TY - JOUR
T1 - NH4-exchanged zeolites
T2 - Unexpected catalysts for cyclohexane selective oxidation
AU - Graça, I.
AU - Chadwick, D.
N1 - Acknowledgments: This work was performed with financial support from EPSRC(UK) under grant EP/K014749/1. The authors thank Senpei Peng for help with catalyst recovery and analysis.
PY - 2020/3/1
Y1 - 2020/3/1
N2 - NH4-, H-, Na-, Cs-exchanged ZSM-5 zeolites have been investigated as catalysts for the selective oxidation of cyclohexane under mild conditions using molecular oxygen as oxidant. For comparison, Mn- and Fe-exchanged ZSM-5 zeolites were also studied, as Mn and Fe are well-known oxidation metals. It has been shown that the type of compensating cation in the zeolite framework is of extreme importance for the activity of these catalysts in this reaction. Surprisingly, superior selective oxidation performance was achieved with a commercial NH4-ZSM-5 zeolite. The ion-exchanged transition metals (Mn and Fe) were shown to have higher selective oxidation ability compared to the alkali metals, as expected owing to their better redox properties. The rate of cyclohexyl-hydroperoxides transformation into cyclohexanol and cyclohexanone also appears to depend on the ion-exchanged cation, being also much faster over the ammonium and transition metal-exchanged zeolites. Overall, this work has shown for the first time the potential of zeolites ion-exchanged with ammonium to catalyse the selective oxidation of cyclohexane, which in principle offers the possibility of avoiding or reducing the need for more expensive and less environmentally friendly transition metals.
AB - NH4-, H-, Na-, Cs-exchanged ZSM-5 zeolites have been investigated as catalysts for the selective oxidation of cyclohexane under mild conditions using molecular oxygen as oxidant. For comparison, Mn- and Fe-exchanged ZSM-5 zeolites were also studied, as Mn and Fe are well-known oxidation metals. It has been shown that the type of compensating cation in the zeolite framework is of extreme importance for the activity of these catalysts in this reaction. Surprisingly, superior selective oxidation performance was achieved with a commercial NH4-ZSM-5 zeolite. The ion-exchanged transition metals (Mn and Fe) were shown to have higher selective oxidation ability compared to the alkali metals, as expected owing to their better redox properties. The rate of cyclohexyl-hydroperoxides transformation into cyclohexanol and cyclohexanone also appears to depend on the ion-exchanged cation, being also much faster over the ammonium and transition metal-exchanged zeolites. Overall, this work has shown for the first time the potential of zeolites ion-exchanged with ammonium to catalyse the selective oxidation of cyclohexane, which in principle offers the possibility of avoiding or reducing the need for more expensive and less environmentally friendly transition metals.
KW - Cyclohexane
KW - Ion-exchanged zeolites
KW - KA oil
KW - Selective oxidation
KW - OXYGEN
KW - FE-MFI ZEOLITES
KW - METHANE
KW - ALKALI
KW - PROMOTION
KW - IRON
KW - BETA
UR - http://www.scopus.com/inward/record.url?scp=85075376361&partnerID=8YFLogxK
U2 - 10.1016/j.micromeso.2019.109873
DO - 10.1016/j.micromeso.2019.109873
M3 - Article
AN - SCOPUS:85075376361
VL - 294
JO - Microporous and Mesoporous Materials
JF - Microporous and Mesoporous Materials
SN - 1387-1811
M1 - 109873
ER -