Asymmetric dual-phase MIEC membrane reactor for energy-efficient coproduction of two kinds of synthesis gases

An asymmetric 75 wt% Sm_0.15Ce_0.85O_1.925-25 wt% Sm_0.6Sr_0.4Al_0.3Fe_0.7O_3-δ (SDC-SSAF) dual-phase mixed ionic-electronic conducting (MIEC) oxygen-permeable membrane reactor was applied to coproduce ammonia synthesis gas (ASG, H₂/N₂ = 3) and liquid fuels synthesis gas (LFSG, H₂/CO = 2). The effects of CH₄ concentration, CH₄ flow rate, steam flow rate and temperature on the performance of the membrane reactor were studied. The SDC-SSAF membrane reactor showed an excellent performance for the coproduction of ASG and LFSG. An ASG production rate of 20.7 mL cm⁻² min⁻¹, a LFSG production rate of 51.0 mL cm⁻² min⁻¹ and an oxygen permeation rate of 9.1 mL cm⁻² min⁻¹ were achieved at 925 °C. Compared with traditional industrial processes, the energy saving of this membrane reactor process is expected as high as 66.5%. The post-mortem of the membrane reactor using scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) characterization revealed that the membrane has an excellent structural stability under operation condition.     

Environmentally friendly molten salt synthesis of high-entropy AlCoCrFeNi alloy powder with high catalytic hydrogenation activity

A molten salt synthesis method was used to prepare high-entropy AlCoCrFeNi alloy powder with a high specific surface area of 67.5 m²/g, exhibiting remarkable catalytic activity in the hydrogenation of p-nitrophenol by NaBH₄. The life cycle assessment of the proposed method indicated that AlCoCrFeNi production was associated with greenhouse gas emission of 125 kgCO₂e/kg-product, whose main contributors were CaH₂ and citric acid used during the precursor's reduction and formation, respectively. On the other hand, that for a previously reported dealloying method was 277 kg CO₂e/kg-product. Thus, a minimum of 54% greenhouse gas emission reduction compared to the conventional dealloying method is achievable in the proposed molten salt method. The results indicated the possible environmentally friendly production of high-surface-area, high-entropy alloy powders suitable for industrial applications.     

Hydrogen production from waste-derived synthesis gas over Ni(x)Fe(3-x)-CeO2 catalyst: optimization of Ni/Fe ratio

In this study, the effect of the Ni/Fe molar ratio on the Ni_(x)Fe_(3-x)-CeO₂ catalyst was investigated for the high-temperature water-gas shift reaction, which produces hydrogen from waste-derived synthesis gas. The catalysts were synthesized via a co-precipitation method, using different Ni/Fe molar ratios (0.5:2.5, 1.0:2.0, 1.5:1.5, 2.0:1.0, and 2.5:0.5). The physicochemical properties of these catalysts were analyzed by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), temperature-programmed reduction using hydrogen (H₂-TPR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and H₂-O₂ pulse analyses to determine their reaction performance. The Ni_1.0Fe_2.0-CeO₂ catalyst exhibited the highest activity (X_co = 88%, T = 500 °C) without any side reactions at a high gas hourly space velocity of 41,823 mL·g⁻¹ h⁻¹, compared to the other catalysts tested, owing to its high oxygen vacancies and oxygen storage capacity (OSC). In addition, when the Ni/Fe molar ratio was higher than 1, a side reaction (methanation) occurred. Therefore, it was concluded that the Ni_1.0Fe_2.0-CeO₂ catalyst is optimal for hydrogen production via the high-temperature water-gas shift reaction from waste-derived synthesis gas.     

