Open Access
Three-dimensional printing of acrylonitrile butadiene styrene microreactors for photocatalytic applications
(American Chemical Society, 2020) Cabrera Barrios, Aarón; Pellejero, Ismael; Oroz Mateo, Tamara; Salazar, Cristina; Navajas León, Alberto; Fernandez Acevedo, Claudio; Gandía Pascual, Luis; Institute for Advanced Materials and Mathematics - INAMAT2; Gobierno de Navarra / Nafarroako Gobernua, PC003-004; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Miniaturization is a key aspect for many technological applications and the use of microreactors is an excellent solution for the intensification of chemical processes for a variety of applications. However, standard microfabrication requires large facilities and intricate fabrication protocols, and consequently it is not easily available, generally resulting in high production costs. Herein, we present a very cheap, fast and easy microreactor design for photocatalytic applications based on direct fused filament 3D printing as a facilitating and widespread technology. The microreactor consists of three bodies directly printed in ABS (Acrylonitrile Butadiene Styrene): a main body with a serpentine microchannel pattern where the photocatalyst is placed, a top holder with a transparent polymer window, and a base to clamp the parts. Several microreactor units were coated with TiO2 doped with Cu (2.4 wt.%) nanoparticles synthesized by FSP (Flame Spray Pyrolysis) and tested for the photocatalytic degradation of two water pollutants showing excellent performance.
Open Access
UiO-66 MOF-Derived Ru@ZrO2 catalysts for photo-thermal CO2 hydrogenation
(MDPI, 2023) Almazán, Fernando; Lafuente Adiego, Marta; Echarte Villeras, Amaya; Imizcoz Aramburu, Mikel; Pellejero, Ismael; Gandía Pascual, Luis; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The use of metal–organic frameworks (MOFs) as templates or precursors in the manufacture of heterogeneous catalysts is highly attractive due to the transfer of MOFs’ inherent porosity and homogeneous metallic distribution to the derived structure. Herein, we report on the preparation of MOF-derived Ru@ZrO2 catalysts by controlled thermal treatment of zirconium-based MOF UiO66 with ruthenium moieties. Ru3+ (3 or 10 mol%) precursor was added to UiO-66 synthesis and, subsequently, the as-synthesized hybrid structure was calcined in flowing air at different temperatures (400–600 ◦C) to obtain ZrO2 -derived oxides doped with highly dispersed Ru metallic clusters. The materials were tested for the catalytic photo-thermal conversion of CO2 to CH4 . Methanation experiments were conducted in a continuous flow (feed flow rate of 5 sccm and 1:4 CO2 to H2 molar ratio) reactor at temperatures from 80 to 300 ◦C. Ru0.10@ZrO2 catalyst calcined at 600 ◦C was able to hydrogenate CO2 to CH4 with production rates up to 65 mmolCH4·gcat. –1 ·h –1, CH4 yield of 80% and nearly 100% selectivity at 300 ◦C. The effect of the illumination was investigated with this catalyst using a high-power visible LED. A CO2 conversion enhancement from 18% to 38% was measured when 24 sun of visible LED radiation was applied, mainly due to the increase in the temperature as a result of the efficient absorption of the radiation received. MOF-derived Ru@ZrO2 catalysts have resulted to be noticeably active materials for the photo-thermal hydrogenation of CO2 for the purpose of the production of carbon-neutral methane. A remarkable effect of the ZrO2 crystalline phase on the CH4 selectivity has been found, with monoclinic zirconia being much more selective to CH4 than its cubic allotrope.
