Etude in situ par EXAFS de la réductibilité d'un catalyseur Fischer-Tropsch à base de cobalt supporté sur silice

Abstract

La réduction sous flux d'hydrogène d'un catalyseur, 25% Co/Si02, pour la synthèse d'hydrocarbures a été suivie par spectroscopie d'absorption des rayons X (EXAFS) in situ. Les analyses numériques EXAFS ont permis d'identifier la phase spinelle CqOq du catalyseur avant traitement. La réduction de Co304 en deux étapes, Co0 puis Co0, observée en EXAFS, confirme ainsi les études menées en XPS (surface) et en TPR (bulk).Le nombre de coordination du cobalt a été déterminé à chaque étape de réduction.

Surface and Structural Features of Co‐Fe Oxide Nanoparticles Deposited on a Silica Substrate

“…Figure 6A depicts the Co 2p 3/2 peaks of Co10‐c after reduction. The calcined Co10‐c sample shows two components: one associated with Co 3+ in an octahedral position and the other assigned to Co 2+ in the tetrahedral position of the Co 3 O 4 spinel 77,78. Upon reduction with H 2 , three components are observed: octahedral Co 3+ ions present in an unreduced Co 3 O 4 phase,57,77 octahedral Co 2+ ions in CoO79–81 and Co 0 81–83.…”

The application of synchrotron methods in characterizing iron and cobalt Fischer–Tropsch synthesis catalysts

“…The authors only detected Co 0 in the working catalyst; no evidence for either oxides or carbides of Co was observed. The group also studied the reduction of a 25%Co/SiO 2 catalyst and identified the Co 3 O 4 to CoO and CoO to Co 0 steps [40]. Arcon et al [41] were able to successfully fit EXAFS data with up to four coordination shells using an FCC model for three Co/SiO 2 catalysts (i.e., prepared by reaction of silica with CoF 3 in diglyme and precipitation of cobalt nitrate with ammonia, followed by H 2 activation at 650 • C for 2 h).…”

“…The first section demonstrates how these uncertainties were overcome by coupling XANES and EXAFS spectroscopies to temperature programmed reduction/carburization [32][33][34][35][36][37][38][39][40]. The influence of catalyst preparation [39][40][41][42][43][44] and pretreatment [37,44,45] on activation is also addressed to some extent in this section. The working state of unpromoted catalysts has also been investigated by EXAFS [e.g., 56].…”

Characterization and Catalytic Behavior of Co/SiO2 Catalysts: Influence of Dispersion in the Fischer–Tropsch Reaction

“…However, EXAFS is not a direct method for particle size determination, the average size being obtained from the average number of neighbors, with an assumption on the particle shape. Corrections for partial disorder at the surface of clusters have been used (12,13) to reconcile the size estimates with results of other methods.…”