“…In addition to finding that multiple-exchange was more likely at high temperatures (consistent with Kemball’s work above), the authors also found that lower D 2 pressures and larger crystallites promoted multiple exchange; this was ascribed to having more open sites to activate additional C–H bonds . Allylic and pi-bonded intermediates have been proposed as intermediates, similar to studies above with the chiral alkanes, and the mechanism by which multiple exchange occurs has been studied in depth. − More detailed studies on the exchange between cyclopentane and D 2 on Pd/alumina exhibited five product distributions, which the authors suggested indicate five distinguishable processes. , They assigned this distribution to different sets of surface sites; these results show that multideuteration, and thus the propensity to have a second C–H activation occur, is dependent not only on temperature, metal, and crystallite size but also on the facet and crystal termination (e.g., terrace, face, edge, step, corner) at which exchange occurs. This is not surprising because many catalysis studies show dependency of crystallite size and facet …”