Gérôme Melaet

High-performance hybrid oxide catalyst of manganese and cobalt for low-pressure methanol synthesis

Carbon dioxide capture and use as a carbon feedstock presents both environmental and industrial benefits. Here we report the discovery of a hybrid oxide catalyst comprising manganese oxide nanoparticles supported on mesoporous spinel cobalt oxide, which catalyses the conversion of carbon dioxide to methanol at high yields. In addition, carbon-carbon bond formation is observed through the production of ethylene. We document the existence of an active interface between cobalt oxide surface layers and manganese oxide nanoparticles by using X-ray absorption spectroscopy and electron energy-loss spectroscopy in the scanning transmission electron microscopy mode. Through control experiments, we find that the catalysts chemical nature and architecture are the key factors in enabling the enhanced methanol synthesis and ethylene production. To demonstrate the industrial applicability, the catalyst is also run under high conversion regimes, showing its potential as a substitute for current methanol synthesis technologies.

Structure and chemical state of the Pt(557) surface during hydrogen oxidation reaction studied by in situ scanning tunneling microscopy and X-ray photoelectron spectroscopy.

The surface structure of Pt(557) during the catalytic oxidation of hydrogen was studied with in situ scanning tunneling microscopy and X-ray photoelectron spectroscopy. At 298 K, the surface Pt oxide formed after exposing Pt(557) to approximately 1 Torr of O2 can be readily removed by H2, at H2 partial pressures below 50 mTorr. Water is detected as the product in the gas phase, which also coadsorbs with hydroxyl groups on the Pt(557) surface.

Platinum and Other Transition Metal Nanoclusters (Pd, Rh) Stabilized by PAMAM Dendrimer as Excellent Heterogeneous Catalysts: Application to the Methylcyclopentane (MCP) Hydrogenative Isomerization

Pt, Rh, and Pd nanoclusters stabilized by PAMAM dendrimer are used for the first time in a gas flow reactor at high temperature (150-250 °C). Pt nanoclusters show a very high activity for the hydrogenation of the methylcyclopentane (MCP) at 200-225 °C with turnover freqency (TOF) up to 334 h-1 and selectivity up to 99.6% for the ring opening isomerization at very high conversion (94%). Rh nanoclusters show different selectivity for the reaction, that is, ring opening isomerization at 175 °C and cracking at higher temperature whereas Pd nanoclusters perform ring enlargement plus dehydrogenation, while maintaining a high activity. The difference in these results as compared to unsupported/uncapped nanoparticles, demonstrates the crucial role of dendrimer. The tunability of the selectivity of the reaction as well as the very high activity of the metal nanoclusters stabilized by dendrimer under heterogeneous conditions open a new application for dendrimer catalysts.

Isomerization of n-Hexane Catalyzed by Supported Monodisperse PtRh Bimetallic Nanoparticles

Composition and size of PtxRh1−x bimetallic nanoparticles were varied in order to study the effects in the catalytic reforming of n-hexane. Hexane isomerization, an analogue to the important industrial process of hydrocarbon reforming is a reaction in which we aim to investigate the molecular level details of catalysis. It is known, that in hydrocarbon isomerization, Pt atoms act to isomerize the reactants, while small amounts of “promoter metal” atoms (such as Rh, Ir, Re and Sn) provide C–C and C–H bond breaking activity. Herein, we report on the effect of composition and size in model bimetallic PtxRh1−x nanoparticle catalysts utilized in n-hexane reforming. Both nanoparticle composition and size were shown to influence catalytic turnover frequency and product selectivity. It was found, through ambient pressure X-ray photoelectron spectroscopy, that the surface of these nanoparticles is both dynamic, and Rh rich under relevant reaction conditions. The findings suggest that an ensemble effect exists, in which the highest isomer production occurs when Rh atoms are surrounded by Pt atoms on the metal surface.Graphical Abstract