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Rh and Rh-Ge catalysts; Tailor-made catalysts; MCP ring-opening
Methylcyclopentane ring opening
Abstract:
The reaction mechanism of methylcyclopentane (MCP) ring-opening on Rh catalysts (the participation of each intermediate in further hydrogenolysis versus their desorption) was studied on a special series of Rh(Ge)/Al2O3 catalysts. These were obtained by wet impregnation and adding different amounts of Ge by anchoring of Ge(n-C4H9)4 on the surface of Rh with preadsorbed hydrogen. As shown earlier [Appl. Catal. A: Gen. 245 (2003) 15], low amounts of Ge were deposited selectively on low-Miller-index microfacets, whereas excess use of Ge(n-C4H9)4 caused statistical deposition on Rh. This difference induced also alterations in the classical ring-opening pattern: the sample with randomly located Ge behaved like the Parent
catalyst with dispersion of 80%. Each ring-opening intermediate hydrogenolyzed further nearly to the same extent; the ring-opening product distribution (ROPD) showing thus no variation as a function of reaction conditions. The catalyst with selective Ge deposition followed, however, the pattern of a sintered sample: the surface intermediate of 2-methylpentane underwent preferential hydrogenolysis to smaller fragments. Thus, changing the position of Ge deposits (without modifying
the particle size) induced changes in the prevailing reaction route.
