No abstract

In an effort to better understand the excellent synergism of certain physical mixtures of supported catalysts for the 1-butene double bond shift described previously, the butadiene hydroisomerization selectivity/activity of the same mixtures was studied. Limited activity/selectivity synergism for the hydroisomerization of butadiene was measured for physical mixtures of FeCe/Grafoil (alloy) and Pt/Grafoil or Pd/Grafoil (noble metal). A high degree of synergism was noted for mixtures in which the ratio of alloy to noble metal was less than about 20:1. Additions of alloy to mixtures which increased the ratio to values higher than 20 did not change the activity or selectivity. For Pd/Grafoil containing mixtures both activity and selectivity synergism could be explained completely on the basis of a hydrogen spillover model. For example, the limit in activity synergism was ascribed to the depletion of hydrogen atoms away from palladium centers (radial gradient around each noble metal particle) due to the use of these atoms in hydrogenation of butadiene on FeCe particles. In contrast, to explain the nonequilibrium ratio of 2-butenes in platinum-containing mixtures, it is necessary to hypothesize two processes:  both hydrogen spillover and bifunctional catalysis.

No abstract

With excellent control of their synthetic compositions and condition, noble metal nanoparticles@mesoporous silicas of large surface area (≈ 300 m 2 g -1 ), large pore size (> 5.0 nm), and high noble metal nanoparticle content (≈ 10 wt.%) have been conveniently prepared using natural polymer gelatin with many amide (-CO-NH 2 ) groups as an organic template of mesoporous silica and a protecting agent for stabilizing Au nanoparticles. This synthetic method is extensive and can be used to prepare Au, Ag, and Ag-Au alloy nanoparticles@mesoporous silicas. Because the metal nanoparticles are accessible to the environment, noble-metal nanoparticles@mesoporous silicas can be used in SERS applications and act as superior catalysts in CO oxidation at high temperatures. In addition, bare Au nanoparticles anchored on a silica matrix can have direct contact with S. aureus cells to enhance the Raman spectrum intensity of S. aureus cells absorbed onto a Au nanoparticles@mesoporous silica.