(448t) Synthesis and Characterization of Nickel-Cobalt Oxide for Ethanol Decomposition
In this work we use combustion synthesis method to prepare cobalt catalysts which have been reported to be active for ethanol-hydrogen production. This work focuses primarily on understanding the reaction mechanism leading to various products using in situ DRIFTS studies. Bimetallic NiCo were synthesized from the aqueous solution of nickel nitrate (Ni(NO3)2Î?6H2O), cobalt nitrate (Co(NO3)2Î?6H2O) and glycine (C2H5NO2) in solution combustion synthesis (SCS) method using a fuel to oxidizer ratio of (Ï?) 0.5,1,1.75,2 and 2.5. Time-temperature profile of NiCo shows an increase in combustion temperature with increase in fuel ratio with maximum temperature at Ï? = 1 and after that it decreases. The XRD shows the presence of nickel-cobalt component in their oxidized states. SEM of as-synthesized nanoparticles of different molar ratios from 0.5 to 2.5 in SCS mode shows the nanoparticles of high porosity that are randomly distributes as well as agglomerated. Mostly this high porosity is due to the escaping of excess gases during combustion process. Also the EDS results are in consistent with the XRD results showing higher amount of oxide in the synthesized NiCo compound. TEM image also shows agglomeration that is common in solution combustion mode with non-uniform sized particles. The particle size increases with temperature and in the range of 10-40nm. Nickel-cobalt oxide synthesized using combustion technique has been reduced to pure nanocrystal by passing hydrogen in the reaction chamber at 300°C. An FTIR spectrum at 50 and 100°C shows the presence of adsorbed ethanol and ethoxy species over the reduced catalyst. IR band at 3669 cm-1 indicates the presence of OH from adsorbed ethanol on the catalyst surface. At higher temperature the molecularly adsorbed ethoxy species is converted into acetate species along with the presence of carbonate species. After increasing the temperature from 200°C the intensity CO2 band at 2335-2367 cm-1 is evident. At this temperature the acetate species are dehydrogenated to acetaldehyde and other intermediate species. Strong acetate band of 1760 cm-1 above 200ºC could be due to the transformation of acetaldehyde formed by the dehydrogenation of ethanol to either ethyl acetate or acetic acid though the nucleophilic reaction of ethoxy or hydroxyl species with the surface aldehyde. The presence of IR band between 2830-2695 cm-1 shows the presence of aldehyde group in the decomposition reaction. At higher temperature, the presence of carbonate species is evident with the carbonate layer formation from SEM and TEM images. This carbon layer at higher temperature hinders the action of catalyst in ethanol decomposition reaction.
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