Search Results (7)

The conversion of CO₂ into CH₄ through the Sabatier reaction is one of the key processes that can reduce CO₂ emissions into the atmosphere. This work aims to develop Ni-Al aerogel-based thermo-photocatalysts with large specific surface areas prepared using a sol–gel method and subsequent supercritical drying in CO₂. Different Al/Ni molar ratios were selected for the development of the catalysts, characterized using ICP-OES, N₂ adsorption–desorption isotherms, XRD, H₂-TPR, TEM, UV-Vis DRS, and XPS techniques. Thermo-photocatalytic activity tests were performed in a photoreactor with two different light sources (λ = 365 nm, λ = 470 nm) at a temperature range from 300 °C to 450 °C and a pressure of 10 bar. The catalyst with the highest Ni loading (AG 1/3) produced the best catalytic results, reaching CO₂ conversion and CH₄ selectivity levels of 82% and 100%, respectively, under visible light at 450 °C. In contrast, the catalysts with the lowest nickel loading produced the lowest results, most likely due to their low amounts of active Ni. These results suggest that supercritical drying is an efficient method for developing active thermo-photocatalysts with high Ni dispersion, suitable for Sabatier reactions under mild reaction conditions. Full article

In this work, three catalysts, TiO₂, WO₃ and TiO₂/WO₃, have been synthesized through flame spray pyrolysis synthesis (FSP) and have been tested for CO₂ photoreduction. The catalysts were fully characterized by XRD, DRS UV–Vis, N₂ physisorption and SEM. Experimental tests were performed in a one-of-a-kind high-pressure reactor at 18 bar. TiO₂ P25 was used as a benchmark to compare the productivities of the newly synthetized catalysts. The two single oxides showed comparable productivities, both slightly lower than the P25 reference value (ca. 17 mol/kg_cat·h). The mixed oxide, TiO₂/WO₃, instead showed an impressive productivity of formic acid with 36 mol/kg_cat·h, which is around 2.5 times higher than both of the single oxides alone. The formation of a type-II heterojunction has been confirmed through DRS analysis. The remarkable productivity demonstrates how FSP synthesis can be a crucial tool to obtain highly active and stable photocatalysts. This approach has already been successfully scaled up for the industrial production of various catalysts, showcasing its versatility and efficiency. Full article

Solar-boosted photo-technology stands out as a powerful strategy for photosynthesis and photocatalytic processes due to its minimal energy requirements, cost-effectiveness and operation under milder, environmentally friendly conditions compared to conventional thermocatalytic options. The design and development of photocatalysts have received a great deal of attention, whereas photoreactor development must be studied deeper to enable the design of efficient devices for practical exploitation. Furthermore, scale-up issues are important for this application, since light distribution through the photoreactor is a concurrent factor. This review represents a comprehensive study on the development of photoreactors to be used mainly for the photoreduction of CO₂ to fuels, but with concepts easily transferable to other photosynthetic applications such as ammonia synthesis and water splitting, or wastewater treatment, photovoltaics combined to photoreactors, etc. The primary categories of photoreactors are thoroughly examined. It is also explained which parameters influence the design of a photoreactor and next-generation high-pressure photoreactors are also discussed. Last but not least, current technologies for solar concentrators are recalled, considering their possible integration within the photoreactor. While many reviews deal with photocatalytic materials, in the authors’ view, photoreactors with significant scale and their merged devices with solar concentrators are still unexploited solutions. These are the key to boost the efficiency of these processes towards commercial viability; thus, the aim of this review is to summarise the main findings on solar photoreactors for the photoreduction of CO₂ and for related applications. Full article

