Full Papers
doi.org/10.1002/cctc.202001346
ChemCatChem
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Product Control in Conversion of Ethanol on MIL-101(Cr)
with Adjustable Brønsted Acid Density
Zheng Ming,[a, b, c] Yingli Wang,[b] Tiexin Zhang,[c] Lingyun Li,[b] Chunying Duan,*[a, c] and
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MIL-101(Cr) with adjustable Brønsted acid density was prepared
via post-synthetic sulfation strategy, which was carried out with
sulfuric acid in the presence of trifluoromethanesulfonic anhy-
dride, using nitromethane as solvent. XRD, TG, EDS, XPS, IR,
NH3-TPD and acid-base titration were used to characterize
structure and acidity. Adopting conversion of ethanol as a
probe reaction, gas-solid catalytic characteristics on MIL-101(Cr)
and post-synthetic sulfated MIL-101(Cr) in a micro fixed-bed
reactor were studied by continuous feeding. Combined with
the regulation of reaction parameters, selective production of
ethylene (100%) or diethyl ether (99%) could be achieved.
Introduction
compounds.[17] A large amount of works on the catalytic
properties of Lewis acidic MOF had been done in recent years.
By contrast, study of Brønsted acidic MOF was just at its
initial stage.[18] So far, there were three main methods to
prepare Brønsted acidic MOF. One way was to encapsulate
protonic acid molecules (e.g. polyoxometalates,[19] H2SO4 and
H3PO4[20]), which might cause channel blockage and the
leaching of encapsulated molecules. Another method was to
bound proton compounds such as H2O, ROH, HOOCCOOH and
Metal-organic framework (MOF)[1] was a newly developed series
of crystalline porous material self-assembled by metal ions and
organic ligands. They had aroused keen interest of academia
and industry due to their multiple potential adhibition on gas
storage,[2] separation,[3] sensing[4] and catalysis.[5] Comparison
with conventional porous material such as zeolite and meso-
porous silicamaterial,[6] MOF possessed the advantageous
characteristics of more variable structures,[7] much stronger
designability[8] and porosity adjustability,[8d,9] larger surface
areas,[10] artful immobilization of guest species,[11] precisely and
orderly located atoms.[12] Such characteristics made it possible
to serve MOF as a new type of highly selective catalyst where
functional sites could be designed precisely[13] at the molecular
level.
Over the past decades, unsaturated coordination metal sites
or open metal sites on secondary building units (SBUs) of MOF
were made and applied in catalysis,[14] which served not only as
structural building units, but also Lewis acid used as catalytic
sites. For example, MIL-101(M) [M3X(H2O)2O(BDC)3; M=Al, Cr, Fe;
X=F, OH; BDC=benzene-1,4-dicarboxylate] were found to be
catalytically active in citronellal cyclization,[15] aldehyde
cyanosilylation,[16] and selective oxidation of organic
[21]
H2SO4 directly to metal sites, which would consume Lewis
acid and usually get unstable Brønsted acid. The most
extensively studied approach was to covalently graft functional
+ [22]
group containing active hydrogen such as À NH3
,
À SO3H,[23]
À COOH[24] on organic linking units, thereinto grafted À SO3H
group had aroused much interest and shown great catalytic
potential of Brønsted acidic MOF due to its strong Brønsted
acidity.[18,25]
Brønsted acid catalysis was widely used in industrial
catalytic process, such as methanol to hydrocarbons[26] and
C2H5OH dehydration.[27] Within the precisely located active sites,
Brønsted acidic MOF had the potential application in such
industrial catalytic process. But so far, the published works in
this field mainly focused on fundamental research under mild
reaction conditions[28] in liquid-phase batch reactor. Researchers
paid more attention to active phase attribution and mechanism
deduction. Few studies was concerned with gas-solid catalytic
characteristics, which was close to the actual industrial
production process.[18]
[a] Z. Ming, Prof. C. Duan, Prof. Z. Liu
Zhang Dayu College of Chemistry
Dalian University of Technology
Dalian 116024 (P. R. China)
In this work, MIL-101(Cr), a kind of MOF with relatively good
thermal stability, was used as the starting material. After post-
synthetic sulfation, MIL-101(Cr) with adjustable Brønsted acid
density was prepared. Adopted conversion of C2H5OH as a
probe reaction, gas-solid catalytic characteristics on MIL-101(Cr)
and post-synthetic sulfated MIL-101(Cr) were studied in a micro
fixed-bed reactor by continuous feeding. Effect of adjustable
acidity on product distribution were investigated. C2H5OH was
an important industrial raw material, mainly produced from
E-mail: cyduan@dlut.edu.cn
[b] Z. Ming, Prof. Y. Wang, L. Li, Prof. Z. Liu
National Engineering Laboratory for Methanol to Olefins
Dalian National Laboratory for Clean Energy
Dalian Institute of Chemical Physics
Chinese Academy of Sciences
Dalian 116023 (P. R. China)
[c] Z. Ming, Prof. T. Zhang, Prof. C. Duan
State Key Laboratory of Fine Chemicals
Dalian University of Technology
Dalian 116024 (P. R. China)
[27]
biomass and coal,[29] which was used for production of C2H4
Supporting information for this article is available on the WWW under
as
a
building block of polyolefins,[30] C2H5OC2H5 and
ChemCatChem 2020, 12, 1–8
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