Contents lists available at ScienceDirect Applied Catalysis A, General journal homepage: www.elsevier.com/locate/apcata Rational design of bifunctional catalyst from KF and ZnO combination on alumina for cyclic urea synthesis from CO 2 and diamine Nagendra Kulal a,b , Crowny John c , Ganapati V. Shanbhag a, * a Materials Science and Catalysis Division, Poornaprajna Institute of Scientific Research (PPISR), Bidalur Post, Devanahalli, Bengaluru, 562 164, Karnataka, India b Graduate Studies, Manipal Academy of Higher Education (MAHE), Manipal, 576104, Karnataka, India c Chemistry Department, Christ University, Bengaluru, 560029, Karnataka, India ARTICLEINFO Keywords: CO 2 Ethylenediamine 2-Imidazolidinone Cyclic urea Bifunctional catalyst ABSTRACT This study is mainly focused on the design of stable, active and selective catalyst for direct synthesis of 2- imidazolidinone (cyclic urea) from ethylenediamine and CO 2 . Based on the rationale for the catalyst properties needed for this reaction, KF, ZnO and Al 2 O 3 combination was selected to design the catalyst. ZnO/KF/Al 2 O 3 catalyst was prepared by stepwise wet-impregnation followed by the removal of physisorbed KF from the sur- face. High product yield could be achieved by tuning acid-base sites by varying the composition and calcination temperature. The catalysts were characterized by various techniques like XRD, N 2 -sorption, NH 3 -TPD, CO 2 -TPD, TEM, XPS and FT-IR measurements. It is shown that acidic and basic properties of the solvent can influence the activity and product selectivity for this reaction. Under optimized condition; 180 °C, 10 bar and 10 wt.% catalyst in batch mode, 96.3 % conversion and 89.6 % selectivity towards the 2-imidazolidinone were achieved. 1. Introduction Carbon dioxide (CO 2 ) plays a vital role in increasing global warming ever since the industrial revolution had occurred. The burning of fossil fuels and coal paved the way for the increase of this greenhouse gas. This issue of global warming has been taken up seriously by scientists and they also warned the nations which release high content of carbon dioxide into the atmosphere. Since this has become a very important issue internationally, scientists are keen to reduce this greenhouse gas from the atmosphere. Carbon dioxide is non-toxic and abundantly available gas, can be utilized to produce several products like cyclic carbonates, carbamates, urethanes, substituted ureas, organic carbo- nates, methanol, and hydrocarbons. One such transformation is cy- cloaddition of CO 2 with a diamine to make cyclic urea. 2-imidazolidi- none, a product of CO 2 and ethylenediamine (EDA) shows promising industrial applications such as an additive in plastics, intermediate in the synthesis of pharmaceuticals, agricultural chemicals [1]. This che- mical is used in the manufacture of polymers and it is a finishing agent for textiles and leather. It is also used to formulate lacquers, plasticizers and adhesives and insecticides. As a formaldehyde remover, it can re- move residual formaldehyde in fabrics treated by epoxy resin, 2D-resin painting, urea-formaldehyde resin, melamine formaldehyde resin, etc [2]. Conventionally, reactions of diamines with several kinds of reagents used as carbonyl sources such as phosgene, urea, organic carbonates [3,4], carbonyl selenide [5], carbonyldiimidazole [6], dithiocarbonate [7]. From the toxic point of these reagents, the reaction of a diamine with CO 2 provides a direct eco-friendly route for the synthesis of cyclic urea. Homogeneous catalysts for this reaction such as Ph 3 SbO/P 4 S 10 [8] and TBA 2 [WO 4 ][9] were reported as efficient catalysts but they possess several limitations including catalyst separation, recyclability and high cost of catalyst production. Arai [10] and Zhao [11] reported non- catalytic routes for direct synthesis of cyclic urea from CO 2 and dia- mine. However, these reactions were carried out under harsh conditions such as high temperature (≥200 °C), and pressure (≥6.0 MPa). There are very few reports on heterogeneous catalysts for this reaction in the previous literature. Among them, polyethylene-glycol-supported po- tassium hydroxide(KOH/PEG1000) [12] have been reported to be ef- ficient catalysts for direct synthesis of cyclic urea from diamine and CO 2 . This catalyst showed a low yield of cyclic urea (≤82 %), at a pressure of 80 bar CO 2 and 150 °C. CeO 2 [13] synthesized by biopo- lymer template method gave low yield for cyclic urea (≤ 37 %) at 7 bar CO 2 pressure and 160 °C. Among heterogeneous catalysts, Tomishige and co-workers reported pure commercial CeO 2 as the most efficient catalyst among different metal oxides such as ZnO, CaO, La 2 O 3 , TiO 2 , MgO, ZrO 2 , Pr 6 O 11 and Al 2 O 3 [1]. Although CeO 2 catalyst shows pro- mising catalytic activity for CO 2 and amine reaction and moreover, CeO 2 is an expensive chemical [14–20]. Based on this literature, https://doi.org/10.1016/j.apcata.2020.117550 Received 22 October 2019; Received in revised form 27 March 2020; Accepted 1 April 2020 ⁎ Corresponding author. E-mail address: shanbhag@poornaprajna.org (G.V. Shanbhag). Applied Catalysis A, General 598 (2020) 117550 Available online 16 April 2020 0926-860X/ © 2020 Elsevier B.V. All rights reserved. T