A review of catalytic partial oxidation of fossil fuels and biofuels: Recent advances in catalyst development and kinetic modelling

Emerging trends in hydrogen and synfuel generation: a state-of-the-art review

The current work investigated emerging fields for generating and consuming hydrogen and synthetic Fischer-Tropsch (FT) fuels, especially from detrimental greenhouse gases, CO2 and CH4. Technologies for syngas generation ranging from partial oxidation, auto-thermal, dry, photothermal and wet or steam reforming of methane were adequately reviewed alongside biomass valorisation for hydrogen generation, water electrolysis and climate challenges due to methane flaring, production, storage, transportation, challenges and opportunities in CO2 and CH4 utilisation. Under the same conditions, dry reforming produces more coke than steam reforming. However, combining the two techniques produces syngas with a high H2/CO ratio, which is suitable for producing long-chain hydrocarbons. Although the steam methane reforming (SMR) process has been industrialised, it is well known to consume significant energy. However, coke production via catalytic methane decomposition, the prime hindrance to large-scale implementation of these techniques for hydrogen production, could be addressed by coupling CO with CO2 conversion to alter the H2/CO ratio of syngas, increasing the reaction temperatures in dry reforming, or increasing the steam content fed in steam reforming. Optimised hydrogen production and generation of green fuels from CO2 and CH4 can be achieved by implementing these strategies.

The Impact of Thermochemical Exhaust Energy Recovery Using Ethanol-Gasoline Blend on Gasoline Direct Injection Engine Performance

Thermochemical exhaust energy recovery in a modern gasoline direct injection engine is investigated using ethanol-gasoline blend (E25) and gasoline, as base fuel. The primary objectives of this research are focused on reducing carbonaceous emissions as well as improving thermal efficiency and fuel economy in combustion engines. These are consistent with the global commitment to lessen carbon emissions and meet environmental regulations and agreements.

The possibility of hydrogen production through catalytic reforming of mentioned fuels using actual exhaust composition is investigated on full-scale Rh (Rhodium)—Pt (Platinum) catalysts. ANSYS-Chemkin is utilized for thermodynamic equilibrium analyses based on the Gibbs energy minimization method to explore the key reaction pathways for E25 reforming. Main reforming parameters including steam to carbon molar ratios and reforming temperatures are selected to investigate the feasibility of ethanol-gasoline blend reforming as well as to identify the reformate composition and evaluate the whole process efficiency. The results revealed that the presence of ethanol in reforming fuel mixture facilitates endothermic reactions and improves hydrogen-rich mixture, particularly at high engine load conditions where maximum heat recovery is obtained. Furthermore, E25 fuel reforming helped achieving up to 16% greater CO2 compared to gasoline fuel reforming under the same engine condition. Overall, the experimental results of full-scale reforming tests using E25 can be accredited for effective implementation of the reforming technique in practical application.

Ni/(R2O3,CaO) Nanocomposites Produced by the Exsolution of R1.5Ca0.5NiO4 Nickelates (R = Nd, Sm, Eu): Rare Earth Effect on the Catalytic Performance in the Dry Reforming and Partial Oxidation of Methane

In order to clarify the role of R₂O₃ in the metal-oxide catalysts derived from complex oxide precursors, a series of R_1.5Ca_0.5NiO₄ (R = Nd, Sm, Eu) complex oxides was obtained. A significant systematic increase in the orthorhombic distortion of the R_1.5Ca_0.5NiO₄ structure (K₂NiF₄ type, Cmce) from Nd to Eu correlates with a corresponding decrease in their ionic radii. A reduction of R_1.5Ca_0.5NiO₄ in the Ar/H₂ gas mixture at 800 °C causes a formation of dense agglomerates of CaO and R₂O₃ coated with spherical 25-30 nm particles of Ni metal. The size of metal particles and oxide agglomerates is similar in all Ni/(R₂O₃,CaO) composites in the study. Their morphology is rather similar to the products of redox exsolution obtained by the partial reduction of complex oxides. All obtained composites demonstrated a significant catalytic activity in the dry reforming (DRM) and partial oxidation (POM) of methane at 700-800 °C. A systematic decrease in the DRM catalytic activity of composites from Nd to Eu could be attributed to the basicity reduction of R₂O₃ components of the composite catalysts. The maximum CH₄ conversion in POM reaction was observed for Ni/(Sm₂O₃,CaO), while the maximum selectivity was demonstrated by Nd₂O₃-based composite. The possible reasons for the observed difference are discussed.

