Determination of the crucial functional groups in graphene oxide for vanadium oxide nanosheet fabrication and its catalytic application in 5-hydroxymethylfurfural and furfural oxidation

Abstract

Graphene oxide (GO) sheets are emerging as a new class of carbocatalyst, and also a perfect platform for metal-oxide catalyst assembling. The oxygen groups on either side of GO basal plane can be functioned as the anchor by employing GO as scaffolds. Vanadium-oxo nanosheets (VON) were assembled onto the surface of GO material from homogeneously dissolved VO(acac)₂ solution via a facile route. Control experiments with different methods prepared graphene materials illustrate the nucleation and fabrication process of VON on GO surface with detailed TEM and XPS investigation. The evolution of oxygen groups in graphene material was also investigated. Hydroxyl/epoxy in GO sheets was considered to be important and favorable for the fabrication of VON on GO surface. The developed material was shown to be an efficient and recyclable heterogeneous catalyst for aerobic oxidation of 5-hydroxymethyfurfural (HMF) and furfural into maleic anhydride. Up to 90.9% yield of maleic anhydride from HMF and 59.9% from furfural were achieved under optimized reaction conditions, the reaction rate difference between HMF and FAL was studied on the basis of oxidation mechanism and their molecular structures.

Introduction

Concern over diminishing fossil reverses and the environmental impact of their utilization has expanded interest in the production of biomass-based commodities (Chatzidimitriou and Bond, 2015; James et al., 2010; Huber et al., 2006; Bond et al., 2014). As a renewable carbon resources, biomass is often viewed as an ideal alternative to fossil resources (Chatzidimitriou and Bond, 2015). Replacement of petroleum-derived chemicals with those from biomass will play a key role in sustaining the growth of the chemical industry (Dodds and Gross, 2007; Cai et al., 2014; Carlos Serrano-Ruiz and Dumesic, 2009; Gallezot, 2012; Jin and Enomoto, 2011). Significant effort has been devoted into convert renewable biomass into fuels, (James et al., 2010; Huber et al., 2006; Bond et al., 2014) and valuable chemicals over various catalysts and routes (Besson et al., 2014; Caes et al., 2013; Corma et al., 2007; Xu et al., 2017; Zhang and Deng, 2015; Xu and Zhang, 2015; Zhang and Huber, 2018; Zhang et al., 2015).

5-Hydroxymethylfrufural (HMF), derived from C6-based carbohydrates and owned an aldehyde group, a hydroxymethyl group and a furan ring, has been regarded as one of the most promising platform chemicals and used as a versatile precursor for the production of fine chemical, plastics, pharmaceuticals, polymer and liquid fuels (Gallezot, 2012; Antunes et al., 2014; Balakrishnan et al., 2012; Chheda et al., 2007; Lange et al., 2012). Besides, C5-based furfural (FAL) is an analog of HMF and comes from rich agricultural materials like corncobs, oat, wheat bran, and sawdust, and they are not competitive with food of human beings. Particularly, unlike HMF, which is currently synthesized on a lab scale, furfural production is an on-going industrial process, therefore, it is considered that furfural is a better starting material than HMF in bio-refinery (Lan et al., 2014; Li et al., 2016). Selective oxidation of HMF and FAL to value-added fine chemicals is one of the most pivotal transformation in biorefinery (Zhang and Deng, 2015; Xu and Zhang, 2015; Zhang and Huber, 2018; Zhang et al., 2015). One important route in biorefinery is the high efficient production of maleic anhydride (MA) via HMF or FAL oxidation. MA, which is widely employed to synthesize unsaturated polyester resins, agricultural chemicals, food additives, lubricating oil additives, pharmaceuticals et al. (Lan et al., 2015) is mainly produced via oxidation of petroleum-derived chemicals such as n-butane and benzene (Lan et al., 2015). Recently, MA production with HMF and FAL as start materials have been developed (Lan et al., 2015; Du et al., 2011). To obtain a relative high MA yield in HMF and FAL conversion, many vanadium-based catalysts, such as VO(acac)₂, (Du et al., 2011) VMo containing heteropolyacid, (Lan et al., 2015; Guo and Yin, 2011; Shi et al., 2011) supported or unsupported VO_x, (Alonso-Fagundez et al., 2012) MoV metal oxide, (Li et al., 2016) have been reported to catalyze the oxidation of HMF and FAL into MA. However, lower efficiency of heterogeneous VO catalysts is often encountered for their low surface area or low catalytic behavior. Researchers developed VO supported on Al₂O₃, (Alonso-Fagundez et al., 2012) SiO₂, (Li and Zhang, 2016) MoV binary metal oxide, (Li et al., 2016) and V-containing heteropolyacid (Lan et al., 2015; Guo and Yin, 2011; Shi et al., 2011) and a relative enhanced catalytic behavior was observed in some extent. To obtain a higher MA yield from HMF and FAL, a VO-based catalyst with unique structure and morphology is needed.

Layered graphene oxide (GO), decorated with hydroxyl, epoxide on graphene sheets basal plane, has been widely used as a solid acid, green oxidant, redox catalyst, and catalyst support et al. in chemical synthesis (Su and Loh, 2012). Owing to its large surface area and abundant hydroxyl/epoxy on basal plane, GO shows a great potential as a scaffold to anchor active species such as organocatalyst or photocatalysts. The synergistic interactions between active sites and GO can result in enhanced catalytic reactivity in chemical synthesis. In this work, vanadium oxide nanosheets (VON) was fabricated to GO surface from homogeneous dissolved VO(acac)₂ aqueous solution with oxygen groups in GO as an anchor in a facile route. Hydroxyl/epoxy groups were demonstrated to be the vital functionalities in VON fabrication on GO surface. The developed VON anchoring on GO surface were demonstrated to be an efficiency catalytic material in HMF and FAL oxidation. Compared with V₂O₅ and supported VO on active carbon or SiO₂, the prepared heterogeneous material VO-GO shows super catalytic activity in HMF and FAL aerobic oxidation.