Heteropoly acid supported on silicalite–1 possesing intracrystalline nanovoids prepared using biomass – an efficient and recyclable catalyst for esterification of levulinic acid

Abstract

• Silicalite-1 with intracrystalline nanovoids was prepared using corn stem pith powder. • The prepared silicalite-1 possessed larger external surface area and led to higher dispersion of heteropoly acid. • 31 P-MAS NMR and XPS results indicated interfacial bond formation between support and heteropoly acid. • The supported catalyst showed better catalytic activity in esterification of levulinic acid. • The catalyst was stable even after four recycles and no leaching of heteropoly acid observed. Silicalite-1, a silicious zeolite having intracrystalline nanovoids in addtion to its intrinsic micropores was prepared under hydrothermal condition using corn stem pith powder as a hard template. The zeolite was used as a support for 12-phosphotungstic acid (HPA) and the resulted catalyst was characterized using powder X-ray diffraction, N 2 adsorption, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, 31 P − magic angle spinning nuclear magnetic resonance spectroscopy ( 31 P-MAS NMR), X-ray photoelelctron spectroscopy, ultraviolet-visible spectroscopy and temperature programmed desorption of ammonia. Supporting HPA on the zeolite containing nanovoids improved dispersion of HPA and hence increased the number of accessible acid sites. X-ray photoelectron and 31 P-MAS NMR spectra indicated interfacial bond formation between the zeolite surface and HPA. The supported HPA was tested as a hetergeneous catalyst for esterifiation of levulinic acid with 1-propanol, 1-butanol and 1-heptanol. Heteropoly acid supported on the zeolite with intracrytalline nanovoids exhibited enhanced catalytic activity and the activity was stable even after four recycles.