JORGE MOREIRA VAZ
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Artigo IPEN-doc 30352 Methane conversion and hydrogen production over TiO2/WO3/Pt heterojunction photocatalysts2024 - CARMINATI, SAULO A.; JANUARIO, ELAINE R.; MACHADO, ARTHUR P.; SILVAINO, PATRICIA F.; VAZ, JORGE M.; SPINACE, ESTEVAM V.Along with the advantages of mild reaction conditions, simple operation, and low energy consumption, the photocatalytic conversion of methane in the presence of water presents great potential in facilitating direct methane conversion into value-added chemicals and H-2 generation. In this work, TiO2/WO3 heterojunction photocatalysts modified with Pt nanoparticles were synthesized and their performances towards methane conversion into ethane (C2H6) and hydrogen (H-2) in the presence of water were evaluated. The ternary photocatalysts were characterized by X-ray diffraction, UV-vis, scanning and transmission electron microscopy and X-ray photoelectron spectroscopy. The highly active TiO2/WO3/Pt photocatalyst achieved C2H6 and H-2 production rates of 1.18 mmol g(-1) h(-1) and 57 mmol g(-1) h(-1), respectively. These values were 37% (for C2H6) and 34% (for H-2) higher than those produced by a TiO2/Pt photocatalyst. The results show that the presence of WO3 in a very small concentration on TiO2 with the introduction of Pt as a co-catalyst contributes to achieving higher activities towards both C2H6 and H-2 evolution.Artigo IPEN-doc 30182 Methane conversion coupled with hydrogen production from water using Au/Ga2O3 photocatalysts prepared by different methods2023 - JANUARIO, ELAINE R.; CARMINATI, SAULO A.; TOFANELLO, ARYANE; SILVA, BRUNO L. da; SILVAINO, PATRICIA F.; MACHADO, ARTHUR P.; VAZ, JORGE M.; SPINACE, ESTEVAM V.Au/Ga2O3 photocatalysts were prepared by three different methods (pre-formed Au nanoparticles, borohydride reduction, and impregnation-H2 reduction) and tested as photocatalysts for methane conversion coupled with hydrogen production from water. The photocatalysts were characterized by Xray fluorescence, X-ray diffraction, UV-vis, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, and PL spectroscopy. The reactions were performed with the photocatalysts dispersed in water in a bubbling methane stream under UV-light illumination. The products were identified and quantified by gas chromatography (GC-FID/TCD/MSD). The main products formed were H2, C2H6, CO, and CO2 with minor quantities of C2H4, C3H8, and C4H10. The best performances were observed for the photocatalysts prepared with the nominal Au content of 0.1 wt% regardless of the method used. A production rate of about 100 mmol g−1 h−1 for C2H6 and 15 000 mmol g−1 h−1 for H2 was obtained. The Au content, nanoparticle sizes and interactions with Ga2O3 strongly influenced the photocatalytic activity.Artigo IPEN-doc 29618 Photocatalytic methane conversion over Pd/ZnO photocatalysts under mild conditions2023 - MACHADO, ARTHUR P.; CARMINATI, SAULO A.; JANUARIO, ELIANE R.; FERREIRA, PATRICIA S.; VAZ, JORGE M.; SPINACE, ESTEVAM V.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%.Resumo IPEN-doc 29570 Photocatalytic oxidation of methane coupling with hydrogen evolution from water over Au decorated Ga2O3 catalysts2022 - JANUARIO, ELIANE R.; VAZ, JORGE M.; SPINACE, ESTEVAM V.Methane is a major constituent of natural gases and is an important source of carbon and hydrogen for the chemical industry. However, CH4 is one of the most stable molecule and high reaction temperatures are required to transform CH4 into more valuable chemicals [1]. In this work, we investigated the use of β-Ga2O3 loaded with Au nanoparticles (0.1–1.0%) as photocatalysts that were prepared 3 different methods: pre-formed NNTS; in-situ; and H2 reduction. The materials were characterized by XRD, UV-Vis, TEM, and Raman. The reactions were performed on a photocatalytic reactor with Hg lamp (450W, UV/A/B/C). CH4 gas was bubbled into H2O, Au/Ga2O3 in suspension and the products were identified by GC-MS and quantified by GC-FID/TCD using calibration curves. C2H6, CO2, H2 with minor quantities of C2H4, C3H8, C4H10, and CO were produced. The best performance was observed for the photocatalyst prepared with 0.03% of Au that produced 112 mol.gcat-1h-1 of C2H6 and 16.500 mol.gcat-1h-1 of H2.Resumo IPEN-doc 29569 Photocatalytic coupling of methane over TiO2/WO3 heterojunction photocatalysts to enhance the production of ethane and hydrogen2022 - CARMINATI, S.A.; VAZ, J.M.; SPINACE, E.V.Resumo IPEN-doc 29568 Development of noble metals/TiO2 photocatalysts for photocatalytic conversion of methane coupling with hydrogen evolution from water2022 - SILVAINO, PATRICIA F.; SPINACE, ESTEVAM V.; VAZ, JORGE M.Methane, the main component of natural gas (< 80%), is an expressive source of carbon and hydrogen, with large world reserves and can be used as raw material to produce petrochemicals and fuels; however, efficient CH4 conversion under mild conditions remains a challenge due to its low reactivity. In addition, the methane conversion coupled with water splitting, which is the purpose of this work, is quite interesting and desirable, due to the production of hydrogen in a more sustainable way. One of the alternative ways to convert CH4 under low temperatures is Heterogeneous Photocatalysis, which will be used in the present study. When a semiconductor photocatalyst absorbs light with a wavelength greater than or equal to its bandgap, electrons