Al2O3 nanofibers prepared from aluminum Di(sec-butoxide)acetoacetic ester chelate exhibits high surface area and acidity

M.A Rodriguez-Olguin,H Atia,M Bosco,A Aguirre,R Eckelt,E.D Asuquo,M Vandichel,J.G.E Gardeniers,A Susarrey-Arce

doi:10.1016/j.jcat.2021.11.019

Abstract

Alumina (Al2O3) is a widely used material for catalysis in the chemical industry. Besides a high specific surface area, acid sites on Al2O3 play a crucial role in the chemical transformation of adsorbed molecules, which ultimately react and desorb from the catalyst. This study introduces a synthetic method based on electrospinning to produce Al2O3 nanofibers (ANFs) with acidity and porosity tuned using different aluminum precursor formulations. After electrospinning and heat treatment, the nanofibers form a non-woven network with macropores (∼4 μm). Nanofibers produced from aluminum di(sec-butoxide)acetoacetic ester chelate (ASB) show the highest total acidity of ca. 0.70 µmol/m2 determined with temperature-programmed desorption of ammonia (NH3-TPD) and BET. The nature of the acid site in ASB ANFs is studied in detail with infrared (IR) spectroscopy. Pyridine is used as a molecular probe for the identification of acid sites in ASB. Pyridine showed the presence of Lewis acid sites prominently. Density-functional theory (DFT) is conducted to understand the desorption kinetics of the adsorbed chemical species, such as ammonia (NH3) on crystalline γ-Al2O3. For our analysis, we focused on a mobile approach for chemisorbed and physisorbed NH3. The computational results are compared with NH3-TPD experiments, ultimately utilized to estimate the desorption energy and kinetic desorption parameters. The experiments are found to pair up with our simulation results. We predict that these non-woven structures will find application as a dispersion medium of metallic particles in catalysis.

Highlights

Al2O3 is one of the most important acid catalysts applied in biomass conversion to produce chemicals and fuels [1,2,3,4,5,6]
We studied different Al-formulations (e.g., ASBchelate, aluminum nitrate, alumina nanoparticles used as additives, and combinations) as a first step towards the structural design of Al2O3 nanofibers (ANFs) networks for catalysis
The one-electron Kohn-Sham orbitals were expanded on a plane-wave basis with a kinetic energy cut-off of 550 eV for all calculations

Summary

Introduction

Al2O3 is one of the most important acid catalysts applied in biomass conversion to produce chemicals and fuels [1,2,3,4,5,6]. Various polymorphs a-, c-, g-, h-, d-, j-, and v- of Al2O3 can be found in literature [14,15] This wide range of Al2O3 has unique properties, such as acidity, high specific surface area, and excellent chemical and thermal stability [4,13,16,17,18,19,20]. Among these properties, a key characteristic in Al2O3 is the acid site [21,22,23].

Objectives

Methods

Conclusion