Self-optimized and renewable Ni–Co alloy@Co–Co2C catalyst for higher alcohols synthesis from syngas

Higher alcohols synthesis (HAS) from syngas (CO/H₂) has attracted widespread attention, while the low selectivity and poor stability of the catalysts mainly stumbled its industrial application. In the work, Ni–Co alloy nanoparticles (NPs) derived from Co_1-xNi_xAl₂O₄ loaded on the SiO₂ with large specific surface area were prepared; and during reaction, the highly dispersed Ni–Co alloys were self-optimized to Ni–Co alloy@Co–Co₂C. Importantly, Ni–Co alloy@Co–Co₂C can be regenerated through oxidation - reduction - self-optimization process. Characteristic results indicated that the structural liberalization during the reaction process inhibited the loss of Ni, regulated and balanced the dual active sites of the catalyst and the Ni–Co alloys were regenerated after the re-oxidation and re-reduction process. The optimized catalyst exhibited excellent catalytic performance, including a high total selectivity to alcohols of 39.3% and an excellent catalytic stability at 250 °C, 3.5 MPa (H₂/CO = 2) and a space velocity of 6000 mL (g_cat h)^?1. In addition, the Ni–Co alloy@Co–Co₂C catalyst after stability test could recover its original catalytic performance after re-oxidation and re-reduction. The renewable characteristics and superior catalytic performance of Ni–Co alloy@Co–Co₂C made the catalyst to be one of the potential industrial catalysts for HAS.     

Combustion synthesis of copper ceria solid solution for CO2 conversion to CO via reverse water gas shift reaction

The reverse water–gas shift chemical (RWGS) reaction is a promising technique of converting CO₂ to CO at low operating temperatures, with high CO selectivity and negligible side products. In this study, we investigate the synthesis of Cu/CeO₂ catalyst using Solution Combustion Synthesis (SCS) technique and its performance for the RWGS reaction using a tubular packed bed reactor. Results indicate that the catalytic activity and stability of CeO₂ at low and moderate temperatures can be effectively improved by the addition of a small quantity of copper (1 wt%). The conversion of CO₂ improves with an increase in temperature, with a maximum value of 70% at 600 °C, showing a steady time on stream (TOS) performance for 1200 min with negligible carbon deposition of <0.05 wt%. The high catalyst activity is due to the synergistic interaction between the active Cu⁰ species and Ce³⁺-oxygen vacancy. The Cu/CeO₂ catalyst was also found to have 100% selectivity for CO, and no CH₄ was detected in the outlet stream. Moreover, the morphological characteristics of the support and catalysts (fresh and post-reaction samples), as well as the impact of reaction on the catalysts surface were investigated using various methods such as x-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy with energy dispersive x-ray spectra (SEM/EDX). The results demonstrate that Cu/CeO₂ offers a good potential for being a robust RWGS catalyst with exclusive selectivity for CO without the undesired methanation side-reaction.     

Highly selective and efficient ammonia synthesis from N2 and H2O via an iron-based electrolytic-chemical cycle

Ammonia production via electroreduction of N₂ and water under mild conditions is emerging as a promising alternative to the fossil fuels-reliance and CO₂ emitting Haber-Bosch process. However, the achievement of high Faradaic efficiency and high ammonia formation rate is still challenging. Here, we demonstrate how ammonia can be selectively produced from N₂ and H₂O via a two-step iron-based cyclic process using a molten hydroxide electrolyte. The first step is the production of Fe by electrochemical reduction of Fe₂O₃. The second step is the steam-hydrolysis of Fe with bubbling N₂ to produce NH₃ and reform Fe₂O₃. Both reaction steps proceed isothermally at 250 °C in a molten salt electrolytic cell without switching of temperature and needing separation of the mediator, resulting in more easily putting into industrial practice. The cycle achieves an ultrahigh Faradaic efficiency of 79.8% at 1.15 V and a high ammonia formation rate of 1.34 × 10⁻⁸ mol s⁻¹ cm⁻² at 1.75 V. This is a critical advance in breaking the domination of hydrogen evolution reaction (HER) competition to achieve highly selective and efficient NH₃ synthesis from N₂ and H₂O beyond reliance of fossil fuels.     

