Heterogeneous, enzyme, and homogeneous catalysis share so many characteristics on the molecular level that we hope they become one field of science that permits deeper understanding of the molecular ingredients of structure and dynamics that makes them function to obtain high reaction selectivity. and understand their role in supporting cluster molecules and to explore the reactivity of metal clusters towards cluster It is our hope that these three fields of catalysis will merge to become one field in the foreseeable future. Image credit: Stephanie Gamez (University of California San Diego, La Jolla, CA). We synthesize platinum and rhodium nanoparticles in the 1–10 nm range in colloidal solutions in the presence of polymers (47, 48). Temperature-dependent rearrangement of adsorbed ethylene as monitored by SFG on Pt(111) surfaces. For the reaction to occur under high pressures where the surface is at nearly saturated coverage, statistical fluctuation of adsorbate density must be maintained to open up active sites crucial for the catalytic reaction. For both the (111) and (100) surfaces of platinum, the crystal must be heated to a temperature at which platinum carbonyls are formed to produce step and kink sites, which are needed for dissociation, which deposits carbon on the metal surfaces. However, major differences in catalytic behavior emerge when the platinum catalysts are poisoned by the addition of CO. CO poisoning of the platinum single crystal increases the activation energy to 20 kcal/mol from ≈10 kcal/mol and decreases the turnover rate at 300 K by 7 orders of magnitude to ≈10−6 s−1. This process occurs to optimize the adsorbate-metal bonding. (a) Diagram of submonolayer metal oxide islands formed on Rh foil. The size, surface structure, and shape of the metal cluster catalyst are known to influence reaction selectivity. The turnover rates remain in the range of 5 × 10−2 s−1, which are orders of magnitude greater than for the single crystal surface. This mobility is detectable on metal single crystals by STM. Fig. We call this green chemistry, and it requires catalysts that exhibit 100% selectivity toward needed products for multipath reactions where each reaction channel is thermodynamically feasible. Thus, dynamics of the catalyst structure and that of the reactant molecules and reaction intermediates control both the activity (rates) and the selectivity (product distribution) of the catalysts. However, if the oxide–platinum interface sites are considered to be the only active sites for reaction during CO poisoning (Fig. CO and CO2 hydrogenation to methane over a Rh foil decorated with submonolayer quantities of TiOx, VOx, ZrOx, NbOx, TaOx, and WOx were carried out (45). Enter multiple addresses on separate lines or separate them with commas. SFG studies indicate π-allyl (C6H9) species are present on the surface (32, 44). 5). They are characterized by transmission electron microscopy, small-angle x-ray scattering, and x-ray diffraction ( Fig. The mesoporous silica is actually synthesized around the nanoparticle. On the Pd(111) surface, ethylene dehydrogenates to ethylidyne at 300 K, which reacts to form methylidyne >400 K (29). Adsorbate-induced restructuring of the metal surface is, therefore, an important part of C–H activation, even on the (111) crystal face of platinum, which is the closest-packed and lowest surface free-energy plane of this face-centered cubic metal. This different site occupancy of ethylidyne on the Rh(111) surface changes the nature of adsorbate-induced restructuring of the metal surface around the chemisorption bond, as shown by LEED crystallography. By using the same assumption, the CO-poisoned turnover frequencies for the alumina and silica supported samples are 0.071 and 0.041 s−1, respectively. Future directions include synthesis, characterization, and reaction studies with 2D and 3D monodispersed metal nanoclusters to obtain 100% selectivity in multipath reactions. Some of these catalytic reactions are very fast. Its C–C bond is normal to the metal surface and the nearest- and next-nearest-neighbor metal atoms change their locations as compared with their positions on the metal surface before C–H bond dissociation occurs. The unpoisoned turnover frequencies for the Pt nanoparticle samples on alumina and silica are 7.3 and 5.3 s−1, respectively, assuming that all available platinum surface atoms are active for the reactions. Our model studies of heterogeneous catalysis that started with the use of metal single crystal surfaces are being continued using monodispersed metal nanoparticles. Just as for ethylene hydrogenation, introduction of CO stops the mobility and results in the formation of ordered surface structures and the total poisoning of catalytic activity. The surface density can be altered by changing the applied surface pressure as shown in Fig. Heterogeneous catalysis was practiced mostly by physical chemists and chemical engineers, enzyme catalysis by biochemists, and homogeneous catalysis by inorganic and organometallic chemists. The same rate of catalytic hydrogenation is found for the Pt(100) crystal face because this reaction is a structure-insensitive one (32). (Upper) Three single crystal surface diagrams representing the (111), (100), and stepped (557) surfaces of a face-centered cubic crystal lattice. Sci. NOTE: We only request your email address so that the person you are recommending the page to knows that you wanted them to see it, and that it is not junk mail. Clearly the oxide–metal interface is implicated in increasing the activity of rhodium of these hydrogenation reactions. After oxidation and reduction treatments to remove the polymer that coats the metal nanoparticles, catalytic reactions can be carried out where the variables are the size and shape of the cluster. They are characterized by transmission electron microscopy, small-angle x-ray scattering, and x-ray diffraction (Fig. In this overview, we focus on metal heterogeneous catalysts from the physical chemistry perspective. This mobility is essential for maintaining the catalyst activity. It also should be noted that the oxides alone are not active for these reactions.