Contents lists available at ScienceDirect Catalysis Communications journal homepage: www.elsevier.com/locate/catcom Short communication Di-methyl carbonate transesterification with EtOH over MOFs: Basicity and synergic effect of basic and acid active sites Luca Desidery a , Somboon Chaemcheun a , Mekhman Yusubov b , Francis Verpoort a,b,c,⁎ a Laboratory of Organometallics, Catalysis and Ordered Materials, State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan, China b National Research Tomsk Polytechnic University, Lenin Avenue 30, 634050 Tomsk, Russian Federation c Ghent University, Global Campus Songdo, 119 Songdomunhwa-Ro, Yeonsu-Gu, Incheon, Republic of Korea ARTICLE INFO Keywords: Diethyl carbonate Dimethyl carbonate Ethyl methyl carbonate MOFs Acid/base active sites ABSTRACT The catalytic activity of metal-organic frameworks (MOFs) towards the transesterification of dimethyl carbonate with ethanol has been unprecedented assessed. The relation between the catalytic activity and the amount of base active sites has been proved as well as the inability of the Lewis acid sites alone to catalyze this transes- terification. The synergic effect of both acid and base sites cannot be completely excluded and a plausible reaction mechanism has been proposed. MOF-808 resulted to be more efficient than every heterogeneous commercial catalyst. MOF-808 can be recycled up to 4 times with exceptional retention of both catalytic activity and crystal structure. 1. Introduction Due to their low toxicity and ubiquitous applications in several in- dustries (lithium-ion battery technology, pharmaceuticals, agrochem- icals, etc.) di-ethyl carbonate (DEC) and ethyl methyl carbonate (EMC) have attracted considerable interest in the last decades [1,2]. It is, therefore, necessary to develop efficient and environmentally benign synthetic routes in order to replace the classical, dangerous and toxic synthesis via phosgene [3,4] and chloroformate [5–7] transformations (Supporting information (SI) Scheme 1). Among the alternative routes (direct synthesis [8,9], alcoholysis of urea [10], decarbonylation of dimethyl oxalate [11], carbonylation of ethanol/ethyl nitrite [12–14], transesterifications [5–7,15–17]), trans- esterification reactions are some of the most promising routes since the starting materials present low toxicity and high biodegradability, the processes do not require pressurized systems and the working tem- perature is considerably low. Transesterification can be catalyzed by both acid and basic catalysts even though the basic catalysts proved to be the most active catalysts, even in the particular case of the trans- esterification of carbonic acid di-alkyl esters [18]. The transesterification of dimethyl carbonate (DMC) with EtOH to produce EMC and DEC consists in a two-step reaction where EMC is the intermediate and methanol a side product of both consecutive trans- formations (Scheme 1). Possible competitive reactions (hydrolysis of the di-alkyl esters and their thermal decomposition) can be minimized via reactants dehydration and working at reduced reaction tempera- tures [19–21]. The main drawbacks of this synthetic route consist in the unfavorable equilibrium and the formation of three homogeneous binary azeotropes (MeOH-DMC, EtOH-DMC, and EtOH-EMC) difficult to separate [22–24]. Reactive distillation (RD) is considered to be the most promising method to intensify this process for industrial applications [15,20]. Several homogeneous and heterogeneous, acid and base catalysts have been so far investigated. Unfortunately, a preferable heterogeneous catalysts usually exhibit slow kinetics and/or issues concerning their stability and recyclability. Mg-Al-O-t-Bu hydrotalcite [2], KF/Al 2 O 3 [25] and dipotassium carbonate coated on polyethylene glycol [17,26] re- present the most active catalysts reported till now. Metal-organic frameworks (MOFs), a class of porous ordered ma- terials that combine some of the best characteristics of both homo- geneous and heterogeneous catalysts, can provide structures with dif- ferent amounts of base and acid active sites. To the best of our knowledge, MOF 5 [16], ZIF 8 [5] and ZIF 67 [6] are the only MOFs that have been investigated as catalysts for the transesterification of DMC with DEC, while till now, no studies are reported about applica- tions of MOFs in the transesterification of DMC with EtOH. Herein, the catalytic activity of various MOFs towards the transes- terification of DMC with EtOH and the relationship between their http://dx.doi.org/10.1016/j.catcom.2017.10.022 Received 27 September 2017; Received in revised form 23 October 2017; Accepted 24 October 2017 ⁎ Corresponding author at: Laboratory of Organometallics, Catalysis and Ordered Materials, State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan, China. E-mail addresses: Francis.verpoort@ugent.be, francis.cn@qq.com (F. Verpoort). Catalysis Communications 104 (2018) 82–85 Available online 28 October 2017 1566-7367/ © 2017 Elsevier B.V. All rights reserved. MARK