Pyrite ashes as a catalyst for glucose conversion processes

Hexose monosaccharides, which can be obtained through various processes from plant biomass (cellulose), are excellent raw materials for producing high-value-added derivatives. For example, glucose can be converted, under heterogeneous catalytic conditions, into derivatives such as hydroxymethylfurfural (HMF) and furan dicarboxylic acids (FDCA), compounds applicable to the preparation of polymeric materials and biofuels. The catalytic (chemical) conversion of glucose is carried out through isomerization processes (producing fructose under basic catalytic conditions); through dehydration processes (obtaining 1,6-anhydroglucose); and through retroaldol condensation to obtain HMF. However, acidic properties are also required to facilitate dehydration and obtain furan derivatives. In this context, the use of acidic catalysts such as pyrite ash—a classic inorganic multiphase waste material from the sulfuric acid production process—may be suitable for an industrial glucose green conversion process at the micro- and mesoscale, due both to its acidic and basic properties and to its low cost given its status as a waste product of the metallurgical industry. Based on this, the conversion of glucose in the presence of pyrite ash as a heterogeneous catalyst was studied. The reactions were carried out as a function of reaction time (2, 4, 6, and 8 h) and temperature (393, 403, 413, and 423 K). Structural characterization by XRD showed that the pyrite ash was present in a polymorph where the predominant phases were goethite (FeOOH), hematite (Fe₂O₃), plumbojarosite (PbFe₆(SO₄)₄(OH)₁₂), quartz (SiO₂), and pyrite (FeS₂). The catalytic results showed that lower reaction temperatures and shorter reaction times increase fructose yield, whereas at higher reaction temperatures and longer reaction times, HMF formation is observed.