Characterizations of nanostructured nickel aluminates as catalysts for conversion of glycerol: Influence of the preparation methods

Mechanochemical preparation of a modified NiAl2O4 structure

Mechanochemical synthesis routes offer a sustainable, simple method for preparing materials. In this work, NiAl₂O₄ was synthesised by a mechanically activated method using a high-energy planetary mill and a calcination step. This study aims to identify the effect of different milling energies on the phases, chemical environments and surface composition of the material. In addition, it explores the thermal impact on the decomposition and structure of the materials. The materials were characterised by X-ray phosphorescence (XPS), solid-state UV-VIS (SS-UV-VIS), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), high-resolution transmission electron microscopy (HR-TEM) and thermal gravimetry differential scanning calorimetry (TGA-DSC). A co-precipitated material is used as a reference along with the ground reagents which were used as a baseline. From this in-depth analysis of the material, a good understanding of the disordered partially inverse spinel structure is provided. This study has found that with calcination temperatures of 750 °C and 900 °C a mixed NiAl₂O₄ : NiO phase is produced with a Ni enriched surface. The surface is found to be relatively stable with the increase from 750 °C to 900 °C.

Optimization and Characterization of Mesoporous Sulfonated Carbon Catalyst and Its Application in Modeling and Optimization of Acetin Production

In this study, an optimized mesoporous sulfonated carbon (OMSC) catalyst derived from palm kernel shell biomass was developed using template carbonization and subsequent sulfonation under different temperatures and time conditions. The OMSC catalyst was characterized using acid-base titration, elemental analysis, XRD, Raman, FTIR, XPS, TPD-NH₃, TGA-DTA, SEM, and N₂ adsorption–desorption analysis to reveal its properties. Results proved that the OMSC catalyst is mesoporous and amorphous in structure with improved textural, acidic, and thermal properties. Both FTIR and XPS confirmed the presence of -SO₃H, -OH, and -COOH functional groups on the surface of the catalyst. The OMSC catalyst was found to be efficient in catalyzing glycerol conversion to acetin via an acetylation reaction with acetic acid within a short period of 3 h. Response surface methodology (RSM), based on a two-level, three-factor, face-centered central composite design, was used to optimize the reaction conditions. The results showed that the optimized temperature, glycerol-to-acetic acid mole ratio, and catalyst load were 126 °C, 1:10.4, and 0.45 g, respectively. Under these optimum conditions, 97% glycerol conversion (GC) and selectivities of 4.9, 27.8, and 66.5% monoacetin (MA), diacetin (DA), and triacetin (TA), respectively, were achieved and found to be close to the predicted values. Statistical analysis showed that the regression model, as well as the model terms, were significant with the predicted R² in reasonable agreement with the adjusted R² (<0.2). The OMSC catalyst maintained excellent performance in GC for the five reaction cycles. The selectivity to TA, the most valuable product, was not stable until the fourth cycle, attributable to the leaching of the acid sites.

Catalytic reforming of oxygenated hydrocarbons for the hydrogen production: an outlook

The catalytic steam reforming of oxygenated hydrocarbons has been holding an interest in scientific societies for the past two decades. The hydrogen production from steam reforming of glycerol, ethanol and other oxygenates such as ethylene glycol and propylene glycol are more suitable choice not just because it can be produced from renewable sources, but it also helps to decrease the transportation fuel price and making it more competitive. In addition, hydrogen itself is a green fuel for the transportation sector. The studies on the production of hydrogen from various reforming technologies revealed a remarkable impact on the environmental and socio-economic issues. Researchers became more focused on glycerol steam reforming (GSR), ethanol steam reforming (ESR) and other oxygenates to investigate the catalyst suitability, their kinetics and challenges for the sustainability of the oil and gas production. In the present work, the authors critically addressed the challenges and strategies for hydrogen production via GSR, ESR and other oxygenates reforming process. This review covers extensively thermodynamic parametric analysis, catalysts developments, kinetics and advancement in the operational process for glycerol, ethanol and few other oxygenates. This detailed investigation only highlights the steam reforming process (SRP) of these oxygenates at the laboratory experimental stage. It was found that from this review, there are many technical issues, which lead to economic challenges. The issues are yet to be addressed and thus, these particular applications require faster accelerations at the pilot scale, taking into the consideration of the current pandemic and economic issues, for a safer and greener environment. Graphical abstract.