A review on dry reforming of methane in aspect of catalytic properties

Formation of a Porous Crystalline Mg1-xAl2Oy Overlayer on Metal Catalysts via Controlled Solid-State Reactions for High-temperature Stable Catalysis

Catalyst deactivation by sintering and coking is a long-standing issue in metal-catalyzed harsh high-temperature hydrocarbon reactions. Ultrathin oxide coatings of metal nanocatalysts have recently appeared attractive to address this issue, while the porosity of the overlayer is difficult to control to preserve the accessibility of embedded metal nanoparticles, thus often leading to a large decrease in activity. Here, we report that a nanometer-thick alumina coating of MgAl2O4-supported metal catalysts followed by high-temperature reduction can transform a nonporous amorphous alumina overlayer into a porous Mg1-xAl2Oy crystalline spinel structure with a pore size of 2-3 nm and weakened acidity. The high porosity stems from the restrained Mg migration from the MgAl2O4 support to the alumina overlayer through solid-state reactions at high temperatures. The resulting Ni/MgAl2O4 and Pt/MgAl2O4 catalysts with a porous crystalline Mg1-xAl2Oy overlayer achieved remarkably high stability while preserving much higher activity than the corresponding alumina-coated Ni and Pt catalysts on MgO and Al2O3 supports in the reactions of dry reforming of methane and propane dehydrogenation, respectively.

Nickel-based cerium zirconate inorganic complex structures for CO2 valorisation via dry reforming of methane

The increasing anthropogenic emissions of greenhouse gases (GHG) is encouraging extensive research in CO2 utilisation. Dry reforming of methane (DRM) depicts a viable strategy to convert both CO2 and CH4 into syngas, a worthwhile chemical intermediate. Among the different active phases for DRM, the use of nickel as catalyst is economically favourable, but typically deactivates due to sintering and carbon deposition. The stabilisation of Ni at different loadings in cerium zirconate inorganic complex structures is investigated in this work as strategy to develop robust Ni-based DRM catalysts. XRD and TPR-H2 analyses confirmed the existence of different phases according to the Ni loading in these materials. Besides, superficial Ni is observed as well as the existence of a CeNiO3 perovskite structure. The catalytic activity was tested, proving that 10 wt.% Ni loading is the optimum which maximises conversion. This catalyst was also tested in long-term stability experiments at 600 and 800°C in order to study the potential deactivation issues at two different temperatures. At 600°C, carbon formation is the main cause of catalytic deactivation, whereas a robust stability is shown at 800°C, observing no sintering of the active phase evidencing the success of this strategy rendering a new family of economically appealing CO2 and biogas mixtures upgrading catalysts.

Performance of NiO doped on alkaline sludge from waste photovoltaic industries for catalytic dry reforming of methane

Alkali sludge (AS) is waste abundantly generated from solar photovoltaic (PV) solar cell industries. Since this potential basic material is still underutilized, a combination with NiO catalyst might greatly influence coke resentence, especially in high-temperature thermochemical reactions (Arora and Prasad, RSC Adv. 6:108,668-108688, 2016). This paper investigated alkaline sludge containing 3CaO-2SiO2 doped with well-known NiO to enhance the dry reforming of methane (DRM) reaction. The wet-impregnation method was used to prepare the xNiO/AS (x = 5-15%) catalysts. Subsequently, all catalysts were tested by using X-ray diffraction (XRD), nitrogen adsorption/desorption (BET), temperature-programmed reduction of hydrogen (H2-TPR), temperature-programmed desorption of carbon dioxide (TPD-CO2), field emission scanning electron microscopy (FESEM-EDX), and X-ray photoelectron spectroscopy (XPS). The spent catalysts were analyzed by thermogravimetric analysis (TGA/DTG), transmission electron microscopy (TEM), and temperature-programmed oxidation (TPO). The catalytic performance of xNiO/AS catalysts was investigated in a fixed bed reactor connected with gas chromatography thermal conductivity detector (GC-TCD) at a CH4:CO2 flow rate of 30 mL-1 during a 10-h reaction by following (Shamsuddin et al., Int. J. Energy Res. 45:15,463-15,480, 2021d). For optimization parameters, the effects of NiO concentration (5, 10, and 15%), reaction temperature (700, 750, 800, 850, and 900 °C), catalyst loading (0.1, 0.2, 0.3, 0.4, and 0.5 g), and gas hourly space velocity (GHSV) range from 3000, 6000, 9000, 12,000, and 15,000 h-1 were evaluated. The results showed that physical characteristics such as BET surface area and porosity do not significantly impact NiO percentages of dispersion, whereas chemical characteristics like reducibility are crucial for the catalysts' efficient catalytic activity. Due to the active sites on the catalyst surface being more accessible, increased NiO dispersion resulted in higher reactant conversion. The catalytic performance on various parameters that showed 15%NiO/AS exhibited high reactant conversion up to 98% and 40-60% product selectivity in 700 °C, 0.2 g catalyst loading, and 12,000 h-1 GHSV. According to spent catalyst analyses, the catalyst was stable even after the DRM reaction. Meanwhile, increased reducibility resulted in more and better active site formation on the catalyst. Synergetic effect of efficient NiO as active metal and medium basic sites from AS enhanced DRM catalytic activity and stability with low coke formation.

