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Mesoporous Zeolite Y-Supported Co Nanoparticles as Efficient Fischer-Tropsch Catalysts for Selective Synthesis of Diesel Fuel Jincan Kang, Xiaojie Wang, Xiaobo Peng, Yudan Yang, Kang Cheng, Qinghong Zhang, and Ye Wang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b03810 • Publication Date (Web): 01 Dec 2016 Downloaded from http://pubs.acs.org on December 7, 2016
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Industrial & Engineering Chemistry Research
Mesoporous Zeolite Y-Supported Co Nanoparticles as Efficient Fischer-Tropsch Catalysts for Selective Synthesis of Diesel Fuel Jincan Kang, Xiaojie Wang, Xiaobo Peng, Yudan Yang, Kang Cheng, Qinghong Zhang,* and Ye Wang* State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, National Engineering Laboratory for Green Chemical Productions of Alcohols, Ethers and Esters, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China *CORRESPONDING AUTHOR: E-mail:
[email protected] or
[email protected]; Phone: +86-592-2186156; Fax: +86-592-2183047
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ABSTRACT: Cobalt nanoparticles were loaded onto mesoporous zeolite Na-Y (Na-meso-Y) by melt infiltration and impregnation methods. As compared to the impregnation, the melt infiltration resulted in Co nanoparticles with a narrower size distribution. The Co/Na-meso-Y catalyst prepared by the melt infiltration exhibited higher C10–C20 (diesel fuel) selectivity. The hydrogenolysis of heavier hydrocarbons was confirmed to occur under Fischer-Tropsch reaction conditions. Our studies for the hydrogenolysis of n-hexadecane revealed that the catalyst by the melt infiltration was more active and selective for the formation of C10–C15 hydrocarbons. We propose that the narrower Co size distribution favors the selective hydrogenolysis and thus the C10–C20 selectivity in Fischer-Tropsch synthesis. The addition of Mn with a proper content could further improve the diesel fuel selectivity to 65% by suppressing the formations of CH4 and lighter hydrocarbons. The Mn-modified Co/Na-meso-Y catalyst was very stable and no deactivation was observed in 1000 h.
KEYWORDS: Synthesis gas; Fischer-Tropsch synthesis; selectivity control; hydrogenolysis; diesel fuel; mesoporous zeolite; manganese
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1. INTRODUCTION Fischer-Tropsch (FT) synthesis is a heterogeneous catalytic reaction, which transforms synthesis gas (CO/H2) into hydrocarbons. FT synthesis has attracted much attention in recent years because of the increasing importance of the non-petroleum carbon resources including shale gas (also conventional natural gas or other unconventional natural gas reserves), coal and biomass for production of fuels and chemicals. Although FT synthesis has a long history,1 some key scientific challenges still remain for fundamental research. One of the most important but difficult challenges is selectivity control.2 The product selectivity of FT synthesis usually follows the Anderson-Schulz-Flory (ASF) distribution, which is a statistical distribution determined by the chain-growth probability factor.2 Such a product distribution is wide and unselective for the middle-distillate products. For example, according to the ASF distribution, the highest selectivity to gasoline-range (C5−C11) hydrocarbons is 45% and that to diesel-range (C10−C20) hydrocarbons is 39%.2 Hence, the development of novel catalysts with controllable product distributions is a challenging goal. A number of studies have been devoted to investigating the factors that determine the catalytic behaviors including the product selectivity. Besides the engineering factors such as reactor design and operation conditions,3-5 many catalyst factors can exert significant influences on the activity and selectivity. These factors include the identity of active metal (typically, Co, Fe and Ru), chemical state and crystalline phase of active metal, support, promoter, size of active metal, exposed facets and microenvironment (location) of active metal.2,6-12 By optimizing these factors, the C5+ selectivity, i.e., the selectivity to hydrocarbons with carbon numbers ≥ 5, could reach 90%. However, the distribution of products inside C5+ is still wide and to tune the selectivity of products inside C5+ hydrocarbons is highly challenging.
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Bifunctional catalysts that combine a conventional FT catalyst for CO hydrogenation to heavier hydrocarbons with a solid acid, in particular acidic zeolite, capable of catalyzing the hydrocracking of heavier hydrocarbons have attracted much attention in recent years for the direct conversion of syngas into middle-distillate hydrocarbons with high selectivity.13-17 For example, a core-shell structured bifunctional catalyst with the conventional FT catalyst (Co/Al2O3) as the core and zeolite membrane as the shell could catalyzed the direct conversion of syngas into gasoline-range (C5–C11) hydrocarbons with a good selectivity, although the selectivity of CH4 was high.18 We found that the utilization of mesoporous ZSM-5 (meso-ZSM-5) instead the conventional microporous ZSM-5 as the acid component could significantly decrease the selectivities to CH4 and C2–C4 alkanes and increase that to C5-C11 hydrocarbons.19-21 The C5– C11 selectivity reached ~80% over Ru/meso-ZSM-519 or Ru/meso-beta20 and ~70% over Co/meso-ZSM-521 catalyst, which was markedly higher than the maximum C5–C11 selectivity predicted by the ASF distribution (45%). Kapteijn and co-workers also reported that Co/H-mesoZSM-5 was an efficient catalyst for the selective formation of C5–C11 hydrocarbons from syngas.22,23 The production of diesel fuel from syngas is a highly attractive target in FT synthesis.24 As compared to petroleum-based diesel, the diesel fuel produced from FT synthesis has many advantages such as the low sulfur and aromatic contents, and the decreased NOx and particulate matter (PM) emissions.25 However, the diesel selectivity over the conventional FT catalysts is limited (
