Temperature-mediated control of the growth of an entangled carbon nanofiber layer on stainless steel micro-structured reactors Lucia Martı´nez-Latorre, Sabino Armenise, Enrique Garcia-Bordeje ´ * Instituto de Carboquimica (C.S.I.C.), Miguel Luesma Casta ´ n 4, 50018 Zaragoza, Spain ARTICLE INFO Article history: Received 15 September 2009 Accepted 10 February 2010 Available online 15 February 2010 ABSTRACT A well-adhered layer of carbon nanofibers (CNFs) was grown on stainless steel microreac- tors by decomposition of a hydrocarbon over microreactors previously coated with Ni dis- persed on alumina. In a previous work, we reported that the growth temperature and hydrocarbon (methane or ethane) modulated the morphology and size of the grown carbon species. Using ethane, the carbon yield increased dramatically for temperatures exceeding 898 K. At these temperatures some carbon protrusions arise, which plug microreactor channels and render the microreactor unsuitable for use. For methane at all the tested tem- peratures or for ethane at the lowest temperatures (853 and 873 K), the microreactor chan- nels were covered completely by a uniform mat of entangled CNFs ready for catalytic use. Here, we show that the growth temperature and hydrocarbon can also control the primary structure of CNFs, either rolled graphitic planes parallel to the axis (multi-wall carbon nanotubes) or graphitic planes forming an angle with respect to the axis (fishbone type). Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Carbon nanofibers (CNFs) and carbon nanotubes (CNTs) hold many promises as catalyst support [1]. For instance, some gas-phase reactions benefit from the use of graphitic materi- als as catalyst support compared with metal oxide supports [2–5]. The benefit can be due to different causes such as the absence of microporosity and the more conductive nature of graphite which induces electronic effects or modification of catalyst morphology [6]. In addition, graphitic nanomaterials by themselves have outstanding performance in dehydroge- nations reactions [7,8]. Unlike metal oxide support, CNFs form aggregates with high surface areas, high mesopore volumes and low tortuos- ity. Additionally, diameter and length of the fibres and hence the bulk density of the CNF layer, can be manipulated to tailor porosity and overcome tortuosity problems. This eliminates the internal diffusion limitations by preventing concentration gradients inside the CNF layer. This is favourable for fast and highly exothermic gas-phase reactions and for sluggish liquid phase reactions because mass/heat transfer limitations are prevented while keeping low pressure drop [9]. Nevertheless, CNFs in powder form have some drawbacks such high-pressure drop, plugging and flow maldistribution for fixed bed operation, and agglomeration and difficulty of filtration due to the formation of fines for slurry operation. The macroshaping of CNFs would circumvent these draw- backs. In the literature, macrostructures of CNFs have been produced either as self-supporting macrostructures [10,11] or by the attachment of CNFs to different structured macro- scopic supports such ceramic monoliths [12–14], carbon felts [15–17] or foams [9], metal filters [18] or foams [19]. The man- ufacture of chemicals in catalytic micro-structured reactors (MSR) has become recently a new branch of chemical reaction 0008-6223/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2010.02.015 * Corresponding author: Fax: +34 976733318. E-mail address: jegarcia@icb.csic.es (E. Garcia-Bordeje ´). CARBON 48 (2010) 2047 – 2056 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon