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Author: search.filters.author.Boonchun, AdisakSubject: search.filters.subject.Alkali hexatitanate

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    Direct conversion of carboxylic acid to olefins over Pt-loaded, oxygen-deficient alkali hexatitanate catalysts with ketonization-hydrogenation-dehydration activity
    (2021-09-01)
    Promchana, Pratya
    ;
    Boonchun, Adisak
    ;
    T-Thienprasert, Jiraroj
    ;
    Sooknoi, Tawan
    ;
    Maluangnont, Tosapol
    The production of long chain olefins from fatty acids via decarbonylation is limited by low olefins selectivity at high conversion. Here, we reported the direct acid-to-olefins conversion via the ketonization-hydrogenation-dehydration sequence at 400 °C and atmospheric 10 %H<inf>2</inf>/Ar. The oxygen vacancy defects (V<inf>O</inf>) were essential in acetic acid ketonization over the oxygen-deficient alkali hexatitanate A<inf>2</inf>Ti<inf>6</inf>O<inf>13-</inf><inf>x</inf> (A[dbnd]K, Na and Li) catalysts, as evidenced from the activity of reduced vs non-reduced catalysts. The presence of V<inf>O</inf> was deduced spectroscopically with XPS and DRUV-VIS, and the ease of V<inf>O</inf> formation was ranked via the DFT calculations. The ketonization activity was proportionated to the square of the V<inf>O</inf> content (x<sup>2</sup>), consistent with the bimolecular reaction mechanism. The Pt-loaded K<inf>2</inf>Ti<inf>6</inf>O<inf>13-</inf><inf>x</inf> enabled the direct acid-to-olefins transformation as shown by a complete conversion of two model compounds (heptanoic acid and lauric acid) with ∼30–40 % yield of long chain olefins. Heptanoic acid (C<inf>7</inf>) underwent ketonization to 7-tridecanone (a C<inf>13</inf> ketone) prior to the hydrogenation-dehydration to 7-tridecene, a C<inf>13</inf> olefin. The strong metal-support interaction (SMSI) between Pt and K<inf>2</inf>Ti<inf>6</inf>O<inf>13-</inf><inf>x</inf> inhibited further hydrogenation of the olefin to a low-value alkane. For lauric acid (C<inf>12</inf>), 12-tricosene (a C<inf>23</inf> olefin) was produced analogously. The catalytic activity and products selectivity over Pt-loaded K<inf>2</inf>Ti<inf>6</inf>O<inf>13-</inf><inf>x</inf> significantly depended on the Pt content (0–1.0 wt%). The simultaneous C[sbnd]C coupling and oxygen removal prior to the subsequent hydrogenation and dehydration is a potential approach toward the production of long chain olefins with the (2n-1) carbon atoms from C<inf>n</inf>-fatty acids.