A structured catalyst has been fabricated by immobilizing cobalt phthalocyanine tetrasulfonate (CoPcS) on a MgNiAl mixed metal oxide (MgNiAl-MMO) film derived from calcination of layered double hydroxide (LDH). The resulting CoPcS/MgNiAl-MMO catalyst exhibits excellent activity, stability, and recyclability for the reaction of mercaptan sweetening. SEM images show that the structured catalyst is composed of thin MMO nanoflakes perpendicular to the Al substrate. The synergistic effect between the oxidation center (CoPcS) and the abundant moderate basic sites on the surface of the MgNiAl-MMO substrate plays an important role in the sweetening process, accounting for the largely enhanced catalytic behavior (conversion: 92.8%; selectivity: 100%). In addition, the structured catalyst exhibits superior catalysis regeneration performance, owing to its specific architecture and strong mechanical stability. This work demonstrates a facile approach for modulating the synergistic effect between the active center and the basicity for the structured catalyst, for the purpose of achieving largely enhanced catalytic behavior in the petroleum refining industry.

Colloidal layered double hydroxides (LDH) nanosheets were sorted by their lateral sizes using a density gradient ultracentrifuge separation technique. Composition investigations on these size-sorted nanosheets indicated that larger sheets had higher Mg:Al ratio than the smaller ones. Experiments using different Mg:Al feed ratios confirmed that high Mg:Al ratio induced fast sheet growth speed. Tracking the source of the Mg:Al spatial distribution difference in one batch of synthesis at the nucleation process revealed the coprecipitation-redissolution of Mg2+. Thus the discriminative separation of these nanosheets led to a new insight into the structure-composition relationship of LDH nanomaterials and more understanding on their formation mechanism.