One-Pot Electrospinning Synthesis of Nanofibrous Nickel-Magnesia-Alumina for Advancing Steam Reforming Catalysts

Abstract

Scaffolding one-dimensional (1D) nanomaterials to produce three-dimensional (3D) catalysts may retain unique physicochemical properties that are not typically attained through bulk material synthesis. By reducing the catalyst particle size into 1D nanostructures one can optimize the surface area of contact, acid-base behavior, and electron transport properties owing to geometric confinement effects. In steam reforming (SR) applications, such properties largely influence a wide network of reactions that dictate the catalyst activity and on-stream stability. Using one-pot electrospinning (ESP) followed by a calcination step, this thesis project focused on developing Ni-loaded MgO-Al2O3 nanofibers (NFs) as advanced geometries for multicomponent SR catalysts. The one-pot synthesis approach aims to reduce the catalyst preparation time while producing 3D nanofiber mats with a uniform elemental distribution. To establish a one-pot process, the distribution of metal ion precursors, nickel loading, molecular weight of polyvinylpyrrolidone (PVP) polymer used in the spinning solution, ESP feed flow rate, applied voltage, needle tip-to-collector distance, and calcination temperature were systematically varied to study their influence on the morphology, microstructure, and chemisorption properties of the resulting fibers. The parametric study showed that the fiber diameter increased with the polymer molecular weight, whereas an inverse relationship was found between the applied voltage and working distance. In addition, extremely high (21 kV) and low (15 kV) applied voltages resulted in beaded nanofibers. The feed flow rate mainly controlled the nanofibrous mat density, resulting in either a uniform or clumpy mat owing to solution dripping. In this study, two protocols (protocols A and B) were designed and adopted to successfully synthesize three main systems: single (Al2O3), binary (MgOAl2O3), and ternary (5-10wt%Ni/MgO-Al2O3) systems. SEM images of the calcined ternary systems revealed the successful preparation of Ni/MgO-Al2O3 NFs with an average diameter of 178 nm. The catalyst exhibited a mixture of NiAl2O4 and MgAl2O4 spinel. Moreover, XRD and TEM data confirmed that a higher Ni loading (10 wt%) produced a segregated NiO phase. Hydrogen temperature-programmed reduction (H2-TPR) measurements revealed that the low-temperature reducibility of the alumina-support-based catalysts was enhanced by the incorporation of magnesia and nickel ions. Ammonia temperature-programmed desorption (NH3-TPD) and carbon dioxide temperature-programmed desorption (CO2-TPD) results indicated that the Al2O3 fibers exhibited acidic properties, while the addition enhanced the number of basic sites. The Ni-loaded fibers had an increased total quantity of acidic and basic sites, with a relative distribution between those of Al2O3 and MgO-Al2O3. These results agree with those of the bulk catalysts previously explored in the literature. The difference is within the same temperature range, and the nanofibrous catalyst has more weak acid sites, whereas the bulk has more strong acid sites. Based on these findings, the SR of biomass (palmitic acid) is expected to enhance reforming reactions owing to the enhanced reducibility, acidic sites, and basic sites. In addition, the presence of NiAl2O4 and MgAl2O4 spinel in the nanofibrous structure is expected to further enhance the coke and sintering resistance of the catalyst.

Date of Award	9 May 2024
Original language	American English
Supervisor	Maguy Abi Jaoude (Supervisor)