Rake mechanism for the deoxygenation of ethanol over a supported Ni 2P/SiO2 catalyst

Article abstract of DOI:10.1016/j.jcat.2012.02.001

The catalytic conversion of ethanol was studied on a metallic Ni ₂P/SiO₂ catalyst, and comparison was made with an acidic HZSM-5 catalyst. Chemisorption probes indicated that the Ni₂P had substantial CO adsorption sites (134 μmol g^-1), while the HZSM-5 catalyst had large quantities of NH₃ adsorption sites (565 μmol g^-1). The catalytic activity in ethanol deoxygenation of the Ni ₂P/SiO₂ was higher than that of the HZSM-5 catalyst on the basis of these chemisorptions sites. In steady-state catalysis, contact time experiments indicated that for Ni₂P, acetaldehyde was a primary product and ethylene was a secondary product. However, this was not the result of a sequential oxidation reaction followed by a reduction process, but rather, it was due to the formation of a surface intermediate that could desorb as acetaldehyde or react further to produce ethylene. This rake-type mechanism was supported by a simulation of the reaction sequence that produced good agreement with the experimentally determined acetaldehyde and ethylene yields. The mechanism was also supported by in situ Fourier transform infrared measurements, which revealed the presence of signals compatible with adsorbed acetaldehyde, the likely surface intermediate species involved in the reaction. The present studies indicate that the reactions of alcohols on metallic catalysts like Ni₂P involve dehydrogenation/hydrogenation steps, rather than simple acid/base-catalyzed dehydration steps as occur in HZSM-5.