Mendeleev Commun., 2011, 21, 125–128 – 125 – © 2011 Mendeleev Communications. All rights reserved. Mendeleev Communications Multiwall carbon nanotubes (MWCNTs) can be used as supports for nickel nanocrystals with controlled pore size distributions and surface areas and great thermal and chemical stability. They demonstrated wide opportunities in decoration of the outer sur- face of MWCNT 1–16 and/or filling their internal channels. 17,18 The synthesis of Ni/MWCNT composites by nickel-catalyzed decomposition of hydrocarbons gives a material with low metal loading where it is located mainly at the ends of nanotubes. In order to obtain appropriate catalysts, it is important to combine a small crystal size with a maximal metal loading. In this study, different nickel deposition methods on MWCNT surfaces were compared. Sonochemical deposition from Ni(CO) 4 in decaline was used for the first time to prepare Ni/MWCNT composite with nickel size less than 10 nm under loadings of 25–50 wt%. † Starting MWCNTs were obtained as bundles of nanotubes (ex- ternal diameter, 30–80 nm) aggregates of ~2 mm size [Figure 1(a),(b)]. Nanotubes contained narrow empty channels with a diameter of 3–4 nm and formed voids as wider mesopores inside the aggregates. Nanotube walls consisted of parallel slightly disoriented graphene layers [Figure 1(c)], as confirmed by XRD after the removal of residual nickel, which occurred in the forms of metallic (Ni 0 ) and oxide (NiO) nanoparticles (Figure 2, curve 1). It consumed hydrogen in the same temperature range as pure NiO (Figure 3, curves 2, 3). Nickel nanocrystals in sample S1 demonstrated size distribution of 20–100 nm and were located mainly at the ends of tubes [Figure 1(b)]. The average size was estimated at 30 nm from XRD data (Table 1). The nickel content of sample S2, obtained by nickel deposition on purified carboxylated MWCNTs was 11 wt% according to chemical and XRD phase analysis with an average crystal size Decoration of multiwall carbon nanotubes with nickel nanoparticles: effect of deposition strategy on metal dispersion and performance in the hydrogenation of p-chloroacetophenone Miron V. Landau,* a Sergei V. Savilov, b Marina N. Kirikova, b Nikolai B. Cherkasov, b Anton S. Ivanov, b Valery V. Lunin, b Yuri Koltypin c and Aharon Gedanken c a Department of Chemical Engineering, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel. Fax: +972 8 647 9427; e-mail: mlandau@bgu.ac.il b Department of Chemistry, M. V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation c Department of Chemistry, Bar-Ilan University, 52900 Tel-Aviv, Israel 04.003 DOI: 10.1016/j.mencom.2011. The sonochemical deposition of nickel nanoparticles onto the multiwall carbon nanotube aggregates leads to a uniformly distributed metal phase at high loadings and an average nickel crystal size of 4–8 nm at a 25–50 wt% nickel content. Its application enhances the catalytic activity of Ni/multiwall carbon nanotube material in the selective hydrogenation of chloroacetophenone by factors of 2–18, as compared with that prepared by traditional decoration methods. † The MWCNTs with a diameter of 50–100 nm (sample S1) were syn- thesized by the pyrolysis of a benzene–ethanol solution of nickel acetyl- acetonate at 1000 °C. 12 After nickel extraction with 65% HNO 3 , the surface of MWCNTs was carboxylated by treatment with H 2 SO 4 /HNO 3 (3:1, v/v) under sonication for 3 h at 40 °C followed by washing with water 19 and drying at 80 °C in air. MWCNT surface area was determined as 216±8 m 2 g –1 . Carboxylated MWCNTs were decorated with metallic nickel by: (1) deposition of reducible Ni-containing precursors from aqueous solutions [1 M acetate (samples S2, S4) or formate (sample S3)] sonicated (20 kHz) at room temperature for 1 h followed by heating at 350 °C in nitrogen and reducing in an H 2 flow (100 cm 3 min –1 ) for 3 h at 550 °C (sample S2, S3). For sample S4 final reduction step after heating in nitrogen was conducted in 5% hydrazine hydrate in NaCl solution under sonication followed by treatment with an aqueous NaOH solution, washing with water and drying in vacuo at room temperature in a glove box. Sonochemical deposition was done by sonication of carboxylated MWCNTs in Ni(CO) 4 solution in decalin with Ti-horn (20 kHz, 100 W cm –2 ) sonicator (VCX 750, Sonics&Materials) under Ar at 5–10 °C for 3 h. The metal loading was controlled varying the concentration of metal precursor at the sonochemical deposition step in a range from 0.02 (sample S5) to 0.05 M (sample S6). For preparation of sample S7 the water–ethanol solution of nickel nitrate was added to MWCNTs at amount corresponding to their solution capacity. The material was heated at 350 °C in nitrogen and reduced in an H 2 flow (100 cm 3 min –1 ) for 3 h at 550 °C. H 2 -TPR experiments were performed on AMI-100 (Zeton-Altamira Co.) equipped with a TCD detector at 10% H 2 –Ar flow of 25 ml min –1 with gradual temperature increase of 5 K min –1 . Conventional wide-angle XRD patterns were obtained with a Philips 1050/70 powder diffractometer fitted with a graphite monochromator and Crystal Logic software. The nickel content of Ni/MWCNT-supported catalysts was calculated based on metal/carbon atomic ratios measured by energy-dispersive X-ray analysis spectro- scopy (EDAX, Quanta-2000, SEM-EDAX, FEI Co) and by ICP method (Instrument Optima 3000, Perkin Elmer Co.) in the solution obtained after HNO 3 (70%) treatment. Adsorption-desorption isotherms were obtained with a NOVA-2000 (Quantachrome Inc., version 7.11) surface area analyzer. HRTEM analysis was conducted on a FasTEM JEOL 2010 microscope operating at 200 kV. Activity and selectivity of Ni/MWCNT catalysts was tested in hydrogenation of p-chloroacetophenone (PCAP), conducted in a 20 ml stainless steel batch reactor with internal Teflon coating equipped with a magnetic stirrer. The reduced or vacuum-dried (direct nickel deposi- tion) catalysts were loaded in the glow box to the reactor filled with liquid reaction mixture that protected it from contacting with air at the following testing steps. The testing conditions: P H 2 = 30 atm, T = 100 °C, catalyst loading 0.2 g, reaction mixture – 0.3 g of PCAP in 12 ml of Pr i OH, reaction time t = 5–12 h needed for keeping the PCAP conversion in the range of 10–30%. The reaction rate was calculated as V [mmol (g cat.) –1 h –1 ] = = [(10 3 × 0.3/MW)X]/wt, where X is PCAP conversion, MW is PCAP molecular weight, and w is catalyst weight (g). The contents of residual PCAP and its hydrogenation products were analyzed by GC [an HP-6890 instrument equipped with FID employing a capillary DB-WAX column (30 m, i.d. = 0.25 mm) and He as a carrier gas]. 2-Methoxyethyl ether was used as an internal standard. The selectivity for 1-(p-chlorophenyl)ethanol (hydrogenation route) and acetophenone (hydrodechlorination route) was calculated based on the concentrations of these compounds found in the products mixture by GC analysis.