Cu-Ag Synergistic Effect And Ethanol Hydrothermal Treatment On Propylene Epoxidation Over Cu-Based Catalysts

Propylene oxide(PO)is an important intermediate in organic synthesis.At present the industrial production mainly has the chlorohydrin method and the co-oxidation method.Chlorine-containing wastewater will produce environmental pollution in the process of chlorohydrin production.Co-oxidation process is long.Equipment requirements are high and the entire production process is susceptible to the by-product market.As an environmentally friendly,low-cost and relatively easy to obtain oxidant,oxygen is favored by people.As the most ideal and economical epoxy resin,epoxy propane can be converted into epoxy propane by direct epoxidation with 100%atomic utilization.The industrial production route of propane is also a challenging work.This paper is divided into two parts.In the first part,a series of Cu-Ag/SiO2 bimetallic catalysts with different Cu-Ag ratios were synthesized by hydrothermal-combustion method.The results showed that when the molar ratio of Cu and Ag was 9,the epoxidation activity of Cu-Ag bimetals was the highest,and the addition of NaCl modifier could further promote the generation of propylene oxide.In Cu90-Ag10/SiO2-NaCl catalyst,when the reaction temperature is 200℃,at C3H6 conversion of 0.5%,selectivity to PO reached 17%.XRD and TEM analysis showed that Cu and Ag bimetals did not form alloys.In Cu/SiO2 and Ag/SiO2,the particle sizes of Cu and Ag are 5 nm and 7 nm respectively.With the increase of Ag content in Cu-Ag bimetallic catalyst,the particle size of Cu does not change much.The particle size of silver increased rapidly from 7 nm to 70 nm,and NaCl promoted the dispersion of Ag.H2-TPR showed that the addition of Ag and NaCl could promote the decrease of highly dispersed CuO species.The synergistic effect of Cu and Ag is the key factor to improve the epoxidation activity of propylene.In the second part,the influence of different solvent heat treatment on the epoxidation performance of Cu/CNT catalyst was studied.The results show that 150℃ ethanol water heat treatment on the production of PO is most favorable,The PO selectivity of Cu/CNT catalyst modified with Na2CO3 was further increased,when the reaction temperature is 220℃,the C3H6 conversion rate is 0.24%,the selectivity of PO is 35%.XRD analysis showed that part of changed from CuO to Cu2O after ethanol heat treatment.With the increase of hydrothermal temperature,the content of Cu20 increased gradually,but the particle size of Cu2O also increased significantly.Transmission electron microscopy(TEM)results show that Cu is mainly distributed in carbon tubes.The addition of Na2C03 was beneficial to the dispersion of copper species,while NaCl modification increased the size of copper species.XPS results showed that the content of Cu+increased significantly after Na2CO3 modified Cu/CNT catalyst.It is speculated that Cu+with small particle size may be the active center of the oxidation reaction of propylene oxide.