Highly loaded Ni-based catalysts for low temperature ethanol steam reforming

Novel nano spinel-type high-entropy oxide (HEO) catalyst for hydrogen production using ethanol steam reforming

Catalyst sintering caused by high temperature operating conditions during ethanol steam reforming (ESR) is a common issue for traditional catalysts with low Tammann temperature metals. In recent years, high entropy oxides have been popular in thermal catalysis due to their special thermodynamics and kinetics characteristics, which is expected to be a suitable approach for enhancing catalyst stability. This paper first reports the application of HEO in ESR and the characterization. The results exhibited a nano structure (CoCrFeNiAl)₃O₄ HEO with a spinel-phase and was successfully synthesized by a polyol hydrothermal precipitation-calcination method. An abundance of oxygen vacancies were formed, and were further enriched in a hydrogen atmosphere as the M-O bond opened. Interestingly, its self-reorganization featured the rendered the metals spilling out of the HEO bulk phase as active species for hydrogen production during ESR, whereas the isolated metal cation randomly dissolved into the parent metal oxide cell again after the reaction instead of agglomerating over the catalyst surface. This gave the (CoCrFeNiAl)₃O₄ a large number of dispersed active sites, as well as a high thermal stability. In addition, 81% of the hydrogen yield as well as 85% of H₂ selectivity were achieved at 600 °C. This research might offer possibilities for the development of thermal catalytic hydrogen production under high temperature conditions such as steam reforming.

Role of Fe Species of Ni-Based Catalysts for Efficient Low-Temperature Ethanol Steam Reforming

The suppression of methane and coke formation over Ni-based catalysts for low temperature ethanol steam reforming remains challenging. This paper describes the structural evolution of Fe-modified Ni/MgAl₂O₄ catalysts and the influence of iron species on methane and coke suppression for low temperature ethanol steam reforming. Ni-Fe alloy catalysts are gradually oxidized by water to generate Ni-rich alloy and γ-Fe₂O₃ species at steam-to-carbon ratio of 4. The electron transfer from iron to nickel within Ni-Fe alloy weakens the CO adsorption and effectively alleviates the CO/CO₂ methanation. The oxidation capacity of γ-Fe₂O₃ species promotes the transformation of ethoxy to acetate groups to avoid methane formation and the elimination of carbon deposits for anticoking. Ni10Fe10/MgAl₂O₄ shows a superior performance with a highest H₂ yield of 4.6 mol/mol ethanol at 400 °C for 15 h. This research could potentially provide instructions for the design of Ni-based catalysts for low-temperature ethanol steam reforming.

Highly Nickel-Loaded γ-Alumina Composites for a Radiofrequency-Heated, Low-Temperature CO2 Methanation Scheme

In this work, we joined highly Ni-loaded γ-Al₂ O₃ composites, straightforwardly prepared by impregnation methods, with an induction heating setup suited to control, almost in real-time, any temperature swing at the catalyst sites (i. e., "hot spots" ignition) caused by an exothermic reaction at the heart of the power-to-gas (P2G) chain: CO₂ methanation. We have shown how the combination of a poor thermal conductor (γ-Al₂ O₃ ) as support for large and highly interconnected nickel aggregates together with a fast heat control of the temperature at the catalytic bed allow part of the extra-heat generated by the reaction exothermicity to be reused for maintaining the catalyst under virtual isothermal conditions, hence reducing the reactor power supply. Most importantly, a highly efficient methanation scheme for substitute natural gas (SNG) production (X CO 2 up 98 % with >99 % S CH 4 ) under operative temperatures (150-230 °C) much lower than those commonly required with traditional heating setup has been proposed. As far as sustainable and environmental issues are concerned, this approach re-evaluates industrially attractive composites (and their large-scale preparation methods) for application to key processes at the heart of P2G chain while providing robust catalysts for which risks associated to nano-objects leaching phenomena are markedly reduced if not definitively suppressed.

A sinter-resistant catalytic system based on ultra-small Ni-Cu nanoparticles encapsulated in Ca-SiO2 for high-performance ethanol steam reforming

To enhance the catalytic performance of catalysts for the ethanol steam reforming (ESR) reaction, a facile reverse micelle strategy was adopted to prepare a core@shell Ni-Cu@Ca-SiO2 (Ni-Cu@CS) nanoreactor composed of an ultra-small Ni-Cu alloy (∼2.8 nm) encapsulated in Ca-functionalized SiO2 nanoparticles. Benefiting from its core@shell structural features and unique components, the Ni-Cu@CS nanoreactor exhibited superior activity (69.91% H2 selectivity and 99.99% ethanol conversion) and stability compared to reference samples. The regenerated Ni-Cu@CS nanoreactor showed high stability, maintaining 98.14% ethanol conversion and only 1.98 mg gcat-1 h-1 in carbon deposition. The high catalytic performance of Ni-Cu@CS is attributed to not only its encapsulated structure, which effectively prevented the sintering of neighboring Ni-Cu alloy nanoparticles, but also to its Ca-functionalized porous SiO2 shell, suppressing the carbon deposition. Moreover, its porous thin shell facilitated the mass transfer and diffusion of reactants and products. Thus, the Ni-Cu@CS nanoreactor is expected to become a new type of high-efficiency nanoreactor for the ESR reaction.

Precise control of the growth and size of Ni nanoparticles on Al2O3 by a MOF-derived strategy

Homogeneous and small Ni nanoparticles are generated from a MOF-derived strategy, originating from the formation of surface NiAl₂O₄ and the inherent confinement effect.