| As an eco-friendly organic intermediate, diethyl carbonate (DEC) has a wide applicationvalue. In this dissertation, copper based catalysts for the gas phase synthesis of DEC byoxidative carbonylation of ethanol were investigated. Based on the fact that the active centrewas copper in this catalytic system, three kinds of catalysts were designed and prepared tomake the valence of main active centre clear, solve the problem that the by-product mayinfluence the catalytic performance and realize maintaining the high selectivity of DEC aswell as improving the conversion of reactants.Firstly, nano copper based oxides and Cu-Pd composite oxides were prepared by a simplehydrothermal method. And the effects of the concentration of NaOH, the content of Cu2O andthe existence form of Pd were investigated. The structure and morphology of catalysts werestudied by XRD, TG, SEM and ICP. It was summarized that PdCl2/CuO and PdCl2/Cu-Cu2Ocatalysts both possessed perfect thermal stability and morphology. But the catalyticperformances of PdCl2/Cu-Cu2O catalysts were better, and the catalyst with a higher contentof Cu2O exhibited a better catalytic activity. The conversion of ethanol over PdCl2/Cu-Cu2O-2catalyst with a higher content of Cu2O reached7.2%, the selectivity of DEC was97.9%andthe space time yield of DEC was151.9mg·g-1·h-1. Therefore, it was concluded that Cu+wasthe main active centre in the catalytic system. However, compared with catalysts preparedwith loading PdCl2, the the PdO-CuO and PdO-Cu-Cu2O catalysts showed a relatively worsecatalytic performance.Secondly, based on the advantage that PdCl2/Cu-HMS catalyst had a selectivity of100%to DEC, the hydrophobic PdCl2/Cu-HMS catalysts were synthesized via silylation to maintainthe selectivity as well as improve the catalytic performance. From FT-IR, XRD, BET, contactangle, it indicated that the silylating agent (trimethylchlorosilane, TMCS) had grafed on thesurface of Cu-HMS successfully, and the PdCl2/Cu-HMS catalyst hydrophobically modifiedwith a mesoporous structure, high specific surface area and good hydrophobicity exhibited anincreasing catalytic performance. The optimized conditions of silylation reaction were: atemperature of60oC, a time of12h and a dosage of silylation agent of5%(the volume ratioof TMCS and beneze); Meanwhile, Surface hydrophobically modified PdCl2/Si-Cu-HMS-mcatalysts were successfully synthesized using methyltrichlorosilane and phenyltrichlorosilaneas silylating agents respectively. In comparison with PdCl2/Si-Cu-HMS-Ben catalyst,PdCl2/Si-Cu-HMS-CH3showed a higher catalytic activity for the gas phase oxidativecarbonylation of ethanol to diethyl carbonate (DEC) because of its small steric hindrance andsome hydrophobicity. It was demonstrated that catalytic performance was relative to bothby-product water and structure of molecular sieves catalysts, but the latter was a main factorin the catalytic system. In addition, a probable mechanism had been proposed to explain thisresult that structure of molecular sieves was the main factor of influencing catalyticperformance.Finally, PdCl2-CuCl2/ZIF-8and PdCl2/Cu(Im) catalysts were synthesized by thesolvothermal method considering the high hydrophobicity of MOFs and similarity to molecular sieve on structure. Through FT-IR, XRD, BET, contact angle and catalytic activitytest, it can be seen that both of the catalysts had excellent pore structure and perfecthydrophobicity. However, PdCl2-CuCl2/ZIF-8catalyst exhibited better catalytic activity,whose ethanol conversion reached6.2%, the space time yield was141.2mg·g-1·h-1. AndPdCl2/Cu(Im) catalyst showed a better selectivity of98.7%, which had the only theby-product of acetaldehyde, which was similar to the former results of PdCl2-CuCl2/HMS andPdCl2/Cu-HMS catalysts in HMS system. Although this chapter simply explored two kinds ofcatalysts, their superior catalytic performances in our catalysic system bring up new ideas forthe design and research of catalysts in the synthesis of DEC by oxidative carbonylation in gasphase. |
PDF Full Text Request