Water enhanced methanol decomposition for simultaneous heat recovery and ready-to-use synthesis gas production over CO2 capture enhanced Ni/zeolite 4A catalyst

Methanol decomposition is considered as a “one stone two birds” approach for simultaneously recovering waste heat and affording synthesis gas. However, this approach requires efficient catalysts with high CO selectivity and low selectivity to byproducts. Herein, a rational design of CO₂ capture enhanced Ni/zeolite 4 A catalyst for synthesis gas production by water enhanced methanol decomposition is reported. 5%-Ni/NaA-500 catalyst achieves the Y_H2 of 80.6%, Y_CO of 76.2%, H₂/CO molar ratio of 2.11, high stability, low selectivity to CO₂ and CH₄, and no coke at 325 °C. Ni atoms highly disperse on the surface and microporous of zeolite 4 A, and the strong interaction between Ni atoms and zeolite 4 A inhibits the reduction of Ni atoms. Consequently, Ni³⁺, Ni²⁺ and Ni⁰ coexist in 5%-Ni/NaA-500, and the redox couples of Ni³⁺↔Ni²⁺, Ni²⁺↔Ni⁰, and Ni³⁺↔Ni⁰ will enhance the redox processes during methanol decomposition. CO₂ capture capacity of x%-Ni/NaA-Y below 350 °C promotes the reverse water gas shift reaction by concentrating CO₂ molecules, which hence increases CO selectivity and declines the selectivity to byproducts. The reaction path follows CH₃OH→CH₃O→CH₂O→CHO→CO. This work will pave the way to industrial applications that combine ready-to-use synthesis gas production and heat recovery.     

Comparison of hydrothermal and electrodeposition methods for the synthesis of CoSe2/CeO2 nanocomposites as electrocatalysts toward oxygen evolution reaction

Promoting efficacious and low-cost catalysts for the oxygen evolution reaction (OER), as the sluggish half-reaction of the water splitting, is inevitable to make sustainable energy technologies more promising. In this work, we report a series of novel nanocomposites comprising CeO₂ nanorods decorated with CoSe₂ nanoparticles. The nanocomposites were prepared via a conventional hydrothermal synthesis or a rapid electrodeposition process, and their structure, morphology, and electrochemical performance toward OER in alkaline solution were compared. To tune the electrocatalytic activity, the mass ratio of CoSe₂ to CeO₂ was systematically varied. Compared with the hydrothermal synthesis, the much faster electrodeposition method yielded a nanocomposite with a similar or slightly better performance in OER. This nanocomposite exhibited an overpotential of 290 mV (at 10 mA cm^?2 current density), a Tafel slope of 53 mV dec^?1, and excellent electrochemical stability for 15 h. Overall, these findings demonstrate the great potential of CoSe₂/CeO₂ nanocomposites as effective OER electrocatalysts for future applications.     

One-pot synthesis Pr6O11 decorated Pr2CuO4 composite cathode for solid oxide fuel cells

It is a big challenge to develop composite materials with high catalytic activity and stability in a fast and simple way in the field of solid oxide fuel cells (SOFCs). In this paper, Pr₂CuO₄-Pr₆O₁₁ composites are prepared by a novel one-pot synthesis method. The temperature dependent phase evolution of the composite material is studied, and the oxygen reduction reaction (ORR) properties are characterized in detail by electrochemical impedance spectroscopy combining with the distribution of relaxation time analysis. The decoration of Pr₆O₁₁ effectively inhibits the coarsening of Pr₂CuO₄ particles, enlarging the specific surface area and thereby promoting the oxygen adsorption capability of the composite cathode. Compared to Pr₂CuO₄, the polarization resistance of Pr₂CuO₄-20%Pr₆O₁₁ is 0.07 Ω cm² at 700 °C, and the power (current) density reachs to 0.97 W cm^?2 (1.62 A cm^?2) at 0.6 V for the anode supported fuel cell. This result proves that one-pot synthesis method is an effective strategy to design cathode materials with high activity, and Pr₂CuO₄-20%Pr₆O₁₁ is potential cathode material for SOFC.     

