Prospects of Heterogeneous Hydroformylation with Supported Single Atom Catalysts

The potential of oxide-supported rhodium single atom catalysts (SACs) for heterogeneous hydroformylation was investigated both theoretically and experimentally. Using high-level domain-based local-pair natural orbital coupled cluster singles doubles with perturbative triples contribution (DLPNO-CCSD(T)) calculations, both stability and catalytic activity were investigated for Rh single atoms on different oxide surfaces. Atomically dispersed, supported Rh catalysts were synthesized on MgO and CeO. While the CeO-supported rhodium catalyst is found to be highly active, this is not the case for MgO, most likely due to increased confinement, as determined by extended X-ray absorption fine structure spectroscopy (EXAFS), that diminishes the reactivity of Rh complexes on MgO. This agrees well with our computational investigation, where we find that rhodium carbonyl hydride complexes on flat oxide surfaces such as CeO(111) have catalytic activities comparable to those of molecular complexes. For a step edge on a MgO(301) surface, however, calculations show a significantly reduced catalytic activity. At the same time, calculations predict that stronger adsorption at the higher coordinated adsorption site leads to a more stable catalyst. Keeping the balance between stability and activity appears to be the main challenge for oxide supported Rh hydroformylation catalysts. In addition to the chemical bonding between rhodium complex and support, the confinement experienced by the active site plays an important role for the catalytic activity.X-ray absorption experiments were performed at the ALBA Synchrotron Light Source (Spain), experiment 2019023278. Beamline scientists L. Simonelli and C. Marini are gratefully acknowledged for their contribution to beam setup. E. Andrés, E. Martı́nez-Monje, I. López, and M. Garcı́a-Farpón (ITQ) are acknowledged for their assistance with XAS data acquisition. J. Ternedien (MPI-KOFO) is acknowledged for the performance of XRD experiments. N. Pfänder (MPI-CEC) is acknowledged for his contribution to STEM characterization. The authors acknowledge support by the state of Baden-Württemberg through bwHPC (bwUnicluster and JUSTUS, RV bw17D01). The authors gratefully acknowledge support by the GRK 2450. Financial support from the Helmholtz Association is also gratefully acknowledged. The experimental work received funding from the Max Planck Society and the Spanish Ministry of Science, Innovation and Universities (projects SEV-2016-0683 and RTI2018-096399-A-I00). B.B.S. acknowledges the Alexander von Humboldt Foundation for a postdoctoral scholarship