Mechanistic Insights for Dry Reforming of Methane on Cu/Ni Bimetallic Catalysts: DFT-Assisted Microkinetic Analysis for Coke Resistance

Density functional theory (DFT) calculations have been utilized to evaluate the complete reaction mechanism of methane dry reforming (DRM) over Ni2Cu (111) bimetallic catalyst. The detailed catalytic cycle on Ni2Cu (111) catalyst demonstrated superior coke resistance compared to pure Ni (111) and Ni2Fe (111) reported in the literature. Doping Cu in the Ni–Ni network enhanced the competitive CH oxidation by both atomic O and OH species with the latter having only 0.02 eV higher than the 1.06 eV energy barrier required for CH oxidation by atomic O. Among the C/CH oxidation pathways, C* + O* → CO (g) was the most favorable with an energy barrier of 0.72 eV. This was almost half of the energy barrier required for the rate-limiting step of CH decomposition (1.40 eV) and indicated enhanced coke deposition removal. Finally, we investigated the effect of temperature (800~1000 K) on the carbon deposition and elimination mechanism over Ni2Cu (111) catalyst. Under those realistic DRM conditions, the calculations showed a periodic cycle of simultaneous carbon deposition and elimination resulting in improved catalyst stability.

Dry reforming of methane over nickel supported on Nd-ceria: enhancement of the catalytic properties and coke resistance

Nickel (5 wt%) supported on Nd-doped ceria was studied as catalysts in the DRM reaction at stoichiometric conditions in the range of 600–800 °C. Ce_1−xNd_xO_2−δ supports with different Nd contents (x = 0, 0.05, 0.1 and 0.2) were successfully synthesized. The role of oxygen vacancies by the incorporation of Nd³⁺ into the ceria lattice was investigated. These species were quantified by XRD and Raman spectroscopy, showing a linear dependence as a function of Nd content. Ni/Nd–ceria catalysts were prepared by wet impregnation. Although formation of oxygen vacancies, as well as microstructural features of the support (smaller crystallite sizes, higher surface area, and developed mesoporous structure) were improved as a function of the Nd content, no significant differences were observed in the catalytic properties of Ni/Nd–ceria in the DRM reaction. Despite this, compared to undoped ceria, all the Nd-doped CeO₂ catalysts present an enhanced activity and stability, and the best catalytic performance was observed in the Ni/Ce_0.95Nd_0.05O_2−δ sample. Quantification of carbon residues in spent catalysts showed, as expected, lower amounts in the Ni/Nd–ceria samples; nevertheless, among them, the catalyst with the higher amount of oxygen vacancies, is the one with the higher carbon residues. Incorporation of Nd in ceria changes the acid/base properties, diminishing the gasification capacity of the carbonaceous species. These results emphasize that the activity and stability in the Ni/Nd–ceria catalysts for the DRM reaction depend on two key factors, the redox and the acid/base properties of the CeO₂ supports, offering insights about the necessary and adequate balance between these properties.

The Nd-doped CeO₂ support enhances the reactivity of the catalysts, selectivity toward hydrogen and stability by improving coke deposition resistance.

In situ X-ray emission and high-resolution X-ray absorption spectroscopy applied to Ni-based bimetallic dry methane reforming catalysts

The promoting effect of cobalt on the catalytic activity of a NiCoO Dry Methane Reforming (DMR) catalyst was studied by a combination of in situ Kβ X-ray Emission Spectroscopy (XES) and Kβ-detected High Energy Resolution Fluorescence Detected X-ray absorption spectroscopy (HERFD XAS). Following the calcination process, Ni XES and Kβ-detected HERFD XAS data revealed that the NiO coordination in the NiCoO catalyst has a higher degree of symmetry and is different than that of pure NiO/γ-Al₂O₃. Following the reductive activation, it was found that the NiCoO/γ-Al₂O₃ catalyst required a relatively higher temperature compared to the monometallic NiO/γ-Al₂O₃ catalyst. This finding suggests that Co is hampering the reduction of Ni in the NiCoO catalyst by modulation of its electronic structure. It has also been previously shown that the addition of Co enhances the DMR activity. Further, the Kβ XES spectrum of the partly reduced catalysts at 450 °C reveals that the Ni sites in the NiCoO catalyst are electronically different from the NiO catalyst. The in situ X-ray spectroscopic study demonstrates that reduced metallic Co and Ni are the primary species present after reduction and are preserved under DMR conditions. However, the NiCo catalyst appears to always be somewhat more oxidized than the Ni-only species, suggesting that the presence of cobalt modulates the Ni electronic structure. The electronic structural modulations resulting from the presence of Co may be the key to the increased activity of the NiCo catalyst relative to the Ni-only catalyst. This study emphasizes the potential of in situ X-ray spectroscopy experiments for probing the electronic structure of catalytic materials during activation and under operating conditions.

