Carbon dioxide reforming of methane with supported rhodium

Integrated CO2 Capture and Utilization by Combining Calcium Looping with CH4 Reforming Processes: A Thermodynamic and Exergetic Approach

This study investigates a novel concept to coproduce high-purity H2 and syngas, which couples steam methane reforming with CaO carbonation to capture the generated CO2 and dry reforming of methane with CaCO3 calcination to directly utilize the captured CO2. The thermodynamic equilibrium of the reactive calcination stage was evaluated using Aspen Plus via a parametric analysis of various operating conditions, including the temperature, pressure, and CH4/CaCO3 molar ratio. Introducing a CH4 feed in the calcination stage promoted the driving force and completion of CaCO3 decomposition at lower temperatures (∼700 °C) compared to applying an inert flow, as a result of in situ CO2 conversion. A conceptual process design was investigated that employs a system of two moving bed reactors to produce nearly equivalent volumetric flows of pure H2 and a syngas stream with a H2/CO molar ratio close to 1. A solar reactor was examined for the reactive calcination step to cover the energy requirements of endothermic CaCO3 decomposition and dry reforming. The overall exergy efficiency of the process was found equal to ∼75.9%, a value ∼4.0 and ∼8.0% higher compared to sorption-enhanced reforming with oxy-fuel and solar calciner, respectively, without direct utilization of the captured CO2.

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.

Simulation of Biogas Conversion Using Porous Solid Oxide Electrochemical Cells: Virtual Prototyping

The computer-aided engineering approach has made it possible to achieve virtual prototypes and to describe expected performances of new apparatuses. In this study, a direct production of syngas with biogas using the configuration of the cascade conversion cell in the supply feed direction of the system was exhibited. Momentum, heat, mass and charge balances were solved using COMSOL Multiphysics® commercial software. These simulations allowed calculation of distributions of partial pressures for all gas species within the anode (CH4, H2, CO, CO2, H2O, N2), as well as velocity field and temperature. The conversion process included methane reforming (steam and dry) associated with the water–gas shift reaction. The computing results showed that the configuration of three porous oxide solid cells based on a solid oxide fuel cell (SOFC) system conferred a larger active surface area and limited thermal stress in oxide materials. In addition, depending on the production process of the biogas, feeding composition strongly influences the conversion rate of CO2 and CH4. We observed that production of syngas was optimal for a CO2/CH4 ratio = 1.

Variation of the Number of Heat Sources in Methane Dry Reforming: A Computational Fluid Dynamics Study

To overcome the weak point of the gas type heating (failure in heating uniformly and persistently), liquid type molten salt as a concentration of solar energy was considered as a heat source for dry reforming. This high-temperature molten salt flowing through the center of the tubular reactor supplies necessary heat. The dependence on the number of heat source of the hydrogen production was investigated under the assumption of the fixed volume of the catalyst bed. By changing these numbers, we numerically investigated the methane conversion and hydrogen flow rate to find the best performance. The results showed that the methane conversion performance and hydrogen flow rate improved in proportion to the number of heating tubes. For the one heat source, the reactor surrounded by a heat source rather than that located in the center is the best in terms of hydrogen yield. In addition, this study considered the case in which the system is divided into several smaller reactors of equal sizes and a constant amount of catalyst. In these reactors, we saw that the methane conversion and hydrogen flow rate were reduced. The results indicate that the installation of as many heating tubes as possible is preferable.

State-of-the-art in methane-reforming reactor modeling: challenges and new insights

The reforming of methane is an important industrial process, and reactor modeling and simulation is frequently employed as a design and analysis tool in understanding this process. While much research work is devoted to catalyst formulations, reaction mechanisms, and reactor designs, this review aims to summarize the literature concerning the simulation of methane reforming. Applications in industrial practice are highlighted, and the three main approaches to representing the reactions are briefly discussed. An overview of simulation studies focusing on methane reforming is presented. The three central methods for fixed-bed reactor modeling are discussed. Various approaches and modern examples are discussed, presenting their modeling methods and key findings. The overall objective of this paper is to provide a dedicated review of simulation work done for methane reforming and provide a reference for understanding this field and identifying possible new paths.

