Development of Highly Selective Support for CO Hydrogenation to Light Olefins with Partially Passivated Iron Catalysts

Abstract

To rule out disturbances from water‐soluble efficient promoters (e. g., K2O or combination of S/Na), a simplified iron/support catalyst system was employed to investigate novel supports for the catalytic conversion of syngas (CO+H2) to light olefins (FTO). A series of supports with nominal compositions of ZnAl2O4 ⋅ xAl2O3 (x=1, 2, 3) were prepared by coprecipitation and subsequent high temperature calcination at 1200 °C for 24 h to generate partially passivated ZnAl2O4 and Al2O3 phases, through which each formed component of a catalyst may minimize interactions among them and exhibit unique activity. Iron catalysts were prepared by incipient wetness of iron salts over these supports. At a total pressure of ca. 20 bar and a CO conversion of 35 %, a catalyst with a nominal composition of 15 %Fe/85 %(ZnAl2O4 ⋅ 3Al2O3) exhibits a surprising C2=‐C4= hydrocarbon distribution of 58 %, which reaches a huge increase by almost 100 % in comparison with iron catalysts over regular supports (e. g., carbon, gamma‐Al2O3, etc.). This catalyst demonstrates the 1200 °C passivated ZnAl2O4 ⋅ 3Al2O3 as probably the most selective support material for iron‐based FTO catalysts. At CO conversion of 35 %, the contents of ethylene in C2, propylene in C3, and butylene in C4 products achieve extraordinary values of 82 %, 92 %, and 91 %, respectively.

Selective Iron Catalysts for Direct Fischer–Tropsch Synthesis to Light Olefins

“…Argon is used as the internal standard component of syngas for GC analysis. The GC measurement is similar to our previous reports. − …”

“…Adjustment of product selectivity for CO hydrogenation through addition of special element attracts attention. − Since the beginning of 2015, our team has been reporting the introduction and great potential of Zn-containing spinels in Fischer–Tropsch reactions. − Later, researchers reported important applications of Zn-containing spinels in Fischer–Tropsch reactions ,− in which a mainstream route is to join a Zn-containing spinel with a molecular sieve (e.g., AlPO-18, MOR, or SAPO-34 ,, zeolites) for the generation of light olefins from syngas. Literature studies about spinel-containing iron catalysts for FTO reactions are also sparse. , Our recent study shows that Zn-containing composite oxides are promising support candidates for Fe-based FTO catalysts. , Herein, we report zeolite-free, potassium-promoted iron FTO catalysts modulated by high-temperature annealed composite oxides. A catalyst, 15%Fe/2%K 2 O/83%ZnAl 8 O 13 , exhibits a C 2 = –C 4 = hydrocarbon selectivity of 64% at a total pressure of ca.…”

Production of Light Olefins via Fischer-Tropsch Process Using Iron-Based Catalysts: A Review

“…The REF-b catalyst, 100% Fe, had the highest olefin to paraffin ratio. The O/P ratio of the catalysts at about 45-55% of CO conversion were in the order of REF-b(7.8) > F3(6.6) > F∞(3.2) > F2(2.1) > F1(1.9) > REF-a(1.7) [97]. Later, the same research group [98] prepared a series of K2O promoted catalysts, including 15%Fe/2%K2O/83%ZnAl2O4•1Al2O3 (N1), 15%Fe/2%K2O/83%ZnAl2O4•5Al2O3 (N5), 15%Fe/2%K2O/83%Al2O3 (REF ∞ ), and 15%Fe/2%K2O/83%ZnAl2O4 (REF0).…”

“…Xing et al [97] prepared a series of iron catalysts supported on Al2O3 and ZnAl2O4•xAl2O3 (x=1, 2, 3) by incipient wetness impregnation of the support with an aqueous solution of ammonium iron citrate. Two reference catalysts were also prepared by the coprecipitation of metal nitrates (REF-a: a mixture of 15%Fe/85% ZnAl2O4⋅1Al2O3, and REF-b: 100%Fe).…”

Ternary Fe–Zn–Al Spinel Catalyst for CO2 Hydrogenation to Linear α-Olefins: Synergy Effects between Al and Zn

“…On the basis of BET results (Table S1) and TEM images (Figure S6), the doping of Al decreases the particle size and increases the pore volume and surface area of the working catalyst, probably contributing to the conversion. Since spinel structures have higher resistance against sintering and the steam environment, − the increase in catalyst stability is believed to originate from the slow phase transition as Al stabilizes the spinel structure during the reduction and reaction (Figures and S8: XRD and in-/ex situ Raman). However, the negative influence of Al is also obvious as more undesirable CH 4 is formed (Table ).…”