Switchable Selectivity in Styrene Hydroformylation Using Single-Atom Rhodium Supported on g-C₃N₄ as Catalysts

A highly dispersed Rh catalyst supported on graphitic carbon nitride (Rh/g-C3N4) was used to investigate the hydroformylation of styrene. The results reveal that Rh/g-C3N4 exhibits high selectivity toward hydroformylation products; notably, no hydrogenated byproducts were detected within the span of reaction conditions tested. An empirical model was developed to predict the selectivity to the branched (and linear) hydroformylation products using design of experiments, including three factors, temperature, partial pressure of carbon monoxide, and partial pressure of hydrogen. The selectivity toward the branched aldehyde is favored at low temperatures and high pressures; the test at 100 bar confirmed the model prediction (a range of 88.2–98.1%) with an observed branched selectivity of 86.3%. Conversely, linear aldehydes are predominantly formed at high temperatures, achieving the best selectivity to the linear aldehyde of 65.4% at 150 °C and 16 bar total pressure of CO/H2 (1:1).