Journal of Molecular Catalysis A: Chemical 425 (2016) 147–156 Contents lists available at ScienceDirect Journal of Molecular Catalysis A: Chemical journal homepage: www.elsevier.com/locate/molcata Surface-exposed Pd nanoparticles supported over nanoporous carbon hollow tubes as an efficient heterogeneous catalyst for the C C bond formation and hydrogenation reactions Arindam Modak, Asim Bhaumik ∗ Indian Association for the Cultivation of science, Jadavpur, Kolkata, India a r t i c l e i n f o Article history: Received 24 August 2016 Received in revised form 28 September 2016 Accepted 30 September 2016 Available online 1 October 2016 Keywords: Carbon hollow tubes N-doped carbon Pd nanoparticles C C coupling Hydrogenation reaction a b s t r a c t Designing uniformly dispersed Pd nanoparticles over nanoporous carbon supports is very demanding in the context of heterogeneous catalysis. However in most of the cases cluster/agglomerated Pd particles are formed over carbon matrixes, which lack sufficient stability and formation of a sustainable passive layer that can prevent the direct contact between the active metal sites with the reactants. Herein we report the in-situ preparation of surface-exposed Pd nanoparticle over N-doped carbon hollow tubes i.e. Pd@CHT, which showed high catalytic activity compared with agglomerated Pd on carbon. The simplicity in the preparation of Pd@CHT via one step direct carbonization of hypercrosslinked polymer tubes followed by reduction in the presence of NaBH 4 can offer huge potential in liquid phase heterogeneous catalysis. High dispersibility of the catalyst in the reaction medium, good stability and reusability of Pd@CHT is observed for the Sonogashira, cyanation and hydrogenation reactions for the synthesis of a wide range of value added fine chemicals, suggesting its future potential in heterogeneous catalysis. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Over the past decade considerable progress has been made in the synthesis and applications of nanoporous carbon ranging from nanometer to micrometer level [1–3]. It is to be believed that nanoporous carbon derived from high surface area porous poly- mers with/without activating agent is quite simple and elegant than templated methods involving zeolite, silica etc. [4–6]. However, soft porous polymers are generally suffered from huge loss in porosity and morphology during carbonization at high temperature, which is supposed to be disadvantageous for their application. Therefore, it would be challenging to retain the shape of porous polymers after its carbonization at high temperature in order to generate porous carbon. Carbon hollow tubes (CHT) are among such nanoporous carbon, which are demanding for several applications, but is devoid of any suitable and facile preparation methods [7]. On the other hand, metal nanoparticles and/or cluster of few atoms that are stabilized on various solid supports like silica, zeo- lites, porous polymers, metal oxides (TiO 2 , Alumina etc.), graphene, possesses significant applications in catalysis, hydrogenation reac- tions, energy conversion, fuel cell etc. [8–14]. Although single atom ∗ Corresponding author. E-mail addresses: msab@iacs.res.in, abhaumik68@yahoo.co.in (A. Bhaumik). catalysis is exciting as far as the efficiency of the process, but its’ preparation, characterization, active sites isolation is very difficult task. Also, because of high surface mobility of single atoms, they possess enough surface energy for agglomeration, which actually precludes its single atom stage and subsequently becomes agglom- erated nanoparticles [14]. However, unlike oxides as support, nanoparticles or single atoms supported on hollow carbon spheres/N-doped carbon nano- tubes (CNT) showed considerable improvement in stability of active sites, owing to significant interaction between supported carbon and metal species [15–17]. This means that carbons containing unique hollow nanostructure are better support for nanoparticles, because of the advantages of two distinguishable surfaces i.e. hol- low interior and the exterior, which decreases mobility of the active sites and hence prevents agglomeration, sintering etc. Therefore there remains a great significance for the utilization of N-doped hollow carbon tubes as support for metal particles, in contrast to solid amorphous carbon. Although activated carbon is well known for metal supported catalysis, but it suffers from diffusion limitation due to its inher- ent microporosity, as well as less tensile strength and presence of impurity substances further direct its disadvantageous perfor- mances for catalytic applications [11]. Compared to commercially available CNT and activated carbon, carbon hollow tubes may provide good dispersibility of Pd NPs at the catalyst surface http://dx.doi.org/10.1016/j.molcata.2016.09.037 1381-1169/© 2016 Elsevier B.V. All rights reserved.