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Green, efficient and economical coal fly ash based phosphomolybdic acid catalysts: preparation, characterization and application

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Cost-effective, efficient and green solid acid catalysts have been synthesized by incipient wetness impregnation of various weight fractions of phosphomolybdic acid (5, 10, 15 and 25 wt. %) on mechanically and thermally activated coal fly ash. N2 adsorption–desorption, XRD, FT-IR, SEM, SEM–EDX, TEM, TGA, UV–Vis DRS, solid state 31P MAS NMR were used for characterization of as synthesized catalysts. Catalytic active sites were developed on inert surface of coal fly ash by using various activation techniques whose performance was assessed over a series of acylation of various aliphatic alcohols. For rapid and higher catalytic activity, reactions were conducted in microwave heating mode. Impregnation of phosphomolybdic acid generates Lewis acidic sites on coal fly ash surface as inferred by pyridine adsorbed FT-IR studies which were then utilized in acylation reactions. Various reaction parameters like weight fraction of catalysts, molar ratio of reactants, time, temperature, etc. were optimized for attaining highest conversion %. The catalyst with 15 wt. % of phosphomolybdic acid was found to be more efficient and could be recycled up to five reaction cycles with analogous conversion %. Negligible leaching of catalyst was confirmed by hot filtration test. This work suggests an alternative approach for valorisation of industrial solid waste, coal fly ash in development of innovative, economical solid catalysts.

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XRD, UV‒Vis DRS characterizations were performed at UGC-DAE Consortium for Scientific Research, Indore. The authors are thankful to Dr. Mukul Gupta for XRD analysis, Dr. T. Shripathi for UV‒Vis DRS analysis, University of Pune for TGA, BET surface area and SEM analysis, SAIF-Chandigarh for TEM analysis and IIT-Bombay for solid state 31P MAS NMR analysis.

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Correspondence to Ashu Rani.

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Malpani, S.K., Goyal, D., Katara, S. et al. Green, efficient and economical coal fly ash based phosphomolybdic acid catalysts: preparation, characterization and application. Chem. Pap. 75, 3017–3034 (2021).

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