Conversion of carbon dioxide and methane in biomass synthesis gas for liquid fuels production

The premise of this research is to find whether methane (CH₄) and carbon dioxide (CO₂) produced during biomass gasification can be converted to carbon monoxide (CO) and hydrogen (H₂). Simultaneous steam and dry reforming was conducted by selecting three process parameters (temperature, CO₂:CH₄, and CH₄:steam ratios). Experiments were carried out at three levels of temperature (800 °C, 825 °C and 850 °C), CO₂:CH₄ ratio (2:1, 1:1 and 1:2), and CH₄:steam ratio (1:1, 1:2 and 1:3) at a residence time of 3.5 × 10³ g_cat min/cc using a custom mixed gas that resembles biomass synthesis gas, over a commercial catalyst. Experiments were conducted using a Box-Behnken approach to evaluate the effect of the process variables. The average CO and CO₂ selectivities were 68% and 18%, respectively, while the CH₄ and CO₂ conversions were about 65% and 48%, respectively. The results showed optimum conditions for maximum CH₄ conversion was at 800 °C, CO₂:CH₄ ratio and CH₄:steam ratios of 1:1.     

Syngas from CO2 reforming of coke oven gas: Synergetic effect of activated carbon/Ni–γAl2O3 catalyst

The CO₂ reforming of coke oven gas for the production of synthesis gas has been studied over an activated carbon, an in-lab prepared Ni/Al₂O₃ catalyst and physical mixtures of both materials in different proportions (AC + Ni) at 800 °C. It was found that there are two possible coexisting reaction pathways: the direct dry reforming of methane (decomposition of methane followed by gasification of the carbon deposits) and the reverse water gas shift reaction followed by the steam reforming of methane. If the process is carried out with the physical mixtures AC + Ni, there is a synergetic effect between both materials. The experimental conversions are higher than the conversions predicted by the law of mixtures, whereas the production of water is lower, resulting in a higher selectivity. The mixtures also showed a lower loss of porosity than when the activated carbon and the in-lab prepared Ni/Al₂O₃ were used individually. Therefore, the combination of these materials may produce catalysts that are more resistant to deactivation. The synthesis gas obtained was analyzed and it was found suitable for the production of methanol.     

Highly conductive proton-conducting electrolyte with a low sintering temperature for electrochemical ammonia synthesis

BaCe_0·7Zr_0.1Gd_0.2O_3-δ (BCZG) powder is synthesized by a citrate sol-gel method, and different amounts of Li₂CO₃ are introduced to lower the sintering temperature. The densification temperature of BCZG ceramic is decreased drastically to 1250 °C by using Li₂CO₃ as sintering aid. BCZG with 2.5 wt% of Li₂CO₃ (BCZG-2.5L) can not only remarkably promote the sintering process of BCZG but also enhance its electrical conductivity. The total ionic conductivity of BCZG-2.5L attains to 1.9 × 10⁻² S cm⁻¹ at 600 °C in a wet H₂ atmosphere. Ammonia synthesis at atmospheric pressure is conducted on (2K, 10Fe)/Ni-BCZG | BCZG-2.5L | Ni-BCZG electrolytic cell with an applied voltage of 0.2–1.6 V at a temperature of 450–600 °C. The highest NH₃ formation rate of 1.87 × 10⁻¹⁰ mol s⁻¹ cm⁻² and the highest current efficiency of 0.53% is achieved at 500 °C with an applied voltage of 0.8 V.     

MgH2 synthesis during reactive mechanical alloying studied by in-situ pressure monitoring

The synthesis of MgH₂ by reactive mechanical milling has been studied by monitoring H₂ pressure changes inside a milling chamber. Mg and a Mg-10 wt.% C mixture were used as starting materials and milled under 0.5 MPa of H₂. The addition of C doubles the MgH₂ synthesis efficiency due to C acting as a process control agent. MgH₂ formation has been observed throughout milling and during the rest periods between milling stages. Mg hydriding during the rest periods has been found to be controlled by hydrogen diffusion through MgH₂. High-diffusivity paths along grain boundaries seem to be operative during the process. A lower bound for the diffusion coefficient of H in MgH₂ at room temperature of 10⁻²⁵ m² s⁻¹ has been estimated from the data.     

