The active sites that carry out catalytic transformations within enzymes and over homogeneous and heterogeneous catalysts are controlled by the reaction conditions. The conditions set the chemical potentials for bound intermediates as well as the rates of formation and removal of such intermediates which dictate the local reaction environment at the active site.  Changes in the reaction conditions can therefore significantly alter the catalytic sites that carry out particular transformations as well as the mechanisms which ultimately control catalytic kinetics.  Many heterogeneous catalyzed systems are carried out at high pressures where their surfaces are covered by key reaction intermediates that can block surface sites or assist in the activation of strong bonds.  The adlayer can behave much like the ligand-sphere of a homogeneous catalyst or the 3D environment of an enzyme and control catalytic kinetics.  As a result, the catalytic behavior over supported metal particles at working conditions can be very different than that carried out over idealized surfaces at low pressures or ultrahigh vacuum conditions.<br/><br/>The tremendous advances that have occurred in theory and computation over the past decade have allowed simulation to become integral partner with experiments in providing insights into the molecular transformations and mechanisms that control catalysis under working conditions. In this talk, we examine three different catalytic systems and explore the nature of the active site and the influence of the local surface coverage and reaction environment on the catalytic activity and selectivity. We show that the adsorbates present within the adlayer can assist in activating strong adsorbate bonds and controlling catalysis. More specifically we examine the catalytic conversion of methane, Fischer Tropsch synthesis and the hydrogenolysis of polyols over supported metal particles to establish the unique influence of the reaction environment on the mechanisms and kinetics on catalytic performance.  <br/>

Engineering active sites and their environments under working catalytic conditions

251st National Meeting (2016)

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