Hydrogenolysis of methylcyclopentane over the bimetallic Ir-Au/γ-Al_2O_3 catalysts

摘要

The gas-phase hydrogenolysis of methylcyclopentane (MCP) was investigated over the bimetallic Ir-Au/γ-Al_2O_3 catalysts. The bimetallic systems containing the atomic Au/Ir ratios in the range of 0.125-8 and a fixed total metal content of 8 wt.%, were prepared by the sequential impregnation (SI) and co-impregnation (CI) methods. The corresponding monometallic Ir/γ-Al_2O_3 and Au/γ-Al_2O_3 catalysts were also prepared. The materials were characterized by ICP, XRD, N_2 adsorption, TEM, and H_2 chemisorption. Highly dispersed Ir nanoparticles were obtained in all cases, while the size of Au nanoparticles increased (up to 50 nm) upon the increasing Au content in the catalyst. The monometallic gold catalyst did not adsorb H_2. The incorporation of Au increased the amount of irreversible adsorbed H_2 in the Ir-Au/γ-Al_2O_3 catalysts with respect to the monometallic ones. The products obtained in the MCP hydrogenolysis were 2-methylpentane (2-MP), 3-methylpentane (3-MP) and n-hexane (n-H). The initial rate (molecules of MCP reacted s~(-1) g_(Ir)~(-1)) increased with the Au content. The deactivation was lower for bimetallic catalysts, particularly for the CI ones. The addition of Au played a significant effect on chemisorption and catalytic properties of Ir.