Abstract
Carbon nanotubes (CNTs) were functionalized and were then used as supports of Fe1.5PMo12O40 (FePMo) Keggin heteropolyanions catalysts. The characterization of the resulting catalysts was investigated by inductively coupled plasma spectrometry (ICP), Fourier transform infrared (FTIR) spectra, X-ray diffraction (XRD), ultraviolet-visible (UV-Vis) light spectroscopy, and transmission electron microscopy (TEM). FTIR and XRD results confirmed that FePMo was bounded on CNTs successfully and the Keggin structure was preserved. Characterization by TEM showed that solids with high FePMo content exhibited aggregation of FePMo in large particles. The as-prepared catalysts were tested in the synthesis of propylene carbonate (PC) from CO2 and propylene oxide (PO) in a solvent-free reaction and under mild conditions. Effects of various parameters, such as reaction temperature, reaction time, FePMo content on the support, and catalyst loading on the reaction, were investigated. It has been found that CNTs supported FePMo achieved 57.7% PO conversion and 99.0% PC selectivity, whereas unsupported FePMo led only to 8.5% conversion and 48.6% selectivity. The remarkable enhancement of the catalytic activity over the supported catalyst can be attributed mainly to the better dispersion and reactivity of the FePMo catalyst in the supported material.
Highlights
The utilization of carbon dioxide as a raw material for the production of chemicals has attracted much attention [1]
These features prompted us to investigate the catalytic potential of functionalized Carbon nanotubes (CNTs) supported POMs for the synthesis of propylene carbonate from propylene oxide and CO2
S (PC) 16.6 56.2 31.0 48.6 selectivity in propylene carbonate (PC) (56.2%) but to the lowest conversion (2.86%), whereas FePMo catalyst led to the highest conversion (8.45%) and to a relatively higher selectivity in PC (48.6%). These results indicated that FePMo was the suitable catalyst for the conversion of PO into PC
Summary
The utilization of carbon dioxide as a raw material for the production of chemicals has attracted much attention [1]. Various heterogeneous catalysts, such as metal oxides [10, 11], immobilized complexes or ionic liquids [12,13,14], titanosilicates [15], metal-organic frameworks [16,17,18,19], and zeolites [19], were tested Most of these heterogeneous systems require high pressures and high temperature. Since polyoxometalates are Journal of Chemistry known to be very active catalysts, it would be advantageous to load them on suitable supports, for example, on carbon nanotubes It has been mentioned in the literature that carbon nanotubes capture large quantities of carbon dioxide. The synthesis of PC was achieved under mild conditions without using any solvent, which is attractive from both economic and environmental viewpoints
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