Methane-H2S Reforming Catalyzed by Carbon and Metal Sulfide Stabilized Sulfur Dimers

H2S reforming of methane (HRM) provides a potential strategy to directly utilize sour natural gas for the production of COx-free H2 and sulfur chemicals. Several carbon allotropes were found to be active and selective for HRM, while the additional presence of transition metals led to further rate enhancements and outstanding stability (e.g., Ru supported on carbon black). Most metals are transformed to sulfides, but the carbon supports prevent sintering under the harsh reaction conditions. Supported by theoretical calculations, kinetic and isotopic investigations with representative catalysts showed that H2S decomposition and the recombination of surface H atoms are quasi-equilibrated, while the first C-H bond scission is the kinetically relevant step. Theory and experiments jointly establish that dynamically formed surface sulfur dimers are responsible for methane activation and catalytic turnovers on sulfide and carbon surfaces that are otherwise inert without reaction-derived active sites.

High activity in the dry reforming of methane using a thermally switchable double perovskite and in situ generated molecular level nanocomposite

This work emphasizes the dry reforming of methane (DRM) reaction on citrate sol-gel-synthesized double perovskite oxides. Phase pure La2NiMnO6 shows very impressive DRM activity with H2/CO = 0.9, hence revealing a high prospect of next-generation catalysts. Although the starting double perovskite phase gets degraded into mostly binary oxide phases after a few hours of DRM activity, the activity continues up to 100 h. The regeneration of the original double perovskite out of decomposed phases by annealing at near synthesis temperature, followed by the spectacular retention of activity, is rather interesting and hitherto unreported. This result unravels unique reversible thermal switching between the original double perovskite phase and decomposed phases during DRM without compromising the activity and raises challenge to understand the role of decomposed phases evolved during DRM. We have addressed this unique feature of the catalyst via structure-property relationship using the in situ generated molecular level nanocomposite.

Influence of NiO into the CO2 capture of Li4SiO4 and its catalytic performance on dry reforming of methane

Carbon capture, utilization, and storage (CCUS) technology offer promising solution to mitigate the threatening consequences of large-scale anthropogenic greenhouse gas emissions. Within this context, this report investigates the influence of NiO deposition on the Li4SiO4 surface during the CO2 capture process and its catalytic behavior in hydrogen production via dry methane reforming. Results demonstrate that the NiO impregnation method modifies microstructural features of Li4SiO4, which positively impact the CO2 capture properties of the material. In particular, the NiO-Li4SiO4 sample captured twice as much CO2 as the pristine Li4SiO4 material, 6.8 and 3.4 mmol of CO2 per gram of ceramic at 675 and 650 °C, respectively. Additionally, the catalytic results reveal that NiO-Li4SiO4 yields a substantial hydrogen production (up to 55 %) when tested in the dry methane reforming reaction. Importantly, this conversion remains stable after 2.5 h of reaction and is selective for hydrogen production. This study highlights the potential of Li4SiO4 both a support and a captor for a sorption-enhanced dry reforming of methane. To the best of our knowledge, this is the first report showcasing the effectiveness of Li4SiO4 as an active support for Ni-based catalysis in the dry reforming of methane. These findings provide valuable insights into the development of this composite as a dual-functional material for carbon dioxide capture and conversion.

