Alexandre Barros Gaspar

Glycerol recovery processes, such as glycerol hydrogenolysis, are of industrial interest as they allow obtaining 1,2‐propanediol (1,2‐PDO), 1,3‐propanediol (1,3‐PDO), and ethylene glycol (EG), important chemicals intermediates. Ru‐ and Pd‐based catalysts were prepared on commercial Siral support (40% SiO ₂ – 60% Al ₂ O ₃ ) impregnated with phosphotungstic acid (HPW). The formation of WO ₃ was verified by thermal decomposition of HPW. The catalysts were active in the reaction, and the influence of the metal (Pd more active than Ru) and the precursor (chloride more active than nitrate) was verified. The greater activity of the monometallic RuSiralHPW catalyst (188 mmol Gly.h ⁻¹ .gPd ⁻¹ ) in relation to the bimetallic PdRuSiralHPW catalyst (165 mmol Gly h ⁻¹ gPd+Ru ⁻¹ ) or PdSiralHPW catalyst (152 mmol Gly h ⁻¹ gRu ⁻¹ ) was associated to the better Ru dispersion, observed by H ₂ ‐chem and TEM and higher Brønsted/Lewis acid ratio. The promoting effect of RuO ₂ reduction by Pd in the bimetallic sample did not influence the metallic dispersion by TEM or H ₂ ‐chem. Residual chlorine was responsible for the presence of acidic sites suitable for the formation of up to 16.5% of 1,3‐PDO in the RuSiralHPW catalyst in 3 h. Methanol was the main product of extensive hydrogenolysis.

One-step DME synthesis from CO2/H2 was investigated using physical mixtures composed of Hf-promoted CuZnO catalysts and zeolites. The two steps of this process namely, methanol synthesis from CO2/H2 and methanol dehydration to DME were also analyzed separately using Cu-Zn-Hf-based catalysts and zeolites, respectively. The Cu-based catalysts were characterized by XRD with Rietveld refinement, CO2-TPD, H2O dissociation, XRF, specific area measurements, N2O-RFC, DTA and DRIFTS, whereas the acidity of the zeolites was evaluated by NH3-TPD. Density Functional Theory (DFT) calculations were also performed. The addition of Hf to the CuZnO catalyst increases methanol and DME yields in both reactions up to an optimal loading of 4 at.%. This behavior is associated with an increase in the specific area and in the oxygen vacancies (Vo) concentration, both induced by substitution of Zn2+ by Hf4+ in the ZnO lattice. The metallic Cu surface area remains essentially unchanged for Hf < 7 at.%. DFT calculations indicate that Vo are spontaneously formed when Hf4+ substitutes Zn2+ in defective ZnO nanoparticles and on ZnO crystal surfaces. In contrast, higher Hf contents lead to the formation of HfO2, which blocks Vo, active sites, and pores, resulting in decreased methanol and DME yields. The reversibility of the methanol synthesis reaction during one-step DME synthesis from CO2/H2 promotes higher selectivity to methanol + DME and lower to CO, particularly when methanol synthesis sites are located in close proximity to methanol dehydration sites. Furthermore, the zeolite framework types and acidity of the dehydration catalysts are identified as relevant properties governing DME formation from methanol. Catalyst deactivation during one-step DME synthesis is mainly attributed to metallic Cu sintering promoted by H2O. Finally, the experimental results indicate that methanol formation is the rate-limiting step of one-step DME synthesis from CO2/H2. Although CO is not an intermediate in methanol or DME syntheses, at high residence times CO formed via the RWGS reaction may be re-adsorbed and converted into methanol and DME, allowing the system to approach thermodynamic equilibrium.