In situ facile synthesis of ruthenium nanocluster catalyst supported on carbon black for hydrogen generation from the hydrolysis of ammonia-borane

Ligand-free Ru nanoclusters supported on carbon black have been synthesized in situ for the first time from the reduction of RuCl₃ by ammonia-borane concomitantly with its hydrolysis process at room temperature, and their catalytic activity has been investigated. Well dispersed Ru nanoclusters (∼1.7 nm) are stabilized and immobilized by carbon black. Due to the small size and the absence of ligands on the surface, the Ru catalysts exhibit high catalytic activity, which is partly retained after 5 reaction cycles. A kinetic study shows that the catalytic hydrolysis of ammonia-borane is first order with respect to Ru catalyst concentration; the turnover frequency is 429.5 mol H₂ min⁻¹ mol⁻¹ Ru. The activation energy for the hydrolysis of ammonia-borane in the presence of Ru/C catalysts has been measured to be 34.81 ± 0.12 kJ mol⁻¹, which is smaller than most of the values reported for other catalysts, including those based on Ru, for the same reaction.     

A direct synthesis of nickel nanoclusters embedded on multicomponent mesoporous metal oxides and their catalytic properties for glycerol steam reforming to hydrogen

Nickel nanoclusters embedded in multicomponent mesoporous metal oxides (Ni–MMOs) are obtained at various support compositions by a single-step synthesis of Ni ion incorporated mesoporous metal oxides (NiO–MMOs) followed by selective reduction of the NiO to Ni metal clusters. The resultant Ni–MMOs catalysts displayed enhanced Ni dispersion with well-developed mesopore structures at various support composition, exhibiting superior catalytic properties when compared to a siliceous SBA-16-supported Ni catalyst prepared by a conventional impregnation method. Glycerol steam reforming conducted at 873 K on 1Ni–2Al₂O₂–2ZrO₂ and 1Ni–2SiO₂–2ZrO₂ catalysts exhibited considerably higher glycerol conversions over the 10 wt%-Ni/SBA-16 catalyst with similar Ni loading amount. This was primarily due to the enhanced Ni dispersion resulting from the direct synthesis process. The multicomponent mesoporous supports also significantly affect product selectivity, favoring higher hydrogen concentration in the product stream. The water–gas shift reaction appears to be positively affected by the 2Al₂O₂–2ZrO₂ and 2SiO₂–2ZrO₂ multicomponent metal oxide matrices, which facilitated the conversion of the CO produced by the glycerol reforming further to additional hydrogen. Direct single-step synthesis of Ni–MMO catalysts was effective in enhancing the dispersion of Ni nanoclusters, as well as variation of the support components of the mesoporous catalyst systems.     

Tungsten carbide synthesized by low-temperature combustion as gas diffusion electrode catalyst

Tungsten carbide powder, which is used as the catalyst for a gas diffusion electrode, has been prepared by low-temperature combustion synthesis for the first time. The average particle size of the prepared tungsten carbide is 200 nm, determined by X-ray diffraction and field-emission scanning electron microscopy. The effects of the carbon/tungsten (C/W) molar ratio on the formation of tungsten carbide and carbon content on the complete carbonization temperature are discussed. The optimal synthesis temperature is 1100 °C, and the optimal C/W molar ratio is 19/3. The electrocatalytic properties of tungsten carbide for the oxygen reduction reaction are evaluated through the use of polarization curves and electrochemical impedance spectroscopy in neutral and alkaline electrolytes. The current density of the tungsten carbide-based gas diffusion electrode is as high as 350 mA cm⁻² at 0.4 V versus Hg/HgO. It is demonstrated that the tungsten carbide catalyst exhibits excellent electrocatalytic performance, comparable with that of Pt.     