are photoexcited to the conduction band and holes (h+) are formed in the valence band, forming the so-called electron-hole pairs, which in turn can initiate various redox reactions (Figure 1). Solar Photocatalysis would be an ideal method to convert methane and produce hydrogen from water. In this project, photocatalysts with different compositions and morphologies will be developed based on noble metals nanoparticles (Pt, Pd, Au, Ag) supported on TiO2 P25. The final goal is to obtain more active photocatalysts to increase the quantum efficiency of the system.Resumo IPEN-doc 29192 Au/Ga2O3 photocatalysts for methane conversion coupling with hydrogen evolution from water2022 - JANUARIO, ELIANE R.; VAZ, JORGE M.; SPINACE, ESTEVAM V.Methane is a major constituent of natural gases and is an important source of carbon and hydrogen for the chemical industry. However, methane is one of the most stable molecule and high reaction temperatures are required to transform methane into more valuable and useful chemicals [1]. The use of solar energy and a photocatalyst would be an ideal method to convert methane in milder conditions.[1] Recently, it was reported the direct combination of hydrogen evolution from water and the methane conversion in a photocatalytic system over Pt/TiO2.[2] In this study, we investigated the use of β-Ga2O3loaded with different amounts of Au nanoparticles (0.1–1.0%) as photocatalysts that were prepared by impregnation of HAuCl4 solution onto a commercial β-Ga2O3 and reduction at 200 °C under hydrogen flow. The photocatalysts were characterized by X-ray diffraction (XRD), UV-Vis spectroscopy, Transmission Electron Microscopy (TEM), and Raman Spectroscopy. The photocatalytic reactions were performed on a commercial Ace photocatalytic reactor equipped with a mercury lamp (450W, UV/A/B/C). A steady stream of methane gas was bubbled into water containing the photocatalyst in suspension and the products were identified by GC-MS and quantified by GC-FID/TCD using calibration curves. The principal products formed were C2H6, CO2, and H2 with minor quantities of C2H4, C3H8, C4H10, and CO. The best performance was observed for the photocatalyst prepared with 0.1% of Au that produced 129 μmol.gcat -1h-1of C2H6 and 10,062 μmol.gcat -1h-1of H2.Artigo IPEN-doc 28346 Methane Conversion Under Mild Conditions Using Semiconductors and Metal-Semiconductors as Heterogeneous Photocatalysts2021 - JANUARIO, ELIANE R.; SILVAINO, PATRICIA F.; MACHADO, ARTHUR P.; VAZ, JORGE M.; SPINACE, ESTEVAM V.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.Artigo IPEN-doc 27899 AuCu/TiO2 catalysts prepared using electron beam irradiation for the preferential oxidation of carbon monoxide in hydrogen-rich mixtures2021 - ALENCAR, C.S.L.; PAIVA, A.R.N.; SILVA, L.G.A.; SOMESSARI, E.S.R.; VAZ, J.M.; SPINACE, E.V.The major part of the world production of hydrogen (H2) is originated from a combination of methane steam reforming and water gas shift reaction resulting in an H2 rich mixture known as reformate gas, which contains about 1% vol (10,000 ppm) of carbon monoxide (CO). The preferential oxidation reaction of CO in H2 rich mixtures (CO PROX) has been considered a very promising process for H2 purification, reducing CO for values below 50 ppm allowing its use in PEMFC Fuel Cells. Au nanoparticles supported on TiO2 (Au/TiO2) catalysts have been shown good activity and selectivity for CO PROX reaction in the temperature range between 20 80 ºC; however, the catalytic activity strongly depends on the preparation method. Also, the addition of Cu to the Au/TiO2 catalyst could increase the activity and selectivity for CO PROX reaction. In this work, AuCu/TiO2 catalysts with composition 0.5%Au0.5%Cu/TiO2 were prepared in a single step using electron beam irradiation, where the Au3+ and Cu2+ ions were dissolved in water/2 propanol solution, the TiO2 support was dispersed and the obtained mixture was irradiated under stirring at room temperature using different dose rates (8 64 kGy s 1) and total doses (144 576 kGy). The catalysts were characterized by energy dispersive X ray analysis, X ray diffraction transmission electron microscopy, temperature programmed reduction and tested for CO PROX reaction. The best result was obtained with a catalyst prepared with a dose rate of 64 kGy s 1 and a total dose of 576 kGy showed a CO conversion of 45% and a CO2 selectivity of 30% at 150 ºC.Artigo IPEN-doc 27791 One-Step synthesis of PtFe/CeO2 catalyst for the Co-Preferential oxidation reaction at low temperatures2021 - ANTONIASSI, RODOLFO M.; MACHADO, ARTHUR P.; PAIVA, ANA R.N.; QUEIROZ, CARLA M.S.; VAZ, JORGE M.; SPINACE, ESTEVAM V.; SILVA, JULIO C.M.; CARMINE, EDUARDO; CAMARGO, PEDRO H.C.; TORRESI, ROBERTO M.Active Pt-based catalysts at low temperature towards the preferential oxidation of carbon monoxide in hydrogen-rich stream reaction (CO-PROX) are of great importance for H2-fueled fuel cells, but still remain a challenge. Herein, we propose a simple approach to synthesize a highly active Pt20Fe/CeO2 catalyst employing the borohydride reduction process. Transmission electronic microscopy revealed monodispersed 2.8 nm-Pt nanoparticles on CeO2, and the role of Fe species on the activity is discussed. The excellent CO conversion of 99.6% and CO2 selectivity of 92.3% carried out at ambient temperature meet the CO-PROX requirements for an adequate supply of hydrogen in fuel cell device.