(43f) First-Principles Design of Rh-Based Alloy Catalysts for Selective Propane Dehydrogenation

The non-oxidative propane dehydrogenation (PDH) on metal alloys selectively converts propane to value-added propylene. Recent studies on Rh-based alloy catalysts showed high catalytic activity for C-H bond dissociation and thus are being evaluated as the possible alternative for the state-of-the-art PtSn/Al₂O₃ catalyst.^{1, 2} However, high PDH efficiency of Rh-based materials remains still elusive due to the lack of deep understanding on the complex PDH reaction network at the atomic scale.

In this study, density functional theory (DFT) calculations are used in conjunction with kinetic Monte Carlo (kMC) simulations to acquire a thorough understanding of the PDH and to screen potential Rh-based metal alloys. First, we conduct kMC simulations using the DFT-calculated 112 possible PDH elementary reactions on Rh(111) under the PDH operating conditions. The overall PDH reaction mechanism is thoroughly revealed and kinetic parameters are obtained, which are then used to identify selectivity-limiting steps and deactivation pathways. Based on our understanding of the PDH mechanism on Rh(111), a design principle for Rh-based alloy is proposed; alloying active Rh with inactive carbophobic elements such as Sn and Ga to cover selectivity-limiting Rh ensemble sites. The effectiveness of the design concept is validated by high-throughput screening of 82 Rh-based bimetallic alloy combinations. The constructed selectivity map successfully identifies 8 new alloy combinations as the promising PDH catalysts. Lastly, a detailed computational kinetic study of an as-screened candidate Rh-Sn alloy further validates that the carbophilic secondary metals can effectively promote the PDH selectivity while preserving high C-H bond dissociation activity of Rh. Our comprehensive theoretical analysis on the Rh-based alloy will provide informative insight, which will guide the development of highly active and selective PDH catalyst.

1. R. T. Hannagan et al., Science, 372, 1444 (2021)

2. P. Natarajan et al., Journal of Catalysis, 392, 8 (2020)