Promising Utilization of CO2 for Syngas Production over Mg2+- and Ce2+-Promoted Ni/γ-Al2O3 Assisted by Nonthermal Plasma

Dry reforming of methane is conducted in a catalyst packed-bed dielectric barrier discharge (DBD) reactor aiming to improve the reaction efficiency. The MgO- and CeO₂-promoted Ni/γ-Al₂O₃ catalyst is tested to carry out the reaction. An interesting observation is that Ni/MgO_Al₂O₃ integration provides ∼35 and 13% conversion of CH₄ and CO₂, respectively. The highest syngas ratio of 0.94 is obtained with Ni/MgO_Al₂O₃, whereas the ratio is only 0.57 with Ni/CeO₂_Al₂O₃ and 0.64 with bare DBD. In addition, Ni/CeO₂_Al₂O₃ offers the highest selectivity (68%) of CO due to the oxygen buffer property of CeO₂. Finally, the optimal acid/base property is highly desirable for the dry reforming reaction.

Highly Active and Carbon-Resistant Nickel Single-Atom Catalysts for Methane Dry Reforming

The conversion of CH4 and CO2 to syngas using low-cost nickel catalysts has attracted considerable interest in the clean energy and environment field. Nickel nanoparticles catalysts suffer from serious deactivation due mainly to carbon deposition. Here, we report a facile synthesis of Ni single-atom and nanoparticle catalysts dispersed on hydroxyapatite (HAP) support using the strong electrostatic adsorption (SEA) method. Ni single-atom catalysts exhibit excellent resistance to carbon deposition and high atom efficiency with the highest reaction rate of 1186.2 and 816.5 mol.gNi−1.h−1 for CO2 and CH4, respectively. Although Ni single-atom catalysts aggregate quickly to large particles, the polyvinylpyrrolidone (PVP)-assisted synthesis exhibited a significant improvement of Ni single-atom stability. Characterizations of spent catalysts revealed that carbon deposition is more favorable over nickel nanoparticles. Interestingly, it was found that, separately, CH4 decomposition on nickel nanoparticle catalysts and subsequent gasification of deposit carbon with CO2 resulted in CO generation, which indicates that carbon is reacting as an intermediate species during reaction. Accordingly, the approach used in this work for the design and control of Ni single-atom and nanoparticles-based catalysts, for dry reforming of methane (DRM), paves the way towards the development of stable noble metals-free catalysts.

Response to Comment on "Dry reforming of methane by stable Ni-Mo nanocatalysts on single-crystalline MgO"

Hu and Ruckenstein state that our findings were overclaimed and not new, despite our presentation of evidence for the Nanocatalysts on Single Crystal Edges (NOSCE) mechanism. Their arguments do not take into account fundamental differences between our Ni-Mo/MgO catalyst and their NiO/MgO preparations.

