Using Pt in the form of sub-nanometer dispersed clusters is a way to save precious metal in catalysis, but making such clusters stable against sintering is an uphill battle. Sn is a known agent used to increase the selectivity of dehydrogenation of alkanes on Pt. Through a joint experimental and theoretical approach, we show that adding Sn to the size-selected Pt clusters deposited on amorphous SiO 2 also dramatically enhances the thermal stability of the clusters against sintering.CO temperature programmed desorption (TPD) and He + ion scattering indicate that no Pt sites are lost, and XPS shows no change in the electronic structure of Pt, upon repeated system heating and cooling. DFT results indicate that the binding energy of Pt clusters to the support increases by >1 eV upon adding Sn, and Sn forms strong polar covalent bonds with Pt within the clusters and quenches all the unpaired spins. As a result, the energy needed to remove a Pt atom from Pt 4 Sn 3 /SiO 2 and put it on the support is 0.15 eV larger than that from Pt 4 /SiO 2 , and in fact it is significantly easier to dissociate a Sn atom. Both factors would tend to stabilize the Pt core of the clusters against sintering, as is observed experimentally. CO adsorbates further facilitate Ostwald ripening of the pure Pt clusters, and even in that case nano-alloying with Sn suppresses sintering.
The Sabatier activity volcano provides intuitive guide for catalyst design, but also imposes fundamental limitations on the composition and maximal activity of catalysts. We show that the ORR activity volcano is shifted and reshaped by the potential-dependent fluxionality of subnano cluster catalysts. Fluxionality causes the typically under-binding Ag/Au to gain optimal activity in the cluster form, and surpass Pt/Pd. Furthermore, isomerization of clusters as a function of the potential breaks linear scaling relationships, enabling surpassing the volcano "apex" relative to the bulk. The effect is likely general for fluxional cluster catalysts.
The synthesis of graphene nanoribbons (GNRs) that contain site-specifically substituted backbone heteroatoms is one of the essential goals that must be achieved in order to control the electronic properties of these next generation organic materials. We have exploited our recently reported solid-state topochemical polymerization/cyclization-aromatization strategy to convert the simple 1,4-bis(3pyridyl)butadiynes 3a,b into the fjord-edge nitrogen-doped graphene nanoribbon structures 1a,b (fjord-edge N2[8]GNRs). Structural assignments are confirmed by CP/MAS 13 C NMR, Raman, and XPS spectroscopy. The fjord-edge N2[8]GNRs 1a,b are promising precursors for the novel backbone nitrogen-substituted N2[8]AGNRs 2a,b. Geometry and band calculations on N2[8]AGNR 2c indicate that this class of nanoribbons should have unusual bonding topologies and metallicities.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.