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    Extending the basic function of lattice oxygen in lepidocrocite titanate – The conversion of intercalated fatty acid to liquid hydrocarbon fuels
    (2017-12-01)
    Maluangnont, Tosapol
    ;
    Arsa, Pornanan
    ;
    Sooknoi, Tawan
    We report herein the basicity of the external and internal lattice oxygen (O<inf>L</inf>) in lepidocrocite titanates with respect to CO<inf>2</inf> and palmitic acid, respectively. Several compositions have been tested with different types of the metal M aliovalently (co)substituted for Ti, K<inf>0.8</inf>[M<inf>y</inf>Ti<inf>2−y</inf>]O<inf>4</inf> (M = Li, Mg, Fe, Co, Ni, Cu, Zn, Cu/Ni and Cu/Zn). The low CO<inf>2</inf> desorption peak temperature (70–100 °C) suggests that the external O<inf>L</inf> sites are weakly basic similar to TiO<inf>2</inf>. However, the internal O<inf>L</inf> sites are sufficiently basic to deprotonate palmitic acid, forming the intercalated potassium palmitate at the interlayer spaces. The latter serves as a two-dimensional (2D) molecular reactor for the production of liquid hydrocarbon fuels via deoxygenation under atmospheric N<inf>2</inf>. A relationship has been observed between the yield of the liquid products vs the partial charge of the lattice oxygen (δ<inf>O</inf>). Since the deoxygenation pathway is highly dependent on the metal substitution, the redox-active sites might also play some roles. The co-substituted K<inf>0.8</inf>[Cu<inf>0.2</inf>Ni<inf>0.2</inf>]Ti<inf>1.6</inf>O<inf>4</inf> produced ~68.0% yield of the liquid products, with ~ 51% saturated and ~ 15% unsaturated C<inf>15</inf> hydrocarbons at 350 °C.
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    Surface and interlayer base-characters in lepidocrocite titanate: The adsorption and intercalation of fatty acid
    (2016-06-01)
    Maluangnont, Tosapol
    ;
    Arsa, Pornanan
    ;
    Limsakul, Kanokporn
    ;
    Juntarachairot, Songsit
    ;
    Sangsan, Saithong
    While layered double hydroxides (LDHs) with positively-charged sheets are well known as basic materials, layered metal oxides having negatively-charged sheets are not generally recognized so. In this article, the surface and interlayer base-characters of O<sup>2-</sup> sites in layered metal oxides have been demonstrated, taking lepidocrocite titanate K<inf>0.8</inf>Zn<inf>0.4</inf>Ti<inf>1.6</inf>O<inf>4</inf> as an example. The low basicity (0.04 mmol CO<inf>2</inf>/g) and low desorption temperature (50-300 °C) shown by CO<inf>2</inf>- TPD suggests that O<sup>2-</sup> sites at the external surfaces is weakly basic, while those at the interlayer space are mostly inaccessible to CO<inf>2</inf>. The liquid-phase adsorption study, however, revealed the uptake as much as 37% by mass of the bulky palmitic acid (C<inf>16</inf> acid). The accompanying expansion of the interlayer space by ~0.1 nm was detected by PXRD and TEM. In an opposite manner to the external surfaces, the interlayer O<sup>2-</sup> sites can deprotonate palmitic acid, forming the salt (i.e., potassium palmitate) occluded between the sheets. Two types of basic sites are proposed based on ultrafast <sup>1</sup>H MAS NMR and FTIR results. The interlayer basic sites in lepidocrocite titanate leads to an application of this material as a selective and stable two-dimensional (2D) basic catalyst, as demonstrated by the ketonization of palmitic acid into palmitone (C<inf>31</inf> ketone). Tuning of the catalytic activity by varying the type of metal (Zn, Mg, and Li) substituting at Ti<sup>IV</sup> sites was also illustrated.