Transition metal catalysts find nowadays their application in major industrial processes to obtain sustainable chemicals and renewable fuels. Activation of water has been suggested to play a key role in the water–gas shift and multiple reforming processes, being in some cases acknowleged as the rate-detemining step. Since the industrial catalysts operate at the nano scale, atomic-level understanding of the water activation on relevant transition metals could provide useful information for rational design of catalysts with higher activity and selectivity. We present a density functional theory study of the water activation on Rh and Pt metals, where the metals are represented by M55 and M147 cuboctahedral nanoparticles accompanied by the extended (100), (111), and (211) surfaces, mimicking facets and edges of the nanoparticles. We systematically evaluate adsorption and activation of a single water molecule on each relevant surface site of each structural model. Our findings indicate that both Rh and Pt are nearly equally active towads the water activation, which is refrected in a difference of &lt;0.10 eV in adsorption and transition state energies between the two metals. Moreover, in the case of the nanoparticle models, we observe strong linear dependences of adsorption and transition state energies on the centers of the d-band projected onto the corresponing surface sites and on the generalized coordination numbers, which quantify the surface site coordination accounting for their first coordination spheres. These trends do not withhold for the extended surface models, hinting their insufficiency in describing the electronic and structural properties of the nanoparticles in the chosen size regime. The difference between Rh and Pt is observed in the stability of the dissociated water, which is higher in the case of Rh. These results are qualitatively in line with the experimental evidence of lower thermodynamic stability of Pt oxides.

Adsorption and activation of water on cuboctahedral rhodium and platinum nanoparticles

253rd National Meeting (2017)

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