Characterizations Of Cu-containing Molecular Sieves And Its Applications In The Green Catalytic Syntheses

This dissertation focuses on the syntheses, characterizations and catalytic applications of Cu-containing molecular sieves in the green synthesis, and is composed of three parts.In the first part, a series of CuNaX catalysts with different Cu-containing were synthesized by a simple ion-exchange method. The catalytic performance of CuNaX for the solvent-free oxidation of alcohols with tert-butyl hydroperoxide (TBHP) in liquid phase was studied. The catalytic activity of CuNaX with Cu-containing of 10.4% was the highest, and the benzyl alcohol conversion was 42% with benzyldehyde yield of 35% at 70oC in 6 h. The catalyst could be recycled for several runs without appreciable loss of its activity. The results of X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS) and hydrogen temperature-programmed reduction (H2-TPR) suggested that the incorporated Cu ions were mainly located in the supercages of NaX when the Cu-containing was as low as 6.0%, whereas Cu ions would be exchanged into the sodalite cages and/or the hexagonal prism cages of NaX when the incorporated Cu was higher than 6.0%. The Cu ions located inside the supercages of NaX, mainly existed as six coordinated Cu(II), account for the high activity of CuNaX in the solvent-free oxidation of alcohols with TBHP. The higher calcination temperature would result in a strong interaction between the incorporated Cu ions and the framework oxygen atoms of NaX and a migration of Cu ions from the supercages of NaX to the sodalite cages and/or the hexagonal prism cages, and a destruction of NaX structure and a decrease of catalytic activity occurred accordingly.In the second part, a series of Cu-M-NaX (M =K, Mg, Ca, Sr, Ba) catalysts prepared by the conventional impregnation method were investigated for the solvent-free selective oxidation of alcohols with TBHP. It was found that adding a small amount of alkali metal or alkaline earth metal could significantly improve the catalytic activity and selectivity in the alcohol oxidation. Among alkali metal and alkaline earth metal studied, Sr showed the highest catalytic activity and selectivity. The results of diffuse reflectance spectroscopy (DRS) and hydrogen temperature-programmed reduction (H2-TPR) implied that there is a strong interaction between added Sr and CuOx located inside the pores of NaX, which results in a highly dispersion of CuOx and a significant improvement of the catalytic activity in the alcohol oxidation. Cu loadings were found to be important in controlling the dispersion and existence of supported CuOx, and thus result in a significant influence on the alcohol oxidation. When the Cu loadings was less than 4%, Cu species mainly existed as small CuOx particles highly dispersed in the pores of NaX. Whereas, the aggregation of large CuOx particles located outside the pores of NaX occurred as the Cu loadings was higher than 4%. Small CuOx particles highly dispersed in the pores of NaX showed high catalytic activity in the alcohol oxidation, while the aggregated large CuOx resulted in a low alcohol conversion.In the third part, a series of CuNaX prepared by the ion-exchange method were investigated for the liquid-phase selective oxidation of ethylbenzene with TBHP. As compared with other transition metal containing NaX, CuNaX showed the highest ethylbenzene oxidation acitivity and acetophenone selectivity. Under optimized conditions, 78% ethylbenzene conversion with acetophenone selectivity of 98% was achieved. The catalyst could be recycled for several times without appreciable loss of the activity. The existence and the micro-environment of Cu ions in NaX play an important role in the oxidation of ethylbenzene with TBHP. Cu ions located inside the supercages of NaX, mainly existed as six coordinated Cu(II), account for the high activity in the selective oxidation of ethylbezene. Alkali metal, alkaline earth metal ions added to Cu-NaX resulted in a dramatic improvement of the ethylbenzene oxidation activity, in which the alkaline earth metal ions, such as Mg, Ca, Sr, are more efficient.