Fabrication of Pd-based metal-acid-alkali multifunctional catalysts for one-pot synthesis of MIBK

Article abstract of DOI:10.1016/S1872-2067(18)63092-X

The one-pot synthesis of methyl isobutyl ketone (MIBK) from acetone using multifunctional catalysts is an important sustainable organic synthesis method with high atom and energy efficiency. Herein. we report a series of Pd supported on mixed metal oxide (MMO) catalysts with controllable acidic/basic/metallic sites on the surface. We study the relationship between the nature, synergy, and proximity of active sites and the catalytic performance of the multifunctional catalyst in the tandem reaction, in detail. In the existence of Lewis acid and base sites, the catalysts with medium-strength acidic/basic sites show preferred activity and/or MIBK selectivity. For multifunctional catalysts, the catalytic properties are more than just a collection of active sites, and the Pd/Mg₃Al-MMO catalyst possessing 0.1% Pd loading and ~0.4 acid/base molar ratio exhibits the optimal 42.1% acetone conversion and 37.2% MIBK yield, which is among the best reported so far for this tandem reaction under similar conditions. Moreover, the proximity test indicates that the intimate distance between acidic/basic/metallic sites can greatly shorten the diffusion time of the intermediate species from each active site, leading to an enhancement in the catalytic performance.

Full text of DOI:10.1016/S1872-2067(18)63092-X

Chinese Journal of Catalysis 39 (2018) 1384–1394
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Fabrication of Pd‐based metal‐acid‐alkali multifunctional catalysts
for one‐pot synthesis of MIBK
Rui Ma a,b, Yunpeng Lia,b, Guandong Wua,b, Yufei Hea,b,*, Junting Fenga,b, Yingying Zhaoa,b,*,
Dianqing Li a,b
a State Key Laboratory of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China
b Beijing Engineering Center for Hierarchical Catalysts, Beijing University of Chemical Technology, Beijing 100029, China
A R T I C L E I N F O
A B S T R A C T
Article history:
The one‐pot synthesis of methyl isobutyl ketone (MIBK) from acetone using multifunctional cata‐
lysts is an important sustainable organic synthesis method with high atom and energy efficiency.
Herein. we report a series of Pd supported on mixed metal oxide (MMO) catalysts with controllable
acidic/basic/metallic sites on the surface. We study the relationship between the nature, synergy,
and proximity of active sites and the catalytic performance of the multifunctional catalyst in the
tandem reaction, in detail. In the existence of Lewis acid and base sites, the catalysts with medi‐
um‐strength acidic/basic sites show preferred activity and/or MIBK selectivity. For multifunctional
catalysts, the catalytic properties are more than just a collection of active sites, and the
Pd/Mg3Al‐MMO catalyst possessing 0.1% Pd loading and ~0.4 acid/base molar ratio exhibits the
optimal 42.1% acetone conversion and 37.2% MIBK yield, which is among the best reported so far
for this tandem reaction under similar conditions. Moreover, the proximity test indicates that the
intimate distance between acidic/basic/metallic sites can greatly shorten the diffusion time of the
intermediate species from each active site, leading to an enhancement in the catalytic performance.
© 2018, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Received 26 February 2018
Accepted 24 April 2018
Published 5 August 2018
Keywords:
One‐pot synthesis of methyl isobutyl
ketone
Multifunctional catalyst
Pd
Mg3Al mixed metal oxide
Synergy effect
Proximity
Published by Elsevier B.V. All rights reserved.
1. Introduction
intermediate species. In addition, a homogeneous acid catalyst
(sulfuric acid) and base catalyst (sodium carbonate) are widely
Methyl isobutyl ketone (MIBK) is one of the most widely
used aliphatic ketones, and is as an excellent solvent in the
paint industry and an important reagent for dewaxing mineral
oils [1–3]. Traditionally, MIBK is manufactured through a
three‐step process including the aldol condensation of acetone
to diacetone alcohol (DAA), dehydration of DAA to mesityl ox‐
ide (MO), and hydrogenation of MO to MIBK. There are com‐
mon problems in this three‐step process, including the inter‐
mittent operation and multiple separation and purification of
used in the process, which causes severe environmental pollu‐
tion and equipment corrosion [4,5]. Therefore, the conversion
of acetone using a practical and efficient process will be highly
beneficial. The one‐pot synthesis strategy, allowing for differ‐
ent reactions to be carried out in a single vessel without com‐
plicated separation and purification between steps, is an alter‐
native to stop‐and‐go syntheses and has economic and envi‐
ronmental benefits [6–8]. As for the one‐pot synthesis of MIBK,
the overall process is exothermic (ΔH = −117 kJ/mol), making
* Corresponding author. Fax: +86‐10‐64425385; E‐mail: yfhe@mail.buct.edu.cn
# Corresponding author. Fax: +86‐10‐64437866; E‐mail: zhaoyy@mail.buct.edu.cn
This work was supported by the National Key Research and Development Program of China (2016YFB0301601), the National Natural Science Foun‐
dation (21706009) and the Fundamental Research Funds for the Central Universities (BUCTRC201725, JD1816).
DOI: 10.1016/S1872‐2067(18)63092‐X | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 39, No. 8, August 2018

