Deposition Precipitation for the Preparation of Carbon Nanofiber Supported Nickel Catalysts

Abstract

Deposition precipitation of nickel hydroxide onto modified carbon nanofibers has been studied and compared to deposition onto silica. The carbon nanofiber support materials consisted of graphite-like material of the fishbone-type with a diameter of 20-50 nm and a specific surface area of 150 m2/g. Modification involved surface oxidation (CNF-O) optionally followed by partial reduction (CNF-OR) or thermal treatment (CNF-OT). Titration of the support materials showed the presence of 0.17 and 0.03 mmol/g carboxylic acid groups for CNF-O and CNF-OR, respectively. For the CNF-OT only basic groups were present. The deposition precipitation of 20 wt % nickel onto these supports has been studied by time dependent pH and nickel loading studies. With silica, nickel ion adsorption did not occur prior to nucleation of the nickel hydroxide phase at pH = 5.6. With CNF-O, nickel ion adsorption took place right from the start of the deposition process at pH = 3.5, and at pH = 5.6 already 4 wt % nickel was adsorbed. Nucleation of nickel hydroxide onto adsorbed nickel ion clusters proceeded subsequently. Characterization of the dried Ni/CNF-O samples with TEM and XRD showed well dispersed and thin (5 nm) platelets of nickel hydroxide adhering to the carbon nanofibers. After reduction at 773 K in hydrogen the Ni/CNF-O contained metallic nickel particles of 8 nm homogeneously distributed over the fibers. With CNF-OR and CNF-OT, precipitation of large platelets (> 500 nm) separate from the support took place. Clearly, the presence of carboxylic acid groups is essential to successfully deposit nickel hydroxide onto modified carbon nanofibers.

Bio-oil upgrading in supercritical water using Ni-Co catalysts supported on carbon nanofibres

“…The role of the surface oxygen groups in the morphology of the deposited metallic phase largely depends on the metal precursor and the catalyst preparation method [57,58]. In this work, the characterisation results indicate that the surface chemistry did not have a significant impact on the Ni-Co nanoparticle morphology, as determined by the TEM, XRD and XPS studies, which permits assessing the effect of the CNF support without any interference of the morphology of the active phase (Ni-Co).…”

Iron impregnation on the amorphous shell of vapor grown carbon fibers and the catalytic growth of secondary nanofibers

“…2B that the calcination of supported AFC does not show a peak similar to the one at 70 min (655 K) in trace m/z = 44 of Fig. 2A, which indicates that the decomposition of AFC is not complete at the calcination temperature of 573 K and pure Fe 2 O 3 is not yet obtained. The intermediate is likely to be Fe 2 O n (CO 3 ) 3-n , which releases CO 2 at higher temperatures around 655 K.…”

“…A variety of methods have been developed for the preparation of supported catalysts in recent years including impregnation and drying [2], deposition precipitation [3], and chemical vapor deposition (CVD) [4,5]. For the wetting methods, the metal precursor may be crucial to achieve a homogeneous distribution.…”

Activity of Nitrogen Containing Carbon Nanotubes in Base Catalyzed Knoevenagel Condensation

“…Silica-supported Ni and Co catalysts with a metal loading of 20 wt% for the growth of NCNT were prepared via Homogeneous Deposition Precipitation (HDP) using Ni-nitrate or Co-nitrate as described before [34,35]. For NCNT growth 0.5 g of the calcined catalyst was loaded into a vertical quartz reactor and heated (5°C min -1 ) in He (100 mL min -1 ) to 973 K followed by reduction at that temperature in 20% H 2 /He (100 mL min -1 ) for 2 h. Next, the temperature of the reactor was adjusted to the desired temperature (5°C min -1 ) for NCNT growth (823-1123 K) while keeping the catalyst in He (50 mL min -1 ).…”