Dry Reforming of Methane (DRM) by Highly Active and Stable Ni Nanoparticles on Renewable Porous Carbons

In this study, Ni nanoparticles supported on renewable porous carbon were prepared using hydrochar as a carbon precursor via in situ formation and self-reduction. The structure properties of the prepared nanocatalysts were characterized by multiple techniques, including XRD, SEM, and HR-TEM, and the dry reforming of methane (DRM) performance of the nanocatalysts in terms of conversion efficiency and reactivity stability was evaluated. The results revealed that the Ni2+ was uniformly anchored on the surface of the hydrochar, and subsequently the Ni nanoparticles were well dispersed in the composite with a diameter of less than 8 nm and had a narrow particle size distribution at a temperature lower than 800 °C. With an increased temperature from 800 to 900 °C, the significant sintering and agglomeration of nickel particles and the transformation from amorphous carbon to graphitic structure were observed in the composite. The nanocatalysts prepared at a temperature of 700 °C (Ni@C-700) and 800 °C (Ni@C-800) exhibited a high reforming conversion rate and catalytic stability of CH4 by CO2 (around 52% for Ni@C-700 and 70% for Ni@C-800 after 800 min of run-time, respectively). As for the composite obtained at 900 (Ni@C-900), the highly graphitic degree was coupled with the significantly increased nickel particle size, and this resulted in a remarkably decreased conversion efficiency. The present study offers a valuable application of the hydrochar and a facile and green approach to prepare highly active and cost-efficient Ni nanoparticles on porous carbons towards the dry reforming of methane.

Nickel-Based Structured Catalysts for Indirect Internal Reforming of Methane

A structured catalyst for the dry reforming of methane (DRM) was investigated as a biogas pre-reformer for indirect internal reforming solid oxide fuel cell (IIR-SOFC). For this purpose, a NiCrAl open-cell foam was chosen as support and Ni-based samarium doped ceria (Ni-SmDC) as catalyst. Ni-SmDC powder is a highly performing catalyst showing a remarkable carbon resistance due to the presence of oxygen vacancies that promote coke gasification by CO2 activation. Ni-SmDC powder was deposited on the metallic support by wash-coating method. The metallic foam, the powder, and the structured catalyst were characterized by several techniques such as: N2 adsorption-desorption technique, X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), focused ion beam (FIB), temperature programmed reduction (H2-TPR), and Raman spectroscopy. Catalytic tests were performed on structured catalysts to evaluate activity, selectivity, and stability at SOFC operating conditions.

Formation of silica-supported platinum nanoparticles as a function of preparation conditions and boron impregnation

Preparation of supported metal nanoparticles for catalytic applications often relies on an assumption that the initially prepared wet-impregnated support material is covered with approximately a monolayer of adsorbed species that are shaped into the target nanoparticulate material with a desired size distribution by utilizing appropriate post-treatments that often include calcination and reduction schemes. Here, the formation and evolution of surface nanoparticles were investigated for wet-chemistry deposition of platinum from trimethyl(methylcyclopentadienyl)platinum (IV) precursor onto flat silica supports to interrogate the factors influencing the initial stages of nanoparticle formation. The deposition was performed on silicon-based substrates, including hydroxylated silica (SiO₂) and boron-impregnated hydroxylated silica (B/SiO₂) surfaces. The deposition resulted in the immediate formation of Pt-containing nanoparticles, as confirmed by atomic force microscopy and x-ray photoelectron spectroscopy. The prepared substrates were later reduced at 550 °C under H₂ gas environment. This reduction procedure resulted in the formation of metallic Pt particles. The reactivity of the precursor and dispersion of Pt nanoparticles on the OH-terminated silica surface were compared to those on the B-impregnated surface. The size distribution of the resulting nanoparticles as a function of surface preparation was evaluated, and density functional theory calculations were used to explain the differences between the two types of surfaces investigated.

Dry Reforming of Methane Using Ce-modified Ni Supported on 8%PO4 + ZrO2 Catalysts

