Sustainable Synthesis of Epoxides from Halohydrin Cyclization by Composite Solid-Based Catalysts

Abstract

A facile synthesis of CaO- and MgO-based composite solid-based catalysts is demonstrated for a sustainable synthesis of epoxides from halohydrin cyclization (i.e., via heterogeneous catalysis). The cyclodehydrohalogenation of 3-chloro-1,2-propanediol (3-MCH) to glycidol (GLD) was chosen as the representative of the study. The activity, selectivity, and operation stability of the developed composite catalysts versus their material properties were studied through the establishment of a suitable synthesis, characterization, and performance testing platform. An X-ray diffractometer, a scanning electron microscope, a Brunauer–Emmett–Teller N2 adsorption analyzer, a chemisorption analyzer, and an inductively coupled plasma–optical emission spectrometer were used complementarily for the characterization of catalyst materials. The results show that we can successfully synthesize composite solid-based catalysts with adjustable chemical and physical properties, including surface basicity. The liquid–solid reaction system is useful for the mechanistic understanding of the cyclodehydrohalogenation of 3-MCH catalyzed by the solid-based catalysts, especially the byproduct generation paths and the catalyst deactivation by surface poisoning. The results show that the conversion rate of cyclodehydrohalogenation of 3-MCH to GLD was proportional to the amount of total basic sites on the catalyst, and the selectivity to GLD was proportional to the medium basicity strength of the catalyst. The fundamental understanding obtained in this study provides valuable design principles for composite solid-based catalysts for a wide variety of dehydrohalogenation reactions.

From Lewis Acid to Lewis Base by La3+-to-Y3+ Substitution in α-YB5O9: Local Structure Modification Induced Lewis Basicity

“…The optimized structures for the host and α-Y 0.75 La 0.25 B 5 O 9 are provided in Figure S13 consequently, the substitution-induced basicity is proposed to be due to O 2− . 21,22 Moreover, a model with the (100) crystal plane exposed, in which this O is on the topmost layer, was employed during the DFT calculations to check the effect of La 3+ -doping on the surface. A similar elongation of La−O bonds can be also observed (see Figure S14).…”

“…The optimized structures for the host and α-Y 0.75 La 0.25 B 5 O 9 are provided in Figure S13 along with the [YO 7 –O 2 –YO 7 ] and [YO 7 –O 2 –LaO 7 ] dimmers. As a representative, Figure a highlights the bridging O 2– bonded with Y 3+ and the La 3+ dopant, where the La–O bond (2.44 Å) is significantly longer than the original Y–O bond (2.31 Å); consequently, the substitution-induced basicity is proposed to be due to O 2– . , Moreover, a model with the (100) crystal plane exposed, in which this O is on the topmost layer, was employed during the DFT calculations to check the effect of La 3+ -doping on the surface. A similar elongation of La–O bonds can be also observed (see Figure S14).…”