Characterization of steam-reforming catalysts

Abstract

-The effect of the addition of Mg and Ca to Ni/ -Al 2 O 3 catalysts was studied, aiming to address their role as promoters in the steam reforming reaction. Temperature-programmed reduction and H 2 and CO temperature-programmed desorption experiments indicated that Mg interacts with the metallic phase. Mg-promoted catalysts showed a greater difficulty for Ni precursor reduction besides different probe molecule (H 2 and CO) adsorbed states. In the conversion of cyclohexane, Mg inhibited the formation of hydrogenolysis products. Nonetheless, the presence of Ca did not influence the metallic phase.

Influence of the addition of promoters to steam reforming catalysts

“…Bands in this range for Ni catalyst are usually ascribed to charge transfer of octahedral Ni 2+ species [10]. From previous temperature-programmed reduction studies [11,12], we may explain the occurrence of these two bands: the first by the formation of NiO with Al 3+ ions incorporated due to the dissolution of a-Al 2 O 3 during the impregnation step, and the second to NiO with less interaction with the support, for catalysts with and without promoters.…”

Synthesis of alumina supported nickel nanoparticle catalysts and evaluation of nickel metal dispersions by temperature programmed desorption

“…The existence of a single reduction peak without any additional peak at temperature above 500°C in all these catalysts implies that the catalysts are composed of mainly NiO species dispersed on the Al 2 O 3 support and does not contain any NiAl 2 O spinel or a phase wherein NiO has very strong interaction with the Al 2 O 3 support [22,26]. It should be noted that the formation of NiAl 2 O 4 spinel or strongly interacting NiO-Al 2 O 3 phase is generally observed in most of the Ni/Al 2 O 3 catalysts with higher nickel loadings [14,26].…”

“…The profiles, in general, show two domains of H 2 desorption peaks, one below 450°C referred to as type-1 peaks and the other above 450°C denoted as type-2 peaks. The low temperature type-1 peaks are generally attributed to H 2 desorbed from the metal particles and indicates the exposed fraction of Ni atoms [4,12,13,20,22]. The high temperature type-2 peaks are attributed to the H 2 located in the subsurface layers and/or to spillover H 2 .…”

“…This is because, during prereduction of the catalyst, part of H 2 molecules dissociated on the Ni surfaces are migrated to subsurface layers and/or to the support, a phenomenon known as spillover effect [4,22]. These H 2 species are also desorbed at higher temperature during TPD.…”

Hydrogen Production from Carbonaceous Solid Wastes by Steam Reforming

“…Nonetheless, the presence of Ca did not influence the metallic phase. The impregnated Ni/MgO-catalyst performed better than the other types (Santos et al, 2004).…”