4 research outputs found
Hydrodesulfurization of Dibenzothiophene over MCM-41-Supported Pd and Pt Catalysts
Three series of aluminosilicate MCM-41 (Al-MCM-41) were
synthesized
using different aluminum sources, including aluminum isopropoxide
(AlM-I), pseudoboehmite, and aluminum sulfate, by a hydrothermal method.
The hydrodesulfurization (HDS) performance of the Al-MCM-41-supported
Pd and Pt catalysts prepared with chlorided precursors were evaluated
with dibenzothiophene (DBT) as the model sulfur-containing molecule,
in comparison with those supported on a siliceous MCM-41 (SiM). Pd/SiM
and Pt/SiM were not promising for DBT HDS because of their relatively
low activities and the rapid irreversible deactivation. Pd and Pt
supported on the acidic Al-MCM-41 materials showed higher dispersion
and enhanced HDS performances. AlM-I, which possessed the strongest
acidity, was the most promising among the mesoporous materials investigated.
The deactivated Pd/AlM-I and Pt/AlM-I can be reversibly regenerated
by H<sub>2</sub> reduction. DBT HDS over the Pd catalysts predominantly
took the hydrogenation (HYD) pathway, whereas the direct desulfurization
(DDS) pathway and HYD pathway were comparable for the Pt catalysts.
Increasing the support acidity had no positive effect on the DDS activity
of Pd but significantly enhanced its HYD activity, while the increase
in the rate constant of DDS pathway was close to that of the HYD pathway
for Al-MCM-41-supported Pt catalysts. The effect of the acid properties
of the supports on the HDS performance of Pd and Pt catalysts was
discussed by considering the formation of “electronic-deficient”
particles and the hydrogen spillover process
Phase Effect of Ni<sub><i>x</i></sub>P<sub><i>y</i></sub> Hybridized with g‑C<sub>3</sub>N<sub>4</sub> for Photocatalytic Hydrogen Generation
The
use of noble metal-free nickel phosphides (Ni<sub><i>x</i></sub>P<sub><i>y</i></sub>) as suitable cocatalysts in
photocatalytic hydrogen (H<sub>2</sub>) generation has gained a lot
of interest. In this paper, for the first time, three different crystalline
phases of nickel phosphides, Ni<sub>2</sub>P, Ni<sub>12</sub>P<sub>5</sub>, and Ni<sub>3</sub>P, were synthesized and then hybridized
with g-C<sub>3</sub>N<sub>4</sub> to investigate the phase effect
of Ni<sub><i>x</i></sub>P<sub><i>y</i></sub> on
photocatalytic H<sub>2</sub> generation. It has been found that all
three phases of Ni<sub><i>x</i></sub>P<sub><i>y</i></sub> work as effective cocatalysts for the enhancement of visible
light H<sub>2</sub> generation with g-C<sub>3</sub>N<sub>4</sub>.
The effective charge transfer between g-C<sub>3</sub>N<sub>4</sub> and Ni<sub><i>x</i></sub>P<sub><i>y</i></sub>, demonstrated by photoelectrochemical properties, photoluminescence,
and time-resolved diffused reflectance, contributes to the enhanced
photocatalytic H<sub>2</sub> generation performance. Interestingly,
Ni<sub>2</sub>P/g-C<sub>3</sub>N<sub>4</sub> showed the highest photocatalytic
activity among the three Ni<sub><i>x</i></sub>P<sub><i>y</i></sub>/g-C<sub>3</sub>N<sub>4</sub>. Ni<sub><i>x</i></sub>P<sub><i>y</i></sub> with a higher ratio of phosphorus
(Ni<sub>2</sub>P) can accelerate charge transfer and provide more
Ni–P bonds, leading to a preferable H<sub>2</sub> generation
performance
Efficient Ni<sub>2</sub>P/SiO<sub>2</sub> Catalysts with Enhanced Performance for the Hydrogenation of 4,6-Dimethyldibenzothiophene and Phenanthrene
Highly dispersed Ni2P catalysts (Ni2P/SiO2-DPx) were prepared by reducing
the passivation-free
precursors, which were obtained through the phosphidation of nickel
phyllosilicate with sodium hypophosphite. The strong metal–support
interaction of nickel phyllosilicate and the mild phosphidation conditions
prevented the agglomeration of Ni particles and resulted in a smaller
Ni2P particle size. The superior catalytic performance
of the as-prepared Ni2P/SiO2-DP catalysts was
evaluated in hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene
and the hydrogenation of phenanthrene, in comparison with Ni2P/SiO2-IM and CoMoS/Îł-Al2O3 prepared from a conventional incipient wetness impregnation method.
The passivation-free Ni-P/SiO2-DPx precursors
showed great storage stability, and Ni2P/SiO2-DP derived from the stored Ni-P/SiO2-DP precursors exhibited
negligible loss of HDS activity. This method provides a potential
preparation strategy for the industrial applications of transition
metal phosphides without the temperature-programmed reduction and
the subsequent passivation process
Aqueous Phase Hydrodeoxygenation of Phenol over Ni<sub>3</sub>P‑CePO<sub>4</sub> Catalysts
Unsupported Ni<sub>3</sub>P-CePO<sub>4</sub> catalysts were prepared
by coprecipitation, followed by drying, calcination, and temperature-programmed
reduction. The prepared catalysts were characterized by XRD, N<sub>2</sub> adsorption–desorption, TEM, STEM-EDS elemental mapping,
XPS, NH<sub>3</sub>-TPD, FT-IR of adsorbed pyridine, and H<sub>2</sub>-TPR. Their catalytic performances in hydrodeoxygenation (HDO) were
investigated using an aqueous solution of phenol (5.0 wt %) as the
feed. CePO<sub>4</sub> was generated in coprecipitation and stable
in the subsequent drying, calcination, and temperature-programmed
reduction (final temperature 500 °C). It is shown that the addition
of CePO<sub>4</sub> resulted in enhanced HDO activity, and a maximum
activity appeared at a Ce/Ni ratio of 0.3. The presence of CePO<sub>4</sub> improved the dispersion of Ni<sub>3</sub>P significantly,
leading to enhanced hydrogenation activity. CePO<sub>4</sub> served
as the major dehydration sites as well because of its surface acidity
(mainly Lewis acid). In addition, the kinetics of the aqueous phase
HDO of phenol and cyclohexanol catalyzed by Ni<sub>3</sub>P and by
Ni<sub>3</sub>P-CePO<sub>4</sub> with Ce/Ni ratio of 0.3 were investigated