Controlled modification of bifunctional metal/mordenite catalysts: Selectivity, metal anchoring, and accessibility

Methylcyclopentane (MCP) conversion has been used to elucidate the relative contributions of metal and acid sites in bifunctional Metal/Mordenites prepared by ion-exchange.; Metal and protonic sites were found to have an intimate relationship which governs catalyst activity and selectivity. Protons function as chemical anchors and form metal-proton adducts. Carbenium ions which form during reaction effectively compete for acid sites and result in de-anchoring of primary particles as shown by TEM. Monatomic Pt dispersion may be obtained due to favorable proton anchoring; these species are located in side-pocket positions of the zeolite. Side-pocket Pt gave rise to special stereoselectivity for MCP ring opening yielding 2-methylpentane in excess of the statistical and thermodynamic ratio. It is postulated that previously proposed metal-proton adducts gave rise to the observed non-equilibrium quantities of benzene produced during the ring enlargement of MCP; a mechanism has been presented.; Catalyst re-hydration during programmed pretreatment increases catalyst performance. Addition of water vapor at room temperature after calcination and prior to reduction gives the best results. Water interacts most strongly with metal ions. Metal dispersion decreases after water treatment. Acid sites are only marginally increased.; TPO analysis of coke displays the importance of diffusion behavior in one-dimensional zeolites. The activation and deactivation behavior are consistent with the concept that the catalysis is governed by the single file diffusion. The observable catalysis occurs near the pore mouth in the "active zone". Water treatment improves activity despite a loss of surface area because it provides a means for mobilizing more Pt towards the surface region and into the active zone. This situation can be approximated by catalyst preparation using incipient wetness impregnation.