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10.1002/cctc.202000152
ChemCatChem
FULL PAPER
Catalytic Dehydration of 1,4-Butanediol over Mg-Yb Binary
Oxides and the Mechanism Study
Rongli Mi,[a] Zhun Hu,[a] Chunhai Yi,[a] and Bolun Yang*[a, b]
[a]
Rongli Mi, A/Prof. Dr. Zhun Hu, A/Prof. Dr. Chunhai Yi, Prof. Dr. Bolun Yang
Shaanxi Key Laboratory of Energy Chemical Process Intensification
Xi’an Jiaotong University
West Xian-ning Road, Xi’an, Shaanxi, People’s Republic of China
E-mail: blunyang@mail.xjtu.edu.cn
[b]
Prof. Dr. Bolun Yang
State Key Laboratory of Multiphase Flow in Power Engineering
Xi’an Jiaotong University
West Xian-ning Road, Xi’an, Shaanxi, People’s Republic of China
Supporting information for this article is given via a link at the end of the document.
Abstract: In this study, Mg-Yb binary oxides were synthesized using
different MgO concentrations and investigated for the catalytic
dehydration of 1,4-butanediol (BDO) into 3-buten-1-ol (BTO). The
physicochemical properties of the catalysts were characterized by N2
physisorption, X-ray diffraction, Raman spectroscopy, temperature–
programmed techniques, and diffuse reflectance infrared Fourier
transform spectroscopy. The Mg-Yb binary oxides exhibited superior
catalytic activity and better BTO selectivity compared with the pristine
Yb2O3 or MgO. Structures of Mg-O-Yb were generated in the binary
oxides via the interchange of Yb or Mg in the MgO or Yb2O3 crystalline
phases. Extra basic and acidic sites were formed over the Mg-Yb
binary oxides because of the formation of surface defects and the
presence of Mg-O-Yb structures, respectively. The acidic as well as
basic sites were observed to influence the catalytic performance: BDO
reactivity was enhanced by the more acidic sites, while BTO
selectivity was favored by the basic sites. The highest BTO yield of
71.1% was achieved over the Mg7Yb3 catalyst with 90.4% BDO
conversion and 78.6% BTO selectivity at 350 C. The in situ DRIFTS
results indicated that BDO was first adsorbed on the catalyst and then
reacted with the acidic sites to generate butoxides. The β-H of the
surface butoxides was abstracted by the basic oxygen anions to
produce aldehyde species, which dissociated to form BTO.
Similarly, 3-buten-1-ol (BTO), which combines with active
hydroxyl groups and double bonds, is frequently used for the
synthesis of medicines, agrochemicals, polymers, and
additives.[16-19] Hence, direct catalytic dehydration of BDO has
been proposed not only as one of the most promising methods for
BTO production, but also as an essential technology for
expanding BDO downstream products.[20,21] BDO dehydration
forms a complex reaction network that can produce various
chemicals including BTO, tetrahydrofuran (THF), -butyrolactone
(GBL), 1-butanol (BuOH), 2-buten-1-ol (2BT1O), and 1,3-
butadiene (BDE) as shown in Scheme 1.[16,22,23] Among these,
THF is preferentially formed over BTO in the presence of normal
dehydration catalysts. The catalysts used for BDO dehydration,
such as t-ZrO2 and Al2O3, generally exhibit strong surface acidity,
resulting in the cyclodehydration of BDO into THF, which limits
the BTO selectivity to less than 10%.[24] Previously, our group
studied BDO dehydration over m-ZrO2 supported Yb2O3, and the
results showed that the hydroxyl groups of BDO molecules could
be adsorbed onto the acidic sites while β-H could be captured by
the basic sites, resulting in the formation of BTO.[22] Sato et al.
also reported that BDO dehydration proceeded with an acid−base
concerted mechanism over the Er2O3 catalyst, wherein both BDO
conversion and BTO selectivity were markedly suppressed by
poisoning the Er2O3 catalyst with either CO2 or NH3 carrier gas.[25]
Therefore, BDO dehydration is highly dependent on the
acid−base properties of the catalyst—while the strong acidity of
the catalysts facilitates the formation of the byproduct THF, its
strong basicity reduces the BDO conversion.[22] Thus, a proper
acid−base regulation is an effective approach to improving the
catalytic performance for BDO dehydration. Therefore,
amphoteric oxides have received increasing attention for their use
in the dehydration reaction as they contain both acidic and basic
sites. Among these, Yb2O3 exhibits higher BTO selectivity (>85%)
and is generally regarded as a superior catalyst for BDO
dehydration.[16,25,26] However, as the conversion of BDO over
Yb2O3 is generally very low (<40%), it could not meet the
requirements for industrial application, owing to its weak
acidity.[16,23,25,26]
Introduction
The ongoing environmental deterioration and fossil resource
exhaustion have prompted scientists to explore renewable and
green alternative energy sources.[1,2] Recently, several processes
for the conversion of biomass into valuable oil-based products
have increasingly attracted attention, such as hydrogenation of
succinic acid and levulinic acid, esterification of glycerol, oxidation
or hydrogenation of 2-furaldehyde, and dehydration of polyols.[3-
15] In particular, 1,4-butanediol (BDO), which can be manufactured
from not only fossil- and coal-based feedstock, but also biomass
resources, is reportedly the most extensive source among all diols.
The global BDO market has been projected to reach USD 12.6
billion by 2025, and China with its production capacity of over 55%
of the total world’s capacity, continues to be the world’s highest
BDO producer. Furthermore, the increasing BDO production has
led to overcapacity and lower market prices in recent years,
causing sufficient demand for its utilization.[6]
Therefore, two main strategies are reportedly used for the
regulation of the acid−base properties of the Yb2O3 catalyst:
obtaining different crystal forms of Yb2O3 through the calcination
of the Yb2O3 precursor at high temperatures, or loading Yb2O3 on
1
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