Nanoparticulated WO3/NiWO4 Using Cellulose as a Template and Its Application as an Auxiliary Co-Catalyst to Pt for Ethanol and Glycerol Electro-Oxidation

This work reports the use of cellulose as a template to prepare nanosized WO3 or NiWO4 and its application as a co-catalyst in the electro-oxidation of ethanol and glycerol. Microcrystalline cellulose was hydrolyzed with phosphotungstic acid (H3PW12O40) to prepare the nanocrystalline cellulose template. The latter was air-calcinated to remove the template and obtain nanometric WO3. Tungsten oxide was impregnated with Ni(NO3)2, which was subsequently air-calcinated to obtain the nanometric NiWO4. Elemental analysis confirmed the coexistence of nickel and tungsten, whereas thermal analysis evidenced a high thermal stability for these materials. The X-ray diffractograms displayed crystal facets of WO3 and, when Ni(II) was added, NiWO4. The transmission electron micrographs corroborated the formation of nanosized particles with average particle sizes in the range of 30 to 50 nm. Finally, to apply this material, Pt/WO3-C and Pt/WO3-NiWO4-C were prepared and used in ethanol and glycerol electro-oxidation in an alkaline medium, observing a promotional effect of the oxide and tungstate by reducing the onset potential and increasing the current density. These materials show great potential to produce clean electricity or green hydrogen, contributing to energetic transition.

Towards a sustainable waste-to-energy pathway to pequi biomass residues: Biochar, syngas, and biodiesel analysis

The waste-to-energy (WTE) valorization pathway of Caryocar brasiliense (pequi) seeds was investigated via pyrolysis, gasification, and transesterification to understand its potential as biochar, syngas, and biodiesel. First, the pyrolysis (300-700 °C) was conducted in N₂ atmosphere for pequi seeds (PS) and pequi seeds without its extractives (PSWE), characterizing its biochar properties. The PSWE was then gasified at 1000 °C under O₂/N₂, O₂/CO₂/N₂ and O₂/H₂O/N₂ atmospheres to evaluate the characteristics of the producer gas. The PS extractives were then transesterified and characterized for biodiesel production. Finally, a multiple-criteria decision analysis assessed the PS products' potential within the thermochemical routes. The results evidenced better biochar (up to 22.29% HHV enhancement, higher mass and energy yield, up to 75.9 and 85.5% reduction of O/C and H/C, respectively, and enriched N content) via PSWE pyrolysis than PS considering biofuel application and optimistic perceptions for soil amendment. This indicates that the preceding extraction of vegetal fat from PS strengthens the WTE by including further processing of extracted oil. The produced syngas under O₂/H₂O/N₂ gasification atmosphere showed better applicability as a biofuel (16.37 MJ·kg^-1 lower heating value, 107.33% cold gas efficiency, and 113.55% carbon conversion efficiency) with up to 24% higher success rate. The transesterification of the extractives revealed its potential (98% conversion rate) for use as feedstock for in situ power generation, or blended for biodiesel production. The results provide insights into the circular economy in agro-extractivist communities that may support Brazil's small and medium agro-food industries with their energy demands.