Sinter-resistant Rh nanoparticles supported on γ-Al2O3 nanosheets as an efficient catalyst for dry reforming of methane.

γ-Al2O3 nanosheet supported rhodium catalysts with Rh loadings between 0.05 and 2 wt% were prepared by the impregnation method and used for dry reforming of methane (DRM). It was found that Rh species on γ-Al2O3 nanosheets demonstrated excellent stability against sintering at high temperature. After calcining in air at 800 °C followed by reducing with hydrogen at 600 °C, the average particle size of Rh at maximum distribution increases from 1.0 ± 0.3 to 1.8 ± 0.3 nm with an increase in Rh loadings in the catalysts from 0.05 to 2 wt%. Even after reducing with hydrogen at 900 °C, the average size of Rh particles in the catalysts still remained below 2 nm. The results of catalytic performance evaluation show that CH4 and CO2 conversions of 84% and 90%, respectively, with a H2/CO ratio in syngas close to unity can be achieved with a catalyst of Rh loading of only 0.05 wt% at 750 °C. The performance of the catalyst remains stable for more than 200 h. No significant aggregation of the Rh particles is observed on the catalyst after the reaction. The results of XPS, H2-TPR and O2-TPD characterization methods indicate that the strong interaction between Rh and the γ-Al2O3 nanosheets plays a key role in increasing the dispersion of Rh species in the catalyst and preventing it from sintering under high temperature conditions. This factor is also responsible for the superior activity and stability of the catalyst with extremely low Rh loading for the DRM reaction.

Sodium hyaluronate-functionalized urea-formaldehyde monolithic column for hydrophilic in-tube solid-phase microextraction of melamine.

A novel sodium hyaluronate-functionalized urea-formaldehyde (UF) monolithic column has been developed by in-situ polycondensation of urea, formaldehyde and sodium hyaluronate (HA). HA plays both the roles of crosslinking and hydrophilic functionalization. The preparation factors including different molecular weights of HA and different amounts of HA were optimized, and then a uniform monolith with satisfactory permeability and hydrophilic binding capacity was obtained. Due to the excellent hydrophilicity of HA, HA-functionalized UF monolith showed higher hydrophilic extraction efficiency than UF monolith, and was applied for hydrophilic in-tube solid-phase microextraction (SPME) of melamine (MEL). Several factors for hydrophilic in-tube SPME, such as ACN percentage in the sampling solution, salt concentration and pH value of the sampling solution, elution volume, sampling and elution flow rate, were investigated with respect to the extraction efficiency of MEL. Under the optimized SPME conditions, the limit of detection (LOD) of MEL was found to be 0.2ng/mL in the milk formula samples, the recoveries of MEL spiked in milk formula samples ranged from 87.3% to 96.7% with relative standard deviations (RSDs) less than 5.1%. Owing to the excellent hydrophilic extraction ability, the novel HA-functionalized UF monolith could provide a promising tool for the sensitive analysis of polar analytes in complicated samples.