Synthesis Of (111) Facet-Engineered Mgo Nanosheet From Coal Fly Ash And Its Superior Catalytic Performance For High-Temperature Water Gas Shift Reaction

Synthesis of high-value products from coal ash, an otherwise valueless waste is crucial to both sustainable waste treatment and low-cost material fabrication. However, research in this area is still sparse, with majority of the researches being conducted on the synthesis of alumina/silica-based nanomaterials such as zeolite from fly ash. Herein, we report a facile synthesis of high-purity, magnesium hydroxide (Mg(OH)2) nanosheet from a brown coal fly ash (BCFA) waste via leaching, precipitation and ethanol-mediated hydrothermal processing in sequence. The resultant nanosheet from fly ash bears a specific surface area of around 100 m2/g, and an averaged aspect ratio of 11.8, as opposed to only 1.5 for the commercial Mg(OH)2 and the one synthesed without the mediation of ethanol during hydrothermal processing. The fly ash derived Mg(OH)2 nanosheet was subsequently loaded with 30 wt% Fe3+ (as Fe2O3) via incipient wetness impregnation and calcined into a (111) facet-rich MgO, which was proved for a superior catalysis performance for high-temperature water gas shift reaction (HT-WGSR). At the reaction temperatures of 400-450 ?C, the CO conversion was increased by a factor of two compared to a reference catalyst consisting of identical Fe loading on the Mg(OH)2 support synthesized without ethanol, and by a factor of seven compared to a nano-sized hematite catalyst synthesized from same hydrothermal process without ethanol addition. This is mainly due to the abundant oxygen vacancy on the (111) facet of the MgO nanosheet support, which improved the reducibility of Fe3+ as well as facilitated the formation and decomposition of intermediate formates that in turn promoted the forward reaction. This study is expected to open a new direction for the valorisation of fly ash and any Mg-bearing solid wastes into high-value materials such as catalyst or catalyst support for a broad range of catalytic applications.