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Effects of zeolite frameworks and hierarchical structures on catalytic bioethanol dehydration: In-situ DRIFTS and DFT studies
(2023-04-15)
Iadrat, Ploychanok
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Yomthong, Krissanapat
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Rodaum, Chadatip
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Pornsetmetakul, Peerapol
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Thivasasith, Anawat
Herein, the combined in-situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory studies were employed to investigate the effects of different zeolite frameworks and hierarchical structures on catalytic bioethanol dehydration. The findings reveal that different zeolite frameworks enable the formation of distinct intermediates, hence promoting different mechanistic pathways. Interestingly, the FER is highly selective to ethylene and inhibits the formation of by-products thanks to the confined porous structure of the FER. Although the pristine small pore FER often suffers from fast catalyst deactivation, the incorporation of hierarchical structures in the FER framework can mitigate this significantly. Accordingly, the catalytic stability of the hierarchical FER was improved remarkably with a high ethylene yield (∼95%), whereas the pristine FER suffers from fast deactivation. Additionally, coke formation over the hierarchical FER catalyst was also reduced significantly compared to that of the pristine FER. Importantly, the in-situ DRIFTS studies reveal that the different reaction pathways over hierarchical and commercial FER have been observed in which the hierarchical one promotes the monomeric pathway due to the facile desorption of corresponding products and intermediates, whilst the pristine one promotes bioethanol conversion via both pathways of monomeric and dimeric pathways to produce ethylene and diethyl ether, respectively.
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Catalytic conversion of bioethanol to value-added chemicals and fuels: A review
(2022-03-01)
Xiang, Huan
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Xin, Ruojia
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Prasongthum, Natthawan
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Natewong, Paweesuda
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Sooknoi, Tawan
Bioethanol produced via valorisation of renewable biomass is of great interest to many industries. The increased availability and decreased cost of bioethanol make it a promising platform molecule to produce a wide range of value-added chemicals and fuels via the catalytic conversions. This paper provides a comprehensive review of catalytic conversions of bioethanol to a variety of chemicals/fuels such as hydrogen, C<inf>2</inf>–C<inf>4</inf> olefins, gasoline and small oxygenates. Specifically, the focus was placed on the relationship between the catalyst property (such as pore structure, acidity, active metal sites, and catalyst supports) and the catalytic performance (including catalyst activity and stability), as well as the reaction mechanisms involved. Future research avenues on the catalyst design for improving catalytic valorisation of bioethanol are also discussed.
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Higher alcohol production from ethanol over occluded [Mg4(OH)4]4+ clusters in MgO/KNaX
(2022-02-25)
Yotkkham, Nattapol
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Choojun, Kittisak
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Promchana, Pratya
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Fan, Xiaolei
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Sooknoi, Tawan
Conversion of ethanol to higher alcohols was studied over MgO/KNaX, prepared by ion exchange with Mg(OAc)<inf>2</inf>, followed by KOH washing. The catalysts were characterized by XRF, XRD, SEM, BET, 27Al MAS NMR, EXAFS, NH<inf>3</inf>- and CO<inf>2</inf>-TPD. All catalysts showing MgO nanopetals and aggregates on the external surface, contained occluded [Mg<inf>4</inf>(OH)<inf>4</inf>]4+ clusters in the zeolite cavities, providing medium basic (M<inf>b</inf>) and acid (M<inf>a</inf>) sites. Ethanol conversion and higher alcohols selectivity (up to 78%) increased with M<inf>b</inf>/M<inf>a</inf> ratio due to the increase in both MgO (4–6 wt%) and K (14.7–17.3 wt%) loadings. Decreasing occluded [Mg<inf>4</inf>(OH)<inf>4</inf>]4+ clusters and/or increasing MgO aggregates led to the lower conversion and yields of higher alcohols. The essential role of the occluded [Mg<inf>4</inf>(OH)<inf>4</inf>]4+ clusters in producing higher alcohols was verified by the reactions using various control catalysts. The MgO/KNaX showed high stability even after steaming at 380 °C, as well as being regenerated by calcination (450 °C in air).
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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
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Goodarzi, Farnoosh
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Mu, Yibing
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Chansai, Sarayute
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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.

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