Dry reforming of methane (DRM) was studied in the light of Ni supported on 8%PO4 + ZrO2 catalysts. Cerium was used to modify the Ni active metal. Different percentage loadings of Ce (1%, 1.5%, 2%, 2.5%, 3%, and 5%) were tested. The wet incipient impregnation method was used for the preparation of all catalysts. The catalysts were activated at 700 °C for ½ h. The reactions were performed at 800 °C using a gas hourly space velocity of 28,000 mL (h·gcat)−1. X-ray diffraction (XRD), N2 physisorption, hydrogen temperature programmed reduction (H2-TPR), temperature programmed oxidation (TPO), temperature programmed desorption (TPD), and thermogravimetric analysis (TGA) were used for characterizing the catalysts. The TGA analysis depicted minor amounts of carbon deposition. The CO2-TPD results showed that Ce enhanced the basicity of the catalysts. The 3% Ce loading possessed the highest surface area, the largest pore volume, and the greatest pore diameter. All the promoted catalysts enhanced the conversions of CH4 and CO2. Among the promoted catalysts tested, the 10Ni + 3%Ce/8%PO4 + ZrO2 catalyst system operated at 1 bar and at 800 °C gave the highest conversions of CH4 (95%) and CO2 (96%). The stability profile of Cerium-modified catalysts (10%Ni/8%PO4 + ZrO2) depicted steady CH4 and CO2 conversions during the 7.5 h time on stream.

Kinetic study of the methane dry (CO2) reforming reaction over the Ce0.70La0.20Ni0.10O2−δ catalyst

The kinetic behaviour of the Ce_0.70La_0.20Ni_0.10O_2−δ catalyst during the methane dry reforming reaction was investigated in a fixed bed reactor in the temperature range of 923–1023 K with the partial pressure of CH₄ and CO₂ ranging between 5 and 50 kPa.

Impact of small promoter amounts on coke structure in dry reforming of methane over Ni/ZrO2

Choosing the correct alkali metal as a promoter not only reduces coke formation in dry reforming of methane but also removes coke via gasification.

Relationship Between the Pore Structure of Mesoporous Silica Supports and the Activity of Nickel Nanocatalysts in the CO2 Reforming of Methane

The question remains over the role of the pore structure of the support material on the catalytic behaviour of Ni catalysts during the CO2/dry reforming of methane (DRM). For this reason, a series of mesoporous materials with different pore structures, namely MCM-41, KIT-6, tri-modal porous silica (TMS), SBA-15 and mesostructured cellular foams (MCFs) were synthesised via hydrothermal synthesis methods and further impregnated with 15 wt.% NiO (11.8 wt.% Ni). It was observed that synthesised TMS is a promising catalyst support for DRM as Ni/TMS gave the highest activity and stability among these materials as well as the Ni catalysts supported on classic ordered mesoporous silicates support reported in the literature at the relatively low temperature (700 °C). On the other hand, Ni supported on CMC-41 exhibited the lowest activity among them. To understand the reason for this difference, the physicochemical properties of these materials were characterised in detail. The results show that the thickness of the silica wall and the pore size of the support material play a critical role in the catalytic activity of Ni catalysts in the CO2 reforming of methane.

Design and Performance Comparison of Methanol Production Processes with Carbon Dioxide Utilization

Carbon dioxide recycling is one of the possible contributions to CO2 mitigation and provides an opportunity to use a low-cost carbon source. Methanol is a commodity chemical that serves as an important basic chemical and energy feedstock with growing demand. For each of the four types of industrial methanol production processes from natural gas (methane), i.e., steam reforming (SR), autothermal reforming (ATR), combined reforming (CR), and two-step reforming (TSR), CO2 utilization cases of (A) no utilization, (B) as reforming step feedstock, and (C) as methanol synthesis step feedstock were designed based on common industrial operation conditions and analyzed for energy consumption, exergy loss (EXloss), net CO2 reduction (NCR) and internal rate of return (IRR). The utilization of CO2 can reduce energy consumption. The processes with the lowest and the highest EXloss are SR and ATR, respectively. All SR processes give negative NCR. All the B-type processes are positive in NCR except B-SR. The highest NCR is obtained from the B-ATR process with a value of 0.23 kg CO2/kg methanol. All the processes are profitable with positive IRR results and the highest IRR of 41% can be obtained from B-ATR. The utilization of CO2 in the industrial methanol process can realize substantial carbon reduction and is beneficial to process economics.

