Particle growth and redispersion of monodisperse rhodium nanoparticles supported by porous carbon microspherules during catalyzing vapor phase methanol carbonylation

Monodisperse Rh nanoparticles mounted in the porous carbon microspherules were synthesized through the controlled carbonization of poly(vinylidene chloride) beads containing di-μ-chlorotetracarbonyldirhodium as Rh precursors. Rh nanoparticles were formed spontaneously and simultaneously with the evolution of carbon structures from the composite polymeric precursors. X-ray photoelectron spectroscopy (XPS) was used to detect the transformation of high valent Rh species to zero-valent Rh atoms. The dispersion state and particle size were characterized by EPMA and TEM in detail. The as-synthesized Rh nanoparticles were in the monodisperse state with the particle size of about 10 nm. Under catalytic vapor phase methanol carbonylation conditions, particle growth and redispersion take place through a mechanism involving the formation and transportation of Rh-containing volatile molecules. This is evidenced by the comparison of the dispersion state and particle size of the supported Rh nanoparticles before and after catalyzing vapor phase methanol carbonylation. It is clearly demonstrated that the Rh nanoparticles move to the support's surface and grow to about 30 nm after 50-h reaction on stream.