Development of new materials for hydrogen generation and wastewater treatment by photcatalysis

Aquesta tesi consisteix en el desenvolupament de nous materials per a la generació d'hidrogen i el tractament d'aigües residuals. Per tant, en aquesta tesi s'han estudiat principalment catalitzadors basats en pal•ladi, diòxid de titani i triòxid de tungstè (Pd / TiO2 (-WO3)), però també s'han estudiat catalitzadors basats en platí, diòxid de titani i triòxid de tungstè (( Pt / TiO2 (-WO3)), així com també s'ha realitzat un petit estudi sobre catalitzadors del pal•ladi, P25 (diòxid de titani comercial) i coure (Pd / TiO2-Cu). La generació d'hidrogen és duta a terme a partir de mescles aigua-metanol (o glicerol en alguns casos) i també a partir d'algunes aigües residuals. La fotodeposició deL pal•ladi va ser estudiada i es va trobar que l'evolució d'hidrogen està importantment influenciada per les condicions de fotodeposició del metall sobre qualsevol dels tres suports catalítics estudiats: NT-WO3 (NT: nanotubs de diòxid de titani), P25-WO3 i P25. Algunes de les condicions de fotodeposició estudiades van ser la concentració de catalitzador (1000-4000 ppm) i la concentració de metanol (0 - 20 vol.%), quantitat de metall (0.1 - 2 wt.%) i la naturalesa del metall (pal•ladi i platí) en la solució de fotodeposició. Els catalitzadors que contenien 0.25 wt.% de metall (ja sigui platí o pal•ladi), van presentar les més altes evolucions d'hidrogen.Esta tesis consiste en el desarrollo de nuevos materiales para la generación de hidrógeno y el tratamiento de aguas residuales. Por lo tanto, en esta tesis son estudiados principalmente catalizadores basados en paladio, dióxido de titanio y trioxido de tungsteno (Pd/TiO2(-WO3)), pero tambiés son estudiados catalizadores basados en platino, dióxido de titanio y trióxido de tungsteno ((Pt/TiO2(-WO3)), así como también un corto estudio es realizado sobre catalizadores de paladio, P25 (dióxido de titanio comercial) y cobre (Pd/TiO2-Cu). La generación de hidrógeno es llevada a cabo a partir de mezclas agua-metanol (o glicerol en algunos casos) y también a partir de algunas aguas residuales. La fotodeposición de paladio fue estudiada y se encontró que la evolución de hidrógeno está importantemente influenciada por las condiciones de fotodeposición del metal sobre cualquiera de los tres soportes catalíticos estudiados: NT-WO3 (NT: nanotubos de dióxido de titanio), P25-WO3 y P25. Algunas de las condiciones de fotodeposición estudiadas fueron la concentración de catalizador (1000 - 4000 ppm) y la concentración de metanol (0 - 20 vol.%), cantidad de metal (0.1 - wt.%) y la naturaleza del metal (paladio y platino) en la solución de fotodeposición.This thesis consists on the development of new materials for hydrogen generation and wastewater treatment by photocatalysis. Therefore, in this thesis are mainly studied catalysts based on palladium, titanium dioxide and tungsten trioxide (Pd/TiO2(-WO3)), but are also studied catalysts based on platinum, titanium dioxide and tungsten trioxide (Pt/TiO2(-WO3)), as well as a short study is performed on catalysts based on palladium, P25 (commercial titanium dioxide) and cupper (Pd/P25-Cu). The hydrogen generation is carried out from water-methanol (or glycerol in some cases) mixtures and from some municipal wastewater. The palladium photodeposition was studied and it was found that the hydrogen evolution is quite influenced by the metal photodeposition conditions on any of the three catalytic supports studied: NT-WO3 (NT: nanotubes of titanium dioxide), P25-WO3 and P25. Some of the photodeposition conditions studied were the catalyst concentration (1000 - 4000 ppm) and methanol concentrations (0 - 20 vol.%), metal amount (0.1 - 2 wt.%) and metal nature (palladium and platinum) in the photodeposition solution