The Effect of CeO2 Preparation Method on the Carbon Pathways in the Dry Reforming of Methane on Ni/CeO2 Studied by Transient Techniques

The present work discusses the effect of CeO2 synthesis method (thermal decomposition (TD), precipitation (PT), hydrothermal (HT), and sol-gel (SG)) on the carbon pathways of dry reforming of methane with carbon dioxide (DRM) applied at 750 °C over 5 wt% Ni/CeO2. In particular, specific transient and isotopic experiments (use of 13CO, 13CO2, and 18O2) were designed and conducted in an attempt at providing insights about the effect of support’s preparation method on the concentration (mg gcat−1), reactivity towards oxygen, and transient evolution rates (μmol gcat−1 s−1) of the inactive carbon formed under (i) CH4/He (methane decomposition), (ii) CO/He (reverse Boudouard reaction), and (iii) the copresence of the two (CH4/CO/He, use of 13CO). Moreover, important information regarding the relative contribution of CH4 and CO2 activation routes towards carbon formation under DRM reaction conditions was derived by using isotopically labelled 13CO2 in the feed gas stream. Of interest was also the amount, and the transient rate, of carbon removal via the participation of support’s labile active oxygen species.

Catalytic Activity of Nickel and Ruthenium–Nickel Catalysts Supported on SiO2, ZrO2, Al2O3, and MgAl2O4 in a Dry Reforming Process

Dry reforming of methane (DRM) is an eco-friendly method of syngas production due to the utilization of two main greenhouse gases—methane and carbon dioxide. An industrial application of methane dry reforming requires the use of a catalyst with high activity, stability over a long time, and the ability to catalyze a reaction, leading to the needed a hydrogen/carbon monoxide ratio. Thus, the aim of the study was to investigate the effect of support and noble metal particles on catalytic activity, stability, and selectivity in the dry reforming process. Ni and Ni–Ru based catalysts were prepared via impregnation and precipitation methods on SiO2, ZrO2, Al2O3, and MgAl2O4 supports. The obtained catalysts were characterized using X-ray diffractometry (XRD), inductively coupled plasma optical emission spectrometry (ICP-OES), Brunauer–Emmett–Teller (BET) specific surface area, and elemental carbon-hydrogen-nitrogen-sulphur analysis (CHNS) techniques. The catalytic activity was investigated in the carbon dioxide reforming of a methane process at 800 °C. Catalysts supported on commercial Al2O3 and spinel MgAl2O4 exhibited the highest activity and stability under DRM conditions. The obtained results clearly indicate that differences in catalytic activity result from the dispersion, size of an active metal (AM), and interactions of the AM with the support. It was also found that the addition of ruthenium particles enhanced the methane conversion and shifted the H2/CO ratio to lower values.

Dry Reforming of Methane over NiLa-Based Catalysts: Influence of Synthesis Method and Ba Addition on Catalytic Properties and Stability

CO2 reforming of CH4 to produce CO and H2 is a traditional challenge in catalysis. This area is still very active because of the potentials offered by the combined utilization of two green-house gases. The development of active, stable, and economical catalysts remains a key factor for the exploitation of natural gas (NG) with captured CO2 and biogas to produce chemicals or fuels via syngas. The major issue associated with the dry reforming process is catalyst deactivation by carbon deposition. The development of suitable catalyst formulations is one strategy for the mitigation of coking which becomes especially demanding when noble metal-free catalysts are targeted. In this work NiLa-based catalyst obtained from perovskite precursors La1−xBaxNiO3 (x = 0.0; 0.05; 0.1 and 0.2) and NiO/La2O3 were synthesized, characterized by in situ and operando XRD and tested in the dry reforming of methane. The characterization results showed that the addition of barium promoted BaCO3 segregation and changes in the catalyst structure. This partly affected the activity; however, the incorporation of Ba improved the catalyst resistance to deactivation process. The Ba-containing and Ba-free NiLa-based catalysts performed significantly better than NiO/La2O3 catalysts obtained by wet impregnation.

