6 research outputs found
Catalytic Conversion of Guaiacol Catalyzed by Platinum Supported on Alumina: Reaction Network Including Hydrodeoxygenation Reactions
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
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
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
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
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
Layered
borosilicate zeolite precursor ERB-1P (Si/B = 11) is delaminated
via isomorphous substitution of Al for B using a simple aqueous AlÂ(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