6 research outputs found

    Catalytic Conversion of Guaiacol Catalyzed by Platinum Supported on Alumina: Reaction Network Including Hydrodeoxygenation Reactions

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    The conversion of guaiacol catalyzed by Pt/γ-Al<sub>2</sub>O<sub>3</sub> in the presence of H<sub>2</sub> was investigated with a flow reactor at 573 K and 140 kPa. Dozens of reaction products were identified, with the most abundant being phenol, catechol, and 3-methylcatechol. The kinetically significant reaction classes were found to be hydrogenolysis [including hydrodeoxygenation (HDO)], hydrogenation, and transalkylation. Selectivity–conversion data were used to determine an approximate quantitative reaction network accounting for the primary products, and a more detailed qualitative network was also inferred. Catalytic HDO was evidenced by the production of anisole and phenol. The HDO selectivity increased with an increasing H<sub>2</sub> partial pressure and a decreasing temperature. Products formed by transalkylation reactions match those produced in the conversion catalyzed by HY zeolite, in which no deoxygenated products were observed

    Conversion of Anisole Catalyzed by Platinum Supported on Alumina: The Reaction Network

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    The conversion of anisole (a compound representative of bio-oils) in the presence of H<sub>2</sub> was investigated with a flow reactor operated at a temperature of 573 K and a pressure of 140 kPa with a platinum on alumina catalyst. Analysis by gas chromatography–mass spectrometry led to the identification of more than 40 reaction products, the most abundant being phenol, 2-methylphenol, benzene, and 2,6-dimethylphenol. The kinetically significant reaction classes were transalkylation, hydrodeoxygenation, and hydrogenation. Selectivity-conversion data were used to determine an approximate quantitative reaction network accounting for phenol, 2-methylphenol, 2-methylanisole, and 4-methylphenol as primary products. Pseudo-first-order rate constants for the formation of these products are 12, 2.8, 0.14, and 0.039 L/(g of catalyst × h), respectively. A more complete qualitative network was inferred on the basis of the observed products and the assumption that the reaction classes leading to the most abundant primary products were responsible for the minor and trace products. The removal of oxygen was evidenced by the production of benzene

    Design of a High-Pressure Flow-Reactor System for Catalytic Hydrodeoxygenation: Guaiacol Conversion Catalyzed by Platinum Supported on MgO

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    A high-pressure once-through plug-flow-reactor system is reported for characterization of hydroprocessing reactions of biomass-derived compounds. All of the reactants are liquids. Data are presented for conversion of guaiacol catalyzed by Pt/MgO and, in much less detail, CoMo/Al<sub>2</sub>O<sub>3</sub>. The data demonstrate the advantages of high pressure in such reactions, determining a pseudo-first-order rate constant for guaiacol conversion at 523 K and 69 bar of approximately 55 L of organic reactant solution (g of catalyst)<sup>–1</sup> h<sup>–1</sup>. This value is 2 orders of magnitude greater than that observed at 573 K and 1.4 bar

    Nano-sized Metallic Nickel Clusters Stabilized on Dealuminated beta‑Zeolite: A Highly Active and Stable Ethylene Hydrogenation Catalyst

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    Supported Ni catalysts were synthesized using the beta-zeolite framework, with and without the framework Al, as a platform for dispersing Ni. The silanol nest sites of dealuminated zeolite beta provide isolated cationic Ni sites that can be reduced under relatively mild conditions to create highly dispersed metal clusters. Compared to the Ni sites present in Ni-[Al]-beta-19, Ni-[DeAl]-beta exhibit a 20-fold increase in the apparent reaction rate for C2H4 hydrogenation and is stable, with little deactivation over 16 h of catalysis. Ni K-edge X-ray absorption spectroscopy (XAS), as well as CO adsorption monitored with Fourier transform infrared spectroscopy, shows that in the oxidized Ni-[DeAl]-beta catalyst Ni reoccupies vacant silanol nests produced from dealumination. After reductive treatment, XAS shows that approximately 50% of Ni is reduced to metallic Ni, forming clusters that are approximately 1 nm in size. Scanning transmission electron microscopy images are consistent with the absence of large (>1 nm) metallic Ni clusters. These results indicate that [DeAl]-beta can be used to synthesize isolated cationic Ni sites as well as stabilize highly dispersed metal clusters that can be used as a highly active and stable C2H4 hydrogenation catalyst

    Role of Delamination in Zeolite-Catalyzed Aromatic Alkylation: UCB‑3 versus 3‑D Al-SSZ-70

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    Delaminated zeolite UCB-3 exhibits 2.4-fold greater catalytic activity relative to its three-dimensional (3D) zeolite counterpart, Al-SSZ-70, and 2.0-fold greater activity (per catalyst mass) when compared with industrial catalyst MCM-22, for the alkylation of toluene with propylene at 523 K. The former increase is nearly equal to the observed relative increase in external surface area and acid sites upon delamination. However, at 423 K for the same reaction, UCB-3 exhibits a 3.5-fold greater catalytic activity relative to 3D Al-SSZ-70. The higher relative rate enhancement for the delaminated material at lower temperature can be elucidated on the basis of increased contributions from internal acid sites. Evidence of possible contributions from such acid sites is obtained by performing catalysis after silanation treatment, which demonstrates that although virtually all catalysis in MCM-22 occurs on the external surface, catalysis also occurs on internal sites for 3D Al-SSZ-70. The additional observed enhancement at low temperatures can therefore be rationalized by greater access to internal active sites as a result of sheet breakage during delamination. Such breakage leads to shorter characteristic internal diffusion paths and was visualized using TEM comparisons of UCB-3 and 3D Al-SSZ-70

    Single-Step Delamination of a MWW Borosilicate Layered Zeolite Precursor under Mild Conditions without Surfactant and Sonication

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    Layered borosilicate zeolite precursor ERB-1P (Si/B = 11) is delaminated via isomorphous substitution of Al for B using a simple aqueous Al­(NO<sub>3</sub>)<sub>3</sub> treatment. Characterization by PXRD shows loss of long-range order, and TEM demonstrates transformation of rectilinear layers in the precursor to single and curved layers in the delaminated material. N<sub>2</sub> physisorption and base titration confirm the expected decrease of micropore volume and increase in external surface area for delaminated materials relative to their calcined 3D zeolite counterpart, whereas FTIR and multinuclear NMR spectroscopies demonstrate synthesis of Brønsted acid sites upon delamination. Comparative synthetic studies demonstrate that this new delamination method requires (i) a borosilicate layered zeolite precursor, in which boron atoms can be isomorphously substituted by aluminum, (ii) neutral amine pore fillers instead of rigid and large quaternary amine SDAs, and (iii) careful temperature control, with the preferred temperature window being around 135 °C for ERB-1P delamination. Acylation of 2-methoxynaphthalene was used as a model reaction to investigate the catalytic benefits of delamination. A partially dealuminated delaminated material displays a 2.3-fold enhancement in its initial rate of catalysis relative to the 3D calcined material, which is nearly equal to its 2.5-fold measured increase in external surface area. This simple, surfactant- and sonication-free, mild delamination method is expected to find broad implementation for the synthesis of delaminated zeolite catalysts
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