Mg(Al)O is a promising catalyst for the Guerbet synthesis, promoting high yields of 1-butanol at low temperature and short contact time. However, rapid catalyst deactivation is observed under reaction conditions. Combining in situ DRIFTS with XPS, XRD, and DTG analyses, two main deactivation pathways were identified. The first involves the interaction of acetaldehyde, a key reaction intermediate, with Mg(Al)O, leading to the formation of surface acetate species. The second is associated with hydrotalcite formation on the Mg(Al)O surface during the reaction. This process occurs through the reaction of water, a product of 1-butanol synthesis, with the mixed oxide due to the memory effect. Importantly, both deactivation modes are reversible, and an oxidation treatment restores the catalytic performance of Mg(Al)O for 1-butanol synthesis from ethanol.To the best of our knowledge, this is the first report associating Mg(Al)O deactivation with hydrotalcite formation employing ethanol as a reagent.

Glycerol is a sustainable raw material for synthesizing various chemicals, including glycerol carbonate. In this study, a series of Zn-Al-X (where X = La or Zr) mixed oxides derived from hydrotalcite-type precursors were investigated as heterogeneous catalysts for the production of glycerol carbonate via the transesterification reaction between glycerol (GLY) and dimethyl carbonate (DMC). The molar ratio Zn/Al in the catalysts was set at 2, while the content of the promoter (X/Al molar ratio) was set at either 0.02 or 0.3. Their physicochemical properties were characterized using inductively coupled plasma-optical emission spectrometry (ICP-OES), X-ray diffraction (XRD), N2adsorption-desorption at -196 °C, and temperature-programmed desorption of CO2 (TPD-CO2). Solvent-free catalytic tests were conducted at 100 °C with a DMC:GLY molar ratio of 3:1. The reaction conditions were adjusted to compare all catalysts at low glycerol conversion levels (XG < 20%). Glycerol carbonate (GLC) was the only product obtained (SGLC = 100%). The results showed higher yields when using mixed oxides containing stronger basic sites. XRD analysis of the catalyst post-reaction demonstrated that the Zn-Al mixed oxides were structurally stable under the reaction conditions, with no memory effect observed.

Lipases are recognized as the most important group of catalysts in biotechnology. However, utilization of free enzymes is often hampered by the need for more operational stability, high cost, and non-reusability. Most of these obstacles can be solved by lipase immobilization. This work's objective was to evaluate the performance of the activated carbon obtained from sugarcane straw (SAC) as a support for lipase immobilization. Two lipases were immobilized by physical adsorption on SAC: Aspergillus niger 11T53A14 lipase and CalB (lipase B from Candida antarctica, Novozymes). Results revealed that the lipase had been anchored on the activated carbon with the lipase binding efficiency of 89 % (A. niger lipase) and 100 % (CalB) at the optimum experimental conditions (initial protein concentration 0.1 mg mL-1, 0.15 g of SAC, 25 °C, and 120 min). Langmuir isotherm fitted the adsorption equilibrium data of the lipases on SAC. SAC presents a high surface area and protein adsorption capacity. These results show that activated carbon synthesized from the sugarcane straw is a promising support for enzyme immobilization.

Nanocomposites of magnetite anchored on reduced graphene oxide with different magnetite:reduced graphene oxide mass ratios were synthesized and evaluated in indigo carmine photo Fenton discoloration. All nanocomposites are magnetic and showed comparable amounts of magnetite and hematite with a higher level of hematite for low iron contents. The highest value of 63.6 emu g-1 was obtained for the nanocomposite with the highest magnetite content. The nanocomposites presented high dispersion of iron oxide particles, at about 12 nm on reduced graphene oxide surface sheets. The samples also showed bandgap energies below that found for bulk magnetite, showing an important effect of reduced graphene oxide. The nanocomposite with an iron nitrate precursors mass ratio of 17:1 showed the best performance (99.7% of indigo carmine discoloration (2.1 × 10-5 mol L-1) at 30 min of reaction, hydrogen peroxide(2.3 × 10-1 mol L-1), and a catalyst dosage of 0.67 g L-1). Reusability tests were performed, and this nanocomposite was shown to be active for at least three recycles. X-ray photoelectron spectrum of Fe2p3/2 showed that the FeIII/FeII ratio was maintained even after three recycles (4 runs), meaning that reduced graphene oxide is responsible for stabilizing magnetite particles, thus maintaining its photocatalytic activity.