Catalysis Today 293–294 (2017) 167–175 Contents lists available at ScienceDirect Catalysis Today j our na l ho me page: www.elsevier.com/locate/cattod Heteropolyacid catalysts for Diels-Alder cycloaddition of 2,5-dimethylfuran and ethylene to renewable p-xylene Yanuar Philip Wijaya a,1 , Haryo Pandu Winoto a,b,1 , Young-Kwon Park c , Dong Jin Suh a,d , Hyunjoo Lee a,b , Jeong-Myeong Ha a,b,e , Jungho Jae a,b,∗ a Clean Energy Research Center, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea b Clean Energy and Chemical Engineering, Korea University of Science and Technology, Daejeon 34113, Republic of Korea c School of Environmental Engineering, University of Seoul, Seoul 02504, Republic of Korea d Department of Green Process and System Engineering, Korea University of Science and Technology, Daejeon 34113, Republic of Korea e Green School, Korea University, Seoul 02841, Republic of Korea a r t i c l e i n f o Article history: Received 19 August 2016 Received in revised form 19 November 2016 Accepted 16 December 2016 Available online 31 December 2016 Keywords: Biomass Diels-Alder 2,5-Dimethylfuran p-Xylene Heteropolyacids a b s t r a c t The Diels-Alder cycloaddition of biomass-derived furans and subsequent dehydration are promising routes for the sustainable production of commodity chemicals such as p-xylene (PX). In this paper, we have investigated the catalytic performances of a range of phosphotungstic acid (HPW) and silicotungstic acid (HSiW) catalysts supported on various oxides, i.e., SiO 2 , Al 2 O 3 , TiO 2 and ZrO 2 and their structure- activity correlation in the conversion of 2,5-dimethylfuran (DMF) and ethylene to PX. The characterization studies of the catalysts using XRD, BET, Raman and 31 P MAS-NMR spectroscopy reveal that all of the sup- ported heteropolyacid (HPA) catalysts (except HPW/ZrO 2 ) retain their Keggin structure on the surface of oxide supports. Results from ammonia- and n-propylamine-TPD studies show that all of the supported HPA catalysts possess well-defined Brønsted acid sites with the total acidity decreasing in the following order: HPA/SiO 2 > HPA/Al 2 O 3 > HPA/ZrO 2 > HPA/TiO 2 . The conversion of DMF and the initial rate of PX production generally increase with an increase in the total acidity, with HPA/SiO 2 being the most active catalyst. The turnover frequency of PX production for HPA/SiO 2 is also considerably greater than those for the HPAs supported on Al 2 O 3 , ZrO 2 , and TiO 2 , which suggests that the higher activity of HPA/SiO 2 is at least partly due to the enhanced strength of Brønsted acid sites. Both the silica-supported HSiW and HPW catalysts demonstrate remarkably high PX selectivity (82–85%) at high DMF conversion (91–94%) at 250 ◦ C after 6 h reaction. The effects of reaction conditions such as acid loading, reaction temperature, and reaction time have also been investigated with the most active silica-supported HSiW catalysts to optimize the PX yield. © 2016 Elsevier B.V. All rights reserved. 1. Introduction The potential of utilizing biomass as a renewable resource to reduce the dependency on petroleum-based resources has driven research efforts towards the development of sustainable pro- cesses for the production of aromatic chemicals, such as benzene, toluene, and xylenes (BTX) [1–3]. The sustainability of BTX aro- matics is critical because they are used widely in fuels and in the chemicals industry as the precursors for polymers [3]. In partic- ular, p-xylene (PX) is a precursor chemical for the synthesis of ∗ Corresponding author at: Clean Energy Research Center, Korea Institute of Sci- ence and Technology, Seoul 02792, Republic of Korea. E-mail addresses: jjae@kist.re.kr, john.jjae@gmail.com (J. Jae). 1 Co-first authors. polyethylene terephthalate (PET), a thermoplastic polymer with applications in fibers, packaging, and electric devices manufac- ture [4–6]. Fig. 1 presents a fully sustainable integrated process for the production of PX from biomass (the major steps are marked with the bold arrow lines). Glucose, as the major product from the hydrolysis of cellulose, can be isomerized to fructose using biological (i.e. enzymes) [7] or thermochemical catalysts such as Sn-containing beta zeolite [8]. Fructose can then be dehydrated to 5-hydroxymethylfurfural (HMF), which is subsequently converted to 2,5-dimethylfuran (DMF) via hydrogenolysis [9,10]. Meanwhile, glucose can also be fermented to produce ethanol [11], which is then dehydrated to ethylene [12,13]. The reaction between DMF and ethylene can then occur via tandem Diels-Alder cycloaddition (DA) and dehydration reactions to produce PX. http://dx.doi.org/10.1016/j.cattod.2016.12.032 0920-5861/© 2016 Elsevier B.V. All rights reserved.