Hydro-formylation of Styrene on Rh-based Intermetallic Catalyst Surface Structures – A DFT Study

Gupta, Geet
Major Professor
Dr. Luke T. Roling
Committee Member
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Chemical and Biological Engineering

Hydroformylation of olefins to produce C+1 aldehyde is among the most important chemical processes with over 10 million tons of production annually. Numerous efforts have been made to design Rh-based homogeneous catalyst, single atom catalyst (SACs) supported on MOFs that reckons good selectivity and activity. However, challenges like catalyst stability, high metal loading and high linear to branched ratio has gain attention to design Rh based highly controlled catalytic surface. Intermetallic compounds (IMCs) are known for highly controlled catalytic behavior due to presence of an inactive metal, inspired by which we believe that IMCs could boost hydroformylation activity and selectivity. In this work, we report that intermetallic RhZn supported on mesoporous SBA-15 can efficiently catalyze hydroformylation of different olefin substrates with an outstanding turnover frequency and outperforming the benchmark homogeneous catalyst RhCl(PPh3)3. Based on the experimental results, we believe that the performance with RhZn/SBA-15 catalyst is drastically modified by the incorporation of second metal. Therefore, we performed DFT calculations to study the effect of the second metal on the styrene hydroformylation kinetics and the catalytic performance. From the surface energy calculations, Zn-terminated surfaces including ZnRh(100), ZnRh(111), ZnRh(210) and Rh-terminated surface RhZn(110) are screened as possible exposed and active reaction surfaces under H2 synthesis condition. Our reference Rh(111) surface tends to bind intermediates quite strongly in comparison with the mixed Zn and Rh surfaces, therefore, an inactive metal like Zn promotes reaction mechanism by weakening adsorption of intermediates and lowering reaction barriers in the H2 and CO environment. Zn-terminated surfaces accounts for quite weak adsorption of intermediates while Rh-terminated RhZn(110) surface due to one-dimensionally aligned Rh atoms and mixed Rh-Zn atoms favors the reaction mechanism. Strong CO adsorption on Rh atom leads to selective linear product formation. This could be the major advantage of synthesizing intermetallic catalysts (IMCs) in promoting hydroformylation reaction.