Sulfated ordinary clay for acid-catalyzed conversion of biomass derivatives: Impacts of abundance and types of acidic sites on catalytic performance

Abstract

Ordinary clay is an abundantly available material for use as catalyst support. In this study, sulfuric acid was used as sulfonating agent to prepare sulfated clay-based super-acid catalyst. The effects of sulfuric acid concentration and calcination temperature on physiochemical properties, interaction of sulfur species with the oxides in clay, distribution of Brønsted acid sites and Lewis acid sites were characterized with XRD, pore structure analysis, FT-IR, elemental analysis, NH3-temperature programmed desorption (NH3-TPD) and Pyridine-DRIFTS etc. The catalytic performance of different catalysts was evaluated by conversion of furfuryl alcohol (FA) to ethyl levulinate (EL). The results showed that sulfuric acid reacted with alumina in clay to form Al2(SO4)3, thus changing structure and crystal phase of the catalyst. Increasing calcination temperature enhanced the interaction between sulfate species and clay, the retaining of sulfur on clay surface and the formation of more Brønsted acid sites while less Lewis acid sites. In addition, balanced distribution of the acidic sites was crucial for selective conversion of FA to EL. Over the clay catalyst impregnated with 4 ​M ​H2SO4 and calcined at 300 ​°C, the yield of EL could reach 90%. The catalyst was not stable in polar solvent like ethanol due to leaching of sulfur species, while in aprotic solvent like dimethyl sulfoxide, the catalyst maintained a good catalytic stability.