Controllable Synthesis Of Cu-based Catalysts And Their Catalytic Performances In Diethylene Glycol Amination

Bis(2-dimethylaminoethyl)ether and 2-(2-(dimethylamino)ethoxy)ethanol are two of the most important polyurethane catalysts with high prices and growing market demand.The synthesis of DMAEE and BDMAEE by amintion of diethylene glycol with dimethylamine(DMA)is cost-effective and environment-friendly,exhibiting important research significance and a promising application prospect.In this dissertation,Cu-ZnO/A12O3,nano-Cu/Al2O3 and Cu-ZnO/A12O3 interface catalysts were prepared by different methods,whose physicochemical properties,such as structure,morphology,reducibility and chemical state were characterized and catalytic performances in diethylene glycol amination were tested.The relationships between physicochemical properties and catalytic performances of the catalysts were investigated to discover the effects of preparation methods and incorporation of ZnO.1.Controllable synthesis of highly dispersed Cu-ZnO/A12O3 catalysts and their catalytic performances in diethylene glycol aminationCu-ZnO/A12O3 catalysts with different Cu/Zn ratios((Cu+Zn)/Al=9)and(Cu+Zn)/Al ratios(Cu/Zn=1)were prepared by a co-precipitation method.The effects of different Cu/Zn ratios and(Cu+Zn)/Al ratios on the amination of diethylene glycol were investigated.The resulting catalysts were characterized by low temperature nitrogen adsorption,X-ray diffraction(XRD),Fourier Transform infrared spectroscopy(FT-IR),transmission electron microscopy(TEM),high resolution transmission electron microscopy(HRTEM)and X-ray photoelectron spectroscopy(XPS),etc.The results showed that the addition of ZnO with right amounts to Cu/A12O3 catalysts promoted the dispersion of Cu and interacted with Cu to improve their catalytic activity in diethylene glycol amination.A12O3 also promoted the dispersion of Cu,and interacted with Cu and ZnO.However,superfluous Al/(Cu+Zn)ratios led to a decrease in the conversion of diethylene glycol due to relatively low contents of Cu and ZnO.The catalytic performances of the optimized Cu-ZnO/A12O3 catalysts in diethylene glycol amination presented a diethylene glycol conversion of 33.8%and a combined selectivity of DMAEE and BDMAEE of 81.3%at a Cu/Zn/A1 ratio of 4.5/4.5/1.2.Controllable synthesis of nano-Cu catalysts supported on A12O3 and their catalytic performances in diethylene glycol aminationNano-Cu/Al2O3 catalysts were prepared by impregnation of Al2O3 in the nano-copper solution,which was synthesized by a chemical reduction method.The prepared catalysts were characterized by low temperature nitrogen adsorption,XRD,Raman,TEM,HRTEM and XPS,etc,and the nano-Cu/Al2O3 catalysts after drying or calcination with different impregnation times were tested for the amination of diethylene glycol to DMAEE and BDMAEE.It was found that the conversion of diethylene glycol increased while increasing impregnation times,which can be ascribed to the enhanced Cu contents in the repeated impregnation.Although nano-Cu/Al2O3 catalysts prepared only by drying have a relatively low Cu content,they presented a high conversion of diethylene glycol owing to good dispersion and small particle size of metallic Cu.However,nano-Cu/Al2O3 catalysts prepared only by drying contained hexadecyl trimethyl ammonium bromide(CTAB),which led to the conversion of diethylene glycol and the selectivity of the product are lower than those of nano-Cu/Al2O3 catalysts prepared by impregnation followed by a sequential drying and calcination in each repeated impregnation cycle.The content of Cu in nano-Cu/A12O3 catalysts calcined increased due to the removal of CTAB,which resulted in an apparent enhancement in the conversion of diethylene glycol and the selectivity of the desired product in spite of an increase of the particle size of the metallic Cu.Nano-Cu/Al2O3 catalysts calcined with 3 times of impregnation scored the best catalytic activity:a diethylene glycol conversion of 23.4%and a combined selectivity to DMAEE and BDMAEE of 92.6%.3.Controllable synthesis of Cu-ZnO/Al2O3 interface catalysts and their catalytic performances in diethylene glycol aminationCu-ZnO/Al2O3 interface catalysts were prepared by a sequential impregnation method.The effects of different impregnation times and impregnation sequences on the catalytic performance in diethylene glycol amination were investigated.The results showed that ZnO promoted the dispersion of Cu and might form Cu-ZnO interfaces with higher catalytic performances.However,excessive ZnO caused a decline of catalytic performances due to its possible coverage on the Cu surface.Under the optimized impregnation times of Cu(NO3)2 and Zn(NO3)2,the different impregnation sequence of Cu(NO3)2 and Zn(NO3)2 had an obvious influence on their Cu-ZnO interface and catalytic performances.The Cu(2)/ZnO(1)/Al2O3 catalyst prepared by an impregnation of Zn(NO3)2 followed by an impregnation of Cu(NO3)2 exhibited a higher conversion of diethylene glycol due to the higher activity of the Cu-ZnO interface contained in Cu(2)/ZnO(1)/Al2O3 catalyst and higher Cu specific surface area.While the Cu-ZnO interface contained in ZnO(1)/Cu(2)/Al2O3 catalyst prepared by a sequential impregnation of Cu(NO3)2 followed by an impregnation of Zn(NO3)2 presented better selectivities to DMAEE and BDMAEE.The yield of Cu(2)/ZnO(1)/A12O3 catalyst scored the highest value(24.1%).In summary,the highly dispersed copper-based catalysts can be prepared by co-precipitation,chemical reduction impregnation and sequential impregnation.Among these methods,copper-based catalysts prepared by the chemical reduction-impregnation method have not only highly dispersion degree but also uniform particle size of Cu.Metallic copper was found active and selective for the amination of ethylene glycol to DMAEE and BDMAEE with DMA.The introduction of ZnO to Cu/Al2O3 led to its interaction with Cu and formed Cu-ZnO interfaces with higher catalytic activity,whose selectivity to the target product can be related to the chemical environment.The Cu-ZnO interface contained in the ZnO(1)/Cu(2)/Al2O3 catalyst has higher DMAEE and BDMAEE selectivity than the Cu-ZnO interface of the Cu(2)/ZnO(1)/A12O3 catalyst,and the latter exhibited much higher catalytic activity than the former.The conversion of diethylene glycol and the selectivity to DMAEE and BDMAEE can be further improved by improving the dispersion degree of copper and the careful tailoring of the Cu-ZnO interface in Cu-ZnO/A12O3 catalysts.