Rh³⁺ stabilized in KRh@MFI catalyses regioselective hydroformylation

Hydroformylation has been a cornerstone of industrial organometallic catalysis, with regioselectivity being a critical aspect in this process^1,2. Present industrial systems use homogeneous Rh-based catalysts with expensive and toxic phosphine-containing ligands, underscoring the need to develop alternative heterogeneous catalysts that could compete with the actual homogeneous ones³. In this direction, atomically dispersed Rh catalysts have been proposed as promising candidates for hydroformylation^4,5. However, achieving high regioselectivity at high conversion is still a big challenge. Here subnanometre Rh₂O₃ clusters are confined inside the channels of the MFI zeolite, which under reaction conditions disrupt into isolated Rh³⁺ and Rh⁺ species. Density functional theory (DFT) investigations combined with spectroscopic and catalytic studies demonstrate that Rh³⁺-mediated hydroformylation is energetically plausibly similar to Rh⁺, with Rh³⁺ being intrinsically more selective for hydroformylation and less selective for double-bond isomerization than Rh⁺. In the coexistence of both Rh³⁺ and Rh⁺ species, we demonstrate the possibility to selectively inhibit Rh⁺ sites through the addition of N-containing molecules such as N-methylpyrrolidine (MP) or 1-methyl-2-pyrrolidone (NMP), which preferentially coordinate to Rh⁺ inside MFI zeolite channel, thereby suppressing its isomerization function while leaving Rh³⁺ sites catalytically accessible. This strategy results in a notable enhancement of regioselectivity, with a state-of-the-art reported highest linear to branched aldehydes (l/b) ratio of 817 with 96% undecanal selectivity at 99.8% 1-decene conversion, using NMP as additive.