Spatial confinement in Pd@Silicalite-1 neutral zeolite catalysts induces selectivity switching from dimethyl oxalate to dimethyl carbonate in CO esterification with methyl nitrite

The esterification of CO with methyl nitrite provides a pathway for synthesizing ester chemicals such as dimethyl oxalate (DMO) and dimethyl carbonate (DMC). Conventional supported Pd nanoparticles (NPs) typically exhibit a strong preference for DMO. Our previous studies showed that encapsulating Pd NPs within the pores of metal-organic frameworks shifts this preference toward DMC, an effect related to the chemical microenvironment regulated by local Lewis acidity. To better understand these microenvironments, we eliminated the interference of local acidity to uncover how pure spatial confinement intrinsically directs the reaction pathway. Using Silicalite-1 (S-1) as a neutral confinement model, we found that encapsulating Pd NPs within micropores yields a 100% DMC selectivity. This differs from the unconfined Pd NPs /S-1, which predominantly forms DMO (68.9%). Comparative evaluations indicate that while spatial confinement determines this selectivity, the presence of acid sites enhances the catalytic activity. In situ DRIFTS spectroscopy and density functional theory calculations suggest that this physical restriction reduces the surface coverage of the *COOCH 3 intermediate. This suppresses the collision-driven advantage of C-C coupling, favoring the C-O coupling pathway. Consequently, our findings indicate that physical confinement directs selectivity while acid sites drive activity, providing a clear strategy for designing selective catalysts in complex reaction networks.