Catalysis with Nanoparticles and Magnetic Fields

Abstract

Catalysis with Nanoparticles and Magnetic Fields
Bruno Chaudret
Laboratoire de Physique et Chimie des Nano-Objets
Institut National des Sciences Appliquées, Université de Toulouse,
135 avenue de Rangueil 31077 Toulouse (France) - chaudret@insa-toulouse.fr

Magnetic nanoparticles display both interesting core physical properties and interesting surface chemical properties. The composition of the particles allows to modulate their magnetic properties in terms of saturation magnetization, magnetic anisotropy and Curie temperature and hence heating power. Thus magnetic nanoparticles heat when submitted to an alternating magnetic field. Magnetic heating is instantaneous and in principle the best way to transform electrical energy into heat. Iron seemed interesting both for its magnetic and catalytic properties. For the preparation of high quality, unoxidized Fe NPs we have searched for many different precursors but with limited success. The iron bis(amide) {Fe[N(TMS)2]2}2 opened the door to a new chemistry of iron NPs including iron (0), iron carbides and iron alloys.
We have developed in Toulouse a new generation of iron based nanoparticles (NPs) of unprecedented heating power. We have prepared iron carbide particles by carbidization of preformed monodisperse Fe(0) nanoparticles under a CO/H2 atmosphere at 150°C. They consist essentially of crystalline Fe2.2C, display a SAR (heating power) of up to 3.3 kW/g and are able to hydrogenate CO2 into methane in a flow reactor after addition of a catalytic Ru or Ni layer and excitation by an alternating magnetic field. Iron Cobalt NPs have been prepared from {Fe[N(TMS)2]2}2 and the relative {Co[N(TMS)2]2}2, also first synthesized by Prof Andersen. These soft magnetic bimetallic FeCo NPs with a high Curie Temperature allow performing high temperature catalytic reactions such as propane dehydrogenation or methane and propane dry reforming. Iron nickel nanoparticles have been synthesized from iron amide and nickel amidinate precursors and found very active for CO2 hydrogenation. In addition, submitting nanoparticles of iron carbide or iron nickel to magnetic heating in solution leads to local over-heating and to perform under a low H2 pressure difficult reactions such as hydrodeoxygenation of biomass derived platform molecules.
The lecture will briefly present the synthesis of the particles, their magnetic properties, their surface modification to deposit a catalytic layer and their catalytic properties for CO2 hydrogenation in a flow reactor and high temperature catalysis. Further developments of the technique in solution or for electrochemical reactions will also be described.