Electric Field and Mobile Oxygen Promote Low-Temperature Oxidative Coupling of Methane over La1-x Ca x AlO3-δ Perovskite Catalysts

Microalgae gasification over Ni loaded perovskites for enhanced biohydrogen generation

Steam gasification of microalgae upon perovskite oxide-supported nickel (Ni) catalysts was carried out for H₂-rich gas production. Ni-perovskite oxide catalysts with partial substitution of B in perovskite structures (Ni/CaZrO₃, Ni/Ca(Zr_0.8Ti_0.2)O₃, and Ni/Ca(Zr_0.6Ti_0.4)O₃) were synthesized and compared with those of the Ni/Al₂O₃ catalyst. The perovskite oxide supports improved Ni dispersion by reducing the particle size and strengthening the Ni-support interaction. Higher gas yields and H₂ selectivity were obtained using Ni-perovskite oxide catalysts rather than Ni/Al₂O₃. In particular, Ni/Ca(Zr_0.8Ti_0.2)O₃ showed the highest activity and selectivity for H₂ production because of the synergetic effect of metallic Ni and elements present in the perovskite structures caused by high catalytic activity coupled with enhanced oxygen mobility. Moreover, increasing the temperature promoted the yield of gas and H₂ content. Overall, considering the outstanding advantages of perovskite oxides as supports for Ni catalysts is a promising prospect for H₂ production via gasification technology.

H2 generation from steam gasification of swine manure over nickel-loaded perovskite oxides catalysts

In this study, nickel-loaded perovskite oxides catalysts were synthesized via the impregnation of 10%Ni on XTiO₃ (X = Ce, Sr, La, Ba, Ca, and Fe) supports and employed in the catalytic steam gasification of swine manure to produce H₂-rich syngas for the first time. The synthesized catalysts were characterized using BET, H₂-TPR, XRD, HR-TEM, and EDX analysis. Briefly, using perovskite supports resulted in the production of ultrafine catalyst nanoparticles with a uniform dispersion of Ni particles. According to the catalytic activity test, the gas yield showed the increment as 10% Ni/LaTiO₃ < 10% Ni/FeTiO₃ < 10% Ni/CeTiO₃ < 10% Ni/BaTiO₃ < 10% Ni/SrTiO₃ < 10% Ni/CaTiO₃. Meanwhile, zero coke formation was achieved due to the oxygen mobility of prepared catalysts. Also, the increase in the H₂ production for the applied catalysts was in the sequence as 10% Ni/CeTiO₃ < 10% Ni/FeTiO₃ < 10% Ni/LaTiO₃ < 10% Ni/BaTiO₃ < 10% Ni/SrTiO₃ < 10% Ni/CaTiO₃. The maximum H₂ selectivity (∼48 vol%) obtained by10% Ni/CaTiO₃ was probably due to the synergistic effect of Ni and Ti on enhancing the water-gas shift reaction, and Ca on creating the maximum oxygen mobility compared to other alkaline earth metals doped at the A place of perovskite. Overall, this study provides a suitable solution for enhanced H₂ production through steam gasification of swine manure along with suggesting the appropriate supports to prevent Ni deactivation by lowering coke formation at the same time.

Metal Ions (Li, Mg, Zn, Ce) Doped into La2O3 Nanorod for Boosting Catalytic Oxidative Coupling of Methane

A series of La2O3 nanorod catalysts with doping of active metal ions (Li, Mg, Zn and Ce) were synthesized successfully by the hydrothermal method. The La2O3 nanorods show a uniform size with the length of 50–200 nm and the width of 5–20 nm, and the {110} crystal facet is a preferentially exposed surface. The active metal ions (Li, Mg, Zn and Ce) doped into the lattice of La2O3 nanorods enhance the selectivity of the desired products during oxidative coupling of methane (OCM) and decrease the reaction temperature. Among these catalysts, the Mg-La2O3 catalyst exhibits the best catalytic performance during the OCM reaction, i.e., its selectivity and yield of C2 products at 780 °C is 73% and 21%, respectively. The effect of doped metal ions on catalytic activity for OCM was systematically investigated. Insight into the fabrication strategy and promoting factors of the OCM reaction indicates the potential to further design a high-efficient catalyst in the future.

Progress and Recent Strategies in the Synthesis and Catalytic Applications of Perovskites Based on Lanthanum and Aluminum

Lanthanum aluminate-based perovskite (LaAlO₃) has excellent stability at high temperatures, low toxicity, and high chemical resistance and also offers wide versatility to the substitution of La³⁺ and Al³⁺, thus, allowing it to be applied as a catalyst, nano-adsorbent, sensor, and microwave dielectric resonator, amongst other equally important uses. As such, LaAlO₃ perovskites have gained importance in recent years. This review considers the extensive literature of the past 10 years on the synthesis and catalytic applications of perovskites based on lanthanum and aluminum (LaAlO₃). The aim is, first, to provide an overview of the structure, properties, and classification of perovskites. Secondly, the most recent advances in synthetic methods, such as solid-state methods, solution-mediated methods (co-precipitation, sol–gel, and Pechini synthesis), thermal treatments (combustion, microwave, and freeze drying), and hydrothermal and solvothermal methods, are also discussed. The most recent energetic catalytic applications (the dry and steam reforming of methane; steam reforming of toluene, glycerol, and ethanol; and oxidative coupling of methane, amongst others) using these functional materials are also addressed. Finally, the synthetic challenges, advantages, and limitations associated with the preparation methods and catalytic applications are discussed.

