Hongjuan Xi

Reshaping CuO on silica to generate a highly active Cu/SiO2 catalyst

Reduction–oxidation treatment [RO] of an impregnated CuO/SiO2 catalyst has been found to be effective in re-dispersing CuO particles on the support. During the process, CuO was actually reshaped within a confined area on silica, forming an annular morphology consisting of highly dispersed nano CuO particles. The reshaping might happen during the oxidation process following the reduction step, while no re-dispersion could be observed by applying the oxidation step alone. After activation with H2, the RO treated samples demonstrated improved catalytic activity for methanol decomposition. These findings clearly indicate that the “shape” of CuO can be memorized during the activation process, resulting in the formation of a specific Cu metal and thus demonstrating different catalytic activities. Such a memory effect correlates the catalytic performance with the characterization data of CuO directly, which has the potential to provide a convenient approach for further catalyst development.

High selectivity for n-dodecane hydroisomerization over highly siliceous ZSM-22 with low Pt loading

Highly siliceous ZSM-22 was synthesized under hydrothermal conditions with ZSM-22 seeds. Characterization by FT-IR and 1H and 29Si NMR spectroscopy confirms that due to the existence of defective sites in the siliceous ZSM-22, acidic silanol groups including vicinal silanol and silanol nests are detected. Acidic silanol groups are considered as the acid sites of siliceous ZSM-22. As a result, siliceous ZSM-22 shows much lower acid site density and lower acid strength than silica–alumina ZSM-22 which contains hydroxyl groups bridging Si and Al as acid sites. In n-dodecane isomerization, Pt/siliceous ZSM-22 shows much higher isomer selectivity than Pt/silica–alumina ZSM-22. Furthermore, a lower loading amount of Pt on siliceous ZSM-22 (about 0.2 wt% Pt) can lead to high isomer selectivity. Owing to the acidic silanol groups and the low acid site density of siliceous ZSM-22, a good balance between metal and acid function in Pt/siliceous ZSM-22 is achieved, which results in a lower allowable Pt loading value and higher isomer selectivity.