(513d) Synthesis of Co Incorporated MCM-41 Large Particle Pseudomorphs

Pseudomorphic synthesis of Co incorporated MCM-41 has been performed using spherical silica particles of 15 and 40 µm diameter. A pseudomorph, in mineralogy, means a crystal or other body consisting of one mineral but having the equivalent form of another, in consequence of having been formed by substitution, or by chemical or physical alteration. In this study, MCM-41 particles can be considered as pseudomorphs of the large (relative to the usual sub-micron MCM-41) silica gel particles. Each silica particle behaves like a microreactor in which silica may be dissoved by the alkaline solution, and silica species interact with surfactant to form MCM-41 pore structure as in the usual synthesis procedure. However, for catalytic applications of MCM-41, which requires metal ion incorporated MCM-41, a uniform distribution of metal ions through the pore surface is a key requirement in the metal ion incorporated MCM-41 compared to pure siliceous MCM-41 pseudomorphic synthesis. The use of a non-sodium alkaline medium is introduced for the first time in the pseudomorphic synthesis of Co-MCM-41 and may be applied to a wide range of metal ions. The physical and chemical properties were investigated by temperature programmed reduction (TPR), nitrogen physisorption, and scanning electron micrograph (SEM) to suggest the preferred synthesis conditions for obtaining a successful Co-MCM-41 pseudomorph. For a successful pseudomorphic synthesis of Co-MCM-41, the autoclaving time and the initial pH of the synthesis solution are crucial factors to produce a non-ruptured spherical morphology and complete transformation of the parent silica to the MCM-41 structure. These factors also affected the distribution of Co ions in the MCM-41 structure, which is the key to some catalytic applications. The optimum autoclaving time and initial pH were 4 days and 12, respectively. The initial pH adjustment of Co-MCM-41 synthesis solution affected the reduction stability by controlling Co ion location in the silica MCM-41 framework as well as hydrogen spillover on the surface. Finally, successful applications of this catalytic system to the fluidized bed synthesis of SWNT and the synthesis of longer nano-structures are expected.