Rui Ma et al. / Chinese Journal of Catalysis 39 (2018) 1384–1394
1385
this cascade process a practicable reaction in thermodynamics
[9,10]. However, the formation of DAA and MO is thermody‐
namically limited by unfavorable equilibria; therefore, it is vital
to design a catalyst that can simultaneously drive these three
steps. The development of heterogeneous multifunctional cat‐
alysts enables the one‐pot tandem process to be carried out in
an environmentally safe and efficient manner.
Pd and Pt, due to their excellent hydrogenation property,
are commonly selected as the active metals in the one‐pot syn‐
thesis of MIBK from acetone [11–15]. Therefore, studies of het‐
erogeneous multifunctional catalysts for the tandem reaction
mainly focus on designing and synthesizing suitable supports.
there have been few in‐depth studies on the synergistic effect
of acidic/basic/metallic sites on catalytic performance in the
tandem reaction, especially the effect of the number and prox‐
imity of acidic/basic/metallic sites.
In this paper, Pd supported on MOx (M = Ca, Mg, Al, Ti) and
active carbon were prepared for the one‐pot synthesis of MIBK
to study the effect of acidity and basicity over the bifunctional
catalysts on the tandem reaction. A series of multifunctional
catalysts with a combination of metallic/acidic/basic active
sites were designed using LDH materials. By adjusting the met‐
al ratio within the brucite‐like layers of the LDH precursor, the
relationship between the catalytic property and density of
acidic/basic sites was revealed. We further studied the proxim‐
ity of the three active sites on the catalytic performance by a
physical mixing method, and a possible mechanism was pro‐
posed to demonstrate the synergistic effect of
basic/acidic/metallic sites in the one‐pot synthesis of MIBK
from acetone. Moreover, the obtained Pd/Mg3Al‐MMO multi‐
functional catalyst was optimized by using the deposi‐
tion‐precipitation method, followed by testing of the catalyst
stability.
For example, Lin et al. [16] reported
a Na‐modified
MgO‐supported Pd bifunctional catalyst that showed high ace‐
tone conversion due to the enhanced basic strength of the
support. Wang et al. [17] deposited Pd nanoparticles on a
chromium terephthalate MIL‐101, and found that the high den‐
sity and improved accessibility of acid sites (Cr3+) led to high
selectivity towards MIBK; however, this catalyst showed poor
stability, with the activity decreasing by 40% after four usages.
Furthermore, Robert’s study indicated that strong acid sites
could promote the dehydration of DAA to MO under mild reac‐
tion conditions [18]. In recent years, more and more new mate‐
rials have been used in the one‐pot synthesis of MIBK from
acetone, and there is agreement in the literature that the com‐
bination of multiple active sites can shift the equilibrium of the
condensation step in favor of MO by the simultaneous and ir‐
reversible hydrogenation to MIBK [19–21]. However, there
have been few in‐depth studies on the synergistic effect of
these metallic/acidic/basic sites on multifunctional catalysts on
the catalytic performance in this tandem reaction, let alone
research on the effect of proximity of the multi‐active sites.
2. Experimental
2.1. Materials
Analytical‐grade
chemical
reagents
including
Mg(NO3)2·6H2O, Al(NO3)3·9H2O, TiO2, NaCl, MgO, TiCl4, MgO,
AlOOH, Na2SO3·9H2O, PdCl2, and urea were purchased from
Sigma‐Aldrich and used without further purification. The water
used in all the experiments was deionized and had an electrical
conductivity < 10–6 S/cm.
Layered double hydroxides (LDHs) are
a family of
two‐dimensional (2D) anionic clay materials with the general
2.2. Preparation of the support precursor
formula [M2+
M
1–x
x(OH)2]x+(An–)x/n·mH2O, where M2+ and M3+
3+
represent metallic cations and An– is a charge‐balancing anion
[22–24]. Based on the construction principle of LDHs, the metal
cations within the brucite‐like layers are uniformly distributed
at the atomic level, and the ratio of M2+/M3+ can be tuned in a
certain range [25]. In addition, LDHs possess abundant acidic
The MgxAl‐LDHs (x = 1, 2, 3, 4, 5) were prepared by a hy‐
drothermal method. For example, to prepare Mg2Al‐LDHs, 7.52
g Mg(NO3)2·6H2O, 5.48 g Al(NO3)3·9H2O, and 6.19 g urea (n
(urea):n(NO3–) = 1:1) were dissolved in 70 mL of deionized
water, then transferred into a 100 mL autoclave and aged at
150 °C for 6 h. The resulting sediment was centrifuged and
washed with deionized water several times until the pH
reached 7. After drying at 70°C overnight, the Mg2Al‐LDH pre‐
cursor was obtained. LDHs with other Mg/Al ratios as well as
Mg3Ti‐LDHs, MgAl0.5Ti0.5‐LDHs, and Ca1.5Mg1.5Al‐LDHs were
prepared via the same method.
The Ca3Ti‐LDH precursor was prepared by a deposi‐
tion‐precipitation method. A NaOH (1.0 mol/L) and Ca(OH)2
mixed solution was added to TiCl4 (dissolved in diluted HCl
with the volume proportion of 1:1) at constant pH = 12. The
final product was filtered, washed thoroughly with deionized
water, and dried overnight at 70 °C.
–
and basic sites associated with the presence of O2 ‐Mn+ ac‐
id‐base pairs within the brucite‐like layers [26]. Because of the
uniform dispersion of M2+ and M3+ cations in the layers and the
cation‐tunability of LDH materials, the nature, strength and
relative number of acidic/basic sites can be finely controlled.
The memory effect is another important character of LDH ma‐
terials; namely, LDHs can be converted to well‐dispersed mixed
metal oxides (MMO) by calcination at 450–600 °C and retain
the nature of the brucite‐like layers, such as highly dispersed
metal cations and surface acidic/basic sites [27,28]. The large
number of adjustable acidic/basic sites on MMOs makes it a
class of excellent solid acid/base catalysts. Brucite‐like hy‐
drotalcite
containing
Ni2+,
Co2+,
or
Fe2+
and
Pd/MgAl‐hydrotalcites have been reported as catalyst precur‐
sors or catalysts in the synthesis of MIBK, and the effect of ei‐
ther the acidity or alkalinity of hydrotalcites on catalytic per‐
formance have been intensively investigated [29–32]. However,
2.3. Preparation of supported Pd catalysts
Pd was deposited on various supports (MgO, Al2O3, TiO2, C,
MgxAl‐LDHs, Mg3Ti‐LDHs, Ca3Ti‐LDHs, MgAl0.5Ti0.5‐LDHs,

