(476b) The Impact of Support in Syngas Conversion over Rh-Mn Particles on WC

Authors: 
Göltl, F., University of Wisconsin-Madison
Liu, Y., University of Wisconsin-Madison
Zhang, L., University of Wisconsin-Madison
Dumesic, J., University of Wisconsin
Mavrikakis, M., University of Wisconsin-Madison
The conversion of synthesis gas, a mixture of CO/CO2 and H2, is a promising technology to transform carbon-containing feedstocks to higher value platform chemicals. Depending on the catalyst used, a variety of different products can be obtained, ranging from saturated hydrocarbons to methanol and higher alcohols. The synthesis of higher alcohols is challenging, since a catalyst that can activate the appropriate percentage of CO bonds is required. Specifically, Rh shows selectivity towards higher alcohols in synthesis gas conversion and the selectivity can be improved when Mn is used as a promoter. On a silica support, Mn suppresses the formation of methane by passivating cluster edges of Rh nanoparticles[1]. However, on a WC support, formation of methanol is suppressed [2], which indicates a different role for Mn in this case.

Here we use first principles modeling to understand the role of Mn in the conversion of synthesis gas over WC supported Rh clusters. In a first step, we construct 22 different RhxMny clusters containing either 31 or 37 metal atoms and model their stability on a WC support. We find that a distribution of layered clusters with Mn in direct contact with the support is thermodynamically stable. We then calculate C and O binding energies to different high symmetry sites on these clusters. Subsequently, we use selected binding energies as descriptors to assign specific activities and selectivity to each of the active sites on the different clusters. We find that sites at the bottom of the supported clusters, which are mainly selective to methanol for monometallic Rh clusters, become passivated when Mn is introduced to the system. Additionally we find that a core-shell type cluster with Mn in the core and Rh in the shell shows a significantly higher activity in this catalysis and might be the most active part of the cluster distribution.

[1] Y. Liu, F. Göltl, I. Ro, M.R. Ball, C. Sener, I.B. Aragao, D. Zanchet, G.W. Huber, M. Mavrikakis, J.A. Dumesic, ACS Catal. 7, 4550-4563, 2017

[2] Y. Liu, L. Zhang, F. Göltl, M.R. Ball, I. Hermans, T.F. Kuech, M. Mavrikakis, J.A. Dumesic, ACS Catal. 8, 10707-10720, 2018