Applied Catalysis B: Environmental 101 (2010) 21–30 Contents lists available at ScienceDirect Applied Catalysis B: Environmental journal homepage: www.elsevier.com/locate/apcatb Effect of surface oxygen containing groups on the catalytic activity of multi-walled carbon nanotube supported Pt catalyst Xiaoming Wang a,∗∗ , Nan Li a , Jeffrey A. Webb b , Lisa D. Pfefferle a , Gary L. Haller a,∗ a Department of Chemical Engineering, Yale University, New Haven, CT 06520, USA b Department of Chemistry and Chemical Engineering, University of New Haven, West Haven, CT 06516, USA article info Article history: Received 14 June 2010 Received in revised form 13 August 2010 Accepted 27 August 2010 Keywords: Carbon nanotube supported catalyst Aqueous phase reforming Dehydrogenation Competitive adsorption Metal-support interaction abstract Multi-walled carbon nanotubes (MWNT) supported platinum catalysts were employed to study the support functionalization on their catalytic performances. The MWNT were subjected to HNO 3 func- tionalization, in which oxygen containing groups (OCGs) were introduced to improve Pt dispersion. The MWNT supports were characterized by nitrogen physisorption and NEXAFS, and the Pt supported on differently functionalized MWNT characterized by X-ray absorption, TEM and both hydrogen and CO chemisorption. Compared to the as received MWNT supports, Pt dispersion is improved on the HNO 3 treated MWNT supports, but the turnover frequency (TOF) of aqueous phase reforming decreases by half. The TOF can be recovered by removing the OCGs via high temperature annealing. To further investigate the OCGs effect, different probe reactions, including both steam reforming and liquid phase reforming of hydrocarbon oxygenates and dehydrogenation of alkanes in the liquid and gas phases, have been per- formed on the MWNT supported catalysts with different OCGs. A comparison of these reaction results suggests that OCGs are only detrimental to reactions in a binary mixture with two components of different hydrophilicity due to their competitive adsorption on the catalyst supports. © 2010 Elsevier B.V. All rights reserved. 1. Introduction High surface area carbon, e.g., activated carbon, is a well known support for metal catalysts but it has most often been utilized in low temperature reducing reactions in the liquid phase, e.g., in liquid phase hydrogenations, typical of the pharmaceutical indus- try [1]. There are two incentives for renewed interest in carbon as a metal support for heterogeneous catalysts. First, new forms of high surface area carbon have recently been discovered and synthe- sized such as single- and multi-walled carbon nanotubes. Single- and multi-walled carbon nanotubes (SWNT and MWNT) may be one source of much of the excitement surrounding nanotechnol- ogy of the future. Among the many potential applications of carbon nanotubes, their use as a heterogeneous catalyst support is widely recognized [2–8]. Second, any reasonable expectation of a future hydrogen economy is sure to put new demands on heterogeneous catalysis both to produce the hydrogen [9–11] and to consume it as an energy source [7,8,12–16] and in both of these processes carbon ∗ Corresponding author. Tel.: +1 203 432 4378; fax: +1 203 432 4387. ∗∗ Corresponding author. Tel.: +1 203 432 4365; fax: +1 203 432 4387. E-mail addresses: xiaoming.wang@yale.edu (X. Wang), nan.li@yale.edu (N. Li), jwebb@newhaven.edu (J.A. Webb), lisa.pfefferle@yale.edu (L.D. Pfefferle), gary.haller@yale.edu (G.L. Haller). is likely to be the catalyst support of choice because its properties are advantageous over conventional oxide supports. Carbon has several unique properties as a catalyst support not exhibited by oxides: they are resistant to dissolution in high tem- perature aqueous solution, they are stable in acidic or basic media, and their chemical properties can be easily engineered via differ- ent surface functional groups, all of which are desirable attributes for catalyst supports used in aqueous phase processing of biomass [11,17]. They are also electronically conductive, an essential prop- erty for fuel cell catalysts. In order to obtain high dispersion catalysts, carbon supports are usually subjected to oxidation (by HNO 3 ,H 2 O 2 , ozone, etc.) to cre- ate oxygen containing groups (OCGs) [12,15,18–23], which have been demonstrated to help stabilize metal particles on the surface of carbon supports [12,22]. However, the OCGs can also affect the activity of the catalyst in some cases, and the effect appears not to be straightforward. Coloma et al. [18,19] studied the effect of OCGs in the catalytic activity of an activated carbon supported Pt catalyst, and found that OCGs do not affect the turnover frequency (TOF) of the hydrogenation of benzene in the gas phase, but promotes the TOF of gas phase hydrogenation of crotonaldehyde. On the other hand, de Jong et al. [16,24–28] studied the effect of OCGs on the aqueous phase hydrogenation of cinnamaldehyde over carbon nanofiber supported Pt and Ru catalysts, and the result is the oppo- site, i.e., the OCGs generally decreased the activity of the catalyst. 0926-3373/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2010.08.028