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Rui Ma et al. / Chinese Journal of Catalysis 39 (2018) 1384–1394
Ca1.5Mg1.5Al‐LDHs) using an impregnation method. Typically,
3.0 g support was suspended in 25 mL of Na2PdCl4 aqueous
solution with 0.1% nominal Pd loading, then stirred vigorously
at 80 °C until the water was removed by evaporation. Subse‐
quently, the powder was dried at 80°C for 5 h, followed by cal‐
cination at 450 °C in air for 2 h, and reduction in 10% H2/Ar at
450 °C for 5 h. Pd/CaO was prepared by depositing Pd on
Ca(OH)2, calcining at 700 °C, and then reducing at 450 °C for 5 h
in a 10% H2/Ar stream. The corresponding catalysts were de‐
noted Pd/MgO, Pd/Al2O3, Pd/TiO2, Pd/C, Pd/MgxAl‐MMO,
Pd/Mg3Ti‐MMO, Pd/Ca3Ti‐MMO, Pd/MgAl0.5Ti0.5‐MMO, and
Pd/Ca1.5Mg1.5Al‐MMO. A Pd/Mg3Al‐MMO catalyst with 0.1% Pd
loading was also synthesized by a deposition‐precipitation
method (DP). First, 3.0 g of Mg3Al‐MMO powder was mixed
with 10 mL of deionized water, and then a designated amount
of NaOH solution was added to the mixture to obtain a fixed pH
of 12. Subsequently, a Na2PdCl4 aqueous solution (3.0 mL, 10.0
mmol/L) was added dropwise, and the suspension was stirred
for 5 h at room temperature, followed by a centrifugation pro‐
cess, drying at 80 °C overnight, calcination at 450°C in air for 2
h, and reduction in 10% H2/Ar stream for 5 h. The obtained
catalyst was denoted Pd/Mg3Al‐MMODP.
tion in the range of 1675–1400 cm–1.
2.5. Reaction system and procedure
The general process of the one‐pot synthesis of MIBK in liq‐
uid catalyzed by the solid catalysts is as follows. The test was
performed in a 25 mL stainless steel autoclave provided with a
pressure gauge and a magnetic stirrer. Typically, the autoclave
was charged with 0.35 g of catalyst and 10 mL of acetone. Be‐
fore the reaction, the autoclave was purged three times with H2,
followed by pressurizing with H2 to 1.8 MPa. Then, the auto‐
clave was heated to 120 °C with a speed of 220 r/min. When
the temperature rose to 120 °C, the H2 pressure increased to
2.8 MPa, and the experiment was carried out for 5 h. In sum‐
mary, the reactions were all carried out in a 25 mL autoclave
with 10 mL of acetone and 0.35 g of catalyst, and were kept at
120°C for 5 h under 2.8 MPa H2 atmosphere. After the reaction,
the autoclave was cooled using an ice bath, and the reaction
mixture was separated from the catalyst by filtering. Analysis of
the liquid product was performed in a GC‐FID (Agilent 7890B)
with a capillary column (DB‐WAX), using n‐propanol as the
internal standard. The carbon balance determined from the
liquid products was (100 ± 2)%. The conversion of acetone,
selectivity of each product, and yield of MIBK are defined as
follows:
2.4. Characterization
The specific surface area of the samples was calculated ac‐
cording to the Brunauer‐Emmett‐Teller (BET) method using a
Quantachrome Autosorb‐1 system. X‐ray diffraction (XRD)
measurements were carried out on a Rigaku UItima III X‐ray
powder diffractometer (Cu Kα radiation) at a scanning rate of
10°/min. Chemical analysis was performed using inductively
coupled plasma emission spectroscopy (ICP‐AES, Shimadzu
ICPS‐75000). The morphology and particle size of the Pd parti‐
cles were observed by a JEOL‐2100F HRTEM.
Acetone coversion = (1 ‒ mol of acetone in the product/mol
of acetone in the end)  100%
Selectivity of products = (mol of acetone converted to the
product/mol of acetone reacted)  100%
MIBK yield = acetone conversion  selectivity of MIBK.
3. Results and discussion
3.1. Synthesis of MIBK from acetone over bifunctional catalysts
CO2 and NH3 temperature‐programmed desorption (TPD) of
the samples was conducted on a Micrometric ChemiSorb 2750
chemisorption instrument with a thermal conductivity detector
(TCD). About 0.10 g of a sample was loaded in a quartz reactor.
Before CO2‐TPD and NH3‐TPD, the samples were kept in a
stream of CO2/NH3 until the adsorption was saturated, fol‐
lowed by treatment with He for 30 min. CO2/NH3‐TPD signals
were recorded from 50 to 500 °C with a He flow rate of 40
mL/min and a temperature ramp of 10 °C/min.
In situ diffuse reflectance Fourier transform infrared
(FT‐IR) spectroscopy of CO2 was carried out via a Bruker Ten‐
sor 27 instrument. The catalyst was pretreated under N2 flow
at 100°C for 1 h, followed by a background recording at a reso‐
lution of 4 cm–1. The catalyst was then exposed to CO2 flow for
another 1 h. Sample scanning of chemisorption on the catalysts
was conducted under 10–4 mbar at room temperature.
Py‐IR spectra were detected on a Thermo Nicolet FT‐IR
spectrometer. The solid sample was pretreated under H2 at 450
°C for 1 h. The solid sample (30 mg) was then pressed into a
self‐supporting wafer and treated under N2 at 200 °C for 1 h.
The background spectrum was recorded after cooling to room
temperature. Pyridine was introduced into the sample for 60
min. Finally, the spectrum was recorded with a 4 cm–1 resolu‐
The one‐pot synthesis of MIBK from acetone is a green and
economic process, including the condensation of acetone, de‐
hydration of diacetone alcohol, and selective hydrogenation of
the C=C bond. To determine the role of acidic and basic sites in
the tandem reaction, supported Pd bifunctional catalysts were
synthesized and then used in this process. As shown in Table 1,
Pd loaded on both acidic supports (Al2O3 and TiO2) and basic
supports (MgO and CaO) can convert acetone to produce MIBK.
However, Pd supported on active carbon, which is a common
neutral carrier, is inactive. Moreover, about 30% acetone con‐
version was achieved by the Pd/base bifunctional catalyst,
which is almost 2–3 times that of the Pd/acid catalyst, indicat‐
ing that the basic sites on the catalyst favor the condensation
step. IR and TPD were also used to characterize the type and
strength of the acidity and basicity on these catalysts, and the
results are shown in Fig. S1. For Pd/base catalysts, the adsorp‐
tion of bridged carbonates in the CO2‐IR spectrum indicates
that only the L‐basic sites were present on Pd/CaO and
Pd/MgO, and the basic strength of the Pd/CaO catalyst was
stronger than that of Pd/MgO [33,34]. As for the Pd/acid cata‐
lyst, only L‐acid sites existed on Pd/Al2O3 and Pd/TiO2, and the
order of acid strength was Pd/TiO2 > Pd/Al2O3 [35]. Although

