Iron carbide catalysts encapsulated in graphene-like carbon were synthesized via a facile method by pyrolysis of an iron-glucose precursor. Different amounts of potassium (0–5 wt%) were in situ doped into the catalyst simultaneously. Glucose played a role both as the precursor to form a carbon support and a reducing agent that reduced iron oxides to θ-Fe₃C during the catalyst preparation. θ-Fe₃C underwent a phase transformation to χ-Fe₅C₂ as the active phase in Fischer–Tropsch synthesis. Characterization of the structural and chemical properties of the prepared catalysts revealed a core–shell structure with iron carbides enwrapped by several graphene-like layers. The addition of a potassium promoter increased the amount of defects on graphene-like layers and facilitated the formation of iron carbides during the catalyst preparation. Fischer–Tropsch synthesis under typical reaction conditions (320 °C, 20 bar, H₂/CO = 1, GHSV = 15 000 ml g_cat ⁻¹ h⁻¹) was carried out in a fixed bed reactor. A higher light olefin selectivity was obtained than that on common iron catalysts, probably because of the electron-rich surfaces of the prepared catalysts that made it hard for hydrogen to hydrogenate the unsaturated intermediates. A volcano-like evolution of light olefin selectivity was observed on the catalysts with different contents of K, and the highest olefin selectivity reached 41.9% on the 2K-Fe₃C@C catalyst (i.e., doped with 2 wt% of K). The induction period of the catalyst was shortened by K addition. No drastic changes in the catalyst morphology and performance during 100 h time on stream can be ascribed to the protection of graphene-like carbon layers that prevented the supported iron particles from migration and aggregation under harsh conditions in Fischer–Tropsch synthesis.

A morphological effect of Au/CeO₂ catalysts in 5-hydroxymethylfurfural (HMF) oxidation.

In situ methanol steam reforming for hydrogen production is a promising technology to provide a hydrogen source for full cells. However, the conventional methanol steam reforming usually encounters catalyst inefficiency and instability, which make its industrial application difficult. This work proposes a novel and stable Ni-based catalyst supported by spongy mesoporous alumina and achieves an enhancement of hydrogen production. The prepared Ni/γ-Al₂O₃ catalyst exhibits a higher hydrogen production yield of 0.26 mol h⁻¹ than the commercial Ni/γ-Al₂O₃-Com catalyst (0.21 mol h⁻¹) at 450 °C, with an improvement of the hydrogen flow rate of 23.8%. The Ni/γ-Al₂O₃ catalyst also presents a much superior performance to the reported noble metal-based catalysts and Ni-based catalysts. The special spongy mesoporous structure provides favorable conditions for high catalytic activity, mainly based on the high dispersion of the Ni metal site and the high catalyst stability. The Ni metal particles are highly dispersed over spongy mesoporous Al₂O₃ with an average particle size of only 3.7 nm. Characterization analysis shows that the spongy mesoporous structure of the catalyst enables quick adsorption of the reactants and reaction intermediates, and the highly dispersed Ni metal site can lead to the rapid dehydrogenation of methanol to increase the hydrogen yield. Moreover, the stability of the prepared Ni/γ-Al₂O₃-5H catalyst is much superior to that of the commercial Ni/γ-Al₂O₃-Com catalyst, where Ni/γ-Al₂O₃-5H retained 100% of methanol conversion for 12 h, and the spongy mesoporous structure and the high dispersion of Ni particles were also well maintained. In addition, the reaction mechanism of methanol steam reforming over the Ni/γ-Al₂O₃-5H catalyst is revealed in detail, especially based on the in situ DRIFTS characterization results. This research provides valuable insights for the development of catalytic methanol steam reforming for hydrogen production and in the field of green chemistry.