Effect of the C/O ratio on the C60 and C70 formation rates in soot synthesised by laser pyrolysis of benzene-based mixtures

The effect of varying the C to O atomic ratio on the formation of fullerenes in sooting flames produced by the laser pyrolysis of benzene-based mixtures was investigated. Infrared spectra were recorded on soot toluene extracts and quantification of C60 and C70 was performed by High Performance Liquid Chromatography. A strong increase of the fullerenes yield (C60+C70) was observed with decreasing C/O ratio (2.2–1.2). The lowering of the C/O ratio was also found to influence dramatically the ratio of C60 to C70 through an increase of the C60 yield faster than the C70 one. These two effects can be fully interpreted by a kinetically based argument. A strong increase of the fullerenes content was also observed with decreasing residence time in the reaction flame, and a maximum total yield of 0.23% was reached with high conversion rates (from benzene to soot). Ponderable amounts of C84 were also quantified.