Valorization of Char From Biomass Gasification as Catalyst Support in Dry Reforming of Methane

This study responds to the need of finding innovative routes for valorizing char derived from biomass gasification. Char is currently treated as a waste representing an energetic and economic loss for plant owners. However, it displays many similarities to activated carbon (AC) and could replace it in several applications. In this regard, the current work investigates the use of gasification derived char as catalyst support in dry reforming of methane (DRM) reactions. Char collected from a commercial biomass gasifier currently in operation was characterized and employed for the synthesis of cobalt catalysts. The catalysts were characterized and tested in an atmospheric pressure fixed bed reactor operating at 850°C with CH₄:CO₂ = 1 and a weight hourly space velocity of 6,500 mL g⁻¹ h⁻¹. The effectiveness of the synthesized catalysts was defined based on CO₂ and CH₄ conversions, the corresponding H₂ and CO yields and their stability. Accordingly, catalysts were synthesized with cobalt loading of 10, 15 and 20 wt.% on untreated and HNO₃ treated char, and the catalyst with optimum comparative performance was promoted with 2 wt.%MgO. Catalysts prepared using untreated char showed low average conversions of 23 and 17% for CO₂ and CH₄, yields of 1 and 14% for H₂ and CO, and deactivated after few minutes of operation. Higher metal loadings corresponded to lower conversion and yields. Although HNO₃ treatment slightly increased conversions and yields and enhanced the stability of the catalyst, the catalyst deactivated again after few minutes. On the contrary, MgO addition boosted the catalyst performances leading to conversions (95 and 94% for CO₂ and CH₄) and yields (44 and 53% for H₂ and CO) similar to what obtained using conventional supports such as Al₂O₃. Moreover, MgO catalysts proved to be very stable during the whole duration of the test.

Chemistry in supercritical fluids for the synthesis of metal nanomaterials

The supercritical flow synthesis of metal nanomaterials is sustainable and scalable for the efficient production of materials.

Advantages of Yolk Shell Catalysts for the DRM: A Comparison of Ni/ZnO@SiO2 vs. Ni/CeO2 and Ni/Al2O3

Encapsulation of metal nanoparticles is a leading technique used to inhibit the main deactivation mechanisms in dry reforming of methane reaction (DRM): Carbon formation and Sintering. Ni catalysts (15%) supported on alumina (Al2O3) and ceria (CeO2) have shown they are no exception to this analysis. The alumina supported catalysts experienced graphitic carbonaceous deposits, whilst the ceria showed considerable sintering over 15 h of DRM reaction. The effect of encapsulation compared to that of the performance of uncoated catalysts for DRM reaction has been examined at different temperatures, before conducting longer stability tests. The encapsulation of Ni/ZnO cores in silica (SiO2) leads to advantageous conversion of both CO2 and CH4 at high temperatures compared to its uncoated alternatives. This work showcases the significance of the encapsulation process and its overall effects on the catalytic performance in chemical CO2 recycling via DRM.

Introduction: hydrogen storage as solution for a changing energy landscape

The expansion of sustainable technologies and infrastructures for the production and delivery of energy to the final consumer and the development of new technologies for energy production, storage and distribution, are challenging and inevitable tasks. Power plants based on the combustion of fossil fuel resources or nuclear power plants are not suitable to provide energy in the future due to significant disadvantages and dangers associated with these outdated technologies. The development of new sustainable technologies for the production of energy is desirable. Besides focusing on the production step, the change in global energy landscape requires also new and improved energy storage systems. Requirements for these storage solutions will strongly depend on the application. Storing energy by producing and consuming hydrogen is in this context a very attractive approach. It may be suitable for storage of energy for transportation and also for the bulk energy storage. Due to physical restrictions of high pressure hydrogen storage, alternative techniques are developed. This is, in turn, an ongoing task with multidisciplinary aspects, which combines chemistry, physics, material science and engineering. Herein, we review the production and consumption of energy, different energy storage applications, and we introduce the concept of hydrogen storage based on hydrogenation and dehydrogenation reactions of small molecules.

