Journal
ACS APPLIED NANO MATERIALS
Volume 5, Issue 12, Pages 17783-17794Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsanm.2c03757
Keywords
selective oxidation; nanocasting; cobalt oxide; transition-metal substitution; mesoporous materials
Funding
- Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)
- Center for Solvation Science ZEMOS - German Federal Ministry of Education and Research BMBF
- Ministry of Culture and Research of Nord Rhine-Westphalia
- Max Planck Society
- [388390466-TRR 247]
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A series of transition-metal-substituted mesoporous cobalt oxide catalysts were synthesized and applied in the selective oxidation of 2-propanol. Copper and nickel substitutions were found to be beneficial for the catalytic activity, while chromium, manganese, and iron substitutions were detrimental.
A series of transition-metal-substituted (M = Cr, Mn, Fe, Ni, Cu) ordered mesoporous cobalt oxide catalysts were synthesized via nanocasting method using KIT-6 silica as a hard template. While the pristine Co3O4 formed as a perfect replication of KIT-6, metal substitution resulted in less ordered and smaller domains of the replica oxides. The catalysts were applied in the selective oxidation of 2-propanol in the gas phase to reveal the role of the systematic metal substitution. Cu and Ni substitutions were found to be beneficial for the catalytic activity, while Cr, Mn, and Fe substitutions were detrimental. Cofeeding water vapor shifted the onset temperature of 2-propanol conversion to higher temperatures (Delta T = 10-20 K), while a beneficial effect was observed at high temperatures (>260 degrees C) decreasing deactivation by slowing the reduction of active Co3+ and/or reducing coke deposition. The activity scaled with the reducibility of the catalysts probed by H2 temperature-programmed reduction with the positive effect of a higher reducibility, indicating the crucial role of oxygen activation during 2-propanol oxidation at the gas- solid interface. 2-Propanol activation probed by adsorption/desorption experiments monitored by diffuse reflectance infrared Fourier transform spectroscopy showed a weakening of the interaction and changing of the adsorption mode from dissociative to molecular adsorption following the periodic table from Cr to Cu, suggesting that the activation of 2-propanol plays a minor role compared with oxygen activation. Fe-substituted Co3O4 was the least active catalyst due to the decrease of the number of active Co3+ sites.
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