Dimethyl ether synthesis on clinoptilolite zeolite and HZSM5-based hybrid catalysts in a fixed-bed reactor

In this study 4 different acid catalysts were prepared and mixed with commercial CZA catalysts and investigated in direct DME synthesis. Some of the used acid catalysts were not investigated in the literature therefore the work involves novelty. In a fixed-bed reactor, dimethyl ether (DME) was synthesized from the synthesis gas on two catalysts from, natural clinoptilolite and zeolite catalysts. The clinoptilolite (HK and DK) and two (HZSM5(117) and HZSM5(360)) catalysts mixed with commercial CuO/ZnO/Al₂O₃ (CZN) catalysts. The catalysts were also characterized by analytical chemistry techniques such as XRD, BET, TGA, and FTIR. Four different catalysts (HK, DK, HZSM5(117) and HZSM5(360)) and CZA catalysts were mixed at a ratio of 3/1, respectively, and studies were carried out in a fixed-bed reactor. Four different catalyst composition activity tests were made at temperatures 250, 275, and 300 °C. At the same time, the pressure was 30 and 40 bar and four different times (30, 60, 90, and 120 min). The composition of the gases fed to the system for DME was adjusted to N₂/CO₂/CO/H₂ = 36/10/18/36 by volume. DME selectivity (S_DME) and total carbon (X_C) conversion were calculated for each condition. The experimental results showed that the highest DME selectivity of 96.50% was observed in the reaction of the DK + CZA catalyst mixture at 250 °C and 30 min at 40 bar. In addition, high DME selectivity was obtained in all reactions of DK + CZA and HK + CZA catalyst compositions at three different temperatures. The highest DME selectivity obtained is 89.69% for the reaction of the HK + CZA catalyst mixture at 300 °C and 60 min at 30 bar. Experimental results gave insights into Dimethyl ether synthesis from syngas on clinoptilolite zeolite and HZSM5-based hybrid catalysts in a fixed-bed reactor.     

High temperature water-gas shift step in the production of clean hydrogen rich synthesis gas from gasified biomass

The possibility of using the water-gas shift (WGS) step for tuning the H₂/CO-ratio in synthesis gas produced from gasified biomass has been investigated in the CHRISGAS (Clean Hydrogen Rich Synthesis Gas) project. The synthesis gas produced will contain contaminants such as H₂S, NH₃ and chloride components. As the most promising candidate FeCr catalyst, prepared in the laboratory, was tested. One part of the work was conducted in a laboratory set up with simulated gases and another part in real gases in the 100 kW Circulating Fluidized Bed (CFB) gasifier at Delft University of Technology. Used catalysts from both tests have been characterized by XRD and N₂ adsoption/desorption at ?196 °C.In the first part of the laboratory investigation a laboratory set up was built. The main gas mixture consisted of CO, CO₂, H₂, H₂O and N₂ with the possibility to add gas or water-soluble contaminants, like H₂S, NH₃ and HCl, in low concentration (0–3 dm³ m^?3). The set up can be operated up to 2 MPa pressure at 200–600 °C and run un-attendant for 100 h or more. For the second part of the work a catalytic probe was developed that allowed exposure of the catalyst by inserting the probe into the flowing gas from gasified biomass.The catalyst deactivates by two different causes. The initial deactivation is caused by the growth of the crystals in the active phase (magnetite) and the higher crystallinity the lower specific surface area. The second deactivation is caused by the presence of catalytic poisons in the gas, such as H₂S, NH₃ and chloride that block the active surface.The catalyst subjected to sulphur poisoning shows decreased but stable activity. The activity shows strong decrease for the ammonia and HCl poisoned catalysts. It seems important to investigate the levels of these compounds before putting a FeCr based shift step in industrial operation. The activity also decreased after the catalysts had been exposed to gas from gasified biomass. The exposed catalysts are not re-activated by time on stream in the laboratory set up, which indicates that the decrease in CO₂-ratio must be attributed to irreversible poisoning from compounds present in the gas from the gasifier.It is most likely that the FeCr catalyst is suitable to be used in a high temperature shift step, for industrial production of synthesis gas from gasified biomass if sulphur is the only poison needed to be taken into account. The ammonia should be decomposed in the previous catalytic reformer step but the levels of volatile chloride in the gas at the shift step position are not known.     

