Study On Supported Gold Nanocatalysts For Selective Hydrogenation Of Phthalic Anhydride To Phthalide

Phthalide is one important intermediate of fine chemicals,which is conventionally used in pharmaceuticals,pesticides and dye.Selective hydrogenation of phthalic anhydride is a green route for phthalide synthesis.During hydrogenation of phthalic anhydride,several byproducts will be observed.So it's necessary to explore catalysts with high activity and selectivity.In this thesis,a series of supported gold catalysts,prepared by deposition-precipitation method,were firstly used for phthalic anhydride hydrogenation.The influences of support type,Au loading,calcination and reduction temperatures,promoters and pH value on the catalytic properties of the gold catalysts were investigated.The stability and the deactivation mechanism of the gold catalysts were also studied.The catalysts were characterized by means of X-ray diffraction(XRD), nitrogen adsorption-desorption(BET),inductively coupled plasma-atomic emission spectrometry(ICP-AES),transmission electron microscopy (TEM),and fourier transforminfrared spectroscopy(FT-IR).The results show that the gold catalyst prepared with TiO₂ as suppport,2.0 wt%of gold content,and 5.0 wt%of Fe₂O₃ promoter exhibites excellent catalytic activity and selectivity for the hydrogenation of phthalic anhydride.The size of Au particles at the surface Over Au/TiO₂ catalyst prepared under the optimal preparation conditions of pH value about 8.10,calcination temperture 300℃,reduction temperature 200℃and calcination time 4 h,the conversion of phthalic anhydride and the selectivity to phthalide is 97.63%and 95.24%,respectively,when the reaction time is 9 h.Fe³⁺ can expand the crystal lattice of TiO₂ and form sites of crystal defects,which is in favor of integration between gold atom and support. In addition,existence of Fe³⁺ can enhance thermal stability mechanical strength of pore wall.Therefore,addition of 5.0 wt%promoter iron oxide obviously improves the selectivity and stability of Au/TiO₂ catalyst in phthalic anhydride hydrogenation reaction.The reaction conditions of phthalic anhydride hydrogenation over Au/Fe₂O₃-TiO₂ catalyst were optimized as follows:reaction temperature 190℃,reaction pressure 3.0 MPa,catalyst dosage(based on the mass of used phthalic anhydride) 20 wt%,concentration of reactant 0.1 g/mL and reaction time 7 h.Under the optimal conditions,the conversion of phthalic anhydride and the selectivity to phthalide can reach 95.36%and 94.53%,respectively.Compared to the traditional nickel-based catalysts,Au/Fe₂O₃-TiO₂ catalyst developed by us can effectively prohibit the formation of byproducts during phthalic anhydride hydrogenation,and shows much better selectivity to phthalide.