Open Access
Effect of oxygen addition, reaction temperature and thermal treatments on syngas production from biogas combined reforming using Rh/alumina catalysts
(Elsevier, 2019) Navarro Puyuelo, Andrea; Reyero Zaragoza, Inés; Moral Larrasoaña, Ainara; Bimbela Serrano, Fernando; Bañares, Miguel A.; Gandía Pascual, Luis; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
Dry reforming and partial oxidation of biogas were studied using 0.5 wt.% Rh/Al2O3 catalysts, both inhouse prepared and commercial. The effects of O2 addition on syngas yield and biogas conversion were studied at 700 C using different O2/CH4 ratios in the gas feeding stream: 0 (dry reforming), 0.12, 0.25, 0.45 and 0.50. The highest CH4 conversion, H2 yield and H2/CO molar ratio were obtained with an O2/CH4 ratio of 0.45, even though simultaneous valorization of both CH4 and CO2 could be best attained when the O2/CH4 ratio was 0.12. Increased biogas conversions and syngas yields were obtained by increasing reaction temperatures between 650 and 750 C. A detrimental influence on catalytic activity could be observed when the catalyst was subjected to calcination. Increasing the hold time of the thermal conditioning of the catalyst under inert flow altered Rh dispersion, though had no significant impact on catalyst performance in the dry reforming of methane at 700 C and 150 N L CH4/(gcat h). Characterization of spent samples after reaction by Raman spectroscopy revealed the presence of carbonaceous deposits of different nature, especially on the commercial(named as Rh com) and calcined (Rh calc) catalysts, though oxygen addition in the biogas feed significantly reduced the amount of these deposits. The Rh catalysts that had not been calcined after impregnation (Rh prep) did not present any noticeable characteristic peaks in the G and D bands. In particular, scanning transmission electron microscopy (STEM) images of the spent Rh prep sample revealed the presence of very highly dispersed Rh nanoparticles after reaction, of particle sizes of about 1 nm, and no noticeable C deposits. Combined oxy-CO2 reforming of biogas using highly dispersed and low metal-loading Rh/Al2O3 catalysts with low O2 dosage in the reactor feed can be used to effectively transform biogas into syngas.
Open Access
Oxidative steam reforming of glycerol. A review
(Elsevier, 2021) Moreira, Rui; Bimbela Serrano, Fernando; Gandía Pascual, Luis; Ferreira, Abel; Sánchez, José Luis; Portugal, Antonio; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
This review article presents the state-of-the-art on the catalytic oxidative steam reforming (OSR) of glycerol to produce syngas. Concerning the different technologies proposed for the catalytic OSR of glycerol, the following key points can be highlighted: (1) the robustness is much higher than other reforming technologies, (2) several catalysts can work with low deactivation, some of which can recover almost full activity by suitable regeneration, (3) syngas production by catalytic OSR of glycerin is higher than with concurrent technologies, (4) their scaling-up remains an unrealized task, (5) the thermodynamics of the process has been sufficiently covered in the literature, (6) there is a significant lack of kinetic and mechanistic studies that could help gaining deeper insight on the process, (7) novel concepts and reactor designs must be proposed for their development at larger scales, (8) new catalyst formulations must be developed for attaining higher resistance against oxidation and (9) process intensification could help developing them at larger scales.
Open Access
Comparative performance of coke oven gas, hydrogen and methane in a spark ignition engine
(Elsevier, 2020) Ortiz Imedio, Rafael; Ortiz, A.; Urroz Unzueta, José Carlos; Diéguez Elizondo, Pedro; Gorri, D.; Gandía Pascual, Luis; Ortiz, I.; Ingeniaritza; Institute for Advanced Materials and Mathematics - INAMAT2; Ingeniería
In this study, coke oven gas (COG), a by-product of coke manufacture with a high volumetric percentage of H2 and CH4, has been identified as auxiliary support and promising energy source in stationary internal combustion engines. Engine performance (power and thermal efficiency) and emissions (NOx, CO, CO2 and unburned hydrocarbons) of COG, pure H2 and pure CH4 have been studied on a Volkswagen Polo 1.4 L port-fuel injection spark ignition engine. Experiments have been done at optimal spark advance and wide open throttle, at different speeds (2000–5000 rpm) and various air-fuel ratios (λ) between 1 and 2. The obtained data revealed that COG combines the advantages of pure H2 and pure CH4, widening the λ range of operation from 1 to 2, with very good performance and emissions results comparable to pure gases. Furthermore, it should be highlighted that this approach facilitates the recovery of an industrial waste gas.