Unraveling the effect of particle size of active metals in Ni/MgO on methane activation and carbon growth mechanism

For dry reforming of methane, the active metal particle size of the catalyst has a significant effect on both the reaction activity and the resistance to carbon deposition. In this study, nickel particles of different sizes (Ni13, Ni25, and Ni37) supported on the MgO(100) slab are used to study the mechanism of CH4 activation and carbon growth based on DFT theoretical calculations. According to the results, the energy of adsorption for reaction intermediates changes depending on the size of the active metal. The adsorption process of CH3, CH2, CH and C on Ni25/MgO has a maximum exothermic value. Furthermore, the energy barriers of CH4 four-step dehydrogenation are lowest on Ni25/MgO during the CH4 activation process. The growth process of carbon deposition on the catalysts is also investigated in this work. The results indicate that the growth of carbon from C5 to C6 is difficult to proceed on Ni13/MgO due to size and active site limitation. Additionally, with an increase in particle size of the active metal, the absolute value of growth energy and average carbon binding energy of Cn increase on both Ni25/MgO and Ni37/MgO. It is proved that smaller particle size presents better resistance to carbon deposition. In the studied size range, Ni25/MgO is demonstrated to have greater catalytic activity and better resistance to carbon deposition.

The Advances, Challenges, and Perspectives on Electrocatalytic Reduction of Nitrogenous Substances to Ammonia: A Review

Ammonia (NH3) is considered to be a critical chemical feedstock in agriculture, industry, and other fields. However, conventional Haber-Bosch (HB) ammonia (NH3) production suffers from high energy consumption, harsh reaction conditions, and large carbon dioxide emissions. Despite the emergence of electrocatalytic reduction of nitrogenous substances to NH3 under ambient conditions as a new frontier, there are several bottleneck problems that impede the commercialization process. These include low catalytic efficiency, competition with the hydrogen evolution reaction, and difficulties in breaking the N≡N triple bond. In this review, we explore the recent advances in electrocatalytic NH3 synthesis, using nitrogen and nitrate as reactants. We focus on the contribution of the catalyst design, specifically based on molecular-catalyst interaction mechanisms, as well as chemical bond breaking and directional coupling mechanisms, to address the aforementioned problems during electrocatalytic NH3 synthesis. Finally, we discuss the relevant opportunities and challenges in this field.

The effects of Fe, Mg, and Pt-doping on the improvement of Ni stabilized on Al2O3-CeO3 catalysts for methane dry reforming

Herein, the promotional effects of Mg, Fe, and Pt on Ni-based catalysts supported on Al2O3-CeO2 (Ni/Al2O3-CeO2) were investigated in the dry reforming of methane (DRM) reaction. The interaction of a suitable amount of MgO and FeO with Ce2O3 stabilized in the catalysts was demonstrated by the temperature-programmed desorption of CO2 (CO2-TPD). Ce2O3 has a high basicity for adsorbing CO2, generating a monoclinic Ce2O2CO3 species in the DRM reaction. Surface oxygen ions were also produced by adding MgO and FeO, as demonstrated by the temperature-programmed reduction of H2 (H2-TPR). Monoclinic Ce2O2CO3 and surface oxygen may both be used to oxidize and remove the carbon that was deposited, maintaining the high activity and stability of the metal Ni and Pt catalysts. The high dispersion and synergistic interactions between the platinum and oxide phases, which are associated with the decrease in reduction temperature and the rise in the number of basic sites, are responsible for the increased activity of Pt with M-Ni/Al2O3-CeO2 catalysts. The co-doped Ni/Al2O3-CeO2 catalysts with Mg and Fe significantly enhanced the activity (more than 80% methane and 84% CO2 conversion), the selectivity toward syngas (∼90%), and maintained the H2/CO ratio at about 0.97 at 700 °C.