Oxidation of methane and ethylene over Al incorporated N-doped graphene: A comparative mechanistic DFT study

It is generally recognized that developing effective methods for selective oxidation of hydrocarbons to generate more useful chemicals is a major challenge for the chemical industry. In the present study, density functional theory calculations are conducted to examine the catalytic partial oxidation of methane (CH₄) and ethylene (C₂H₄) by nitrous oxide (N₂O) over Al-incorporated porphyrin-like N-doped graphene (AlN₄-Gr). Adsorption energies for the most stable configurations of CH₄, C₂H₄, and N₂O molecules over the AlN₄-Gr catalyst are determined to be -0.25, -0.64, and -0.40 eV, respectively. According to our findings, N₂O can be efficiently split into N₂ and O_ads species with a negligible activation energy on the AlN₄-Gr surface. Meanwhile, CH₄ and C₂H₄ molecules compete for reaction with the activated oxygen atom (O_ads) that stays on the surface. The energy barriers for partial methane oxidation through the CH₄ + O_ads → CH₃° + HO_ads and CH₃° + HO_ads → CH₃OH reaction steps are 0.16 eV and 0.27 eV, respectively. Furthermore, the produced CH₃OH may be overoxidized by O_ads to give formaldehyde and water molecules by overcoming a relatively low activation barrier. The activation barriers for C₂H₄ epoxidation are small and comparable to those for CH₄ oxidation, implying that AlN₄-Gr is highly active for both reactions. The high energy barrier for the 1,2-hydrogen shift in the OCH₂CH₂ intermediate, on the other hand, makes the production of acetaldehyde impossible under normal conditions. According to the population analysis, the AlN₄-Gr serves as a strong electron donor to aid in the charge transfer between the Al atom and the O_ads moiety, which is necessary for the activation of CH₄ and C₂H₄. The findings of the present study may pave the way for a better understanding of the catalytic oxidation the CH₄ and C₂H₄, as well as for the development of highly efficient noble-metal free catalysts for these reactions.

Single-Phase Formation of Rh2 O3 Nanoparticles on h-BN Support for Highly Controlled Methane Partial Oxidation to Syngas

Single-phase formation of active metal oxides on supports has been vigorously pursued in many catalytic applications to suppress undesired reactions and to determine direct structure-property relationships. However, this is difficult to achieve in nanoscale range because the effect of non-uniform metal-support interfaces becomes dominant in the overall catalyst growth, leading to the nucleation of various metastable oxides. Herein, we develop a supported single-phase corundum-Rh₂ O₃ (I) nanocatalyst by utilizing controlled interaction between metal oxide and h-BN support. Atomic-resolution electron microscopy and first-principle calculation reveal that single-phase formation occurs via uniform and preferential attachment of Rh₂ O₃ (I) (110) seed planes on well-defined h-BN surface after decomposition of rhodium precursor. By utilizing the Rh/h-BN catalyst in methane partial oxidation, syngas is successfully produced solely following the direct route with keeping a H₂ /CO ratio of 2, which makes it ideal for most downstream chemical processes.

Production of Hydrogen by Methane Steam Reforming Coupled with Catalytic Combustion in Integrated Microchannel Reactors

This paper addresses the issues related to the rapid production of hydrogen from methane steam reforming by means of process intensification. Methane steam reforming coupled with catalytic combustion in thermally integrated microchannel reactors for the production of hydrogen was investigated numerically. The effect of the catalyst, flow arrangement, and reactor dimension was assessed to optimize the design of the system. The thermal interaction between reforming and combustion was investigated for the purpose of the rapid production of hydrogen. The importance of thermal management was discussed in detail, and a theoretical analysis was made on the transport phenomena during each of the reforming and combustion processes. The results indicated that the design of a thermally integrated system operated at millisecond contact times is feasible. The design benefits from the miniaturization of the reactors, but the improvement in catalyst performance is also required to ensure the rapid production of hydrogen, especially for the reforming process. The efficiency of heat exchange can be greatly improved by decreasing the gap distance. The flow rates should be well designed on both sides of the reactor to meet the requirements of both materials and combustion stability. The flow arrangement plays a vital role in the operation of the thermally integrated reactor, and the design in a parallel-flow heat exchanger is preferred to optimize the distribution of energy in the system. The catalyst loading is an important design parameter to optimize reactor performance and must be carefully designed. Finally, engineering maps were constructed to design thermally integrated devices with desired power, and operating windows were also determined.