Hydroxyapatite as a new support material for cobalt-based catalysts in Fischer-Tropsch synthesis

Hydroxyapatite [HAP, (Ca₁₀(PO₄)₆(OH)₂)] is an emerging catalytic support possessing exciting features such as high thermal and mechanical strength, chemically stable with low water solubility along with tunable porosity and acid-basic character. Despite of these interesting characteristics, it has not yet been investigated in Fischer-Tropsch (FT) synthesis. Herein, for the first time, HAP-supported cobalt catalysts (Co/HAP) prepared by conventional incipient wetness impregnation method were examined in the FT synthesis process. The catalytic performance of these catalysts was compared with alumina-supported cobalt catalysts (Co/Alumina). HAP support was found to exhibit considerably less acid-site density, consequently, reducing detrimental interactions of the support with cobalt precursors leading to hardly reducible Co species that are generally observed with its alumina counterpart. Co/HAP catalysts exhibit relatively larger Co particle sizes (~9 nm versus ~6 nm, as observed from TEM analysis) and better Co reducibility when compared to its counterparts on alumina. FT synthesis at 20 bar, 220 °C and H₂/CO = 2.1 showed that the CO conversion was higher on the catalysts (10 wt% Co loading) using HAP as a support material when compared to alumina. Under different testing conditions (220 or 230 °C) using the Co/HAP catalyst, the C₅₊ selectivity was in the range of 82–88%, whereas the methane selectivity was about ~10%.     

Design of Ni/La2O3 catalysts for dry reforming of methane: Understanding the impact of synthesis methods

Fine-tuning of materials properties, particularly the catalytic properties, through innovative synthesis procedures has gained an increased research interest in the last decades. It is well known that synthesis procedures have considerable impact on the physio-chemical properties of the synthesized materials even if the chemical composition is maintained. Herein, we investigated the impact of selected synthesis methods on the catalytic performance of Ni/La₂O₃ for the dry reforming of methane (DRM), a challenging reaction known for severe coking. Although this catalyst has been frequently studied for DRM, however, tuning the structure-activity relationship by varying the synthesis routes has not been reported. Herein, the chosen synthesis techniques; for example the solution combustion synthesis (Ni/La-SC), sol-gel (Ni/La-SG), homogeneous precipitation (Ni/La-HP), solvothermal (Ni/La-ST), and modified oleylamine-assisted synthesis (Ni/La-ME); considerably affected the morphology, metal support interaction (MSI), and surface area of Ni/La₂O₃ catalysts leading to variation in their performance for DRM. The investigated catalysts were thoroughly characterized by using SEM-EDX, TEM, N₂-physisorption, XRD, XPS, and H₂-TPR to understand the structural properties. Their catalytic performance towards the DRM was evaluated by varying the temperature between 550 and 800 °C. DRM experiments demonstrated that among the studied catalysts, Ni/La-SC showed the best performance for DRM with a high catalytic activity and coking resistance. For instance, Ni/La-SC revealed the highest CO₂ and CH₄ conversions i.e. 97.9 ± 1.5% and 96.6 ± 1.8%, respectively at 800 °C. The same sample revealed the highest hydrogen yield i.e. 71.9% and the highest H₂/CO ratio i.e. 1.03 ± 0.013 at the same temperature. The results revealed that Ni/La-SC demonstrated the lowest increment (20.9%) in the Ni crystallite size after DRM reaction, highest durability, and the lowest rate of coke formation (42 ± 5.2 mg C/g_catalyst) over an operating period of 100 h at 800 °C. The outstanding performance of Ni/La-SC catalyst was credited to the small crystallite size of Ni, high Ni⁰/Ni²⁺ ratio, high BET area, and a good dispersion of nickel sites over the La₂O₃ support. The obtained results may open new frontiers for size and shape-controlled synthesis of nanostructured metals/metal oxides catalysts with controllable morphologies and dispersion that can lead to desirable catalytic properties.