Dr Alexandre Goguet

Research

The vast majority of today's industrial processes comprise at least one catalytic step. Such catalytic steps allow savings in terms of time, energy and quality that are compulsory on an ecological and economical point of view. Our work is to identify the structure of active sites of the catalysts involved as well as the nature of the active reaction intermediates, and determine the kinetic parameters under realistic reaction conditions. The access to this information is crucial for the design and the improvement of the catalysts, in terms of activity and selectivity, and also for the development of industrial processes. To this aim, we develop and apply innovative steady state, transient kinetics and operando techniques.

 

The TAP reactor

The TAP system is a transient technique which uses gas pulses on the millisecond timescale in such a way as to exclude gas-phase reactions and thus reveal details of surface reaction mechanisms. Typically, an extremely narrow gas pulse is injected in the reactor while the exit of this reactor is continuously evacuated. As no carrier gas is employed, the pulse moves as a result of the pressure gradient across the reactor. Because of the low pulse intensity (1012-1018 molecules per pulses) the total pressure becomes negligible and the pulse moves through the reactor via Knudsen diffusion. This very low partial pressure ensures that no gas phase reaction can take place and only surface reactions are investigated. Finally, while travelling through the reactor, the gas pulse is submitted to adsorption/desorption/reaction processes which will be translated in the pulse shapes of the unreacted reactants and of the products detected at the outlet of the reactor by the mass spectrometer. The time resolution at the millisecond scale allows detecting fast phenomena, and therefore the detection of short-life reaction intermediates. This technique is very versatile and can be used in the investigation of numerous catalytic reactions. For instance, we have successfully implemented it to the investigation of reactions such as the oxidative dehydrogenation of light alcanes, isomerisation of butane, water gas shift, DeNOx,

 

 

We are presently adapting Time of Flight mass spectrometry to our TAP reactor.

2009 Taylor conference Prize Winner

 

The SSITKA-DRIFTS-MS

We have recently developed a technique that allows simultaneous monitoring of the surface species concentrations and the rates of product formation using DRIFTS + MS analyses under SSITKA (Steady State Isotopic Kinetic Analysis) condition. This technique couples DRIFT and mass spectrometry simultaneous analysis on a single experimental set-up. By combining the vibrational data with mass spectrometric determination of the isotopic products, this apparatus is capable of distinguishing between surface spectators and those involved in the reaction (minor and major species), quantify and characterise active sites in true operando conditions. This technique has recently been applied to the investigation of reverse and forward water gas shift reaction, CO selective oxidation, Selective oxidation and DeNOx reactions.

 

 

 

Operando EXAFS,

During the catalytic process, the population of adsorbed species present on the surface of the catalyst evolves with the reaction conditions and catalyst structure. In return, it is today widely recognised that exist numerous cases where the structure of the catalyst is modified by the nature of the reaction environment and the adsorbed species. Being able to follow the fine structure of the catalyst under steady state conditions bring essential information to build understanding of the structure-activity relationship. To this aim we develop and apply dedicated in situ XAFS reactors that allow monitoring the evolution of the catalyst structure under steady-state reaction conditions.

 

We also apply HP XPS in order to refine the structure-reactivity understanding of various catalytic processes. Our actual work is focused at the understanding of catalysts involved in the production of hydrogen for fuel-cells, in the reduction of emissions from motor vehicles and selective oxidation.