To overcome the limitations of conventional catalysts in sterically hindered esterification reactions, a radio frequency (RF) plasma-modifiedSO42−/S2O82−/SnO2-Al2O₃ solid superacid catalyst was synthesized via sol-gel and impregnation, followed by RF plasma treatment and calcination. Comprehensive characterization revealed that the RF plasma modification endowed the catalyst with a uniform particle distribution (4.32 nm average size), larger specific surface area (104.44 m2·g−1), elevated total acid content (142.86 μmol·g−1), and increased oxygen vacancy concentration (16.4%), compared to the conventional sol-gel–impregnation–calcination-prepared catalyst. The RF plasma-modifiedSO42−-S2O82−/SnO2-Al2O3was subsequently applied to perform the esterification reaction of Tyr, with a higher steric hindrance. Mechanistic studies indicated that the plasma-induced surface etching and electronic redistribution/intensified electron-withdrawing capability ofSO42−/S2O82−groups synergistically strengthened Brønsted/Lewis acidity. For the esterification of tyrosine—a sterically demanding substrate—the modified catalyst achieved a 92.1% methyl tyrosine yield under the optimized conditions (180 °C, 0.8 MPa N2, 6 h), where the catalyst exhibited a better mechanical strength and better lifetime with five cycles. This work not only provides a scalable plasma-assisted strategy for tuning solid superacids but also establishes an eco-friendly alternative to traditional catalysts, and was applied to the esterification reactions of some high-steric-hindrance substrates.
Pd-SnO 2 heteroaggregate nanocatalysts were synthesized by in-situ transformation of PdSn bimetallic nanoparticles on alumina. The PdSn bimetallic nanoparticles were prepared by co-reduction of Pd and Sn precursors. The obtained PdSn nanoparticles possibly have a core-shell like structure with Pd cores and Sn-rich shells due to the fast reduction of Pd precursors. The Pd-SnO 2 /Al 2 O 3 heteroaggreagte nanocatalysts were synthesized by calcination of PdSn/Al 2 O 3 in air followed by H 2 reduction. Various characterization techniques, such as HRTEM, XRD and XPS, were used to characterize the PdSn and Pd-SnO 2 . The Pd 3 -(SnO 2 ) 1 /Al 2 O 3 heteroaggreagte nanocatalysts with a ratio of Pd/Sn of 3/1 illustrated enhanced catalytic performances for p -nitroacetophenone and p -nitrobenzaldehyde hydrogenations relative to monometallic Pd nanocatalysts. Theoretical calculations using density functional theory suggested that Pd-SnO 2 facilitates the adsorption of reactants in a higher degree than that of products, thus enhancing the catalytic activity even with partial coverage of Pd surfaces with SnO 2 . The blockage effect of SnO 2 on Pd surfaces is speculated to enhance the catalytic selectivity for p -nitroacetophenone and p -nitrobenzaldehyde hydrogenations over Pd-SnO 2 heteroaggregate nanocatalysts.
危险品化学品经营许可证（带存储）