Restructuring Co-CoOx Interface with Titration Rate in Co/Nb-CeO2 Catalysts for Higher Water-Gas Shift Performance

H2 production via water-gas shift reaction (WGS) is an important process and applied widely. Cobalt-modified CeO2 are promising catalysts for WGS reaction. Herein, a series of Co/Nb-CeO2 catalysts were prepared by varying the rate of precipitant addition during the coprecipitation method and examined for hydrogen generation through WGS reaction. The rates of precipitant addition were 1, 5, 15, and 25 mL/min. We obtained ceria supported cobalt catalysts with different sizes and morphology such as 3, 8 nm nanoclusters, 30 nm cubic nanoparticles, and 50 nm hexagonal nanoparticles. The well dispersed small cobalt particles in Co/Nb-CeO2 that was prepared at 5 mL/min titration rate exhibit strong interaction between cobalt oxide and CeO2 that retards the reduction of CoOx producing Co-CoOx pairs. In contrast, 1-Co/Nb-CeO2 and 25-Co/Nb-CeO2 result in bigger and aggregated Co particles, resulting in fewer interfaces with CeO2. The Co0, Coδ+, Ce3+, and Ov species are responsible for improved reducibility in Co/Nb-CeO2 catalysts and were quantitively measured using XPS, XAS, and Raman spectroscopy. The Co-CoOx interface assists dissociation of the H2O molecule; CO oxidation requires low activation energy and realizes a high turnover frequency of 9.8 s-1. The 5-Co/Nb-CeO2 catalyst achieved thermodynamic equilibrium equivalent CO conversion with efficient H2 production during WGS reaction at a gas hourly space velocity of 315,282 h-1. Successively, the 5-Co/Nb-CeO2 catalyst exhibited stable performance for straight 168 h attributed to stable CO-Coδ+ intermediate formation, achieving efficient inhibition of typical CO chemistry over the Co metal, suitable for hydrogen generation from waste derived synthesis gas.

Role of support bio-templating in Ni/Al2O3 catalysts for hydrogen production via dry reforming of methane

Bio-templating, a synthetic approach inspired by nature, is an emerging area in material engineering. In this study, waste leaves of Sycamore were utilized as a bio-template for producing alumina support to prepare catalyst. The performance of Ni and Ce impregnated on bio-templated alumina support was investigated in dry reforming of methane for the first time. The effect of process and catalytic variables were examined in detail. The results showed that impregnation of 20% Ni and 3% Ce on the bio-templated alumina led to improved Ni dispersion and achieving the maximum CH4 conversion of 88.7%, CO2 conversion of 78.5%, and H2 yield of 85.3%, compared to 84.4%, 75.6% and 83.4% for the non-templated catalyst at 700 °C, respectively. Detailed characterization of the catalysts revealed that the enhanced performance in the bio-templated catalyst could be attributed to smaller Ni particles, superior dispersion of Ni on the support, the mesoporous structure of alumina, and the larger surface area of support. Furthermore, analysis of the used catalyst showed reduced coke formation on the catalyst surface and high stability of bio-templated catalysts, highlighting the main advantage of bio-templated catalysts over non-templated ones. The findings presented in this study contribute to the potential future applications of bio-templating materials and shed light on the rational design of bio-templating materials.

Highly Efficient Solar-Driven Dry Reforming of Methane on a Rh/LaNiO3 Catalyst through a Light-induced Metal-To-Metal Charge Transfer Process

As an energy-saving and green method, solar-driven dry reforming of methane (DRM) is expected to introduce new activation processes and prevent sintering and coking of the catalysts. However, it still lacks an efficient way to coordinate the regulation of activation of reactants and lattice oxygen migration. In this study, Rh/LaNiO3 is designed as a highly efficient photothermal catalyst for solar-driven DRM, which performs production rates of 452.3 mmol h-1  gRh -1 for H2 and 527.6 mmol h-1  gRh -1 for CO2 under a light intensity of 1.5 W cm-2 , with an excellent stability. Moreover, a remarkable light-to-chemical energy efficiency (LTCEE) of 10.72% is achieved under a light intensity of 3.5 W cm-2 . The characterizations of surface electronic and chemical properties and theoretical analysis demonstrate that strong adsorption for CH4 and CO2 , light-induced metal-to-metal charge transfer (MMCT) process and high oxygen mobility together bring Rh/LaNiO3 excellent performance for solar-driven DRM.

