Effect of Support Particle Size in Steam Reforming of Ethanol over Co/CeO₂ Catalysts

Co catalysts supported on ceria supports with two different particle sizes, one in the micro- and the other in the nano-range, were investigated for their ethanol and ethylene steam reforming performance. Pre- and post-reaction characterization techniques, including high-resolution transmission electron microscopy, temperature-programmed oxidation, dispersion, pore size measurements, in situ X-ray diffraction (XRD) and X-ray absorption fine structure spectroscopy (XAFS) studies were performed to examine the reducibility of the catalysts. Steady-state-activity testing has shown nanoparticles to have a higher reforming activity for ethanol, but also high ethylene yields. In spite of the high ethylene yields, catalysts supported on nanoparticles proved to be highly resistant to coking while the catalysts supported on larger ceria particles suffered from coke formation. Reforming experiments performed with ethylene showed significant differences in activity and stability. Bare supports were also tested for activity and the nanoparticle support was seen to have high dehydration activity. <i>Operando</i> DRIFTS experiments performed during ESR showed differences in surface species. Pulse experiments performed to use methanol oxidation as a probe reaction suggested differences in the relative abundance of redox sites and basic sites. The bare ceria supports also exhibited significant activity for ethanol dehydration, but not for C–C cleavage. The superior performance of the catalysts supported on nanoparticles is thought to be due to a combination of factors, including increased reducibility, improved metal dispersion, and a difference in relative abundance of redox sites on the surface. All of these properties and, in turn, the catalytic performance, appear to be affected by the particle size of the support

Chemoselective Hydrogenation with Supported Organoplatinum(IV) Catalyst on Zn(II)-Modified Silica

Well-defined organoplatinum­(IV) sites were grafted on a Zn­(II)-modified SiO₂ support via surface organometallic chemistry in toluene at room temperature. Solid-state spectroscopies including XAS, DRIFTS, DRUV–vis, and solid-state (SS) NMR enhanced by dynamic nuclear polarization (DNP), as well as TPR-H₂ and TEM techniques revealed highly dispersed (methylcyclopentadienyl)­methylplatinum­(IV) sites on the surface ((MeCp)­PtMe/Zn/SiO₂, <b>1</b>). In addition, computational modeling suggests that the surface reaction of (MeCp)­PtMe₃ with Zn­(II)-modified SiO₂ support is thermodynamically favorable (Δ<i>G</i> = −12.4 kcal/mol), likely due to the increased acidity of the hydroxyl group, as indicated by NH₃-TPD and DNP-enhanced ¹⁷O­{¹H} SSNMR. <i>In situ</i> DRIFTS and XAS hydrogenation experiments reveal the probable formation of a surface Pt­(IV)-H upon hydrogenolysis of Pt-Me groups. The heterogenized organoplatinum­(IV)-hydride sites catalyze the selective partial hydrogenation of 1,3-butadiene to butenes (up to 95%) and the reduction of nitrobenzene derivatives to anilines (up to 99%) with excellent tolerance of reduction-sensitive functional groups (olefin, carbonyl, nitrile, halogens) under mild reaction conditions