Tuning Ca–Al-based catalysts’ composition to isomerize or epimerize glucose and other sugars

Abstract

One of the key reactions to achieve good productivity in the transformations of cellulose derived from biomass feedstocks is the isomerization of glucose to fructose, the latest being the platform molecule for obtaining other important derivatives. In this work, Ca–Al containing catalysts based on hydrotalcite-type derived materials were used to perform the selective isomerization of glucose to fructose, and the selective epimerization of glucose to mannose, using water as the solvent under mild reaction conditions. The catalysts showed high activity (conversion = 51–87%), and excellent selectivity (63–88%) towards fructose, compared with the current industrial process based on the glucose transformation via biocatalysis. It was also possible to modulate the selectivity towards fructose or mannose by tuning the amount of basic sites of the catalysts and their composition. The combination of basic and acid sites present in the Ca–Al-based catalysts plays a key role in the reaction, a fact that is discussed in the text together with other important operational parameters. The stability and recyclability of the catalysts were tested, detecting only a small activity loss after 5 consecutive runs. The synthesis of the catalysts and their characterization are also discussed since they are one of the few cases found in the literature of this kind of hydrotalcite-type material with such a high level of Ca incorporation. Some green metrics, such as E-factor, have been calculated to evaluate our system as an environmentally friendly process.