Butadiene is an important building block in industrial polymer synthesis which can be obtained from catalytic conversion of biomass-derived ethanol via the Lebedev process. However, the reaction mechanism for this process has not yet been well-described in the literature. In this study, we will propose a model that describes the first step in the Lebedev process: ethanol dehydrogenation over MgO-SiO2 mixed oxides. A 0.5% MgO/SBA-15 catalyst was prepared by incipient wetness impregnation and used to probe the dehydrogenation and dehydration of ethanol. We have studied the reactivity of this catalyst for the formation of the acetaldehyde and ethylene at 723, 698, 673, and 648 K. The rates of acetaldehyde and ethylene production were measured at conversions ranging from 3-9% in a tubular flow reactor, and the catalyst was found to undergo two parallel deactivation processes with respect to time-on-stream. The acetaldehyde and ethylene formation rates, corrected for deactivation, were revealed to be zero-order with respect to ethanol partial pressure in the range of 14–19 torr. We propose a mechanism that is consistent with the measured reaction kinetics wherein an ethanol molecule is first adsorbed molecularly on the surface, followed by O-H bond cleavage to form ethoxide adsorbed on the surface. The ethoxide species subsequently undergoes C-H bond cleavage to form acetaldehyde. Finally, the two H atoms bound to the surface combine and desorb as H2. O-H bond cleavage, leading to the formation of adsorbed ethoxide is assumed to be the kinetically significant elementary step.

Kinetics of ethanol dehydrogenation on MgO-SiO2 mixed oxide catalysts

255th National Meeting (2018)

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