Oxidative Steam Reforming of Raw Bio-Oil over Supported and Bulk Ni Catalysts for Hydrogen Production

Several Ni catalysts of supported (on La2O3-αAl2O3, CeO2, and CeO2-ZrO2) or bulk types (Ni-La perovskites and NiAl2O4 spinel) have been tested in the oxidative steam reforming (OSR) of raw bio-oil, and special attention has been paid to the catalysts’ regenerability by means of studies on reaction-regeneration cycles. The experimental set-up consists of two units in series, for the separation of pyrolytic lignin in the first step (at 500 °C) and the on line OSR of the remaining oxygenates in a fluidized bed reactor at 700 °C. The spent catalysts have been characterized by N2 adsorption-desorption, X-ray diffraction and temperature programmed reduction, and temperature programmed oxidation (TPO). The results reveal that among the supported catalysts, the best balance between activity-H2 selectivity-stability corresponds to Ni/La2O3-αAl2O3, due to its smaller Ni0 particle size. Additionally, it is more selective to H2 than perovskite catalysts and more stable than both perovskites and the spinel catalyst. However, the activity of the bulk NiAl2O4 spinel catalyst can be completely recovered after regeneration by coke combustion at 850 °C because the spinel structure is completely recovered, which facilitates the dispersion of Ni in the reduction step prior to reaction. Consequently, this catalyst is suitable for the OSR at a higher scale in reaction-regeneration cycles.

Measuring the Unmeasurable by IR Spectroscopy: Carbon Deposition Kinetics in Dry Reforming of Methane

Dry reforming of methane converts two greenhouse gases to syngas, and Ni catalysts are commonly used for this reaction. A major catalyst deactivation mechanism is carbon deposition. Although numerous kinetic modelling works have been performed on carbon formation, there have been only scarce attempts to measure carbon deposition kinetics under relevant (but not real) conditions, owing to technical difficulties. Here, we report the first successful measurements of the kinetics under real reaction conditions. This was made possible by using a novel algorithm that we have developed. We use IR to measure the molar fractions of unreacted CH4 and CO2 , and reaction products, CO and H2 O, in the effluent from the reactor. By applying the general mass balance principle and the relevant reaction stoichiometries, the carbon deposition rate as well as the flow rates of all these gases in the effluent, including H2 , are calculated. Compared to the dominant GC-based approach for catalyst performance evaluation, this method has much higher time resolution and much smaller measurement errors.

Understanding the performance and mechanism of Mg-containing oxides as support catalysts in the thermal dry reforming of methane

Dry reforming of methane (DRM) is one of the more promising methods for syngas (synthetic gas) production and co-utilization of methane and carbon dioxide, which are the main greenhouse gases. Magnesium is commonly applied in a Ni-based catalyst in DRM to improve catalyst performance and inhibit carbon deposition. The aim of this review is to gain better insight into recent developments on the use of Mg as a support or promoter for DRM catalysts. Its high basicity and high thermal stability make Mg suitable for introduction into the highly endothermic reaction of DRM. The introduction of Mg as a support or promoter for Ni-based catalysts allows for good metal dispersion on the catalyst surface, which consequently facilitates high catalytic activity and low catalyst deactivation. The mechanism of DRM and carbon formation and reduction are reviewed. This work further explores how different constraints, such as the synthesis method, metal loading, pretreatment, and operating conditions, influence the dry reforming reactions and product yields. In this review, different strategies for enhancing catalytic activity and the effect of metal dispersion on Mg-containing oxide catalysts are highlighted.

The Enhanced Catalytic Performance and Stability of Rh/γ-Al₂O₃ Catalyst Synthesized by Atomic Layer Deposition (ALD) for Methane Dry Reforming

Rh/γ-Al₂O₃ catalysts were synthesized by both incipient wetness impregnation (IWI) and atomic layer deposition (ALD). The TEM images of the two catalysts showed that the catalyst from ALD had smaller particle size, and narrower size distribution. The surface chemical states of both catalysts were investigated by both XPS and X-ray Absorption Near Edge Structure (XANES), and the catalyst from IWI had higher concentration of Rh³⁺ than that from ALD. The catalytic performance of both catalysts was tested in the dry reforming of methane reaction. The catalyst from ALD showed a higher conversion and selectivity than that from IWI. The stability testing results indicated that the catalyst from ALD showed similar stability to that from IWI at 500 °C, but higher stability at 800 °C.