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    Platelet Ceria Catalysts from Solution Combustion and Effect of Iron Doping for Synthesis of Dimethyl Carbonate from CO2
    (2025-01-01)
    Rusta, Nicoletta
    ;
    Mameli, Valentina
    ;
    Ricci, Pier Carlo
    ;
    Porcu, Stefania
    ;
    Seeharaj, Panpailin
    Solution combustion (SC) remains among the most promising synthetic strategies for the production of crystalline nanopowders from an aqueous medium, due to its easiness, time and cost-effectiveness, scalability and eco-friendliness. In this work, this method was selected to obtain anisometric ceria-based nanoparticles applied as catalysts for the direct synthesis of dimethyl carbonate. The catalytic performances were studied for the ceria and Fe-doped ceria from SC (CeO<inf>2</inf>-SC, Ce<inf>0.9</inf>Fe<inf>0.1</inf>O<inf>2</inf>-SC) in comparison with the ceria nanorods (CeO<inf>2</inf>-HT, Ce<inf>0.9</inf>Fe<inf>0.1</inf>O<inf>2</inf>-HT) obtained by hydrothermal (HT) method, one of the most studied systems in the literature. Indeed, the ceria nanoparticles obtained by SC were found to be highly crystalline, platelet-shaped, arranged in a mosaic-like assembly and with smaller crystallite size (≈6 nm vs. ≈17 nm) and higher surface area (80 m<sup>2</sup> g<sup>−1</sup> vs. 26 m<sup>2</sup> g<sup>−1</sup>) for the undoped sample with respect to the Fe-doped counterpart. Although all samples exhibit an anisometric morphology that should favor the exposition of specific crystalline planes, HT-samples showed better performances due to higher oxygen vacancies concentration and lower amount of strong basic and acid sites.
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    Effect of metal dispersion and support structure of Ni/silicalite-1 catalysts on non-thermal plasma (NTP) activated CO2 hydrogenation
    (2020-09-05)
    Chen, Huanhao
    ;
    Goodarzi, Farnoosh
    ;
    Mu, Yibing
    ;
    Chansai, Sarayute
    ;
    Mielby, Jerrik Jørgen
    Non-thermal plasma (NTP) activated heterogeneous catalysis is a promising alternative to thermal catalysis for enabling many challenging reactions (e.g. catalytic CO<inf>2</inf> hydrogenation) under mild conditions. However, the mechanistic insight into the interaction between highly energetic electrons and vibrationally-exited reactive species with metal catalyst is still lacking. Here, catalytically active Ni nanoparticles supported on silicalite-1 zeolites with different configurations regarding the location of Ni active sites and support pore structures were comparably investigated using catalytic CO<inf>2</inf> hydrogenation under the thermal and NTP conditions. Experimental results revealed that the performance of the NTP-catalysis depends on the configuration of the catalysts significantly. Specifically, catalysts with Ni active sites sit on the outer surface of zeolite crystals (i.e. microporous Ni/S1 and Ni/M-S1@Shell with steam-assisted recrystallised micro-meso-porous structure) showed relatively good catalytic performance at a low applied voltage of 6.0 kV. Conversely, the encapsulated catalyst with hierarchical meso-micro-porous structure (i.e. Ni/D-S1) which has relatively small (i.e. average Ni particle sizes of 2.8±0.7 nm) and dispersed Ni nanoparticles (i.e. Ni dispersion of ca. 2.5 %) demonstrated comparatively the best catalytic performance (i.e. CO<inf>2</inf> conversion of ca. 75 %) at 7.5 kV. Additionally, under the NTP conditions studied, Ni on carbon-templated mesoporous silicalite-1 (Ni/M-S1) showed the worst selectivity to CH<inf>4</inf>, which was attributed to the poor accessibility of Ni active sites encapsulated in the enclosed mesopores. This study demonstrated the crucial role of catalyst design in NTP activated catalysis.