Exsolution of Co-Fe Alloy Nanoparticles on the PrBaFeCoO5+δ Layered Perovskite Monitored by Neutron Powder Diffraction and Catalytic Effect on Dry Reforming of Methane

Reversible exsolution and dissolution of metal nanoparticles (NPs) in complex oxides have been investigated as an efficient strategy to improve the performance and durability of the catalysts for thermal and electrochemical energy conversion. Here, in situ exsolution of Co-Fe alloy NPs from the layered perovskite PrBaFeCoO_5+δ (PBFC) and their dissolution back into the oxide host have been monitored for the first time by in situ neutron powder diffraction and confirmed by X-ray diffraction and electron microscopy. Catalytic tests for dry reforming of methane showed stable operation over ∼100 h at 800 °C with negligible carbon deposition (<0.3 mg/g_cat h). The CO₂ and CH₄ conversions are among the highest achieved by layered double perovskites. The cyclability of the PBFC catalyst and the potential to improve the catalytic activity by adjusting the composition, size, and the NP distribution would pave the way for highly efficient energy conversion applications.

Microwave-enhanced hydrogen production: a review

Currently, the massive use of fossil fuels, which still serve as the dominant global energy, has led to the release of large amounts of greenhouse gases. Providing abundant, clean, and safe renewable energy is one of the major technical challenges for humankind. Nowadays, hydrogen-based energy is widely considered a potentially ideal energy carrier that could provide clean energy in the fields of transportation, heat and power generation, and energy storage systems, almost without any impact on the environment after consumption. However, a smooth energy transition from fossil-fuel-based energy to hydrogen-based energy must overcome a number of key challenges that require scientific, technological, and economic support. To accelerate the hydrogen energy transition, advanced, efficient, and cost-effective methods for producing hydrogen from hydrogen-rich materials need to be developed. Therefore, in this study, a new alternative method based on the use of microwave (MW) heating technology in enhanced hydrogen production pathways from plastic, biomass, low-carbon alcohols, and methane pathways compared with conventional heating methods is discussed. Furthermore, the mechanisms of MW heating, MW-assisted catalysis, and MW plasma are also discussed. MW-assisted technology usually has the advantages of low energy consumption, easy operation, and good safety practices, which make it a promising solution to supporting the future hydrogen society.

Plasmonic Photocatalysis for CO2 Reduction: Advances, Understanding and Possibilities

Plasmonic photocatalysis for CO₂ reduction is attracting increasing attention due to appealing properties and great potential for real applications. In this review, the fundamentals of plasmonic photocatalysis and the most recent developments regarding its application in driving CO₂ reduction are reported. Firstly, we present the review on the mechanism of plasmonic photocatalytic CO₂ reduction, the energy transfer of plasmon, and the CO₂ reduction process on the catalyst surface. Then, the modulation on the plasmonic nanostructures and also the semiconductor counterpart to regulate CO₂ photoreduction is discussed. Next, the influence of the core-shell structure and the interface between the plasmonic metal and semiconductor on the CO₂ photoreduction performance is also outlined. In addition, the latest progress on the emerging direction regarding the plasmonic photocatalysis for methane dry reforming with CO₂ is especially emphasized. Finally, a summary on the challenges and prospects of this promising field are provided.

Performance of Modified Alumina-Supported Ruthenium Catalysts in the Reforming of Methane with CO2

Ruthenium (1 wt%) catalysts supported on alumina doped with alkaline (Na and K) and alkaline earth metals (Ba, Ca, and Mg) of different concentrations (1, 5, and 10 wt%) were tested in the dry reforming of methane. All catalysts were prepared by the successive impregnation method. Supports were characterized by X-ray diffraction, BET surface area, temperature-programmed desorption of CO2, and 2-propanol dehydration. Additionally, catalysts were characterized by temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Stability tests to study coke deposition were performed using long-time dry reforming reactions. All the catalysts showed good catalytic activity, and activity falls were never detected. Ru metallic phase seemed to be resistant to coke formation even though its particles are sintered during a long-term reaction.

Profitable Fischer Tropsch realization via CO2-CH4 reforming; an overview of nickel-promoter-support interactions

