Lean Cu-immobilized Pt and Pd films/–H + Conducting Membrane Assemblies: Relative Electrocatalytic Nitrate Reduction Activities Mohammad A. Hasnat a, *, Sami Ben Aoun b, **, Mohammed M. Rahman c , Abdullah M. Asiri c , Norita Mohamed d a Department of Chemistry, School of Physical Sciences, Shahjalal University of Science and Technology, Sylhet 3100, Bangladesh b Department of Chemistry, Faculty of Science, Taibah University, PO Box 30002, Al-Madinah Al-Munawarah, Saudi Arabia c Center of Excellence for Advanced Material Research (CEAMR) and Chemistry Department, Faculty of Science, King Abdulaziz University, PO Box 80203, Jeddah 21589, Saudi Arabia d School of Chemical Sciences, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia Introduction The nitrate reduction reaction (NRR) is persistently essential from the viewpoint of clean environment and controlled synthesis of several specific products (such as NO 2  , NO, N 2 O, NH 2 OH, NH 3 , N 2 etc) by reducing nitrate ions [1–5]. Nowadays, two types of nitrate reduction processes have been developed: (i) Biological processes, consisting of nitrate reduction by microorganisms into gaseous nitrogen, and (ii) Heterogeneous catalytic reduction of nitrate ions [4–9]. The electrocatalytic reduction of nitrate ions has been explored for many years as an ideal example of a complex electrochemical process that involves the instantaneous genera- tion of numerous products. In fact, electrocatalytic processes showed manifold advantageous over other processes since (i) the electrodes can often be shaped ‘‘in–situ’’ under the experimental conditions and (ii) nitrate/nitrite ions can be selectively reduced to the desired products. As a result, a great deal of research has been carried out in conjunction with the electrocatalytic NRR [10–25]. To date, several metal catalysts (Sn, Pt, Pd, Cu, Ag, Rh etc.) have been investigated as electrodes aiming at attaining effective NRR. Among these, Cu has shown an excellent electrocatalytic activity both in acidic [19] and basic media [20,22,24]. It is noteworthy that the major drawback of these works is the unstable performance of Cu electrodes in both media due to either passivation or dissolution of the electrode particles. On the other hand, bimetallic catalysts have been proven to exhibit superior catalytic activities over single metal catalysts for several catalytic processes [12–18,25,26]. Besides the choice of electrode material, the configuration of the electrolysis reactor plays important roles as well. In this respect, sandwich type (MjNafionjM, M = Pt, Pd etc) reactors have Journal of Industrial and Engineering Chemistry 28 (2015) 131–137 A R T I C L E I N F O Article history: Received 27 November 2014 Received in revised form 5 February 2015 Accepted 13 February 2015 Available online 19 February 2015 Keywords: Noble metal films Reactivity Selectivity Nitrate reduction Electrocatalysis A B S T R A C T Asymmetric reactors having the configuration (PtjNafionjM–Cu, M = Pt, Pd) were designed and applied to the electrocatalytic nitrate reduction reaction (NRR) with no supporting electrolyte. The electrochemically–fabricated Cu–M (M = Pt, Pd) catalysts showed a highly-efficient catalytic activity by effectively reducing more than ca. 99% of nitrate ions, under static-reactor conditions, with first-order rate constants of ca. 0.040 min 1 and ca. 0.057 min 1 for Cu–Pt and Cu–Pd, respectively. Similar reactivity trends were observed under flow mode irrespective of flow rates while NRR rates were predominantly controlled by diffusion-limited mass-transfer. A maximum of ca. 93% nitrate removal at Cu–Pd catalyst was achieved within ca. 60 min. The comparatively lower CuO content of ca. 9%, as confirmed by XANES, resulted in a greater number of free NRR active sites inducing the superior catalytic activity of the Cu–Pd catalyst. On the other hand, NRR product selectivity investigations showed that Cu– Pd catalyst was highly ammonia–selective with a maximum of ca. 24% selectivity at a flow rate of 0.1 mL min 1 , while Cu–Pt catalyst was much selective to intermediate nitrite ions reaching a maximum of ca. 35% selectivity at the same flow rate. ß 2015 Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry. * Corresponding author at: Shahjalal University of Science and Technology, School of Physical Sciences, Department of Chemistry, Sylhet 3100, Bangladesh. Tel.: +88 0821 715752; fax: +88 0821 715752. ** Corresponding author at: Taibah University, Faculty of Science, Department of Chemistry, PO Box 30002, Al Madinah Al-Munawarah, Saudi Arabia. Tel.: +966 59 0900 727; fax: +966 14 862 8023x4326. E-mail addresses: mah-che@sust.edu (M.A. Hasnat), sbenaoun@taibahu.edu.sa (S. Ben Aoun). Contents lists available at ScienceDirect Journal of Industrial and Engineering Chemistry jou r n al h o mep ag e: w ww .elsevier .co m /loc ate/jiec http://dx.doi.org/10.1016/j.jiec.2015.02.008 1226-086X/ß 2015 Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry.