Substitution of Co with Ni in Co/Al2O3 Catalysts for Fischer–Tropsch Synthesis

Abstract

The effect of cobalt substitution with nickel was investigated for the Fischer–Tropsch synthesis reaction. Catalysts having different Ni/Co ratios were prepared by aqueous incipient wetness co-impregnation, characterized, and tested using a continuously stirred tank reactor (CSTR) for more than 200 h. The addition of nickel did not significantly modify the morphological properties measured. XRD, STEM, and TPR-XANES results showed intimate contact between nickel and cobalt, strongly suggesting the formation of a Co-Ni solid oxide solution in each case. Moreover, TPR-XANES indicated that nickel addition improves the cobalt reducibility. This may be due to H2 dissociation and spillover, but is more likely the results of a chemical effect of intimate contact between Co and Ni resulting in Co-Ni alloying after activation. FTS testing revealed a lower initial activity when nickel was added. However, CO conversion continuously increased with time on-stream until a steady-state value (34%–37% depending on Ni/Co ratio) was achieved, which was very close to the value observed for undoped Co/Al2O3. This trend suggests nickel can stabilize cobalt nanoparticles even at a lower weight percentage of Co. Currently, the cobalt price is 2.13 times the price of nickel. Thus, comparing the activity/price, the catalyst with a Ni/Co ratio of 25/75 has better performance than the unpromoted catalyst. Finally, nickel-promoted catalysts exhibited slightly higher initial selectivity for light hydrocarbons, but this difference typically diminished with time on-stream; once leveling off in conversion was achieved, the C5+ selectivities were similar (≈ 80%) for Ni/Co ratios up to 10/90, and only slightly lower (≈ 77%) at Ni/Co of 25/75.

Combined Synthesis and Hydroprocessing of Hydrocarbons over Co/SiO2 + ZSM-5 + Al2O3 Catalysts Promoted by Nickel

“…The nickel introduction method does not have a signifi cant effect, although peak 2 of Sample 4 is slightly shifted towards the high-temperature region. Similar regularities were also found in prior studies [52,53].…”

Catalytic Plasma Fischer–Tropsch Synthesis Using Hierarchically Connected Porous Co/SiO2 Catalysts Prepared by Microwave-Induced Co-assembly

“…The use of a plasma, as well as microwave radiation with plasma generation, in catalyst preparation has also been used to enhance activity, selectivity, and long-term stability under service conditions. − ,− These effects can be considered to be the result of structural surface heterogeneity induced in the supported catalyst due to the imposition of high energy density in a short-time span thus creating a nonequilibrium processing conditions with local temperatures reaching several thousand degrees . The chemical and morphological heterogeneity of several SiO 2 -supported catalysts prepared under combined plasma and microwave radiation has recently been characterized. , …”

“…A popular technique for FTS is based on so-called “flow chemistry” in which catalyst-coated microcapillary, monolithic, or foamed reactors are used . One of the advantages of this technique is that heat transfer can also be intensified by using cross-flow reactor configuration in which the reaction channels are separated from the heat-transfer channels by a thin section of highly conductive metal plates , The intensification of FT synthesis using the basic capillary, monolith, or foamed reactors can be further improved by reactor optimization , and through the enhancement of surface area density (surface area per unit volume) for heat and mass transfer in capillary/monolithic reactors and metallic foam reactors where the surface area density enhancement over 100 times is achieved compared with the commercially available foams.…”

“…The effect of pressure in catalytic plasma was further studied and an optimum pressure was determined for conversion and energy efficiency . Cobalt-based catalysts were found to be particularly effective both in conversion and selectivity for higher hydrocarbons. ,− …”

Recent Advances in Cobalt and Related Catalysts: From Catalyst Preparation to Catalytic Performance

“…In the study of Martinelli et al [3] the effect of cobalt substitution with nickel was systematically investigated for the FTS. Catalysts with different Ni/Co ratios were prepared, characterized with various physicochemical techniques, and tested in a continuously stirred tank reactor for more than 200 h. The authors have found that substitution of Co with Ni did not significantly modify the morphological properties of the mixed catalyst.…”