Magnesium Impregnated on NaX Zeolite Synthesized from Cogon Grass Silica for Fast Production of Fructose via Microwave-Assisted Catalytic Glucose Isomerization

Sittichai Kulawong,Saran Youngjan,Narong Chanlek,Jatuporn Wittayakun,Pongtanawat Khemthong,Nattawut Osakoo

doi:10.3390/catal11080981

Abstract

Fructose is a crucial intermediate in the production of several chemical platforms. Fructose is mainly produced from glucose isomerization either through immobilized enzymes or heterogeneous catalysts using a conventional heating source, and this is time-consuming. Thus, this work discloses a fast production of fructose via microwave-assisted catalytic glucose isomerization using Mg catalysts supported on NaX zeolite from cogon grass silica. The catalysts were prepared by the impregnation of magnesium nitrate solution and subsequently transformed into MgO on NaX by calcination. The effect of 3, 6 and 9 wt.% Mg content on NaX on the performance of glucose isomerized to fructose was tested at 90 °C for 15 min. The best catalyst was selected for studying the effect of reaction times of 5, 15, 30 and 60 min. Results from X-ray diffraction (XRD), N2 sorption and CO2 temperature-programmed desorption (CO2-TPD) suggested that crystallinity, surface area and micropore volume decrease but basicity increases with Mg content. The X-ray photoelectron spectroscopy (XPS) result confirmed the presence of mixed phases of MgO and Mg2CO3 in all catalysts. The glucose conversion enhanced with the Mg loading but the fructose yield gave the highest value with Mg of 6 wt.%, probably due to the tuning of high active sites and surface area. The greatest fructose selectivity and yield (71.9% and 25.8%) were obtained within 15 min by microwave-assisted catalytic reaction, shorter than the reported value in the literature, indicating a suitable reaction time. Mg (6 wt.%)/NaX catalyst preserves the original catalytic performance up to three cycles, indicating that it is a promising catalyst for fructose production.

Highlights

The untreated sample gave a broad peak at 22◦ and other peaks at 29◦, 38.5◦, 43.59◦ and 48.17◦ corresponding to a mixed phase between the amorphous silica and CaCO3 phases [26]
The high purity and existence of an amorphous phase of silica from cogon grass in the present work make it reasonable to use as a silica source for zeolite NaX synthesis due to expediently dissolving in NaOH solution, leading to the quick generation of a zeolite synthesis precursor (Na2 SiO3 ) [23]
The reused catalyst was applied with a similar process mentioned above for the third and fourth cycles, respectively. This is the first report on NaX zeolite from cogon grass silica, which was successfully synthesized and used as a catalyst support for magnesium (Mg) species in the fast production of fructose via microwave-assisted catalytic glucose isomerization

Summary

Introduction

Biomass is converted through value-added chemicals and fuels [1,2]. The main compositions of lignocellulosic materials contain many polysaccharides of glucose as the major building block. It is accepted as the most available carbon renewable source and cheap material [2]. Glucose monomers have been widely used in the food industry and medicine [2,4]. They can be utilized in the synthesis of fuels and value-added chemicals [5]. One of the most crucial glucose reactions in the chemical platform is the production of fructose via isomerization because fructose is an important intermediate in the production of several platform chemicals such as

Methods

Results

Conclusion