Fly Ash-Based Geopolymers as Sustainable Bifunctional Heterogeneous Catalysts and Their Reactivity in Friedel-Crafts Acylation Reactions

Abstract

This study presents the synthesis, characteristics and catalytic reactivity of sustainable bifunctional heterogeneous catalysts derived from coal fly ash-based geopolymer, particularly those with a high Ca content (C-class) fly ash. The developed catalysts were synthesized at room temperature and pressure in a simple ecologically-benign procedure and their reactivity was evaluated in the Friedel-Crafts acylation of various arenes. These catalysts can be produced with multilevel porous architecture, and a combination of acidic and redox active sites allowing their use as bifunctional catalysts. The acidic sites (Lewis and Brønsted acidic sites) were generated within the catalyst framework by ion-exchange followed by thermal treatment, and redox sites that originated from the catalytically reactive fly ash components. The developed catalysts demonstrated higher reactivity than other commonly used solid catalysts such as Metal-zeolite and Metal-mesoporous silicate, heteropolyacids and zeolite imidazole frameworks (ZIF).

Eco-friendly Nano-adsorbents for Pollutant Removal from Wastewaters

“…• Adsorbents for heavy metal removal [32,33,[43][44][45] • Adsorbents for organic compounds removal [22][23][24]46] • The catalysts [47,49] • Adsorbents for gas retention [50,51] • Zeolites [7,31,46,[52][53][54] • Geopolymers synthesis [55][56][57] • Alkali-activated materials [58] The main applications of fly ashes are presented in Fig. 2.…”

Geopolymer foams: An overview of recent advancements

“…In recent years, the use of porous geopolymers, intentionally designed to contain pores, for high-added value applications, such as thermal [35,36] and acoustic insulation [37,38], fire resistance [39,40], adsorbents [41,42] and pH regulators [43,44] has been considered. However, in other industrially relevant applications such as their use as catalysts or catalyst supports [45][46][47][48][49] this strategy (e.g. deliberately introducing porosity in the specimens) has yet to be explored.…”

Synthesis and sintering at low temperature of a new nanostructured beta-Eucryptite dense compact by spark plasma sintering

“…In the case of kaolinite activated with Na 2 CO 3 produced zeolite precursors but in the case of Li 2 CO 3 activation β-Eeucriptite precursors are formed. From this fact, the study of different materials should be addressed: in the first case, compounds could be useful in Heterogeneous Catalysis [37][38][39], in the second case formed compounds could be more adequate as solid electrolytes in batteries [19].…”