Contents lists available at ScienceDirect Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser Traversing the history of solid catalysts for heterogeneous synthesis of 5- hydroxymethylfurfural from carbohydrate sugars: A review Bhumica Agarwal a,1 , Kamalakannan Kailasam b,1 , Rajender Singh Sangwan a, ⁎ , Sasikumar Elumalai a, ⁎ a Chemical Engineering Division, Center of Innovative and Applied Bioprocessing (CIAB), Knowledge City, Mohali, Punjab 140306, India b Institute of Nano Science and Technology (INST), Mohali, Punjab 160062, India ARTICLE INFO Keywords: 5-hydroxymethylfurfural Heterogeneous catalysis Heteropoly acids Ion-exchange resin Metal organic frameworks ABSTRACT 5-Hydroxymethylfurfural (HMF) belongs to the group of “drop-in biofuels” and platform molecule of prime importance. Synthesis of HMF from various sugar sources has traversed a long span of time and has witnessed various modifications viz., use of heterogeneous catalysts over homogeneous catalysts, employment of organic phase over aqueous, introduction of biphasic systems to overcome side reaction limitations and still counting. Every modification has been carried out with the objective of improved selectivity and product synthesis, cost and energy optimization, and a shift towards greener process over existing methods. Use of lignocellulosic biomass instead of commercial sugars also finds applicability in direct HMF synthesis along with levulinic acid, furfural etc. However, low yields from these abundant, cheap and readily available sugar sources are still ideal for scale-up of the process strategies. Among large pool of studies available in this area, current review presents the advantages imparted towards HMF synthesis with the advent of heterogeneous catalysis over the course of time and various reaction systems evolved to meet the steeping demand of HMF, specifically from common carbohydrate sources. Special attention has been paid to understand the mechanism of modifications imparted to various solid catalysts for improved HMF synthesis. 1. Introduction The prime concern of researchers for the past few decades is abating the dependence on fossil based energy sources. Concurrently, motiva- tions to protect environment from disastrous carbon emissions from fossil based fuels has led to civilization as well as industrial sectors to be less energy-dependent compared to the past. However, the global en- ergy demand is expected to increase upto 37% by 2040 [1]. Considering the extended time required for the replenishment of natural energy sources and predicted shortage to meet postulated global requirements has motivated the search for development of new renewable resource to substitute petroleum derivatives. 5-Hydroxymethylfurfural (HMF), one such identified energy source and is considered a versatile key value- added chemical (or platform molecule), receiving much attention in petroleum and chemical industries [2–4]. Because HMF is susceptible to many chemical reactions due to its excellent chemical reactivity en- abling synthesis of variety of commercially important chemicals de- pending on the synthesis scheme, as proposed in Fig. 1 [5]. For ex- ample, hydrogenation reactions result in synthesis of 2,5- dimethylfuran, which is a commonly used as transportation fuel (bio- derived), 2,5-bis(hydroxymethyl)furan (BHMF; used in manufacture of polyurethane foam), 2,5-dimethyltetrahydrofuran (used in polyester preparation) and so on. Also, HMF acts as an oxidative precursor to prepare FDCA (2,5-furandicarboxylic acid), an alternative to ter- ephthalic acid in PET manufacturing, and adipic acid, which is ex- tensively used in nylon preparations [2]. Also, 2,5-diformylfuran (DFF) finds application in synthesis of diamine and Schiff bases. The most advantageous property offered by the use of HMF-derivatives in plastic industries resulted better product biodegradability and thus, enabling a vision of low-carbon emission cycle. Similarly, 1,6-hexanediol pro- duced by ring hydrogenation of HMF is considered as another most important additive in plastic and other chemical industries, and further trailing amination of which leads to formation of caprolactam, a monomer of nylon-6. Condensation reactions of HMF resulting in for- mation of long chain alkanes that could also be used as direct trans- portation fuel. Uncontrolled reaction conditions for instance, prolonged reaction, presence of surplus water molecule etc. during HMF hydro- genation reaction typically leads to equimolar synthesis of levulinic http://dx.doi.org/10.1016/j.rser.2017.08.088 Received 21 September 2016; Received in revised form 25 June 2017; Accepted 29 August 2017 ⁎ Corresponding authors. 1 Authors contributed equally. E-mail addresses: sangwan@ciab.res.in (R.S. Sangwan), sasikumar@ciab.res.in (S. Elumalai). Renewable and Sustainable Energy Reviews xxx (xxxx) xxx–xxx 1364-0321/ © 2017 Elsevier Ltd. All rights reserved. Please cite this article as: Agarwal, B., Renewable and Sustainable Energy Reviews (2017), http://dx.doi.org/10.1016/j.rser.2017.08.088