posted on 2022-02-02, 12:34authored bySong-Song Peng, Guo-Song Zhang, Xiang-Bin Shao, Chen Gu, Xiao-Qin Liu, Lin-Bing Sun
Solid strong bases with an ordered
pore structure (OPS-SSBs) have
attracted much attention because of their high catalytic activity
and shape selectivity as heterogeneous catalysts in various reactions.
Nevertheless, high temperatures are required to fabricate OPS-SSBs
by using traditional methods. Herein, we report for the first time
that the coordination solvents affect basicity generation in metal–organic
frameworks (MOFs) greatly and that strong basicity can be formed at
comparatively low temperatures. A typical MOF, MIL-53, was employed,
and three different solvents, namely, water, methanol, and N,N-dimethylformamide (DMF), were coordinated,
respectively, by means of solvent exchange. Thermogravimetry-mass
spectrometer analysis shows that the conversion temperature of base
precursor KNO3 is quite different on MIL-53 coordinated
with different solvents. The conversion of KNO3 to basic
sites takes place at 350, 300, and 250 °C on MIL-53 coordinated
with water, methanol, and DMF, respectively. It is fascinating to
observe the generation temperature of strongly basic sites at 250
°C, which is noticeably lower than that on various supports,
such as mesoporous silica SBA-15 (600 °C), zeolite Y (700 °C),
and metal oxide ZrO2 (730 °C). This is due to the
redox interaction between coordination solvents and KNO3, leading to a significant decrease in the temperature for KNO3 conversion. Consequently, OPS-SSBs were prepared successfully
with an ordered pore structure and strong basicity. The obtained OPS-SSBs
show good shape selectivity in Knoevenagel condensation of aromatic
aldehydes with different active methylene compounds. Moreover, these
solid bases are highly active in the synthesis of dimethyl carbonate
through transesterification reaction. This work might open up a new
avenue for the fabrication of various functional materials at low
temperatures through redox interactions.