Estevam Vitorio Spinace

Schematic representation of the vinasse photoreforming for hydrogen production using Pt/TiO ₂ as catalyst under UV irradiation.

Vinasse, a dark-colored aqueous byproduct of bioethanol production, contains a variety of organic compounds and inorganic salt ions. In this study, vinasse was utilized as a sacrificial agent in the water splitting reaction using Pt/TiO₂ as a photocatalyst under UV irradiation. The gaseous products generated were analyzed, revealing the formation of hydrogen (H₂) along with other gases, including CO₂, CH₄, CO, C₂H₆, C₂H₄, C₃H₈, and C₄H₁₀. When using filtered vinasse as the sacrificial agent, H₂ and other gaseous products were produced solely through photolysis, even in the presence of the Pt/TiO₂ photocatalyst. Notably, H₂ production from the water splitting reaction was enhanced when inorganic salt ions were removed from the vinasse, and a lower concentration of vinasse was employed in the reaction medium.

Boosting ethane and hydrogen generation combining photocatalytic methane conversion and water splitting employing TiO₂/WO₃/Pt-based photocatalysts.

Au/Ga ₂ O ₃ photocatalysts prepared by 3 methods showed to be highly active for CH ₄ conversion and H ₂ production using UV light under mild conditions.

Here, Pd nanoparticles supported on ZnO were prepared by the alcohol-reduction and the borohydride-reduction methods, and their efficiency towards the photocatalytic conversion of methane under mild conditions were evaluated. The resulting Pd/ZnO photocatalysts were characterized by X-ray fluorescence, X-ray diffraction, X-ray photoelectron spectroscopy, UV–Vis, and transmission electron microscopy. The reactions were performed with the photocatalysts dispersed in water in a bubbling stream of methane under UV-light illumination. The products formed were identified and quantified by gas chromatography (GC-FID/TCD/MSD). The principal products formed were C₂H₆ and CO₂ with minor quantities of C₂H₄ and CO. No H₂ production was observed. The preparation methods influenced the size and dispersion of Pd nanoparticles on the ZnO, affecting the performance of the photocatalysts. The best performance was observed for the photocatalyst prepared by borohydride reduction with 0.5 wt% of Pd, reaching a C₂H₆ production rate of 686 µmol·h⁻¹·g⁻¹ and a C₂H₆ selectivity of 46%.

The processes currently used in the chemical industry for methane conversion into fuels and chemicals operate under extreme conditions like high temperatures and pressures. In this sense, the search for methane conversion under mild conditions remains a great challenge. This review aims to summarize the use semiconductors and metal-semiconductors as heterogeneous photocatalysts for methane conversion under mild conditions into valuable products. First, a brief presentation of photochemical conversion of methane is provided and then the focus of this review on the use of heterogeneous photocatalysts for methane conversion are described. Finally, the main challenges and opportunities are discussed.

Síntese e caracterização de híbridos PtRu/Carbono com diferentes cargas metálicas pelo método da carbonização hidrotérmica

RESUMO Neste trabalho, híbridos Ni/Carbono foram preparados em duas etapas (carbonização hidrotérmica e tratamento térmico a 900 °C sob argônio) a partir de diferentes fontes de carbono: glicose, amido e celulose. Eletrocatalisadores PtRu/C foram preparados pelo método da redução por álcool utilizando os híbridos como suportes. Os materiais foram caracterizados por espectroscopia por energia dispersiva de raios-X (EDX), análise termogravimétrica (TGA), espectroscopia no infravermelho com transformada de Fourier (FTIR), isotermas de B.E.T., difração de raios-X (DRX), microscopia eletrônica de transmissão (TEM) e voltametria cíclica em meio ácido. A eletro-oxidação do metanol foi estudada por cronoamperometria. O eletrocatalisador PtRu/C preparado utilizando o híbrido sintetizado a partir da celulose apresentou uma eletroatividade levemente superior aos demais materiais obtidos.

Au/TiO2 (1wt% Au), Cu/TiO2 (1wt% Cu) and AuCu/TiO2 (1wt% AuCu) catalysts with different Au:Cu mass ratios were prepared in one-step synthesis using sodium borohydride as reducing agent. The resulting catalysts were characterized by X-ray diffraction (XRD), X-ray Dispersive Energy (EDX), Transmission Electron Microscopy (TEM) and Temperature Programmed Reduction (TPR) and tested for the preferential oxidation of carbon monoxide (CO-PROX reaction) in H2-rich gases. EDS analysis showed that the Au contents are close to the nominal values whereas for Cu these values are always lower. X-ray diffractograms showed only the peaks of TiO2 phase; no peaks of metallic Au and Cu species or oxides phases were observed. TPR and high-resolution TEM analysis showed that AuCu/TiO2 catalysts exhibited most of Au in the metallic form with particles sizes in the range of 3-5 nm and that Cu was found in the form of oxide in close contact with the Au nanoparticles and well spread over the TiO2 surface. The AuCu/TiO2 catalysts exhibited good performance in the range of 75-100 °C and presented a better catalytic activity when compared to the monometallic ones. A maximum CO conversion of 98.4% with a CO2 selectivity of 47% was obtained for Au0.50Cu0.50/TiO2 catalyst at 100oC.