Controlling surface crowding on a Pd catalyst with thiolate self-assembled monolayers

摘要: Abstract The relationship between surface crowding and catalytic activity was investigated using thiolate self-assembled monolayers (SAMs) on Pd/Al2O3 catalysts. density of the modifier controlled by varying steric bulk organic substituent. A straight-chain alkanethiol 1-octadecanethiol (C18), with a nearest-neighbor spacing ∼4.7 A Pd(1 1 1) surfaces, created denser SAM coating than 1-adamantanethiol (AT) ∼6.4  A. Diffuse reflectance infrared spectroscopy revealed that CO adsorbate molecules adsorbed only threefold hollow atop sites C18-modified surfaces. On AT-modified however, access to bridging additional linear also observed. Analysis adsorption isotherms suggested energies were comparable Acetylene hydrogenation, which results in uncontrolled due carbonaceous “coke” formation catalyst, found be insensitive modification thiols. For hydrogenation reactions less associated coking, – therefore reactivity could systematically SAMs. In particular, ethylene 17 times faster AT-coated surfaces C18-coated consistent accessibility specific unavailable effect dramatically different for several mono- bi-functional reactants manner previous literature reports, suggesting SAMs can used understand reaction structure sensitivity active site requirements catalysis.