Deciphering the mass transfer and diffusion behavior in the oxidation of fatty alcohols to fatty acids over Pt/MCM-41

This study proposed a synergistic catalysis including diffusion, adsorption and reaction for enhanced long-chain fatty alcohols catalytic oxidation to carboxylic acids inside the mesoporous Pt/ZSM-5 via molecular simulation. Catalysts with specific Pt cluster sizes and mesoporous pores can enhance the conversion and selectivity of 2-ethylhexanol oxidation reaction by strengthening internal diffusion and promoting mass transfer of isomeric alcohols on Pt surface. [Display omitted] •The mass transfer diversity between linear and isomeric alcohols/acids in Pt/MCM-41 is systematically discussed.•Mesoporous Pt/ZSM-5 models with specific Pt cconstructed that are consistent with the characterization.•Pioneering study on the effect of different sizes of Pt clusters and mesopores matching for bulky alcohols mass transfer.•The mass transfer dependence of Pt/MCM-41 on the oxidation of n-octanol and 2-ethylhexanol was verified via experiments and characterization. Selective oxidation of long-chain fatty alcohols into acids is an important value-added reaction. However, exploring the basic catalytic steps over Pt-based catalysts throughout the entire oxidation process is still ambiguous. In this work, we systematically investigated the synergistic mechanisms of adsorption, reaction, and diffusion over Pt/MCM-41 for normal/isomeric alcohols oxidation into acids via molecular dynamics, in-situ characterization, and experiments. Specifically, diffusion coefficients decrease with the increase of the molecular weight of normal molecules due to the increased van der Waals forces, while isomeric alcohols exhibit more complex patterns originated from the steric hindrance between Pt particles and mesopores. To quantitatively describe this pattern, a cluster size descriptor of dPt0.75×dPore0.25 was defined. Notably, 2-ethylhexanol exhibits the best self-diffusion coefficients at the descriptor value of 3.14. Correspondingly, the oxidation of 2-ethylhexanol to 2-ethylhexanoic acid displays highest reaction conversion (68.67 %) and selectivity (65.59 %).