Rui Ma et al. / Chinese Journal of Catalysis 39 (2018) 1384–1394
1387
Table 1
Catalytic properties of supported Pd bifunctional catalysts.
Selectivity (%)
Pd loading
(%)
Particle size Acetone conversion
Yield of MIBK
Sample
(nm)
(%)
(%)
DAA
3.4
1.0
1.0
18.8
0.0
MO
MIBK
92.3
62.1
90.0
72.0
0.0
Others *
3.8
2.0
7.4
7.9
Pd/Al2O3
Pd/TiO2
Pd/MgO
Pd/CaO
Pd/C
0.11
0.10
0.09
0.10
0.11
4.1
4.2
4.2
4.5
3.9
11.2
17.5
30.7
33.1
0.0
0.5
34.9
1.7
10.3
10.9
27.6
23.9
0.0
1.3
0.0
0.0
* Byproducts including propene, propane, isopropanol and some higher acetone condensation products.
the stronger basicity results in a higher acetone conversion, the
Pd/CaO catalyst showed poor selectivity to MIBK compared to
that of Pd/MgO, suggesting that stronger basic sites are not
good for the dehydration of DAA to produce MO. In this tandem
reaction, the total selectivity to MIBK + MO indicates that de‐
hydration of the intermediate DAA occurred. In the case of the
Pd/acid bifunctional catalyst, the selectivity to MIBK + MO of
the Pd/Al2O3 and Pd/TiO2 catalysts was higher than that for the
Pd/base bifunctional catalyst, which suggests that acidic sites
are favorable for the dehydration of DAA.
From the evaluation of the bifunctional catalyst, it was
found that basic sites favored the condensation of acetone and
different basic strengths showed distinct dehydration abilities.
Meanwhile, although the Pd/acid catalyst showed limited ace‐
tone conversion, acid sites can effectively inhibit the occur‐
rence of side reactions. In addition, there is a significant differ‐
ence in the interaction between different strengths of acid sites
and Pd particles, affecting the ability of MO hydrogenation to
produce MIBK. The results of the catalytic performance of
Pd/acid or Pd/base bifunctional catalysts indicate that various
active sites play different roles in the specific stages of the tan‐
dem reaction, and therefore, it will certainly be of interest to
Pd/Ca1.5Mg1.5Al‐MMO containing different strengths of acidic
and basic sites showed reduced acetone conversion (< 13%)
and poorer selectivity to MIBK (< 76%) compared with the
corresponding
bifunctional
catalysts.
However,
the
Pd/Mg3Al‐MMO catalyst exhibited enhanced acetone conver‐
sion (38%) and MIBK yield (31.6%) due to a positive synergis‐
tic effect. Moreover, the yield of MIBK was significantly reduced
when Ti was introduced into Mg3Al‐MMO (control of acidic
sites on MMO), indicating that the tandem reaction process is
sensitive to the strength and density of acidic and basic sites on
the multifunctional catalysts; even a slight change in the prop‐
erties of the acidic/basic sites can obviously affect the specific
processes in this tandem reaction. Thus, it is indispensable to
design a series of acid‐base supports with a continuously ad‐
justable density of acidic/basic sites to study the synergistic
effect between the acidic sites and basic sites in detail.
3.3. Role of the synergistic effect of acidic/basic sites
Due to the properties of the LDHs, it is feasible to fine‐tune
the acidic/basic sites by regulating the composition of the la‐
mellar metals. A series of Pd/MgxAl‐MMO multifunctional cata‐
lysts with Mg/Al atomic ratios from 1:1 to 5:1 were prepared
by the LDH precursor method for the investigation of the rela‐
tive amounts and synergistic effect of acidic/basic sites on cat‐
alytic performance in the one‐pot synthesis of MIBK from ace‐
tone. XRD analysis was used to investigate the structure of the
Pd/MgxAl‐MMO catalysts with different Mg/Al molar ratios. As
shown in Fig. 1(a), it is noteworthy that no Al2O3 characteristic
peaks were observed, indicating that alumina was present in an
amorphous form [36]. The diffraction peaks of MgO
(PDF#45‐1946) were detected in all five catalysts, and with
increasing Mg content, the intensity of the characteristic dif‐
fraction peak increased gradually. No Pd characteristic diffrac‐
tion peaks were detected, possibly because of the relatively low
Pd loading. The dispersion of the supported palladium on five
multifunctional catalysts (Pd/MgxAl‐MMO (x = 1, 2, 3, 4, 5)) was
design
multifunctional
catalysts
containing
acid‐
ic/basic/metallic active sites and investigate the relationship
between active sites and catalytic performance.
3.2. Catalytic properties of Pd/MMO multifunctional catalysts
Multi‐site catalysts containing acidic, basic and metallic sites
were prepared by the introduction of Pd on LDH materials that
possess consecutive acid and basic sites, followed by the calci‐
nation and reduction process. The obtained Pd/MMO catalysts
were then used in the tandem reaction, and the results are
listed in Table 2. It was found that the catalytic properties of
the multifunctional catalysts were more than just a collection of
active sites, and both positive and negative synergistic effects
were involved. In detail, Pd/Mg3Ti‐MMO, Pd/Ca3Ti‐MMO, and
Table 2
Catalytic properties of some Pd‐based mixed metal oxides.
Selectivity (%)
Pd loading
(%)
Acetone conversion Yield of MIBK
Sample
(%)
38.2
12.9
6.2
(%)
31.6
7.0
DAA
3.0
2.7
6.4
0.2
1.9
MO
7.4
0.2
0.9
0.0
0.1
MIBK
82.8
54.5
76.2
50.1
93.0
IPA
1.5
Others
5.3
Pd/Mg3Al‐MMO
Pd/Mg3Ti‐MMO
Pd/Ca3Ti‐MMO
Pd/Ca1.5Mg1.5Al‐MMO
Pd/Mg3Al0.5Ti0.5‐MMO
0.12
0.10
0.11
0.11
41.9
13.2
48.6
2.7
0.7
3.4
1.1
2.2
4.7
9.0
4.5
0.09
21.6
20.1
* Byproducts including propene, propane, isopropanol and some higher acetone condensation products.