C-H bond activation in light alkanes: a theoretical perspective

Alkanes are the major constituents of natural gas and crude oil, the feedstocks for the chemical industry. The efficient and selective activation of C-H bonds can convert abundant and low-cost hydrocarbon feedstocks into value-added products. Due to the increasing global demand for light alkenes and their corresponding polymers as well as synthesis gas and hydrogen production, C-H bond activation of light alkanes has attracted widespread attention. A theoretical understanding of C-H bond activation in light hydrocarbons via density functional theory (DFT) and microkinetic modeling provides a feasible approach to gain insight into the process and guidelines for designing more efficient catalysts to promote light alkane transformation. This review describes the recent progress in computational catalysis that has addressed the C-H bond activation of light alkanes. We start with direct and oxidative C-H bond activation of methane, with emphasis placed on kinetic and mechanistic insights obtained from DFT assisted microkinetic analysis into steam and dry reforming, and the partial oxidation dependence on metal/oxide surfaces and nanoparticle size. Direct and oxidative activation of the C-H bond of ethane and propane on various metal and oxide surfaces are subsequently reviewed, including the elucidation of active sites, intriguing mechanisms, microkinetic modeling, and electronic features of the ethane and propane conversion processes with a focus on suppressing the side reaction and coke formation. The main target of this review is to give fundamental insight into C-H bond activation of light alkanes, which can provide useful guidance for the optimization of catalysts in future research.

Upgrading of Bio-Syngas via Steam-CO2 Reforming Using Rh/Alumina Monolith Catalysts

Steam-CO2 reforming of biomass derived synthesis gas (bio-syngas) was investigated with regard to the steam concentration in the feed using Rh-loaded alumina foam monolith catalysts, which was also accompanied by thermodynamic equilibrium calculation. With 40 vol % steam addition, steam methane reforming and water gas shift reaction were prevailed at the temperature below 640 °C, above which methane dry reforming and reverse-water gas shift reaction were intensified. Substantial change of activation energy based on the methane conversion was observed at 640 °C, where the reaction seemed to be shifted from the kinetic controlled region to the mass transfer controlled region. At the reduced steam of 20 vol %, the increase in the gas velocity led to the increase in the contribution of steam reforming. Comparing to the absence of steam, the addition of steam (40 vol %) resulted in the increase in the production of H2 and CO2, which in turn increased the H2/CO ratio by 95% and decreased the CO/CO2 ratio by 60%. Rh-loaded alumina monolith was revealed to have a good stability in upgrading of the raw bio-syngas.

Catalytic Reaction of Carbon Dioxide with Methane on Supported Noble Metal Catalysts

The conversion of CO2 and CH4, the main components of the greenhouse gases, into synthesis gas are in the focus of academic and industrial research. In this review, the activity and stability of different supported noble metal catalysts were compared in the CO2 + CH4 reaction on. It was found that the efficiency of the catalysts depends not only on the metal and on the support but on the particle size, the metal support interface, the carbon deposition and the reactivity of carbon also influences the activity and stability of the catalysts. The possibility of the activation and dissociation of CO2 and CH4 on clean and on supported noble metals were discussed separately. CO2 could dissociate on metal surfaces, this reaction could proceed via the formation of carbonate on the support, or on the metal–support interface but in the reaction the hydrogen assisted dissociation of CO2 was also suggested. The decrease in the activity of the catalysts was generally attributed to carbon deposition, which can be formed from CH4 while others suggest that the source of the surface carbon is CO2. Carbon can occur in different forms on the surface, which can be transformed into each other depending on the temperature and the time elapsed since their formation. Basically, two reaction mechanisms was proposed, according to the mono-functional mechanism the activation of both CO2 and CH4 occurs on the metal sites, but in the bi-functional mechanism the CO2 is activated on the support or on the metal–support interface and the CH4 on the metal.