Environmental pollution, climate change, and fossil fuel extinction have aroused serious global interest in the search for alternative energy sources. The dry reforming of methane (DRM) could be a good technique to harness syngas, a starting material for the FT energy process from greenhouse gases. Noble metal DRM catalysts are effective for the syngas generation but costly. Therefore, they inevitably, must be replaced by their Ni-based contemporaries for economic reasons. However, coking remains a strong challenge that impedes the industrialization of the FT process. This article explains the secondary reactions that lead to the production of detrimental graphitic coke deposition on the surface of active nickel catalyst. The influence of nickel particle size, impact of extra surface oxygen species, interaction of Ni catalysts with metal oxide supports/promoters, and larger fraction of exposed nickel active sites were addressed in this review. Size of active metal determines the conversion, surface area, metal dispersion, surface reactions, interior diffusion effects, activity, and yield. The influence of oxygen vacancy and coke deposition on highly reported metal oxide supports/promoters (Al₂O₃, MgO and La₂O₃) was postulated after studying CIFs (crystallographic information files) obtained from the Crystallography open database (COD) on VESTA software. Thus, overcoming excessive coking by La₂O₃ promotion is strongly advised in light of the orientation of the crystal lattice characteristics and the metal-support interaction can be used to enhance activity and stability in hydrogen reforming systems.

Inhibiting the Laydown of Polymeric Carbon and Simultaneously Promoting Its Facile Burn-Off during the Industrial-Scale Production of Hydrogen with Nickel-Based Catalysts: Insights from Ab Initio Calculations

This paper presents a computational study of the mechanistic models for the laydown of carbon species on nickel surface facets and the burn-off models for their gasification mechanism in methane steam reforming based on density functional theory. Insights into catalyst design strategies for achieving the simultaneous inhibition of the laydown of polymeric carbon and the promotion of its burn-off are obtained by investigating the influence of single atom dopants on nickel surfaces. The effects of single atom dopants on adsorption energies are determined at both low and high carbon coverages on nickel and used to introduce appropriate thermodynamic descriptors of the associated surface reactions. It is found that the critical size of the nucleating polymeric carbon adatom contains three atoms, i.e., C₃. The results show that the burn-off reaction of a polymeric carbon species is thermodynamically limited and hard to promote when the deposited carbon cluster grows beyond a critical size, C₄. The introduction of single atom dopants into nickel surfaces is found to modify the structural stability and adsorption energies of carbon adatom species, as well as the free energy profiles of surface reactions for the burn-off reactions when CH₄, H₂O, H₂, and CO species react to form hydrogen. The results reveal that materials development strategies that modify the sub-surface of the catalyst with potassium, strontium, or barium will inhibit carbon nucleation and promote burn-off, while surface doping with niobium, tungsten, or molybdenum will promote the laydown of polymeric carbon. This study provides underpinning insights into the reaction mechanisms for the coking of a nickel catalyst and the gasification routes that are possible for the recovery of a nickel catalyst during the steam reforming of methane for large-scale production of hydrogen.

Cu and Si co-doping on TiO2 nanosheets to modulate reactive oxygen species for efficient photocatalytic methane conversion

In this study, we successfully construct Cu and Si co-doped ultrathin TiO₂ nanosheets. As confirmed by comprehensive characterizations, Cu and Si co-doping can rationally tailor the electronic structure of TiO₂ to maneuver reactive oxygen species for effective photocatalytic methane conversion. In addition, this co-doping greatly enhances the utilization efficiency of photogenerated charges. Furthermore, it is revealed that Cu and Si co-doping can significantly boost the adsorption and activation of methane on TiO₂ nanosheets. As a result, the optimized catalyst achieves a C₂H₆ production rate of 33.8 μmol g^-1 h^-1 with a selectivity of 88.4%. This work provides insights into nanocatalyst design toward efficient photocatalytic methane conversion into value-added compounds.

Sulfur-Resistant CeO2-Supported Pt Catalyst for Waste-to-Hydrogen: Effect of Catalyst Synthesis Method

To improve the sulfur tolerance of CeO2-supported Pt catalysts for water gas shift (WGS) using waste-derived synthesis gas, we investigated the effect of synthesis methods on the physicochemical properties of the catalysts. The Pt catalysts using CeO2 as a support were synthesized in various pathways (i.e., incipient wetness impregnation, sol-gel, hydrothermal, and co-precipitation methods). The prepared samples were then evaluated in the WGS reaction with 500 ppm H2S. Among the prepared catalysts, the Pt-based catalyst prepared by incipient wetness impregnation showed the highest catalytic activity and sulfur tolerance due to the standout factors such as a high oxygen-storage capacity and active metal dispersion. The active metal dispersion and oxygen-storage capacity of the catalyst showed a correlation with the catalytic performance and the sulfur tolerance.

