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Determining the role of oxygen vacancies in palmitone selectivity and coke formation over acid metal oxide catalysts for the ketonization of methyl palmitate
(2021-11-25)
Guntida, Adisak
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Rattanachartnarong, Thanwarat
;
Jongsomjit, Bunjerd
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Sooknoi, Tawan
;
Weerachawanasak, Patcharaporn
In the present study, TiO<inf>2</inf>, CeO<inf>2</inf>, MnO<inf>2</inf>, and ZrO<inf>2</inf> catalysts were used to investigate the catalytic performance in methyl palmitate ketonization. The reaction was accelerated by weak Lewis acid, while the oxygen vacancies promoted the palmitone selectivity. The use of various characterization techniques revealed that oxygen vacancies played an important role for trapping the hydrogen atom and inhibited its spillover. This caused the suppression of the Lewis acid transformation to new Bronsted acid. Thus, the cracking of palmitone over the new Bronsted acid was diminished, leading to the decrement of selectivity to undesired products. However, when the hydrogen atom was trapped in the oxygen vacancies, the coke deposition was dominant. This phenomenon arose because hydrogen could not suppress the deep dehydrogenation, resulting in the transformation of aliphatic coke to aromatic coke. The role of oxygen vacancies was determined, and it had the positive effect on the palmitone selectivity, whereas it raised the coke formation.
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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
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Boonchun, Adisak
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T-Thienprasert, Jiraroj
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Sooknoi, Tawan
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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 (x2), 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.
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Production of liquid fuel from palmitic acid over nanocrystalline CeO2-based catalysts with minimal use of H2
(2017-01-01)
Maluangnont, Tosapol
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Dararat, Chalinee
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Kulrat, Teerapong
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Soontontaweesub, Surachet
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Anothaiwalaikul, Thitima
The deoxygenation of palmitic acid into diesel-range hydrocarbons can be promoted over nanocrystalline ceria-based catalysts under atmospheric N<inf>2</inf> or 10% H<inf>2</inf>/N<inf>2</inf> in a fixed-bed flow reactor at 400 °C. Oxygen vacancy sites are active for ketonization of palmitic acid to C<inf>31</inf> ketone and also subsequent cracking of the formed ketone to hydrocarbons. The 22–31% selectivity of C<inf>9</inf> to C<inf>17</inf> liquid hydrocarbons can be achieved at 100% palmitic acid conversion. The deoxygenation under N<inf>2</inf> can be facilitated, presumably by hydrogen transfer from coke precursors. Catalytic activity of ceria-based catalysts can be tuned by pretreatment conditions, type of a carrier gas, or lattice modification.
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Surface and interlayer base-characters in lepidocrocite titanate: The adsorption and intercalation of fatty acid
(2016-06-01)
Maluangnont, Tosapol
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Arsa, Pornanan
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Limsakul, Kanokporn
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Juntarachairot, Songsit
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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 O2- 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 O2- 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 O2- 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 1H 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 TiIV sites was also illustrated.
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Condensation reactions of propanal over CexZr 1-xO2 mixed oxide catalysts
(2010-09-15)
Gangadharan, Anirudhan
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Shen, Min
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Sooknoi, Tawan
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Resasco, Daniel E.
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Mallinson, Richard G.
Vapor phase condensation reactions of propanal were investigated over Ce<inf>x</inf>Zr<inf>1-x</inf>O<inf>2</inf> mixed oxides as a model reaction to produce gasoline range molecules from short aldehydes found in bio-oil mixtures. Several operating parameters were investigated. These included the type of carrier gas used (H<inf>2</inf> or He) and the incorporation of acids and water in the feed. Propanal is converted to higher carbon chain oxygenates on Ce <inf>x</inf>Zr<inf>1-x</inf>O<inf>2</inf> by two pathways, aldol condensation and ketonization. The major products of these condensation reactions include 3-pentanone, 2-methyl-2-pentenal, 2-methylpentanal, 3-heptanone and 4-methyl-3-heptanone. It is proposed that the primary intermediate for the ketonization path is a surface carboxylate. The presence of acids in the feed inhibits the aldol condensation pathway by competitive adsorption that reduces the aldehyde conversion. Water also promotes ketonization and inhibits aldol condensation by increasing the concentration of surface hydroxyl groups that enhance the formation of surface carboxylates with the aldehyde. Hydrogen enhances cracking and production of light oxygenates and hydrocarbons. The light oxygenates may in turn be reincorporated into the reaction path, giving secondary products. However, the hydrocarbons do not react further. Analysis of the fresh and spent catalysts by XPS showed varying degrees of reduction of the oxide under different operating conditions that were consistent with the reaction results. Changing the proportion of the parent oxides showed that increased Zr favored formation of aldol products while increased Ce favored ketonization. This occurs by shifting the balance of the acid-base properties of the active sites. © 2010 Elsevier B.V.

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