Abstract
AbstractAn innovative use of a thermoelectric material (BiCuSeO) as a support and promoter of catalysis for CO2 hydrogenation is reported here. It is proposed that the capability of thermoelectric materials to shift the Fermi level and work function of a catalyst lead to an exponential increase of catalytic activity for catalyst particles deposited on its surface. Experimental results show that the CO2 conversion and CO selectivity are increased significantly by a thermoelectric Seebeck voltage. This suggests that the thermoelectric effect can not only increase the reaction rate but also change chemical equilibrium, which leads to the change of thermodynamic equilibrium for the conversion of CO2 in its hydrogenation reactions. It is also shown that this thermoelectric promotion of catalysis enables BiCuSeO oxide itself to have a high catalytic activity for CO2 hydrogenation. The generic nature of the mechanism suggests the possibility that many catalytic chemical reactions can be tuned in situ to achieve much higher reaction rates, or at lower temperatures, or have better desired selectivity through changing the backside temperature of the thermoelectric support.
Highlights
Introduction tional effect on catalytic activityBiCuSeO (BCSO) was selected as the thermoelectric materials for this investigation because it Thermoelectric (TE) materials have recently attracted wide- possesses good TE properties to over 900 K, an extraordinary spread interest in research because they can convert a temper- low intrinsic thermal conductivity of less than 0.5 W m−1 K−1; ature difference directly into an electrical voltage via the a high temperature difference can built up Seebeck effect, S = −V/ΔT, where V is the voltage between across this material; high Seebeck coefficient up to 500 μV K−1 the two ends of the TE material and ΔT the temperature dif- at room temperature and greater than 300 μV K−1 at high temference, S is the Seebeck coefficient
It is worthy to point out that similar experiments were repeated at least once and the results were reproducible, this ruled out the possible explanation that the conversion difference between the TE and Reduced Thermoelectric (RTE) was due to the catalyst particles aggregation at the surface
It is proposed that the thermoelectric effect can change the Fermi level and the work function of the electrons in the catalyst particles supported on a thermoelectric material
Summary
NEMCA, which involves a reversible change of catalytic properties of metal catalysts deposited on solid electrolytes, can be obtained by applying a small external electric current or voltage. As no external charges exist, the change of the work function at the surface is the inverse change of the Fermi level, i.e., Δφ = −ΔεF, so Δφ = eV at the hot surface Th. If a metal particle is deposited on the TE material, at the hot surface, its Fermi level εF,m must be the same as the Fermi level of the TE at the surface, i.e., εF,m = εF,h (Figure 1). Equations (4)–(6) link catalytic activity with Seebeck voltage and temperature for a metallic catalyst supported on a TE material
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