Selective Ring-Opening of Methylcyclopentane Over Titania-Supported Monometallic (Pt, Ir) and Bimetallic (Pt-Ir) Catalysts

An investigation of the selective ring-opening of methylcyclopentane (MCP) was conducted for the first time on Pt/TiO2, Ir/TiO2 and Pt-Ir/TiO2 catalysts with low amounts of noble metals (0.5 wt%) over a temperature range of 180-400 A degrees C under hydrogen at atmospheric pressure. The catalysts were prepared by impregnation or co-impregnation and characterized by different physico-chemical techniques, including SEM, XRD, H-2-TPR, N-2-sorption, TEM and elemental analysis. The metallic particles were highly dispersed on the TiO2 support at isodispersion of similar to 1 nm. The particles exhibited icosahedral Mackay structures limited by (111) planes. The catalytic results show that the activity in the MCP was strongly influenced by the intrinsic nature of the metal and by the temperature. The most active catalyst was Ir/TiO2. The order of the reactivity as a function of the temperature and total conversion was Ir/TiO2 180 A degrees C (alpha A = 2 %) > Pt-Ir/TiO2 220 A degrees C (alpha A = 27.8 %) > Pt/TiO2 260 A degrees C (alpha A = 9.9 %). Under these conditions, all of the catalysts exhibited the ability to open the ring of MCP with an atom economy, without unwanted products of cracking and ring-enlargement reactions. The synergy between Pt-Ir bimetallic particles was assessed by the total conversion of MCP, whereas the ring-opening results indicated that the reaction took place on Ir sites. These results suggest that the bimetallic catalyst contained separate entities of two metals. Increased reaction temperatures led to reduced reaction selectivity with respect to ring-opening of MCP versus the cracking side reaction.