Dry Reforming of Methane with Mesoporous Ni/ZrO2 Catalyst

Dry reforming of methane has exhibited significant environmental benefits as it utilizes two major greenhouse gases (CO2 and CH4) to produce synthesis gas, a major building block for hydrocarbons. This process has gained industrial attention as catalyst deactivation due to coke deposition being a major hindrance. The present study focuses on the dry reforming of methane over Ni-supported mesoporous zirconia support. Ni metal was loaded over in-house synthesized mesoporous zirconia within the 0–15 wt% range using the wet impregnation method. The physicochemical properties of the synthesized catalysts were studied using various characterization techniques, namely, XRD, SEM, FTIR, TGA, and N2 adsorption-desorption techniques. The activity of all the catalysts was evaluated at 750°C and gas hourly space velocity (GHSV) of 72000 ml/h/gcat for 9 hours (540 min). The deactivation factor indicating a loss in conversion with time is reported for each catalyst. 10 wt% Ni/ZrO2 showed the highest feed conversion of about 68.8% for methane and 70.2% for carbon dioxide and the highest stability (15.1% deactivation factor and 21% weight loss) for dry reforming of methane to synthesis gas.

Study of the Synthetic Approach Influence in Ni/CeO2-Based Catalysts for Methane Dry Reforming

This study focuses on the synthetic approach influence in morphostructural features and catalytic performances for Ni/CeO2 catalysts. Incipient wetness impregnation, coprecipitation and nitrate combustion were studied as catalyst preparation approaches, and the materials were then tested at 700 °C for methane dry reforming (MDR). The morphostructural properties of the materials were deeply studied using several techniques, such as temperature programmed reduction (TPR), to investigate reducibility and support-metal interaction, N2 physisorption to evaluate the porosity and the surface area, scanning electron microscopy (SEM) and X-ray diffraction (XRD) to estimate Ni dispersion, and temperature programmed oxidation (TPO) to identify the type and amount of coke formed on catalysts’ surface after reaction. From the data obtained, coprecipitation turned out to be the most suitable technique for this application because this catalyst was able to reach 70% of CO2 conversion and 30% methane conversion, with an H2 yield of 15% and 30% yield of CO at the end of the 30 h test. Moreover, it was also the catalyst with the highest metal dispersion, the strongest interaction with the support, and the lowest coke deposition.

Supercritical fluid-assisted modification combined with the resynthesis of SmCoO3 as an effective tool to enhance the long-term performance of SmCoO3-derived catalysts for the dry reforming of methane to syngas

The dry reforming of methane to syngas (DRM) is of increasing significance concerning, first, the production of raw materials for commercial organic/petrochemical syntheses and for hydrogen energetic, and, second, the utilization of two most harmful greenhouse gases. Herein, new SmCoO₃-based DRM catalysts derived from heterometallic precursors and operated without preliminary reduction are reported. For the first time, the effect of supercritical fluids-assisted modification of the SmCoO₃-derived catalysts combined with the re-oxidation of spent catalysts to SmCoO₃ onto its long-term performance was studied. In particular, the modification of heterometallic precursors by supercritical antisolvent precipitation (SAS) considerably decreases coke formation upon the exploitation of the derived SmCoO₃ sample. Moreover, the re-oxidation of the corresponding spent catalysts followed by pre-heating under N₂ affords catalysts that stably provide syngas yields of 88-95% for at least 41 h at 900 °C. The achieved yields are among the highest ones currently reported for DRM catalysts derived from both LnMO₃ perovskites and related oxides. The origins of such good performance are discussed. Given the simplicity and availability of all the applied methods and chemicals, this result opens prospects for exploiting SAS in the design of efficient DRM catalysts.

Influences of Ni Content on the Microstructural and Catalytic Properties of Perovskite LaNixCr1−xO3 for Dry Reforming of Methane

Perovskite oxides were widely used as precursors for developing metal-support type catalysts. It is attractive to explore the catalytic properties of the oxides themselves for dry reforming of methane (DRM). We synthesized LaNixCr1−xO3 (x = 0.05–0.5) samples in powder form using the sol-gel self-combustion method. Ni atoms are successfully doped into the LaCrO3 perovskite lattice. The perovskite grains are polycrystalline, and the crystallite size decreases with increasing Ni content. We demonstrated that the LaNixCr1−xO3 perovskites show intrinsically catalytic activity for DRM reactions. Reducing the Ni content is helpful to reduce carbon deposition resulting from the metal Ni nanoparticles that usually coexist with the highly active perovskite oxides. The CH4 conversion over the LaNi0.1Cr0.9O3 sample reaches approximately 84% at 750 °C, and the carbon deposition is negligible.

