MFI-type zeolite nanoparticles substituted isomorphously by both Al and Fe and of crystallite size ≤51 nm were prepared via a hydrothermal synthesis method combined with a pre-heating treatment. Quantitative assessment...

MFI-type zeolites containing Ce species were prepared by a mechanochemically assisted two-step method, where first an amorphous Si–Ce–O composite was produced via a mechanochemical reaction of SiO2 and CeO2 and then transformed into an MFI-type zeolite under hydrothermal conditions. The Ce species in this sample were more highly dispersed than those in the two control materials: a Ce-containing MFI-type zeolite synthesized via the conventional one-pot hydrothermal approach and Ce species simply deposited on silicalite-1. The highly dispersed and small Ce species in the zeolite exhibited a unique catalytic performance for the oxidative conversion of methane after the impregnation of Pd species, and the combination of Pd and Ce species produced ethane even at reaction temperatures as low as 100–300 °C.

Ce-containing MFI-type zeolite (Ce-MFI)-supported Pd catalysts modified by a second metal were prepared and applied to low-temperature oxidative coupling of methane reactions. Screening of various second metal species revealed that the combination of Pd and Co supported on Ce-MFI positively affected the catalytic performance and that the C2H6 yield was improved compared with that for the control Ce-MFI-supported Pd catalyst. This benefit would arise from the creation of new active sites by the proximate Pd and Co species on Ce-MFI, as suggested by high-angle angular dark-field scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and H2-temperature-programmed reduction measurements. In addition, the highly dispersed Ce species in Ce-MFI, which were generated via the mechanochemical method, contributed to the creation of catalytically active sites, i.e., concerted Ce, Pd, and Co species.

Cobalt carbide (Co 2 C) nanoparticles were synthesized simply in liquid phase using Co(II) acetylacetonate and oleylamine under reflux conditions. Even in the presence of carbon black XC-72, Co 2 C nanoparticles were formed and simultaneously deposited on the carbon surface. The thin layer consisting of cobalt (oxy)hydroxide was present on the outermost surface of the thus-prepared Co 2 C nanoparticles, which was confirmed by X-ray photoelectron spectroscopy, but the redox treatment using a cyclic voltammetry technique gradually removed such byproduct phase. The resulting Co 2 C nanoparticles supported on XC-72 exhibited high durability for the oxygen reduction reaction.