Open Access
Innovative flow-through reaction system for the sustainable production of phenolic monomers from lignocellulose catalyzed by supported Mo2C
(Wiley, 2024) Maisterra Udi, Maitane; Atienza Martínez, María; Hablich Alvarracin, Karina Lissett; Moreira, Rui; Martínez Merino, Víctor; Gandía Pascual, Luis; Cornejo Ibergallartu, Alfonso; Bimbela Serrano, Fernando; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra - Nafarroako Unibertsitate Publikoa
Molybdenum carbide supported on activated carbon (β-Mo2C/AC) has been tested as catalyst in the reductive catalytic fractionation (RCF) of lignocellulosic biomass both in batch and in Flow-Through (FT) reaction systems. High phenolic monomer yields (34 wt.%) and selectivity to monomers with reduced side alkyl chains (up to 80 wt.%) could be achieved in batch in the presence of hydrogen. FT-RCF were made with no hydrogen feed, thus via transfer hydrogenation from ethanol. Similar selectivity could be attained in FT-RCF using high catalyst/biomass ratios (0.6) and high molybdenum loading (35 wt.%) in the catalyst, although selectivity decreased with lower catalyst/biomass ratios or molybdenum contents. Regardless of these parameters, high delignification of the lignocellulosic biomass and similar monomer yields were observed in the FT mode (13-15 wt.%) while preserving the holocellulose fractions in the delignified pulp. FT-RCF system outperforms the batch reaction mode in the absence of hydrogen, both in terms of activity and selectivity to reduced monomers that is attributed to the two-step non-equilibrium processes and the removal of diffusional limitations that occur in the FT mode. Even though some molybdenum leaching was detected, the catalytic performance could be maintained with negligible loss of activity or selectivity for 15 consecutive runs.
Open Access
Gold supported on CuOₓ/CeO₂ catalyst for the purification of hydrogen by the CO preferential oxidation reaction (PROX)
(Elsevier, 2014) Arzamendi Manterola, Gurutze; Gandía Pascual, Luis; Química Aplicada; Kimika Aplikatua
Hydrogen produced from the conversion of hydrocarbons or alcohols contains variable amounts of CO that should be removed for some applications such as feeding low-temperature polymer electrolyte membrane fuel cells (PEMFCs). The CO preferential oxidation reaction (PROX) is particularly well-suited for hydrogen purification for portable and on-board applications. In this work, the synthesis and characterization by XRF, BET, XRD, Raman spectroscopy and H2-TPR of a gold catalyst supported on a coppercerium mixed oxide (AuCeCu) for the PROX reaction are presented. The comparison of this catalyst with the copper–cerium mixed oxide (CeCu) revealed that the experimental procedure used for the deposition of gold gave rise to the loss of reducible material by copper lixiviation. However, the AuCeCu solid was more active for CO oxidation at low temperature. A kinetic study has been carried over the AuCeCu catalyst for the PROX reaction and compared with that of the CeCu catalyst. The main difference between the models affected the contribution of the CO adsorption term. This fact may be related to the surface electronic activity produced by the interaction of the cationic species in the AuCeCu solid, able to create more active sites for the CO adsorption and activation in the presence of gold.