Sustainable routes for acetic acid production: Traditional processes vs a low-carbon, biogas-based strategy

The conversion of biogas, mainly formed of CO₂ and CH₄, into high-value platform chemicals is increasing attention in a context of low-carbon societies. In this new paradigm, acetic acid (AA) is deemed as an interesting product for the chemical industry. Herein we present a fresh overview of the current manufacturing approaches, compared to potential low-carbon alternatives. The use of biogas as primary feedstock to produce acetic acid is an auspicious alternative, representing a step-ahead on carbon-neutral industrial processes. Within the spirit of a circular economy, we propose and analyse a new BIO-strategy with two noteworthy pathways to potentially lower the environmental impact. The generation of syngas via dry reforming (DRM) combined with CO₂ utilisation offers a way to produce acetic acid in a two-step approach (BIO-Indirect route), replacing the conventional, petroleum-derived steam reforming process. The most recent advances on catalyst design and technology are discussed. On the other hand, the BIO-Direct route offers a ground-breaking, atom-efficient way to directly generate acetic acid from biogas. Nevertheless, due to thermodynamic restrictions, the use of plasma technology is needed to directly produce acetic acid. This very promising approach is still in an early stage. Particularly, progress in catalyst design is mandatory to enable low-carbon routes for acetic acid production.

Effect of La on the catalytic performance of mesoporous Ni/γ-Al2O3 catalysts for dry reforming of methane

Mesoporous Ni/La2O3/γ-Al2O3 catalysts with different La contents (0, 0.5, 1.5, 2.5, 3.5, and 4.5 wt.%) were prepared by the step-by-step impregnation method. The physicochemical properties of the prepared Ni/La2O3/γ-Al2O3 catalysts were characterized by H2-TPR, XRD, BET, O2-TPO, and TG. The effect of La dosage on the catalytic performance of Ni/γ-Al2O3 catalyst for dry reforming of methane was further investigated. The results show that the La content has a significant effect on the reducibility of high-valence Ni species, specific surface area, pore size, and pore volume as well as the catalytic performances. The high-valence Ni species in the NL3.5A catalyst precursor has high reducibility. And the specific surface area, pore size and pore volume of the NL3.5A catalyst are 145.9 m2 g−1, 11.7 nm, and 0.47 cm3 g−1, respectively. The catalytic activity of the series of prepared mesoporous Ni/La2O3/γ-Al2O3 catalysts follows the order: NL3.5A > NL2.5A > NL4.5A > NL1.5A > NL0.5A > NL0A. Namely, the NL3.5A catalyst possesses the best catalytic activity. The CH4 and CO2 conversions of NL3.5A catalyst are 61.6 and 39.1% at 600 °C, respectively. Additionally, it maintains a superior recycle capability for dry reforming of methane reaction because of the high coke resistance compared with the Ni/γ-Al2O3 catalyst.

Precise Modulation of Triple‐Phase Boundaries towards a Highly Functional Exsolved Catalyst for Dry Reforming of Methane under a Dilution‐Free System

Dry reforming of methane (DRM) has been emerging as a viable solution to achieving carbon neutrality enhanced by the Paris Agreement as it converts the greenhouse gases of CO₂ and CH₄ into industrially useful syngas. However, there have been limited studies on the DRM catalyst under mild operating conditions with a high dilution gas ratio due to their deactivation from carbon coking and metal sintering. Herein, we apply the triple‐phase boundary (TPB) concept to DRM catalyst via exsolution phenomenon that can secure elongated TPB by controlling the Fe‐doping ratio in perovskite oxide. Remarkably, the exsolved catalyst with prolongated TPB shows exceptional CO₂ and CH₄ conversion rates of 95.9 % and 91.6 %, respectively, stable for 1000 hours under a dilution‐free system. DFT calculations confirm that the Lewis acid of support and Lewis base of metal at the TPB promote the adsorption of reactants, resulting in lowering the overall CO₂ dissociation and CH₄ dehydrogenation energy.