DMF and mesoporous Zn/SBA-15 as synergistic catalysts for the cycloaddition of CO₂ to propylene oxide

A series of Zn/SBA-15 samples with Zn/Si molar ratios from 0.06 to 0.18 were prepared by one-pot synthesis method. XRD, N₂ adsorption/desorption, TEM, FTIR and XPS techniques were used to determine the textual structures and physicochemical properties of Zn/SBA-15 samples. The mesoporous structure of SBA-15 was well preserved with Zn/Si molar ratio up to 0.18. Thereafter, Zn/SBA-15 was tested for the cycloaddition reaction of CO₂ and propylene oxide to produce propylene carbonate in the presence of DMF. The catalytic results showed that Zn/SBA-15 and DMF synergistically catalyzed the cycloaddition of CO₂ to propylene oxide. Moreover, the effects of various reaction factors, including different metal elements modified SBA-15, reaction temperature, CO₂ pressure, reaction time and DMF amount were also discussed in detail. Propylene carbonate yield as high as 92.3% was achieved on Zn/SBA-15(0.15) catalyst at 160 °C and 2 MPa of CO₂ pressure for 6 h in the presence of DMF. In addition, the recycling property of Zn/SBA-15 catalyst was also investigated. A possible catalytic mechanism for the cycloaddition of CO₂ to propylene oxide was proposed.