Photocatalytic hydrogen production using mesoporous TiO2 doped with Pt

A series of mesoporous TiO2 (meso-TiO2) were synthesized using the sol-gel technique. A Pluronic F127 triblock-copolymer, a structure-directing agent, was incorporated as a soft template into the sol-gel. In addition, and during a separate synthesis, the sol-gel was doped with a Pt precursor. Semiconductors were prepared with 1.00 wt.%, 2.50 wt.%, 5.00 wt.% Pt nominal loadings, respectively. They were calcined at 500 ◦C and 550 ◦C following synthesis. Morphological and structural properties were studied by: a) X-ray diffraction, b) UV–vis spectrophotometry, c) N2 adsorption-desorption (BET, BJH), and d) X-ray photoelectron spectroscopy (XPS). Optical band gap values for meso-TiO2 and Pt-meso-TiO2 were cal- culated by Kubelka-Munk (K-M) function coupled with Tauc plot methodology. It was observed that the prepared semiconductors displayed pore sizes in the 10–40 nm range with bimodal distributions. Their photocatalytic activity forhydrogenproductionvia water splitting was established ina Photo-CRECWater- II reactor under near-UV light irradiation. The aqueous solution contained 2% v/v ethanol, employed as a renewable organic scavenger. The prepared semiconductors showed that the mesoporous 2.50 wt.% Pt-TiO2 has the highest photoactivity for hydrogen generation. This suggests the important role played by the loading of platinum as a TiO2 dopant, reducing the optical band gap, increasing electron storage and diminishing, as a result, electron-hole recombination. The measured Quantum Yield (QY), obtained using a rigorous approach, was established for the mesoporous 2.50 wt.% Pt-TiO2 at a promising level of 22.6%

Procesamiento hidrotermal solar de biomasa: operación de reactor y características de los productos

4 figures, 2 tables.[EN] The use of concentrated solar energy to provide heat in the hydrothermal liquefaction is an attractive method to transform biomass into valuable products reducing the environmental impact. However, the coupling of both technologies requires further research. This work analyses the effect of solar fluctuations on the yields, and main characteristics of products obtained in a solar reactor with direct heating method. Results indicate that by direct heating in a solar furnace, at sustained reaction temperatures of 250 ºC, produced a bio-oil and char yield up 24 and 33%, respectively. The results are consistent with conventional heating systems, however direct heating results in higher temperature gradients between the frontal and nonirradiated walls (above 200 ºC), which results in an unstable system, especially at high heating rates and temperatures above 300 ºC, therefore, at the end of this work a modified solar reactor was proposed.[ES] El uso de energía solar concentrada para suministrar calor en el procesamiento hidrotermal de biomasa representa una alternativa atractiva para la transformación de biomasa en productos valiosos con menor impacto ambiental. Sin embargo, el acoplamiento de ambas tecnologías requiere más investigación en el tema. Este trabajo analiza el efecto de las variaciones en la irradiancia solar en los rendimientos y composición de los productos. Los principales resultados muestran rendimientos en el bioaceite y carbón de hasta 24 y 33%, respectivamente. Adicionalmente, se encontró que el tiempo de residencia entre 30-60 min favorece la formación superficial de una estructura porosa en el carbón. Los resultados obtenidos son consistentes con los sistemas de calentamiento convencional, sin embargo, el calentamiento directo del reactor solar genera grandes gradientes térmicos entre la pared frontal y la pared no irradiada (arriba de 200 ºC), lo que resulta en un sistema inestable, especialmente con rampas de calentamiento rápidas y temperaturas arriba de 300 ºC, por lo tanto, al final de este trabajo se propone un reactor mejorado.Authors would like to acknowledge J.J. Quiñones- Aguilar for the design of the modified solar reactor, and the financial support received from Fondo Sectorial CONACYT-SENER-Sustentabilidad Energética through Grant 207450, “Centro Mexicano de Innovación en Energía Solar (CeMIE-Sol)”, within strategic project No. 120 “Tecnología solar para obtención de productos con valor agregado mediante procesamiento hidrotermal” and DGAPA-PAPIITUNAM Project number IN107923: Licuefacción hidrotérmica solar de biomasa residual.Peer reviewe