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Rui Ma et al. / Chinese Journal of Catalysis 39 (2018) 1384–1394
(a)
(b)
(c)
25
20
15
10
5
40
30
20
10
0
0
2
3
4
5
6
2
3
4
5
6
Particle size (nm)
Particle size (nm)
(e)
(f)
(d)
30
25
20
15
10
5
30
25
20
15
10
5
25
20
15
10
5
0
0
0
2
3
4
5
6
2
3
4
5
6
2
3
4
5
6
Particle size (nm)
Particle size (nm)
Particle size (nm)
Fig. 1. (a) XRD patterns of Pd/Mg1Al‐MMO (1), Pd/Mg2Al‐MMO (2), Pd/Mg3Al‐MMO (3), Pd/Mg4Al‐MMO (4), and Pd/Mg5Al‐MMO catalysts (5), and
HRTEM images of Pd/Mg1Al‐MMO(b), Pd/Mg2Al‐MMO (c), Pd/Mg3Al‐MMO (d), Pd/Mg4Al‐MMO (e),and Pd/Mg5Al‐MMO catalysts (f). The insets in the
corresponding HRTEM images show the particle size frequency distribution histograms.
investigated using HRTEM. As shown in Fig. 1(b)–(f), these
catalysts had a uniform size distribution between 2–6 nm
without obvious aggregation. The mean diameters of the
Pd/MgxAl‐MMO (x = 1, 2, 3, 4, 5) samples were 4.3, 4.4, 4.6, 4.5,
and 4.3 nm. In addition, the Pd, Mg, and Al content of the five
catalysts were determined. As listed in Table 3, Mg/Al atomic
mole ratios and Pd loading in the obtained catalysts roughly
correspond to the feed ratio. Combined with the specific sur‐
face area results, it can be concluded that the different ratios of
Mg/Al upon the MgxAl‐MMO supports had little influence on
the dispersion of the active metal.
catalysts. The FT‐IR spectra of pyridine adsorption onto the
samples are shown in Fig. 2(a), and it was observed that all
catalysts exhibited bands at 1450 cm–1, assigned to pyridine
bound to Lewis acid sites [37,38]. No band around 1540 cm–1
was observed, indicating the absence of Brönsted acid sites
[39]. The basicity of catalysts was determined by IR of CO2 ad‐
sorption. Fig. 2(b) shows that the peaks of CO2 adsorption on all
catalysts’ basic sites were the same, indicating the same type of
surface basic sites [40]. The bridged carbonates (1690 and
1260 cm–1) were formed on the Mg2+ and Mg2+‐O2– pairs
[41,42]. The above results show that the modulation of Mg/Al
ratio has no effect on the acid/base type.
Due to the importance of the acidic and basic sites in the
tandem reaction, in situ IR of pyridine and CO2 was used to
identify the types of acidic/basic sites over Pd/MgxAl‐MMO
To further quantitate the number of acidic/basic sites on
Pd/MgxAl‐MMO catalysts, CO2 and NH3‐TPD analyses were
Table 3
Physicochemical properties of the series catalysts.
Surface areaa
(m2/g)
Pd loadingb
Acidic sitesc
(μmol of NH3/g of catalyst)
Basic sitesd
(μmol of CO2/g of catalyst)
Sample
Mg/Al ratio b
(%)
Pd/Mg1Al‐MMO
Pd/Mg2Al‐MMO
Pd/Mg3Al‐MMO
Pd/Mg4Al‐MMO
30
29
26
28
28
0.9
1.8
2.6
3.3
4.4
0.11
0.12
0.10
0.12
0.12
115
95
72
50
23
102
120
175
203
228
Pd/Mg5Al‐MMO
a Determined by BET analysis.
b Determined by ICP‐AES analysis.
c, d Calibrated using 1 μL of NH3 and CO2 as standards.

Rui Ma et al. / Chinese Journal of Catalysis 39 (2018) 1384–1394
1389
(a)
(1)
(b)
(1)
(2)
(2)
(3)
(3)
(4)
(5)
(4)
(5)
1650
1600
1550
1500
1450
1400
2000
1800
1600
1400
1200
1000
Wavenumber (cm1)
Wavenumber (cm1)
Fig. 2. Py‐IR (a) and CO2‐IR (b) spectra of Pd/Mg1Al‐MMO (1), Pd/Mg2Al‐MMO (2), Pd/Mg3Al‐MMO (3), Pd/Mg4Al‐MMO (4), and Pd/Mg5Al‐MMO (5)
multifunctional catalysts.
(a)
(b)
(1)
(1)
(2)
(3)
(2)
(3)
(4)
(4)
(5)
(5)
100 150 200 250 300 350 400 450
Temperature (oC)
100 150 200 250 300 350 400 450
Temperature (oC)
Fig. 3. CO2‐TPD (a) and NH3‐TPD (b) profiles of Pd/Mg5Al‐MMO (1), Pd/Mg4Al‐MMO (2), Pd/Mg3Al‐MMO (3), Pd/Mg2Al‐MMO (4), and
Pd/Mg1Al‐MMO (5) multifunctional catalysts.
performed. In Fig. 3(a), the profile of CO2‐TPD exhibits two
desorption features: a slight one between 200 to 300 °C and a
sharp one at 370 °C. Generally, the temperature of CO2 desorp‐
tion in the range of 200–420°C reflects the absence of the me‐
dium‐strong‐basic sites [43,44]. In this case, it could be as‐
signed to the adsorption of CO2 on Mg2+‐O2– acid‐base pairs on
the layer of MMO support [40], and with decreasing Mg content
among five catalysts, the area of CO2 desorption peak gradually
decreased, suggesting that the number of basic sites declined
on the surface of the given catalyst, which is consistent with the
results reported in the literature [45–47]. The acidity of the
catalysts was determined by NH3‐TPD. As shown in Fig. 3b,
there are several overlapping peaks in the range of 225–450 °C
on the Pd/MgAl‐MMO and Pd/Mg2Al‐MMO samples, compared
to the single sharp desorption peak at 350°C in the three other
catalysts. The Lewis acid on all the catalysts resulted from ac‐
cessible Al3+ cations in Al3+‐O2–‐Mg2+ species, which could be
ascribed to the medium‐strong‐acid sites [48]. In contrast to
the trend of basicity, the total number of acidic sites of the cat‐
alysts decreased with increasing Mg content. Furthermore, the
corresponding number of acidic and basic sites were evaluated
based on the peak area [49,50], and the results show that the
control of Mg/Al ratio in the LDH precursor layer can result in a
continuous change of the total number of acidic and basic sites
in the obtained multifunctional catalysts.
The gradually tunable basicity and acidity on the surface of
Pd/MgxAl‐MMO catalysts facilitate the further study of the syn‐
ergistic effect of multi‐site catalysts in the one‐pot synthesis of
the MIBK reaction. The catalytic performance of these five cat‐
alysts is shown in Fig. 4. For all the Pd/MgxAl‐MMO (x = 1–5)
catalysts, MIBK was the main product; however, the Mg/Al
ratio had a considerable effect on acetone conversion and yield
to MIBK. Specifically, with increasing Mg content in the cata‐
lysts, the selectivity of MIBK showed a rising trend overall,
while the selectivity to byproduct IPA showed the opposite
trend. It was found that the conversion of acetone for different
Mg/Al ratios can be described as a volcano curve, and the
Pd/Mg3Al‐MMO catalyst possessing a medium number of acidic
and basic sites exhibited the best catalytic performance with
82.8% MIBK selectivity at 38.5% acetone conversion.

