Promotive effect of boron oxide on the iron-based catalysts for Fischer-Tropsch synthesis

[Display omitted] •The dispersion of iron species is greatly enhanced by B2O3.•The interaction between iron and boron render the electron deficiency of iron species.•The promotion of B2O3 result in higher tendency to H2 rather than CO for doped catalysts.•B2O3 greatly inhibit the coke deposition of catalysts and promotes the hydrogenation activity of catalyst. Experimental improvement on the suppression of coke deposition remains a substantial challenge in iron-catalyzed Fischer-Tropsch Synthesis. Here, we performed a thorough study to provide in-depth understanding of the coking resistant as well as intrinsic promotive effect of boron oxide on the iron-based catalysts, by excluding the possible interference from another components. It turns out that the dispersion of catalysts is improved by boron oxide doping, which simultaneously inhibit the reduction of iron species in the catalysts. Strikingly, both the coking resistant behavior and hydrogenation activity of single active site of catalysts is greatly enhanced with addition of boron oxide. Such dual pronounced influence has been tentatively reasoned as the electronic interaction between Fe and B that render the electron deficiency of iron species, which thereby result in weaker adsorption capability of CO while inversely promote the chemisorption of H2 for B2O3-doped catalysts. As a consequence, the ratio of H/C on the surface of B2O3-doped catalysts is greatly enhanced with respect to undoped one, thus facilitate the formation of hydrocarbons via hydrogenation of surface carbon species rather than the competitive coke deposition.