading around 25% achieved the best activity for methanation. The in–situ DRIFTS studies of methanation of CO₂ showed that CO₂ could be absorbed on surface of metallic Ni, NiO or alumina. More metallic nickel species on alumina suppressed formation of carbonate species while promoted further conversion of HCOO¹ species and ¹CH₃ species, achieving a higher catalytic efficiency. Moreover, more metallic nickel species was crucial for gasifying the carbonaceous intermediates, prevented aggregation of the intermediates to coke and achieving a higher catalytic stability.