catalysts Article Catalytic Oxidation of NO over LaCo 1-x B x O 3 (B = Mn, Ni) Perovskites for Nitric Acid Production Ata ul Rauf Salman 1 , Signe Marit Hyrve 1 , Samuel Konrad Regli 1 , Muhammad Zubair 1 , Bjørn Christian Enger 2 , Rune Lødeng 2 , David Waller 3 and Magnus Rønning 1, * 1 Department of Chemical Engineering, Norwegian University of Science and Technology (NTNU), Sem Sælands vei 4, NO-7491 Trondheim, Norway; ata.r.salman@ntnu.no (A.u.R.S.); signemhyrve@gmail.com (S.M.H.); samuel.k.regli@ntnu.no (S.K.R.); muhammad.zubair@ntnu.no (M.Z.) 2 SINTEF Industry, Kinetic and Catalysis Group, P.O. Box 4760 Torgarden, NO-7465 Trondheim, Norway; bjorn.christian.enger@sintef.no (B.C.E.); rune.lodeng@sintef.no (R.L.) 3 YARA Technology Center, Herøya Forskningspark, Bygg 92, Hydrovegen 67, NO-3936 Porsgrunn, Norway; david.waller@yara.com * Correspondence: magnus.ronning@ntnu.no; Tel.: +47-73594121 Received: 31 March 2019; Accepted: 3 May 2019; Published: 8 May 2019   Abstract: Nitric acid (HNO 3 ) is an important building block in the chemical industry. Industrial production takes place via the Ostwald process, where oxidation of NO to NO 2 is one of the three chemical steps. The reaction is carried out as a homogeneous gas phase reaction. Introducing a catalyst for this reaction can lead to significant process intensification. A series of LaCo 1−x Mn x O 3 (x = 0, 0.25, 0.5 and 1) and LaCo 1−y Ni y O 3 (y = 0, 0.25, 0.50, 0.75 and 1) were synthesized by a sol-gel method and characterized using N 2 adsorption, ex situ XRD, in situ XRD, SEM and TPR. All samples had low surface areas; between 8 and 12 m 2 /g. The formation of perovskites was confirmed by XRD. The crystallite size decreased linearly with the degree of substitution of Mn/Ni for partially doped samples. NO oxidation activity was tested using a feed (10% NO and 6% O 2 ) that partly simulated nitric acid plant conditions. Amongst the undoped perovskites, LaCoO 3 had the highest activity; with a conversion level of 24.9% at 350 ◦ C; followed by LaNiO 3 and LaMnO 3 . Substitution of LaCoO 3 with 25% mol % Ni or Mn was found to be the optimum degree of substitution leading to an enhanced NO oxidation activity. The results showed that perovskites are promising catalysts for NO oxidation at industrial conditions. Keywords: NO oxidation; catalytic oxidation; nitric oxide; perovskite; nitric acid; ostwald’s process; in situ; LaCoO 3 ; LaMnO 3 ; LaNiO 3 1. Introduction Oxidation of nitric oxide (Equation (1)) is one of the few known third order reactions. The reaction is unusual, as the rate of reaction increases with a decrease in the temperature [1] 2NO + O 2 ⇌ NO 2 Δ r H 298 = −113.8 kJ/mol (1) NO oxidation is a key reaction in lean NO x abatement technologies and in the Ostwald process for nitric acid production. In Ostwald’s process, NO oxidation is carried out as a non-catalytic process and the forward reaction is favored by the removal of heat and by providing sufficient residence time. Typical gas stream concentrations are 10% NO, 6% O 2 and 15% H 2 O[2]. Using a catalyst for NO oxidation may lead to significant process intensification of the nitric acid plant. In addition to speeding up the oxidation process, it may reduce capital costs and increase heat recovery. Efforts have been made to find a catalyst effective under industrial conditions; but success so far has not been Catalysts 2019, 9, 429; doi:10.3390/catal9050429 www.mdpi.com/journal/catalysts