1390
Rui Ma et al. / Chinese Journal of Catalysis 39 (2018) 1384–1394
100
80
60
40
20
0
100
80
60
40
20
0
MIBK Yield
Ace conversion
MIBK sel
DAA sel
MO sel
IPA sel
MIBK Yield
Ace conversion
MIBK sel
DAA sel
MO sel
IPA sel
MIBC sel
Others
MIBC sel
Others
(a)
(c)
(e)
(b)
(d)
(e)
(b)
(c)
(a)
(d)
Fig. 4. Catalytic properties of Pd/Mg1Al‐MMO (a), Pd/Mg2Al‐MMO (b),
Pd/Mg3Al‐MMO (c), Pd/Mg4Al‐MMO (d), and Pd/Mg5Al‐MMO (e) cata‐
lysts.
Fig. 6. Catalytic properties of Pd/Mg3Al‐MMO with a Pd loading of
0.01% (a), 0.05% (b), 0.1% (c), 0.2% (d), and 1.0% (e).
MIBK from acetone to study the influence of metallic site den‐
sity on the catalytic performance of the Pd/Mg3Al‐MMO multi‐
functional catalyst. As shown in Fig. 6, the conversion of ace‐
tone increased with Pd loading from 0.01% to 0.1%, and
reached a maximum (38%) at 0.1% Pd loading. Lower acetone
conversion over 0.01 wt% Pd/Mg3Al‐MMO catalyst may be due
to the deactivation of the oxide catalyst, which is unavoidable
for aldol condensation on metal oxides [51]. However, when
the density of metallic sites rose to a certain value, it was found
that MIBK selectivity decreased sharply and there was an ob‐
vious increase of IPA, which is the by‐product from acetone
hydrogenation. It is believed that the excessive number of me‐
tallic sites lead to the redundant dissociation of hydrogen,
which then directly caused the hydrogenation of acetone to
produce IPA, rather than the condensation reaction to generate
DAA. Therefore, the optimal amount of Pd loading on
Pd/Mg3Al‐MMO multifunctional catalyst is 0.1%, and it is the
equilibrium point of the acidic/basic/metallic active sites that
produces the maximum yield of the MIBK.
40
30
20
10
0
0.0
0.2
0.4
0.6
0.8
1.0
Molar ratio of acid/base
Fig. 5. The relation between molar ratio of acid/base and yield of MIBK.
In the series of Pd/MgxAl‐MMO multifunctional catalysts, the
different Mg/Al ratios represent the change in the number of
acidic/basic sites. The number of acidic sites on the catalyst
decreased rapidly as the Mg content increased, while the basic‐
ity of the catalyst showed the opposite trend. Thus, we estab‐
lished the connection between the yield of MIBK and the molar
ratio of acidic/basic sites. As shown in Fig. 5, enhanced yield of
MIBK was observed with increasing Mg/Al molar ratio and
reached a maximum value at the Mg/Al molar ratio of 3; the
ratio of acidic/basic sites at this point was about 0.4. Thereaf‐
ter, the yield of MIBK decreased sharply with the further in‐
crease of acidity over the multifunctional catalysts, which was
caused by limited acetone conversion. The change of the rela‐
tionship curve suggests that the number of acid/base sites has
a direct and significant effect on yield of MIBK in this one‐pot
synthesis reaction.
3.5. Proximity effect in multifunctional catalyst
In the tandem reaction, the performance of a multifunction‐
al catalyst is not only affected by the nature of each site and the
corresponding quantity‐synergy; the proximity of the active
sites has been reported to exert significant influence on cata‐
lytic property [52,53]. Therefore, the study of multi‐site prox‐
imity is of great significance for understanding and then de‐
signing an efficient multifunctional catalyst for this tandem
reaction. In our case, the research on the proximity effect be‐
tween acidic/basic/metallic sites was carried out by a physical
mixing experiment. Increasing the distance between the active
sites (e.g. one site away from the other two or three sites away
from each other), poorer catalytic performance was obtained
compared to the catalyst with closest proximity of active sites,
as listed in Table 4. For example, the physical mixing catalyst
(Pd/C+MgO+Al2O3), which was prepared by the loading of Pd
on active carbon and physical mixing with MgO and Al2O3,
showed the poorest acetone conversion (5.3%). Compared to
Pd/C (inactive shown in Table 1), the addition of MgO and
3.4. Effect of metal loading on the performance of the
Pd/Mg3Al‐MMO catalyst
In addition to the synergistic effect of the acidic and basic
sites, a series of Pd/Mg3Al‐MMO catalysts with different metal
loading were synthesized and tested in a one‐step synthesis of