Efficiency Factors in Photocatalytic Reactors: Quantum Yield and Photochemical Thermodynamic Efficiency Factor

Photocatalytic efficiency is evaluated using quantum yields (QYs) and the photo- chemical thermodynamic efficiency factor (PTEF). The PTEF allows establishing reactor efficiency as the ratio of utilized enthalpy for the formation of consumed OH. free radicals over the absorbed photon energy. A key consideration for the evaluation of efficiency factors is the establishment of macroscopic energy balan- ces together with an accurate assessment of evolved and absorbed photons. Of considerable help are the experimental devices developed at the Chemical Reactor Engineering Centre (CREC)/University of Western Ontario (UWO) laboratories. Photoconversion kinetics is required for calculation of the OH. consumption rates and establishment of the related kinetic parameters. PTEFs and QYs have been applied by CREC-UWO researchers for efficiency calculations in photocatalytic reactors for the decontamination of air, water, and hydrogen production

Experimental Evaluation and Modeling of Air Heating in a Ceramic Foam Volumetric Absorber by Effective Parameters

Reticulate porous ceramic reactors use foam-type absorbers in their operation which must fulfill two essential functions: favoring the volumetric effect and increasing the mass and heat transfer by acting as a support for the reactive materials. Heating these absorbers with highly inhomogeneous concentrate irradiation induces high thermal gradients that affect their thermal performance. Owing to the critical function of these component in the reactor, it is necessary to define a selection criterion for the foam-type absorbers. In this work, we performed an experimental and numerical thermal analysis of three partially stabilized zirconia (PSZ) foam-type absorbers with pore density of 10, 20, and 30 PPI (pores per inch) used as a volumetric absorber. A numerical model and an analytical approximation were developed to reproduce experimental results, and calculate the thermal conductivity, as well as volumetric heat transfer coefficient. The results show that an increase in pore density leads to an increase in the temperature difference between the irradiated face and the rear face of the absorber, this occurs because when pore density increases the concentrated energy no longer penetrates in the deepest space of the absorber and energy is absorbed in areas close to the surface; therefore, temperature gradients are created within the porous medium. The opposite effect occurs when the airflow rate increases; the temperature gradient between the irradiated face and the rear face is reduced. This behavior is more noticeable at low pore densities, but at high pore densities, the effect is less relevant because the internal structure of porous absorbers with high pore density is more complex, which offers obstructions or physical barriers to airflow and thermal barriers to heat transfer. When the steady state is reached, the temperature difference between the two faces of the absorber remains constant if the concentrate irradiation changes slightly, even changing the airflow rate. The results obtained in this work allow us to establish a selection criterion for porous absorbers that operate within solar reactors; this criterion is based on knowledge of the physical properties of the porous absorber, the environment, the working conditions, and the results expected

Effective radiation field model to scattering – Absorption applied in heterogeneous photocatalytic reactors

A new mathematical model for the calculation of the radiation field in heterogeneous photocatalytic reactors using the new concept of ‘‘effective radiation field model’’ or ERFM is proposed. In this concept, the incident radiation associated to the photons flow is an energy cloud. The generated space-phase and the properties of the cloud are considered isotropic and independent of the propagation angle and photon frequency. The isotropic nature of the ERFM concept provides a simple estimation of the radiation field of a catalyst in suspension (particles and fluid) for polychromatic radiation and the solar spectrum. The ERFM is an alternative model for the calculus of the radiant energy distribution in heterogeneous photocatalytic reactors as an extension of concept to the overall volumetric rate photon absorption – OVRPA. The local volumetric rate of photon absorption (LVRPA) predicted by the ERFM were compared with the Six Flux Model (SFM) and the rigorous solution using Discrete Ordinate Method (DOM) for the radiative transfer equation (RTE). The calculated LVRPA with the ERFM was found to be closer to the solution of the RTE-DOM. These results were attributed to the performance of the phase function in both models