Pd/TiO2-WO3 photocatalysts for hydrogen generation from water-methanol mixtures

Solar light is inexhaustible, and therefore to take advantage of this energy it is necessary to develop materials capable of absorbing energy in the widest range of the solar spectra. Although TiO2 is one of the most studied photocatalysts, it only absorbs in the UV range. With the aim of increasing this light absorption towards the visible range, in this study Pd and WO3 were supported on bare TiO2 to determine their photocatalytic properties for generating hydrogen from water-methanol mixtures under UVA and solar irradiation. Several parameters for the hydrogen production, such as the amount of Pd and the catalyst as well as the influence of the water matrix were studied. These catalytic materials were characterized by means of inductively coupled plasma with an optical emission spectrophotometer, nitrogen adsorption-desorption isotherms, X-ray diffraction, high resolution – transmission electron microscopy, X-ray photoelectron spectroscopy and diffuse reflectance UV–Vis spectroscopy. The hydrogen evolution was monitored by online gas chromatography. The incorporation of a small amount of Pd (lower than 0.01¿wt%) produced a large increase in the hydrogen production. Furthermore, adding WO3 on the bare titania also increased hydrogen generation. The highest quantum efficiency obtained in this work under solar radiation was 7.7% by the catalyst based on palladium supported on nanotubes of titanium dioxide and tungsten trioxide (Pd/NT-WO3) using an aqueous solution of methanol (50vol%).Peer ReviewedPostprint (author's final draft

Photocatalytic hydrogen production from water-methanol and -glycerol mixtures using Pd/TiO2(-WO3) catalysts and validation in a solar pilot plant

This paper is focused on the photocatalytic hydrogen production on Pd/TiO2(-WO3) catalysts from water-methanol and water-glycerol mixtures under UVA and solar irradiation. The photodeposition method for Pd was studied varying conditions such as Pd amount, catalyst concentration and methanol concentration. The catalysts were tested at lab scale under simulated solar light and UVA radiation and also at large scale (25 L) under solar energy using a pilot-scale solar Compound Parabolic Collector (CPC). The catalysts characterization was performed by means of ICP-OES, N2 adsorption–desorption isotherms, XRD, HR-TEM, XPS and DR–UV–Vis spectroscopy. Hydrogen evolution was monitored by on-line gas chromatography.From results it was found the Pd photodeposition method plays a key role to increase the hydrogen evolution, affecting parameters like the Pd amount deposited, the Pd nanoparticles size and dispersion. The highest quantum efficiency (¿) obtained in this study was 11.8% and 41.2% under simulated solar and UVA irradiation, respectively, using Pd(0.24 wt%)/P25 in an aqueous solution of methanol (50 vol%). In the pilot-scale solar CPC, for Pd(0.24 wt%)//P25 catalysts in 5 vol% of methanol or glycerol as sacrificial agents, the quantum yield were 2.1 and 2.2%, respectively. When the concentration of the sacrificial agents decreased to 0.37 vol%, the quantum yields were 1.3 and 2.4% for methanol and glycerol, respectively. Compared to literature, the low noble metal content of these catalysts (0.25 wt%) seems to be a competitive factor considering their high price.Peer ReviewedPostprint (author's final draft

Pd/TiO2-WO3 photocatalysts for hydrogen generation from water-methanol mixtures

Solar light is inexhaustible, and therefore to take advantage of this energy it is necessary to develop materials capable of absorbing energy in the widest range of the solar spectra. Although TiO2 is one of the most studied photocatalysts, it only absorbs in the UV range. With the aim of increasing this light absorption towards the visible range, in this study Pd and WO3 were supported on bare TiO2 to determine their photocatalytic properties for generating hydrogen from water-methanol mixtures under UVA and solar irradiation. Several parameters for the hydrogen production, such as the amount of Pd and the catalyst as well as the influence of the water matrix were studied. These catalytic materials were characterized by means of inductively coupled plasma with an optical emission spectrophotometer, nitrogen adsorption-desorption isotherms, X-ray diffraction, high resolution – transmission electron microscopy, X-ray photoelectron spectroscopy and diffuse reflectance UV–Vis spectroscopy. The hydrogen evolution was monitored by online gas chromatography. The incorporation of a small amount of Pd (lower than 0.01¿wt%) produced a large increase in the hydrogen production. Furthermore, adding WO3 on the bare titania also increased hydrogen generation. The highest quantum efficiency obtained in this work under solar radiation was 7.7% by the catalyst based on palladium supported on nanotubes of titanium dioxide and tungsten trioxide (Pd/NT-WO3) using an aqueous solution of methanol (50vol%).Peer Reviewe