Design of a Hierarchical Meso/Macroporous Zeolite‐Supported Cobalt Catalyst for the Enhanced Direct Synthesis of Isoparaffins from Syngas

Abstract

A hierarchical meso/macroporous zeolite‐supported Co catalyst (Co/ASB) was designed and employed for the direct synthesis of isoparaffins. The hierarchical porous zeolite (ASB) was developed by a steam‐assisted crystallization method using alumina‐modified meso/macroporous silica as the precursor. Structural characterization indicated that the as‐synthesized ASB exhibited nanosized β‐zeolite crystallites and a hierarchical meso/macroporous structure. The activity of the Co/ASB catalyst was much higher than that of conventional Co catalysts supported on SiO2 (Co/SiO2) and H‐β‐zeolite (Co/B). A high isoparaffins selectivity of 30.5 % was obtained from Co/ASB because of the hydrocracking/isomerization of long‐chain hydrocarbons at the strong acidic sites of the β‐zeolite. Furthermore, as a result of the fast diffusion of syngas in the unique hierarchical pores, the methane selectivity of Co/ASB was lower than that of Co/B.

Insights into the promotional roles of palladium in structure and performance of cobalt-based zeolite capsule catalyst for direct synthesis of C5–C11 iso-paraffins from syngas

“…clear to see that a shell with thickness of 14.6 μm was formed, which was much thicker than that of Co/SiO 2 -HZSM5. During the synthesis of the zeolite shell, part of the silica in the core catalyst could be dissolved (or etched) in the strong basic solution under the hydrothermal condition [9,27]. In Pd-promoted catalyst, Pd might act as a catalyst for improving the etching of silica support, which meant that more silica was dissolved and the etching of the core catalyst was deeper [28].…”

“…The direct synthesis of C 5 -C 11 iso-paraffins (main components of gasoline) from syngas via modified Fischer-Tropsch synthesis (FTS) has received increasing interests due to the dwindling of oil resource and distinctive product advantages of sulphur-free, nitrogen-free, and aromatic-free properties [1][2][3][4][5][6][7] . As a result of higher C 5 -C 11 iso-paraffins selectivities and the complete elimination of the long-chain hydrocarbons (carbon number higher than 12) by the spatial confinement effect, the capsule catalysts with zeolite shells and FTS catalyst cores are more promising [4,[8][9][10][11]. Cobalt-based FTS catalysts, which have the advantages of higher activities per gram catalyst and lower selectivities to CO 2 and C 2 -C 4 gaseous hydrocarbons compared with the iron-based catalysts [12][13][14][15][16], are primarily selected as the cores of the capsule catalysts.…”

“…Meanwhile, the H-type zeolites with strong acidic sites, such as H-ZSM-5, H-Beta, and H-MOR are usually employed as the shells of the capsule catalysts [4,[9][10][11]. For cobalt-based capsule catalysts, the activities and selectivities to iso-paraffins were mainly determined by the reduction levels of cobalt and the hydrocracking/isomerization capability for the primary hydrocarbons formed in the core catalysts.…”

Fischer–Tropsch Synthesis Bifunctional Catalysts: Cobalt Supported on 3D Mesoporous Cellular Silica Foams Assembled by Using ZSM‐5 Seeds

“…Furthermore, strong interactions between cobalt and pure zeolites usually cause low CO conversions . A recent study has attempted to synthesize large pore Co/zeolite bifunctional catalysts for FTS, such as mesopore/macropore zeolites . These materials provide a more open porous network for the transportation of the reactants in FTS and improve the product selectivity.…”

Iron‐Based Fischer–Tropsch Synthesis for the Efficient Conversion of Carbon Dioxide into Isoparaffins

“…The directs ynthesis of isoparaffins startingf rom CO/H 2 has been intensively investigated. [27][28][29][30][31] However,r esearch on the synthesis of the isoparaffins concentrated in the gasoline fraction by using CO 2 is rare. On the basis of the catalytic mechanism of the hydroisomerizationo fF ischer-Tropsch (FT) products, the overall performance of CO 2 conversion into isoparaffins mainly relies on how CO 2 -FTS can be optimized considering the catalytic activity and selectivity of the CO 2 feed gas.…”