SYNTHESIS AND EVALUATION OF METAL-SILICA CORE-SHELL NANOMATERIALS FOR CATALYSIS

Nanocatalysts have drawn considerable interest because of their high selectivity and reactivity compared with conventional catalysts. However, the catalyst deactivation due to the sintering under moderate/high temperature operation and coke formation in hydrocarbon participating systems poses a challenge for their usage. Our work focuses on solving the above issues by designing and developing a series of metal core silica shell materials. The fundamental understanding of core shell materials is facilitated by systematic investigation via synthesis, characterization (XRD, TEM, BET, EDX) and catalytic tests (CO oxidation, ethylene hydrogenation, CO methanation and catalytic partial oxidation of methane). The synthesis and post-treatment methods for this newly developed core shell material are optimized and standardized. We demonstrate fine control over the key structural elements of nickel core silica shell material. Two different nickel core silica shell structures are obtained with the distinction of a pronounced cavity in the core. The synthesis route is not limited to nickel particles, but also applied for a range of other metals (e.g. Cu, Co, Pd). The pore size of silica shell is around ~1nm independent of the shell thickness and structure difference. The thermal stability of nickel particles as a function of particle size as well as silica support is thoroughly studied. The nickel particles in core shell materials are stabilized under 5nm up to 1000C with the comparison of strong sintering of unprotected nickel particles beyond 10nm as low as 500C. The stable core shell material not only shows its advantage for stable operation under high temperature reactive condition (>800C), but also possesses the highly coking resistant property in fuel participating reactions. Even though the presence of silica shell is beneficial for improving stability of nickel particles, it brings up significant mass transfer limitation when shell thickness is beyond 10nm. We not only demonstrate the capability to synthesize the well controlled nanocatalysts with high temperature stability and minimal mass transfer limitation, but also understand the structure correlated reactivity in several reaction systems. Additionally, we highlight the correlation between sintering, mass transfer and coking properties of the catalysts