Strong metal support interaction on Co/niobia model catalysts

Abstract

Abstract.Cobalt was deposited by physical vapor deposition onto thin well-ordered niobia films in order to model niobia supported Co catalysts. Adsorption of CO on the Co/niobia surfaces was studied by temperature programmed desorption and infrared reflection absorption spectroscopy. Structural characterization was performed by photoelectron spectroscopy and scanning tunneling microscopy. Cobalt was found to wet the niobia film and be partially oxidized at 300 K in contrast to Co deposited on thin alumina films, where three-dimensional metal particles are stable up to 600 K. The combined results clearly indicate a strong interaction of Co with the niobia surface including Co migration into the film, which may have implications for the effects of niobia observed in real catalysts.

Preparation and structure of alumina supported niobia model catalysts

“…2b). The strongly blue-shifted frequency of CO as compared to the gas phase (2191 vs 2143 cm -1 ) implies that CO is linearly adsorbed on top of Nb 5+ sites [20,34]. A similar feature at ~2190 cm -1 was also obtained on the thin niobia films (not shown here), i.e.…”

“…In order to understand structure-reactivity relationships for niobia based catalysts and elucidate the reaction mechanisms, we have recently begun model studies using well-ordered niobium oxide thin films grown on a metal substrate [19,20]. In continuation of these studies, here we report on the preparation and structure of niobia/alumina model catalysts.…”

On the superior activity and selectivity of PtCo/Nb2O5 Fischer Tropsch catalysts

“…The promoting effect of niobia as support material at low pressure was extensively studied by XPS, TPR, TPO, CO TPD and IR spectroscopy and was attributed to partial reduction of the support and consequent strong metal support interaction (SMSI) [25][26][27][28][29]. The presence of Co 0 -NbO x species was confirmed by Mendes et al in Co/ Nb 2 O 5 catalysts [27] and model catalysts [28].…”

“…For Nb 2 O 5 -supported cobalt catalysts, high selectivities toward heavy hydrocarbons were reported at 1 bar by Schmal and coworkers [20][21][22][23][24] and more recently at 20 bar by den Otter et al [6]. The promoting effect of niobia as support material at low pressure was extensively studied by XPS, TPR, TPO, CO TPD and IR spectroscopy and was attributed to partial reduction of the support and consequent strong metal support interaction (SMSI) [25][26][27][28][29]. The presence of Co 0 -NbO x species was confirmed by Mendes et al in Co/ Nb 2 O 5 catalysts [27] and model catalysts [28].…”

The Support Effect on Hydrogenolysis of Thiophene and Gas–Oil

“…The sample NiMo/Nb-T in which the Nb was incorporated through a sol-gel method leading to an Nb-T mixed oxide, and where Nb was present as anisolated species forming Ti-O-Nb-O-Ti bonds, exhibited an activity smaller than the NiMoNb/T sample in which the Nb was deposited on the surface of titania, leading to the formation of more polymerized Mo oxide species, which related to the concentration of anionic sulfur vacancies in the active MoS 2 phase. These anion vacancies or coordinative unsaturated sites (CUS) sites are responsible for HDS catalytic activities (Mendes et al, 2006). For comparison, the results from NiMoNb/T and NiMoNb/A have also been included.…”