Fixation Of CO₂ Into Cyclic Carbonates Catalyzed By Zn-based Heterogeneous Catalysts

Carbon dioxide is has been in the spotlight as a renewable C1 feedstock because it is ubiquitous, readily available and non-poisonous. It is an effective way of recycling carbon dioxide that synthesis of cyclic carbonates takes advantage of carbon dioxide as a raw chemical coupling with epoxide.Two effective catalyst systems were developed in our task. Firstly, the combination of guanidine hydrochloride with co-catalyst Zn I2 proved to be a highly efficient heterogeneous catalyst for the environmentally benign, solvent-free synthesis of cyclic carbonates under mild reaction conditions. Excellent yield(94%) and selectivity(≥99%) of propylene carbonate were obtained under 100 °C and at 1 MPa for 1.5 h. The effects of different co-catalysts as well as reaction parameters including catalyst loadings, CO2 pressure, reaction temperature, and reaction time on the coupling reaction of CO2 to propylene oxide were thoroughly investigated. Moreover, the binary catalysts were also versatile when using other epoxides, such as epoxybutane, epoxy chloropropane, styrene oxide and cyclohexene oxide, for CO2 cycloaddition. A possible reaction mechanism was proposed. The synergistic effect of guanidine hydrochloride and Zn I2 ensure the reaction proceeds effectively.Subsequently, the one-component heterogeneous catalytic system NH2-Zn/SBA-15(HI) was examined for the cycloaddition reaction. The catalyst was found exceedingly effective to this transformation and 93% yield and 99% selectivity to propylene carbonate were obtained at 130 °C and 3 MPa of CO2 for 12 h. XRD, N2 adsorption, TEM, FTIR, XPS techniques were used to determine the textual structure and physicochemical properties of NH3I-Zn/SBA-15 samples. Moreover, the effects of various reaction factors, including different amount of zinc elements modified NH2-Zn/SBA-15 and protoned NH2-Zn/SBA-15, reaction temperature, CO2 pressure, and reaction time, were also investigated in detail. The recycle property of catalyst was also investigated. The catalyst exhibited good stability after 3 cycles. Besides, a possible catalytic mechanism for the cycloaddition of CO2 to propylene oxide was proposed.