Open Access
Kinetic analysis and CFD simulations of the photocatalytic production of hydrogen in silicone microreactors from water-ethanol mixtures
(Elsevier, 2017) Castedo, Alejandra; Uriz Doray, Irantzu; Soler, Lluís; Gandía Pascual, Luis; Llorca Piqué, Jordi; Kimika Aplikatua; Institute for Advanced Materials and Mathematics - INAMAT2; Química Aplicada
Silicone microreactors containing microchannels of 500 μm width in a single or triple stack configuration have been manufactured, coated with an Au/TiO2 photocatalyst and tested for the photocatalytic production of hydrogen from water-ethanol gaseous mixtures under UV irradiation. Computational fluid dynamics (CFD) simulations have revealed that the design of the distributing headers allowed for a homogeneous distribution of the gaseous stream within the channels of the microreactors. A rate equation for the photocatalytic reaction has been developed from the experimental results obtained with the single stack operated under different ethanol partial pressures, light irradiation intensities and contact times. The hydrogen photoproduction rate has been expressed in terms of a Langmuir-Hinshelwood-type equation that accurately describes the process considering that hydrogen is produced through the dehydrogenation of ethanol to acetaldehyde. This equation incorporates an apparent rate constant (kapp) that has been found to be proportional to the intrinsic kinetic rate constant (k), and that depends on the light intensity (I) as follows: kapp = k·I0.65. A three-dimensional isothermal CFD model has been developed in which the previously obtained kinetic equation has been implemented. The model adequately describes the production of hydrogen of both the single and triple stacks. Moreover, the specific hydrogen productions (i.e. per gram of catalyst) are very close for both stacks thus suggesting that the scaling-up of the process could be accomplished by simply numbering-up. However, small deviations between the experimental and predicted hydrogen production suggest that a fraction of the radiation is absorbed by the microreactor components which should be taken into account for scaling-up purposes.
Open Access
High power illumination system for uniform, isotropic and real time controlled irradiance in photoactivated processes research
(Elsevier, 2024) Sáenz Gamasa, Carlos; Hernández Salueña, Begoña; Sanz Carrillo, Diego; Pellejero, Ismael; Gandía Pascual, Luis; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
In the study of photocatalytic and photoactivated processes and devices a tight control on the illumination conditions is mandatory. The practical challenges in the determination of the necessary photonic quantities pose serious difficulties in the characterization of catalytic performance and reactor designs and configurations, compromising an effective comparison between different experiments. To overcome these limitations, we have designed and constructed a new illumination system based in the concept of the integrating sphere (IS). The system provides uniform and isotropic illumination on the sample, either in batch or continuous flow modes, being these characteristics independent of the sample geometry. It allows direct, non-contact and real time determination of the photonic quantities as well as versatile control on the irradiance values and its spectral characteristics. It can be also scaled up to admit samples of different sizes without affecting its operational behaviour. The performance of the IS system has been determined in comparison with a second illumination system, mounted on an optical bench, that provides quasi-parallel beam (QPB) nearly uniform illumination in tightly controlled conditions. System performance is studied using three sample geometries: a standard quartz cuvette, a thin straight tube and a microreactor by means of potassium ferrioxalate actinometry. Results indicate that the illumination geometry and the angular distribution of the incoming light greatly affect the absorption at the sample. The sample light absorption efficiency can be obtained with statistical uncertainties of about 3% and in very good agreement with theoretical estimations.
Open Access
Remarkable performance of supported Rh catalysts in the dry and combined reforming of biogas at high space velocities
(Elsevier, 2024) Navarro Puyuelo, Andrea; Atienza Martínez, María; Reyero Zaragoza, Inés; Bimbela Serrano, Fernando; Gandía Pascual, Luis; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Dry and combined (with O2) reforming of synthetic biogas were studied at 700 °C using 0.5 % Rh catalysts prepared by impregnation on different supports: γ-Al2O3, SiO2, TiO2, ZrO2 and CeO2. Gas hourly space velocity (GHSV) was varied between 150 and 700 N L CH4/(gcat·h), and two O2/CH4 molar ratios of 0 and 0.12 were studied. Rh/Al2O3 catalysts (prepared using two different commercial supports here denoted as Sph and AA) presented the highest biogas conversion and syngas yields under both dry and combined reforming conditions. Catalytic activities were as follows: Rh/AA ≈ Rh/Sph > Rh/SiO2 > Rh/ZrO2 ≈ Rh/CeO2 > Rh/TiO2. The effect of catalysts’ calcination pre-treatment at relatively low (200 °C) and high temperatures (750 °C) was also studied. Calcination at high temperatures had a detrimental effect on both dry and combined reforming activities. However, a positive effect on the reforming activities and syngas yields was observed when the catalysts were calcined at 200 °C, especially under biogas combined reforming conditions: higher CH4 conversions and syngas yields could be achieved, as well as increasing CO2 conversions, though at the expense of lower H2/CO molar ratios.