Highly active and stable Ir nanoclusters derived from Ir1/MgAl2O4 single-atom catalysts.

Single-atom catalysts (SACs) prepared by the atom trapping method often possess high stability yet have limited advantages regarding catalytic performance due to the strong metal-support interaction. Using these SACs as seeds to develop supported nanoclusters or nanoparticles has, however, been proven to be effective in improving the catalysts' intrinsic activity. Herein, we have prepared extremely stable Ir SACs supported by MgAl2O4 via atomic trapping and used them as seeds to fabricate highly active and stable Ir nanocluster catalysts by high-temperature reduction. The activity toward N2O decomposition increased by more than ten times compared with that of the parent Ir SACs. This study provides a new avenue to design and develop highly active and stable catalysts for industrial use.

A Hydrothermally Stable Irreducible Oxide-Modified Pd/MgAl2 O4 Catalyst for Methane Combustion.

Catalytic combustion is promising in removing trace amounts of CH4 to address serious environmental concerns. Supported Pd-based catalysts are most effective but often suffer from low stability in applications owing to the water-vapor-induced sintering. Herein, we develop a universal strategy to prepare irreducible-oxide-modified Pd/MgAl2 O4 catalysts which show high activity and excellent stability against both hydrothemal aging at elevated temperatures and deactivation in long-term reaction under wet conditions. The addition of irreducible oxides inhibited the deep oxidation of Pd in the oxygen-rich conditions, which preserved not only the epitaxial structure but also a suitable active phase of Pd-PdOx on MgAl2 O4 , thus promoting both activity and stability. This work provides new insights into the effect of metal-oxide interaction on CH4 combustion and offers an avenue to design hydrothermally stable and active combustion catalysts for industrial applications.

Strong metal-support interaction promoted scalable production of thermally stable single-atom catalysts.

Single-atom catalysts (SACs) have demonstrated superior catalytic performance in numerous heterogeneous reactions. However, producing thermally stable SACs, especially in a simple and scalable way, remains a formidable challenge. Here, we report the synthesis of Ru SACs from commercial RuO2 powders by physical mixing of sub-micron RuO2 aggregates with a MgAl1.2Fe0.8O4 spinel. Atomically dispersed Ru is confirmed by aberration-corrected scanning transmission electron microscopy and X-ray absorption spectroscopy. Detailed studies reveal that the dispersion process does not arise from a gas atom trapping mechanism, but rather from anti-Ostwald ripening promoted by a strong covalent metal-support interaction. This synthetic strategy is simple and amenable to the large-scale manufacture of thermally stable SACs for industrial applications.

The Effect of Exposed Facets of Ceria to the Nickel Species in Nickel-Ceria Catalysts and Their Performance in a NO + CO Reaction.

CeO2 rods with {110} facets and cubes with {100} facets were utilized as catalyst supports to probe the effect of crystallographic facets on the nickel species and the structure-dependent catalytic performance. Various analysis methods (ex and in situ XRD, TEM, Raman, XPS, TPR, TPD) were used to investigate the structural forms of the catalysts, and these results indicated that the deposition of nickel species resulted in the formation of two main active types of the catalyst components: NiO strongly or weakly interacted with the surface and Ni-Ce-O solid solution. Notably, the states and distribution ratio of nickel species were related to the shape of CeO2. It was found that CeO2 rods had more active sites to coordinate with nickel species to form a strong interaction with NiO on the surface and a more stable construction when compared to cubes. Furthermore, the nickel-ceria catalysts with rod shape were more active towards NO oxidation with complete conversion below 191 °C, but for cube shape, complete conversion occurred above 229 °C (e.g., for nickel loading of ∼5%, the complete conversion temperature was 154 °C for the rod shape and 229 °C for the cube shape). On the basis of the analysis of the catalysts structure, the superior catalytic activity was due to a combination of surface structures of NiO (mainly strongly interacting with the surface) and nickel ions Ni(2+) in the Ni-Ce-O bulk phase.

The synthesis of CeO2 nanospheres with different hollowness and size induced by copper doping.

In this paper, copper-doped ceria oxides with different hollowness and size are fabricated by changing the Cu(2+) doping concentration in the mixed water-glycol system. Results show that the copper-doped CeO2 oxides undergo a morphology transformation from the solid nanospheres to core-shell, then to hollow nanospheres with the increase of the Cu(2+) doping concentration. The corresponding size becomes smaller during this transfer process. The Cu(2+) doping induced acceleration in the nucleation and growth process is further investigated. The resultant Cu(2+)-doped CeO2 oxides exhibit enhanced CO conversion performance and better reduction behaviors.

[Determination of Huperzine A in the extract of Huperzia serrata by high performance liquid chromatography].

A high performance liquid chromatographic (HPLC) method was established to determine the Huperzine A in the extract of Huperzia serrata. After extracted by methanol/ water/formic acid (10/90/0.2, v/v/v), the sample was filtered for HPLC analysis. The separation was performed on an XCharge C18 column (150 mm x 4.6 mm, 5 microm) by gradient elution with water (containing 0.1% (v/v) trifluoroacetic acid) and acetonitrile (containing 0.09% (v/v) trifluoroacetic acid) as the mobile phases. Rapid separation was achieved within 10 min at a flow rate of 2 mL/min with ultraviolet absorption detection at a wavelength of 310 nm. Under the optimized conditions, good linearity was obtained in the range of 2. 12 - 106 mg/L with the correlation coefficient (R2) of about 0.999 9. The average recovery was 102.34% with the relative standard deviation (RSD) of 0.46%. The intraday and interday precisions were all below 2%. The results demonstrate that this method is simple, rapid and accurate with good reproducibility, and can be used to evaluate the quality of Huperzia serrata.