Synergistic Promotion of Co/SiO₂ Fischer–Tropsch Catalysts by Niobia and Platinum

Abstract

Transition-metal oxides and noble metals are wellknown selectivity and activity promoters in cobalt-based Fischer− Tropsch catalysis. Niobia has been shown as an effective selectivity promoter as support material; however, its low porosity limits the cobalt loading. To combine the selectivity-promoting properties of niobia with a highly porous support, niobia-modified silica was prepared and applied as a support for Co and PtCo catalysts with cobalt loadings up to 21 wt %. Niobia promotion was found to increase the C 5+ selectivity at 1 bar; however, it appeared to be ineffective at 20 bar. Promotion of Co/SiO 2 by a combination of platinum and niobia yielded an increase of the cobalt-weight normalized activity by a factor of 2−3 in the case of amorphous niobia and by a factor of 3−4 with niobia nanocrystals present, due to both an increased number of active sites and an increased cobalt-surface specific activity (turnover frequency).

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

“…3, right). Pressure-dependent influence of niobia on the catalyst selectivity was previously observed for niobia-promoted catalysts [8] in line with reports on MnOpromoted catalysts [13,17]. At 1 bar, the cobalt weight-normalized activity of Co/c-Al 2 O 3 and Co/Nb 2 O 5 was found to increase by a factor of 1.7 and 2.8 upon Pt-promotion (Fig.…”

“…The selectivity of cobalt catalysts toward liquid hydrocarbons (C 5+ ) is affected by process conditions such as temperature [6,7], pressure [8] and CO conversion [9] and catalyst properties such as support acidity [10,11] and pore diameter [5,10] and can be promoted by partially reducible transition metal oxides such as MnO and ZrO 2 [12][13][14][15][16][17]. These promoters can be present as small particles in the close proximity to cobalt or as support material in the case of Co/TiO 2 [16,18,19] or Co/Nb 2 O 5 [6,[20][21][22][23][24] catalysts.…”

“…During Fischer-Tropsch catalysis, Pt is not expected to be active as catalyst due to the low CO dissociation activity; however, it might assist by facilitating H 2 dissociation or act as adsorption site for CO [34]. Upon noble metal promotion of Co/TiO 2 and Co/Nb 2 O 5 catalysts [2,[35][36][37] and recently also niobia-promoted Co/SiO 2 catalysts [8], an increase in the cobalt-weight normalized activity was observed which could not be explained only by an increased number of active sites.…”

Effect of CO Concentration on the α-Value of Plasma-Synthesized Co/C Catalyst in Fischer-Tropsch Synthesis

“…For example, precious metals like Au [23], and Pt [24], or in some cases, Ru have been employed to create multi-component catalysts such as (Ru + Co + Mn/Zr/SiO 2 ) to enhance Co reducibility [25]. This alters catalyst activity and selectivity or the catalyst's preference for a specific reaction mechanism [26], although some elements acting as promoters have been observed to aggravate metal particle sintering of the metal nanoparticles [27].…”

Carbon Nanotube-Supported Copper-Cobalt Catalyst for the Production of Higher Carbon Number Alcohols through Carbon Monoxide Hydrogenation

“…Strongly interacting supports such as γ-Al 2 O 3 usually lead to high cobalt oxide dispersions, however, there is difficulty to reduce cobalt species. 18 To obtain appropriate Cu and Co nanoparticle properties and distribution in the catalyst, carbon nanotubes (CNTs) are employed as supports. A wealth of interdependent research [19][20][21] has demonstrated the advantages of using CNTs as supports to improve transition metal particle dispersion in catalysts and the confinement effects during catalysis have been systematically studied.…”