Impact of Hydrogenolysis on the Selectivity of the Fischer–Tropsch Synthesis: Diesel Fuel Production over Mesoporous Zeolite‐Y‐Supported Cobalt Nanoparticles

Abstract

Selectivity control is ac hallenging goal in Fischer-Tropsch (FT) synthesis.H ydrogenolysis is knownt oo ccur during FT synthesis,b ut its impact on product selectivity has been overlooked. Demonstrated herein is that effective control of hydrogenolysis by using mesoporous zeolite Y-supported cobalt nanoparticles can enhance the diesel fuel selectivity while keeping methane selectivity low. The sizes of the cobalt particles and mesopores are key factors whichd etermine the selectivity both in FT synthesis and in hydrogenolysis of nhexadecane,amodel compound of heavier hydrocarbons.The diesel fuel selectivity in FT synthesis can reach 60 %with aCH 4 selectivity of 5% over aN a-type mesoporous Y-supported cobalt catalyst with medium mean sizes of 8.4 nm (Co particles) and 15 nm (mesopores). These findings offer an ew strategy to tune the product selectivity and possible interpretations of the effect of cobalt particle sizea nd the effect of support pore sizei nF Tsynthesis.Fischer-Tropsch (FT) synthesis,aprocess for the conversion of syngas (CO/H 2 )d erived from nonpetroleum carbon resources such as natural gas (also shale gas), coal, and biomass,i nto hydrocarbon fuels and chemicals,h as received renewed interest because of the growing global demand for liquid fuels and the depletion of petroleum. Extensive studies have been devoted to developing efficient catalysts for FT synthesis, [1] but the effective control of product selectivity remains one of the grand challenges.T he FT products generally follow the Anderson-Schulz-Flory (ASF) distribution, which is unselective for the middle-distillate products. [1b] Fore xample,t he selectivities of products in gasoline (C 5-11 ) and diesel (C 10-20 )f ractions are limited to 45 and 39 %, respectively.Conventionally,the FT products are subjected to further hydrotreatment to increase liquid fuel selectivity. Compared to this two-stage process,the direct production of specific-range liquid fuels would be more energy and cost efficient.Recently,bifunctional FT catalysts,which combine either ruthenium, cobalt, or iron nanoparticles for CO hydrogenation, and acid sites in az eolite like H-ZSM-5 for hydrocracking,h ave been harnessed to enhance the C 5-11 selectivity. [2,3] However,few studies have succeeded in the direct and selective production of C 10-20 hydrocarbons, [4] even though the FT-based diesel fuel is known to possess many advantages such as low sulfur and aromatic content, and reduced NO x and particulate matter emissions. [5] Herein, we report an ew strategy to improve the C 10-20 selectivity by effective control of hydrogenolysis.We expected that the use of zeolite H-Y,having aweaker Brønsted acidity than H-ZSM-5, might cause milder hydrocracking of heavier primary hydrocarbons formed on FT metals and lead to higher C 10-20 selectivity.H owever,the Co/ H-Y catalyst did not show enhanced C 10-20 selectivity compared to that of Co/SiO 2 and Co/Al 2 O 3 ,w hich are two conventional FT catalysts,b ut its C 21+ selectivity was lower because of the Brønsted a...

Confined small-sized cobalt catalysts stimulate carbon-chain growth reversely by modifying ASF law of Fischer–Tropsch synthesis

“…For example, the maximum selectivities to C 5 ­–C 11 (gasoline-range) and C 10 –C 20 (diesel-range) hydrocarbons are ∼45% and ∼39%, respectively. Conventionally, the FTS products are subjected to further hydro-treatment to improve the selectivity of liquid fuels 4 . The direct production of target-range liquid fuels will be more efficient in energy and economically effective than the multiple-stages process.…”

“…The direct production of target-range liquid fuels will be more efficient in energy and economically effective than the multiple-stages process. It is urgent to design high-performance FTS catalysts with a high selectivity to target products 4 – 6 .…”

Recent advances in multifunctional capsule catalysts in heterogeneous catalysis

“…FTS is an effective process for the conversion of syngas into clean liquid fuels (gasoline, diesel fuel, and jet fuel) and valuable chemicals (light olefins and aromatics) [39][40][41][42][43][44][45][46][47][48][49]. It is a stepwise polymerization reaction and the products generally follow an Anderson-Schulz-Flory (ASF) distribution, which is inherently wide and unselective [50][51][52][53][54][55]. In the past years, we have designed many kinds of capsule catalysts for the isoparaffin synthesis based on FTS [11][12][13][14][15][16][17][18].…”

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

“…Although researchers continuet op ursuet he use of low-carbon gases such as methane and hydrogen as transportation fuels ande ven though electric cars are proliferating, there is no good alternative to liquid fuels for long-distancet rucks and other heavy vehicles, as well as aviation. [1] Given the limited availability of crude oil and the conversion of coal into synthetic liquid fuelb ys yngas (a mixtureo fCOand H 2 )followed by Fischer-Tropsch synthesis (FTS), [2][3][4][5][6][7][8][9] this dependence poses major security and environmental problems. [10] Arguably, the conversion and utilization of such carbon-rich fossil fuels are the main contributors to the emission of the greenhouseg as CO 2 ,w hichl eads to climate change.…”

“…As shown in Table 3, increasingt he H 2 /CO 2 ratio from 3t o6led to an increase in the conversion of CO 2 from 41.7 to 63.9 %. Moreover,ahigher H 2 concentrationa lso led to the formation of ag reater amount of CH 4 ,lower selectivity to olefins, and ad ecrease in the probability of chain growth.…”