Synthesis of alumina nanofibers: Role of calcination temperature on dimethyl ether production

In this work, we present the aluminum oxide (Al2O3) ceramic nanofiber synthesis by means of thermal calcination of polyvinylpyrrolidone–aluminum nitrate (PVP–Al(NO3)3) composite nanofibers previously prepared by electrospinning; the studied calcination temperatures were: 500, 650, and 800 °C. These nanofibers were evaluated for their catalytic conversion of methanol to dimethyl ether (DME) by dehydration reaction. Thermal properties were evaluated via thermal gravimetric analysis (TGA). The results showed full calcination of the PVP polymer support and complete transformation of Al(NO3)3 to Al2O3. The chemical composition was elucidated through Fourier-transform infrared (FTIR) spectroscopy and energy-dispersive X-ray spectroscopy (EDX). Structural characteristics were obtained by X-ray diffraction (XRD) and selected-area electron diffraction (SAED), which demonstrated an amorphous-to-crystalline evolution as the calcination temperature is increased, obtaining the cubic gamma-alumina (γ-Al2O3) structure with a crystallite size of 6 nm at 800 °C. Scanning and transmission electron microscopies (SEM and TEM, respectively) showed a decrease of the diameter fiber from 254 to 160 nm and an increase in surface roughness as the calcination temperature is increased. The Barrett-Joyner-Halenda (BJH) and Brunauer-Emmett-Teller (BET) methods were employed to study the texture properties, and the results indicated an increase in pore volume (from 0.008022 to 0.04 cm3g–1), as well as surface area (from 10.22 to 37.46 g/m2) with increasing the calcination temperature. Finally, the synthesized Al2O3 ceramic nanofibers presented a catalytic conversion of methanol to DME of around 70% and a selectivity of 100% at 350 °C and 1 atm of pressure.