Fabrication of Ni-Based Bimodal Porous Catalyst for Dry Reforming of Methane

Dry reforming of methane (DRM) can effectively convert two greenhouse gases into high-valued chemicals, in which the syngas produced by the reaction can be directly used as raw gases for Fischer–Tropsch synthesis and methanol synthesis. Ni-based catalysts for the DRM reaction with comparable initial activity to noble metals are the focus of most researchers, but their poor carbon deposition resistance easily causes their low stability. More importantly, the nickel loading will affect the catalytic activity and carbon deposition resistance of the catalyst. Herein, a series of Ni/Al2O3 catalysts with bimodal pores was prepared and characterized by X-ray diffraction (XRD), N2 physical adsorption–desorption, H2-temperature programmed reduction (H2-TPR), temperature programmed hydrogenation (TPH), Raman, and thermogravimetric analysis (TG). The results show that the interesting bimodal structure catalysts could provide a high surface area and contribute to the mass transfer. Besides, the catalytic performance of the DRM reaction is sensitive to nickel loadings. In this study, the Ni/Al2O3 catalyst with nickel loadings of 6% and 8% exhibited excellent catalytic activity and carbon deposition resistance. These findings will provide a new strategy to design a highly efficient and stable heterogeneous catalyst for industry.

Dry reforming activity due to ionic Ru in La1.99Ru0.01O3: the role of specific carbonates

Dry reforming of methane was carried out over La_2-2xRu_2xO₃ (x = 0.005, 0.01). Substitution of just 0.5 atom% of Ru in La₂O₃ enhanced the activity by 20 times in terms of conversion when compared to the activity exhibited by La₂O₃. The oxygen storage capacity of the Ru doped sample was considerably higher than undoped La₂O₃, which resulted in higher conversions of CH₄ and CO₂. The measured conversion of CH₄ and CO₂ was 72 and 80%, respectively, at 850 °C. The same was merely 4% with La₂O₃ under the same experimental conditions. DRIFTS studies demonstrated the role of a specific type of carbonates in promoting the activity of the catalyst. DFT calculations provided the rationale behind the selection of the Ru-in-La₂O₃ methane dry reforming catalyst. The surface structures of the pure and Ru-substituted compounds were determined, corroborating the experimental observation of enhanced oxygen storage capacity on Ru substitution. Different active surface oxygen species were identified and their roles in improving reducibilities and improving reactivities were established. The experimentally observed surface carbonate species were also identified using calculations. The combined experiment + calculation approach proved ionic Ru in La_2-2xRu_2xO₃ to be a novel and efficient dry reforming catalyst.

Two-Dimensional Layered Double Hydroxides for Reactions of Methanation and Methane Reforming in C1 Chemistry

CH₄ as the paramount ingredient of natural gas plays an eminent role in C1 chemistry. CH₄ catalytically converted to syngas is a significant route to transmute methane into high value-added chemicals. Moreover, the CO/CO₂ methanation reaction is one of the potent technologies for CO₂ valorization and the coal-derived natural gas production process. Due to the high thermal stability and high extent of dispersion of metallic particles, two-dimensional mixed metal oxides through calcined layered double hydroxides (LDHs) precursors are considered as the suitable supports or catalysts for both the reaction of methanation and methane reforming. The LDHs displayed compositional flexibility, small crystal sizes, high surface area and excellent basic properties. In this paper, we review previous works of LDHs applied in the reaction of both methanation and methane reforming, focus on the LDH-derived catalysts, which exhibit better catalytic performance and thermal stability than conventional catalysts prepared by impregnation method and also discuss the anti-coke ability and anti-sintering ability of LDH-derived catalysts. We believe that LDH-derived catalysts are promising materials in the heterogeneous catalytic field and provide new insight for the design of advance LDH-derived catalysts worthy of future research.

Methane Dry Reforming over Ni-Co/Al2O3: Kinetic Modelling in a Catalytic Fixed-bed Reactor

The dry reforming of CH4 was investigated in a catalytic fixed-bed reactor to produce hydrogen at different temperatures over supported bimetallic Ni-Co catalyst. The reactor model for the dry reforming of methane used a set of kinetic models: The Zhang et al model for the dry reforming of methane (DRM); the Richardson-Paripatyadar model for the reverse water gas shift (RWGS); and the Snoeck et al kinetics for the coke-deposition and gasification reactions. The effect of temperatures on the performance of the reactor was studied. The amount of each species consumed or/and produced were calculated and compared with the experimental determined ones. It was showed that the set of kinetic model used in this work gave a good fit and accurately predict the experimental observed profiles from the fixed bed reactor. It was found that reaction-4 and reaction-5 could be neglected which could explain the fact that this catalyst coked rapidly comparatively with other catalyst. The use of large amount of Ni-Co will lead to carbon deposition and so to the catalyst deactivation.