Victor de Oliveira Rodrigues

This work evaluates the influence of the acidic sites concentration in amorphous silica‐aluminas (ASAs) on the flame‐retardant properties and the thermal stability of intumescent polypropylene (PP) composites. ASAs with different concentrations of alumina and acidic sites were synthesized by surface alumina deposition and coprecipitation methods. The polymeric composites had their flame‐retardant properties evaluated by limiting oxygen index (LOI) and UL‐94. The thermal stability was analyzed by thermogravimetric analysis (TGA). The ASAs had their textural properties evaluated by nitrogen physisorption, their chemical composition by X‐ray fluorescence (XRF) and their acidity by temperature‐programmed ammonia desorption (TPD‐NH ₃ ). The results show that the presence of ASA, regardless of the synthesis method, increased the thermal stability of the composites. Besides, the presence of acidic sites favors the flame‐retardant properties of the intumescent composites, leading to LOI values of 29% and 30%, as well as a V‐0 classification in UL‐94 test. Moreover, after reaching this LOI value threshold, the increase in the acidity of these silica‐aluminas did not promote further increase in the flame‐retardant properties.

Hierarchical ZSM-5 zeolites were prepared by alkali treatment (desilication) at two temperatures, two reaction times, and two NaOH concentrations. A 23 factorial design was used to study the effect of these variables on the crystallinity, microporosity, and mesoporosity of the zeolite due to the desilication treatment. The factorial design analysis showed that the temperature, reaction time and NaOH concentration and the second order interaction between temperature and time have statistically significant effect on the micropore volume. On mesopore volumes (Vmeso) and areas (Smeso), the reaction time and NaOH concentration factors have statistically significant effects. In the case of mesopore volumes, the second order reaction time and NaOH concentration interaction factor are also significant. On the other hand, only the alkali concentration affected, negatively, the relative crystallinity. Two hierarchical ZSM-5 zeolites with the highest relative crystallinity and mesoporosity were selected and further characterized by inductively coupled plasma (ICP) analysis, 29Si nuclear magnetic resonance (NMR), 27Al NMR, Fourier transform infrared (FTIR) spectroscopy in the OH stretch region and pyridine adsorbed FTIR spectroscopy. NMR and FTIR results showed that the alkali treatment selectively removed silica from the zeolite framework, decreasing the SAR (silica-to-alumina ratio) values, while decreasing Brønsted acid site concentrations and increasing Lewis acid sites concentrations.

Several studies show a synergistic effect between intumescent formulations and aluminosilicates, such as zeolites and clays, but little is known about the effect of acidity of these additives on the synergistic action. In this work, H-ZSM-5 zeolite was submitted to desilication treatments for 30 min and for 2 h, and silicalite-1 was synthesized. The objective was to obtain samples of equivalent crystalline structure, but with different amounts of acid sites, in order to evaluate the effect of acid concentration of H-ZSM-5 zeolites on the synergistic action with an intumescent formulation composed by ammonium polyphosphate and pentaerythritol in polypropylene. H-ZSM-5 zeolites and silicalite were characterized by X-ray diffraction, nitrogen adsorption analysis and temperature-programmed desorption of ammonia. The desilication produced H-ZSM-5 zeolites with similar volumes of mesopores in both treatments, but the zeolite resulting from 2 h of desilication presented a higher concentration of acid sites than the zeolite from 30 min. The flame-retardant properties were evaluated by UL-94 classification, limiting oxygen index, glow-wire, thermogravimetric analysis and heating microscopy. The results showed that increasing the concentration and accessibility of the acid sites of H-ZSM-5 zeolites the flame-retardant properties of the studied composites improved. It is suggested that the increase of acid site concentration positively influences the catalysis of the reaction between ammonium polyphosphate and pentaerythritol, favoring the production of the precursors of the intumescent layer.

Hydrotreating catalysts were prepared from CoMgMoAl layered double hydroxides (LDHs) with different Co and Mo contents. Sulphides were characterised by techniques such as X-ray absorption near edge structure spectroscopy, CO adsorption followed by infrared spectroscopy, X-ray diffraction and nitrogen physisorption. The prepared catalysts were tested in the selective hydrotreating of a model feed (thiophene, cyclohexene and n-heptane) under 573 K and 20 bar of H₂, covering a wide range of space velocities (41–439 h⁻¹). All the LDH-derived CoMgMoAl sulphides showed larger selectivity for hydrodesulphurisation when compared to industrial catalysts. The characterisation results allowed a relationship between the nature and concentration of sulphide sites and their catalytic functionalities to be established.