Rui Ma et al. / Chinese Journal of Catalysis 39 (2018) 1384–1394
1391
Table 4
Catalytic performance of intimate mixture catalysts a.
Selectivity (%)
Entry
Sample
Acetone conversion (%)
MIBK yield (%)
DAA
0.4
0.0
0.0
0.1
3.0
MO
MIBK
97.3
95.6
96.1
97.1
82.8
Others
1.4
2.0
3.4
2.6
1
2
3
4
5
0.1% Pd/C+MgO+Al2O3 (Pd+B+A)
0.1%Pd/C+MMO (Pd+B/A)
MgO+0.3%Pd/Al2O3 (Pd/A+B)
0.15%Pd/MgO+Al2O3 (Pd/B+A)
0.1%Pd/MMO (Pd/A/B)
5.3
5.5
9.9
17.4
38.2
0.9
2.4
0.5
0.3
7.4
5.2
5.3
9.5
16.9
31.6
6.8
Note that all five samples were prepared with the same Pd loading and Mg/Al atomic ratio (A for acid sites and B for basic sites).
Al2O3 in the catalytic system facilitates the conversion of ace‐
tone (entry 1). Besides, the increased proximity of metal sites
to acid sites or basic sites could double the conversion of ace‐
tone (entries 3 and 4), indicating that a small distance between
active sites could truly enhance the catalytic performance of a
given catalyst in this tandem reaction. Therefore, the catalyst
obtained by the introduction of MgO and Al2O3 into the
MgAl‐MMO structure followed by the loading of Pd, which pos‐
sessed the closest proximity among metallic sites, acidic sites,
and basic sites, turned out to be the preferable one, exhibiting
38.2% acetone conversion (entry 5). The unique properties of
MMO materials, particularly, the distance between acidic/basic
sites at atomic level, make MMO an extremely promising mate‐
rial in the tandem reaction.
in DAA, resulting in a dehydration reaction to create the C=C
bond, followed by hydrogenation with the dissociated hydro‐
gen that was produced at the Pd site to form MIBK. It can be
seen from the reaction process that intimate and continuous
active sites could facilitate the continuity of the tandem reac‐
tion. Acetone molecules are activated gradually by
basic/acidic/metallic sites on the Pd/MMO multifunctional
catalyst, greatly reducing the diffusion time of intermediate
species from one active site to another, maximize the efficiency
of the continuous reaction, resulting in high MIBK yield [54].
3.7. Optimization of the multifunctional catalyst
The synthesis method was found to greatly influence the
properties and performance of a catalyst [55,56]. Herein,
Mg3Al‐MMO‐supported Pd catalysts were also prepared via DP
methods and the test results are listed in Table 5. Under the
same conditions, 88.36% selectivity to MIBK was achieved at
42.11% acetone conversion on the Pd/Mg3Al‐MMODP catalyst.
The yield of MIBK on the Pd/Mg3Al‐MMODP catalyst was 37.3%,
which is 17.6% higher than that of the Pd/Mg3Al‐MMO catalyst
prepared by an impregnation method. Especially, the
Pd/Mg3Al‐MMODP multifunctional catalyst exhibits excellent
performance compared to the catalysts reported to date (Table
3.6. A proposed mechanism for multifunctional catalysts
Based on the above results, a possible mechanism is pro‐
posed, which is shown in Scheme 1. In a Pd/MMO catalyst, α‐H
of acetone initially adsorbs on the Oδ‐ basic site in Al3+‐O2–‐Mg2+,
which can break the C‐H bond and then form a carbanion in‐
termediate [51]. Subsequently, the formed carbanion reacts
with another acetone, leading to formation of DAA. The acidic
site Alδ+ from Al3+‐O2–‐Mg2+ captures the O‐H functional group
H
C
H
O
H
C
H
H
C+
H
H
H
H
H
H
H
H
H
H
H
O
H
C
H
H
C
H
H
H
C
C
H
H
H
H
C
O
H
C
H
H
H
C
-
C
C
H
C
H
H
C
C
C
C
H
H
C
C
C
H
C
H
C
C
C
H
H
O
H
H
H
OH
O
H
H
H
Pd
Pd
H2
Pd
Pd
Pd
Pd
Pd
Pd
+
+
+
+
+
+
+


+

+
+







Al
Mg
Al
Mg
Al
Mg
Al
Mg
Al
Mg
-

-
-
-
-
-
-


-
-


O

-
-



O
O
O
O
O
O
O
O
Scheme 1. Proposed mechanism of one‐pot synthesis of MIBK from acetone on a Pd/MMOmultifunctional catalyst.
Table 5
Performance comparison of Pd/Mg3Al‐MMOim and Pd/Mg3Al‐MMODP catalysts.
Selectivity (%)
Catalyst
Conversion (%)
MIBK yield (%)
MIBK
82.8
88.4
82.5
80.4
90.3
82.0
46.8
DAA
3.0
2.1
10.8
4.6
5.3
MO
7.4
0.3
N.D.
0.4
0.0
0.0
8.7
Pd/Mg3Al‐MMOim
Pd/Mg3Al‐MMODP
38.2
42.1
26.3
28.5
20.6
39.7
70.6
31.6
37.2
21.7
22.9
18.6
32.6
33.0
0.1% Pd/γ‐Al2O3 [20]
1%Pd/Zn‐Cr oxide [57]
Pd/40 SO3H‐E‐HS [17]
T500/Cor&Pd/Cor [58]
0.87%/Pd@MIL‐101 [59]
12.4
15.4

