Activation of n-octane and cyclohexane to oxygenates using modified zeolites.

Abstract

Three types of zeolites namely ZSM-5, Faujasite Y and MOF-5 were synthesized. The synthesis of Na-Fe-silicalite-1(34), H-Fe-silicalite-1(34), Na-Fe-silicalite-1(41), Na-Fe-silicalite-1(68), Na-Fe-silicalite-1(80), Fe-silicalite-1(128), Na-Fe-ZSM-5(66) and Na-Fe-ZSM-5(114) was conducted using a solid gel method. Further to this, Na-Fe-silicalite-1(41), Na-Fe-silicalite-1(80), Fe-silicalite-1(128), Na-Fe-ZSM-5(66) and Na-Fe-ZSM-5(114) were modified by silanisation using tetraethoxysilane (TEOS) as the silanisation agent to produce Na-Fe-silicalite-1(41:Sil), Na-Fe-silicalite-1(80:Sil), Na-Fe-silicalite-1(128:Sil), Na-Fe-ZSM-5(66:Sil), Na-Fe-ZSM-5(114:Sil). The numbers in brackets represent Si/Fe molar ratio while Sil represent silanisation. Powder XRD results showed that only the ZSM-5 phase was obtained. The second type was synthesized by encapsulation of Fe-TPP (tetraphenylporphyrin) inside faujasite Y to produce Fe-TPP-NaY. Powder XRD results confirmed the faujasite structure after encapsulation. Finally, Fe-MOF-5(1), Fe-Zn-MOF-5(0.5) and Fe-Zn-MOF-5(0.2) were synthesized using conventional methods with the numbers in brackets representing the Fe wt%. Also, XRD results showed that the MOF-5 phase was obtained with a sharp peak at 2θ below 10° which is characteristic of a highly crystalline material. All synthesized catalysts were tested in the oxidation of n-octane to oxygenates with H2O2 as the oxidant in MeCN. Furthermore, Fe-TPP-NaY was also used to activate 1-octene, 4-octene and cyclohexane while Fe-MOF-5 was used to activate cyclohexane. Na-Fe-silicalite-1(34), H-Fe-silicalite-1(34) and Na-Fe-silicalite-1(68) produced selectivities of 24, 2 and 27% respectively to terminal products at 80 °C in 13 mL MeCN. Furthermore, Na-Fe-silicalite-1(41), Na-Fe-silicalite-1(80), Fe-silicalite-1(128), Na-Fe-ZSM-5(66) and Na-Fe-ZSM-5(114) achieved selectivities to terminal products of 20.2, 28.1, 17.6, 24.5 and 21.3 respectively while Na-Fe-silicalite-1(41:Sil), Na-Fe-silicalite-1(80:Sil), Na-Fe-silicalite-1(128:Sil), Na-Fe-ZSM-5(66:Sil) and Na-Fe-ZSM-5(114:Sil) showed selectivities to terminal products of 20.7, 14.3, 12.3, 25.7 and 27.3 % respectively at 80 °C in 80 mL MeCN. Fe-TPP-NaY showed 13% selectivity to terminal products in oxidation of n-octane at 80 C in 13 mL MeCN. In the oxidation of n-octane using Fe-MOF-5 catalysts, selectivity to terminal products was found to increase with a decrease in the wt% of Fe. Hence, selectivities of 9.5, 12.9 and 20.7% were recorded for Fe-MOF-5(1), Fe-Zn-MOF-5(0.5) and Fe-Zn-MOF-5(0.2) respectively.