ACS Catalysis
Research Article
purchased from Sigma-Aldrich. 4-Chlorophenol, 4-bromophe-
nol, 4-iodophenol, 1-chloro-4-fluorobenzene, 4-chlorotoluene,
4-chloroanisole, 4-chloroaniline, hydriodic acid (57 wt %), and
1 wt % Pd on carbon were purchased from Aldrich. 4-Bromo-
2-chlorophenol was purchased from Acros Organics. 4-Bromo-
3-chlorophenol and 2-bromo-4-chlorophenol were purchased
from Alfa Aesar. Hexane (HPLC grade), sodium iodide,
sodium bromide, hydrochloric acid, and ethanol were
purchased from Fisher. Benzene-d6 was purchased from
Cambridge Isotope Laboratories. Sodium hydroxide (NaOH)
pellets and hydrobromic acid (48 wt %) were obtained from
Fisher Scientific. Pluronic P104 was obtained from BASF. All
chemicals were used as received without further purification.
Synthesis of High-Surface-Area Ceria. This material was
prepared following our previously published method.11 In a
typical synthesis, Ce(NO3)3·6H2O (8.80 g, 20.3 mmol) and
the nonionic block copolymer surfactant Pluronic P104 (10.1
g, 1.71 mmol) were dissolved in ethanol (200 mL) with
vigorous stirring (800 rpm) for 3 h. The solution was cast into
a large crystallization dish and placed into an oven preheated at
65 °C for evaporation. After 12 h, the gel was placed into a
preheated (150 °C) oven for an additional 12 h. The yellow
powder was calcined in air at 450 °C for 4 h with a ramp rate
of 1 °C min−1.
HDH Reactions. In a typical procedure, the catalyst (20
mg, 1.9 μmol Pd) and 4-Cl-PhOH solution (4 mL, 10 mM,
solvent) were added to a 10 mL glass tube. The tube was
sealed with a septum and purged with H2 for 5 min at a rate of
20 mL min−1, and the pressure relief needle was removed. The
reaction tube was then placed in an oil bath that was
maintained at 35 °C under stirring (800 rpm). After the
desired time, the reaction mixture (hexane) was centrifuged.
For the reaction in water, the products were extracted with
ethyl acetate (1 mL, 4 times). A 200 μL aliquot of the solution
was taken, mixed with 50 μL of a 4-methylbenzylalcohol (25
mM) internal standard, diluted to 1.00 mL with ethanol, and
analyzed using an Agilent GC-MS instrument (7890A, 5975C)
with an HP-5MS column. The run started at 60 °C held for 2
min, and the temperature was then ramped to 150 °C at 10 °C
min−1. Then, the temperature was ramped to 300 °C at 20 °C
min−1, and then it was held at 300 °C for 1 min. Mass balances
between 90 and 100% were obtained for all the catalytic
conversions.
Apparent rate constants were calculated from the time
versus ln[substrate] plots and normalized to the amount of Pd
catalyst employed in the reaction (MPd). Full kinetic profiles
were modeled as a sequence of 4-Cl-PhOH HDH and
hydrogenation of the intermediate PhOH according to
Synthesis of Ceria Nanorods. This material was prepared
following a previously published method.25 An aqueous
solution of Ce(NO3)3·6H2O (0.4 M, 6.96 g, 40 mL) and
NaOH (10.3 M, 115.2 g, 280 mL) was mixed and kept under
stirring (30 min) at r.t. The solution was transferred into a
Teflon-lined stainless-steel autoclave for hydrothermal treat-
ment in an oven (100 °C for 24 h). The precipitate was
separated by centrifugation and washed several times with
deionized (DI) water and ethanol. The obtained precipitate
was dried under vacuum at r.t. and then calcined at 450 °C for
4 h with a ramp rate of 1 °C min−1.
Synthesis of Silica. This material was prepared following a
previously published method.26 Hexadecyltrimethylammonium
bromide (5.0 g, 13.7 mmol) was dissolved in DI water (2.4 L)
followed by addition of NaOH (2 M, 17.5 mL). The solution
was stirred for 1 h at 80 °C. Tetraethyl orthosilicate (25.0 mL,
113 mmol) was then added dropwise to the solution over 10−
12 min. Stirring was continued for 2 h at 80 °C. The solution
was filtered, washed with abundant water and methanol,
vacuum-dried overnight, and then calcined at 550 °C for 6 h
with a ramp rate of 1 °C min−1.
Synthesis of Pd/MxO2. The supported Pd catalysts were
prepared by incipient wetness impregnation with a 1 wt % Pd
loading relative to the mass of the supports. In a typical
synthesis, Pd(O2CCH3)2 (0.0419 g, 0.187 mmol) was
dissolved in acetone (4.0 mL). The support (2.00 g) was
placed in a mortar and impregnated with the Pd solution in 0.2
mL increments. After each impregnation step, the catalyst was
mixed thoroughly with a pestle until seemingly dry. The
material was calcined at 350 °C for 2 h with a 2.5 °C min−1
ramp rate and then reduced under flowing hydrogen at 350 °C
for 2 h with a 2.5 °C min−1 ramp rate. The flow of hydrogen
gas was set at 0.25 mL s−1.
Synthesis of Sodium 4-Chlorophenoxide. A NaOH
solution (5.1 mmol in 20 mL methanol) was added dropwise
to a 4-chlorophenol (4-Cl-PhOH) solution (5.0 mmol in 15
mL of methanol) under a N2 atmosphere while stirring at 550
rpm and at r.t. The solution was stirred for additional 30 min at
r.t. followed by solvent evaporation under vacuum.
[4ClPhOH] = [4ClPhOH]0 e−k t
1
[cyclohexanone] = [4ClPhOH]0
Ä
Å
Å
Å
Å
Å
1
(k2 e−k t − k1 e−k t
)
1
2
1 −
Å
Å
Å
k2 − k1
Å
Ç
k1[4ClPhOH]
k2 − k1
0 (e−k t − e−k t
)
1
2
[PhOH] =
where k1 is the pseudo-first order rate constant for the first step
(obtained from the initial rate measurement) and k2 is the
pseudo-first order rate constant for the second step.
Surface Area and Porosimetry. Textural properties of
the supports and catalysts were measured by nitrogen sorption
isotherms at −196 °C using a Micromeritics Tristar analyzer.
The surface areas were calculated by the Brunauer−Emmett−
Teller (BET) method. Pretreatment of samples was done
under flowing N2 for 6 h at 100 °C.
Inductively Coupled Plasma-Optical Emission Spec-
troscopy. Pd loadings were analyzed using a PerkinElmer
Optima 2100 DV inductively coupled plasma-optical emission
spectroscope. Pd-containing samples (5 mg) were digested for
24 h in 2 mL of aqua regia. After digestion, the solution was
diluted to 12 mL using DI water (17.6 MΩ cm). The solution
was filtered, and the filtrate (12 mL) was used to analyze the
amount of Pd in the samples.
Powder X-ray Diffraction. Diffraction patterns were
collected on a Bruker Siemens D500 X-ray diffractometer
equipped with Cu Kα radiation (40 kV, 44 mA) over the range
of 10−100° (2θ). PXRD samples were prepared by placing fine
powders onto a background-less polycarbonate sample holder.
Crystallite sizes were calculated using the Scherrer equation
Kλ
β cos θ
Dhkl
=
10554
ACS Catal. 2021, 11, 10553−10564