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Rui Ma et al. / Chinese Journal of Catalysis 39 (2018) 1384–1394
5). The CO2 and NH3‐TPD analyses (Fig. S2) suggest that the
surface of the catalyst treated by NaOH solution in the DP
method contained more acidic and basic sites compared to the
catalyst treated by the impregnation method. The number of
acidic and basic sites on the Pd/Mg3Al‐MMODP catalyst surface
was 86 μmolNH3/g and 214 μmolCO2/g respectively, and the
molar ratio of acid/base (ca. 0.4) is located at the peak of the
obtained volcano curve (Fig. 5). Moreover, the obtained
Pd/Mg3Al‐MMODP catalyst also exhibited an enhanced hydro‐
genation ability of MO, as shown in Table 5, which is also fa‐
vorable for improved MIBK yield. Furthermore, the
Pd/Mg3Al‐MMODP catalyst possessed fairly good stability over 4
cycling reactions (Fig. 7). Therefore, the Pd/Mg3Al‐MMODP mul‐
tifunctional catalysts can be considered as efficient and envi‐
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Graphical Abstract
Chin. J. Catal., 2018, 39: 1384–1394 doi: 10.1016/S1872‐2067(18)63092‐X
Fabrication of Pd‐based metal‐acid‐alkali multifunctional
catalysts for one‐pot synthesis of MIBK
Rui Ma, Yunpeng Li, Guandong Wu, Yufei He *, Junting Feng,
Yingying Zhao *, Dianqing Li
Beijing University of Chemical Technology
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Pd-基金属-酸-碱多功能催化剂的制备及其丙酮一步法合成MIBK性能研究
马 瑞a,b, 李云鹏a,b, 武冠东a,b, 贺宇飞a,b,*, 冯俊婷a,b, 赵莹莹a,b,#, 李殿卿a,b
a北京化工大学, 化工资源有效利用国家重点实验室, 北京100029
b北京化工大学, 北京市多级结构催化材料工程技术研究中心, 北京100029
摘要: 甲基异丁基酮 (MIBK) 是一种重要的化学品, 广泛应用于涂料以及有机合成领域, 下游产品包括特种涂料溶剂、高
品质脱蜡溶剂和高性能橡胶防老剂等. 近年来随国民经济的快速发展, 甲基异丁基酮的年需求量与价格逐年上升, 应用领
域也不断拓宽. 因此, 开展 MIBK 绿色合成工艺的研究对提高原子经济性、打破国际技术壁垒以及满足国内市场需求具有
重要意义. 目前生产 MIBK 最绿色、高效的生产方法是丙酮一步法, 包括缩合、脱水以及加氢等一系列反应过程, 该工艺
顺利实施的关键在于所使用的催化剂. 根据丙酮一步法合成 MIBK 反应特点, 所用催化剂表面必须具备多种催化活性中

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Rui Ma et al. / Chinese Journal of Catalysis 39 (2018) 1384–1394
心, 从而保证缩合、脱水以及加氢反应的顺利进行, 实现从反应物到产物的高效转化. 因此, 高活性和高选择性多功能催化
剂的制备是提高 MIBK 生产效率的有效途径.
本文采用浸渍法将具有加氢活性的贵金属 Pd 负载在表面具有丰富酸性位点或碱性位点的固体酸或固体碱氧化物载
体上, 制备了 Pd/MOx (M = Ti, Ce, Al, Si, La, Ca和Mg) 双功能催化剂, 并用于丙酮一步法合成 MIBK 反应中. 结果表明, Pd
基金属-酸/碱双功能催化剂均可以催化该连串反应的进行, 其性能高于 Pd 基金属-酸双功能催化剂, 其中 Pd/MgO 催化剂
上丙酮转化率为30.67%, MIBK 产率可达27.61%. 构效关系研究显示, 催化剂表面酸性位点和碱性位点对于该连串反应的
各反应步骤催化性能有所不同, 其中碱性位点有利于丙酮缩合反应, 而酸性位点有利于二丙酮醇脱水反应, 且强路易斯碱
性中心位点可以更好的催化缩合反应的进行, 同时中强度路易斯酸性中心位点具有最佳的催化脱水反应的能力. 此外, 表
面具有最强路易斯碱性中心位点 Pd/La2O3 催化剂并未表现出最高的MIBK产率, 说明在丙酮一步法合成MIBK反应中, Pd
基双功能催化剂表面各位点间的协同对其催化性能具有重要的影响.
本文进一步采用水热法和沉淀沉积法制备了系列MgTiOx、MgAlOx和CaTiOx二元复合氧化物 (MMO) 以及 CaMgAlOx
和 TiMgAlOx 三元MMO, 并以其为载体, 通过浸渍焙烧还原制备 Pd 基多功能催化剂, 并用于丙酮一步法合成MIBK反应中,
发现Pd/MgAl-MMO多功能催化剂具有最高的催化活性及 MIBK 产率. 对其表面多功能位点数量进行调变, 并通过 XRD、
o
CO2-TPD、NH3-TPD、吡啶红外、CO2 红外和HRTEM等进行表征, 结果表明, 经过450 C焙烧酸碱中心摩尔量比为0.4的
0.1%Pd/Mg3Al-MMO多功能协同催化剂三种催化活性中心位点协同作用最佳, 其丙酮转化率为38.20%, MIBK产率可达
31.63%. Pd/Mg3AlMMO多功能协同催化剂三种活性位点接近性研究表明, 在多功能催化剂中分离酸中心活性位点、碱中
心活性位点以及加氢活性位点后, 获得的双功能催化剂产率均明显下降, 说明Pd/Mg3Al-MMO多功能催化剂在三种活性位
点相互接近时才能更好催化反应的进行. 根据多功能催化剂构效关系研究结果, 对各催化活性中心的密度及分布进行调
控, 结果显示, 通过沉淀沉积法制备的Pd/Mg3Al-MMO催化剂性能进一步提高, 丙酮转化率为42.11%, 产率高达37.20%.
关键词: 一步法合成甲基异丁基酮; 多功能催化剂; 钯; Mg3Al复合金属氧化物; 协同效应; 位点接近性
收稿日期: 2018-02-26. 接受日期: 2018-04-24. 出版日期: 2018-08-05.
*通讯联系人. 传真: (010)64425385; 电子邮箱: yfhe@mail.buct.edu.cn
#通讯联系人. 传真: (010)64437866; 电子邮箱: zhaoyy@mail.buct.edu.cn
基金来源: 国家重点研发计划 (2016YFB0301601); 国家自然科学基金 (21706009); 中央高校基本科研业务费专项资金
(BUCTRC201725, JD1816).
本文的电子版全文由Elsevier出版社在ScienceDirect上出版(http://www.sciencedirect.com/science/journal/18722067).