The Preparation and Characterization of Co–Ni Nanoparticles and the Testing of a Heterogenized Co–Ni/Alumina Catalyst for CO Hydrogenation

Abstract

Samples of well-controlled nanoparticles consisting of alloys of cobalt and nickel of different atomic ratios were synthesized using wet chemical methods with oleylamine as the solvent and the reducing agent. These materials were characterized by a variety of techniques, including high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Small amounts of heterogenized catalysts were prepared using alumina as the support. However, the potential for use of Co–Ni catalysts in CO hydrogenation was explored using a larger amount of Co–Ni/alumina catalyst prepared from standard aqueous impregnation methods and tested in a continuously stirred tank reactor (CSTR) for Fischer–Tropsch synthesis (FTS). Results are compared to a reference catalyst containing only cobalt. The heterogenized catalysts were characterized using synchrotron methods, including temperature programmed reduction with extended X-ray absorption fine structure spectroscopy and X-ray absorption near edge spectroscopy (TPR-EXAFS/XANES). The characterization results support intimate contact between Co and Ni, strongly suggesting alloy formation. In FTS testing, drawbacks of Ni addition included decreased CO conversion on a per gram catalyst basis, although Ni did not significantly impact the turnover number of cobalt, and produced slightly higher light gas selectivity. Benefits of Ni addition included an inverted induction period relative to undoped Co/Al2O3, where CO conversion increased with time on-stream in the initial period, and the stabilization of cobalt nanoparticles at a lower weight % of Co.

The delicate balance of phase speciation in bimetallic nickel cobalt nanoparticles

“…28 Few reports mention the possibility to form composition-controlled NiCo NPs. [29][30][31] Amongst them, the study by van Schooneveld et al interestingly proposed a synthetic route in one pot, using a Ni(II) precursor and a Co(0) precursor with ratio that were systematically varied. This provided them with alloy of tunable composition, provided that acetone was used to dissolve the cobalt precursor, thus undergoing an intermediate acetonation reaction.…”

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

“…Figures 18 and 19, as well as Table 3, show EXAFS fittings for the Co K-edge and Ni K-edge data following TPR-EXAFS and cooling to ambient temperature. A simple model was developed previously [20] and applied here, wherein metal coordination to Ni (whether the core atom was Co or Ni) was given as a fraction, X, of metal-cobalt coordination. Using this approach, excellent fittings with low r-factors were obtained.…”

PDDA induced step-pyramidal growth of nickel–platinum (Ni–Pt) nanoparticles for enhanced 4-nitrophenol reduction

“…Alloying at the nanoscale produces extended capabilities, providing stability, enhancing their activity, and reducing Pt consumption. 4–6…”

“…Alloying at the nanoscale produces extended capabilities, providing stability, enhancing their activity, and reducing Pt consumption. [4][5][6] Typically, NPs form under a thermodynamic equilibrium where low-index facets are exposed. 7 However, wet-chemistry methods are versatile to produce NPs with complex morphologies, where shape tuning is achieved by controlling the synthesis parameters, such as precursor concentration, capping agents, additives, temperature, etc.…”