Elucidation of the reaction mechanism on dry reforming of methane in an electric field by in situ DRIFTs

With increasing expectations for carbon neutrality, dry reforming is anticipated for direct conversion of methane and carbon dioxide: the main components of biogas. We have found that dry reforming of methane in an electric field using a Pt/CeO₂ catalyst proceeds with sufficient rapidity even at a low temperature of about 473 K. The effect of the electric field (EF) on dry reforming was investigated using kinetic analysis, in situ DRIFTs, XPS, and DFT calculation. In situ DRIFTs and XPS measurements indicated that the amount of carbonate, which is an adsorbed species of CO₂, increased with the application of EF. XPS measurements also confirmed the reduction of CeO₂ by the reaction of surface oxygen and CH₄. The reaction between CH₄ molecules and surface oxygen was promoted at the interface between Pt and CeO₂.

In the dry reforming of methane in an electric field, the reaction between CH₄ molecules and surface oxygen was promoted at the interface between Pt and CeO₂.

Oxidative Coupling of Methane for Ethylene Production: Reviewing Kinetic Modelling Approaches, Thermodynamics and Catalysts

Ethylene production via oxidative coupling of methane (OCM) represents an interesting route for natural gas upscaling, being the focus of intensive research worldwide. Here, OCM developments are analysed in terms of kinetic mechanisms and respective applications in chemical reactor models, discussing current challenges and directions for further developments. Furthermore, some thermodynamic aspects of the OCM reactions are also revised, providing achievable olefins yields in a wide range of operational reaction conditions. Finally, OCM catalysts are reviewed in terms of respective catalytic performances and thermal stability, providing an executive summary for future studies on OCM economic feasibility.

Effects of A-site composition of perovskite (Sr1-x Ba x ZrO3) oxides on H atom adsorption, migration, and reaction

Hydrogen (H) atomic migration over a metal oxide is an important surface process in various catalytic reactions. Control of the interaction between H atoms and the oxide surfaces is therefore important for better catalytic performance. For this investigation, we evaluated the adsorption energies of the H atoms over perovskite-type oxides (Sr1-x Ba x ZrO3; 0.00 ≤ x ≤ 0.50) using DFT (Density Functional Theory) calculations, then clarified the effects of cation-substitution in the A-site of perovskite oxides on H atom adsorption, migration, and reaction. Results indicated local distortion at the oxide surface as a key factor governing H atom adsorption. Subtle Ba2+ substitution for Sr2+ sites provoked local distortion at the Sr1-x Ba x ZrO3 oxide surface, which led to a decrement in the H atom adsorption energy. Furthermore, the effect of Sr2+/Ba2+ ratio on the H atoms' reactivities was examined experimentally using a catalytic reaction, which was promoted by activated surface H atoms. Results show that the surface H atoms activated by the substitution of Sr2+ sites with a small amount of Ba2+ (x = 0.125) contributed to enhancement of ammonia synthesis rate in an electric field, which showed good agreement with predictions made using DFT calculations.

First observation of surface protonics on SrZrO3 perovskite under a H2 atmosphere

This is the first direct observation that surface proton hopping occurs on SrZrO₃ perovskite even under a H₂ (i.e. dry) atmosphere.

Conversion of methane to C2 and C3 hydrocarbons over TiO2/ZSM-5 core–shell particles in an electric field

Catalytic conversion of methane (CH₄) to light olefins is motivated by increasing recoverable reserves of methane resources, abundantly available in natural gas, shale gas, and gas hydrates. The development of effective processes for conversion of CH₄ to light olefins is still a great challenge. The interface of ZSM-5 zeolite and TiO₂ nanoparticles is successfully constructed in their core–shell particles via mechanochemical treatment with high shear stress. The oxidative coupling of methane at a low temperature under application of an electric field may be induced by the O₂ activation via electrons running through the surface of TiO₂ located at the interface of TiO₂ and zeolite particles. Moreover, C₃H₆ was also produced by the ethylene to propylene (ETP) reaction catalyzed by Brønsted acid sites in the ZSM-5 zeolite within core–shell particles.

A TiO₂/ZSM-5 composite catalyst efficiently works for the oxidative coupling of methane and the subsequent ethylene-to-propylene reactions in an electric field.