The solar-induced semiconductor photocatalytic process is one of the greenest and most promising technologies for the elimination of pharmaceuticals in aqueous media. In the context of this study, a bismuth oxychloride (BiOCl) photocatalyst was fabricated and characterized by its morphology, crystallographic structure, and optical properties. Its photocatalytic efficiency was tested towards the degradation of Losartan (LOS), a medication used to treat high blood pressure, in water using a solar simulator. The as-prepared BiOCl exhibited significant photocatalytic efficiency, achieving complete degradation of 0.3 mg/L LOS in short periods of irradiation (15–30 min). The examined system showed optimal efficiency using 500 mg/L of BiOCL (k_app = 0.21 min⁻¹) and pH 3 (k_app = 0.32 min⁻¹). However, LOS removal significantly decreased in environmentally relevant water matrices, including wastewater (k_app = 0.006 min⁻¹) and bottled water (k_app = 0.023 min⁻¹). Additional tests carried out in synthetic water matrices showed that the LOS degradation rate was reduced by more than 40% in the presence of humic acid (k_app = 0.016 min⁻¹) and bicarbonates (k_app = 0.029 min⁻¹), while chlorides did not affect the overall efficiency. Moreover, photogenerated holes and singlet oxygen were the dominant oxidative species. The efficiency of the BiOCl photocatalyst towards LOS degradation was further studied using a flat plate pilot-plant scale photoreactor. It was found that more than 75% of LOS was removed after 100 kJ/L of accumulated solar irradiation. The results obtained in the pilot-plant unit confirmed the suitability of BiOCl as a potential photocatalytic material. Full article

In this study, Desertifilum tharense cyanobacteria, which has energy generation potential, was firstly isolated from the water sources from Denizli/Turkey, the culture-specific parameters were identified, characterization analyses were performed, and the production in photoreactors under laboratory conditions was performed. D. tharense cyanobacterium was subjected to a high temperature–pressure pretreatment process (HTPP) to increase methane production efficiency, and the pretreatment process was optimized for methane production. D. tharense had a total carbon (C) content of 50.2% and total organic carbon content (TOC) of 48.9%. The biochemical methane potential (BMP) of the raw D. tharense sample was measured as 261.8 mL methane (CH₄) per gram of volatile solids (VS). In order to investigate the effects of HTPP and to determine the optimum process conditions, Central Composite Design (CCD) approach-based Response Surface Methodology (RSM) was used. BMP values of the samples treated with HTTP were measured in the range of 201.5–235 mLCH₄ gVS⁻¹ and lower than the raw sample. These results revealed that the HTPP is not suitable for the production of biofuel methane from D. tharense. The optimization of the HTPP was carried out by Design Expert software. For maximum BMP production, the software proposed a reaction temperature of 200 °C and a reaction time of 20 min as optimum conditions. With the proposed model, it was estimated that 227.1 mLCH₄ g VS⁻¹ methane could be produced under these conditions, and 211.4 mLCH₄ g VS⁻¹ methane was produced in the validation experiment. It was determined that D. tharense cyanobacterium could be used as a suitable biomass source for methane production. However, it was not necessary to use the HTTP as a pretreatment process prior to the methane production. Full article

In the current research, the productivity of CO₂ photoreduction has been boosted by performing the reaction in an innovative photocatalytic reactor, which allows for operation up to 20 bar. A set of photocatalysts were used, including three types of pristine TiO₂, i.e., one commercially prepared (Evonik P25), one home-prepared by flame spray pyrolysis (FSP), and one obtained by the hydrolysis of TiCl₄ (TiO₂exCl), a bare thermo-exfoliated carbon nitride (C₃N₄-TE), and binary materials composed of TiO₂ and C₃N₄-TE. The photoreduction was carried out in water at pH 14 and in the presence of Na₂SO₃ as a hole scavenger. Hydrogen and very small amounts of CO were detected in the head space of the photoreactor, while in the liquid phase, the main product was formic acid, along with traces of methanol and formaldehyde. The composites P25/TE and TiO₂exCl/TE were found to have a higher productivity if compared to its single constituents used alone, probably due to the heterojunction formed by coupling the two materials. Moreover, the high pressure applied in the photoreactor proved to be very effective in boosting the yield of the organic products. Full article

In this work we focus on carbon nitride materials to improve the conversion and productivity of the photoreduction of CO₂, developing a coupled strategy to optimize materials and operating conditions. The metal-free polymeric catalyst, graphitic carbon nitride (g-C₃N₄), is a relatively novel material, characterized by a wide absorbance in the visible region and demonstrating a superior performance compared to the commercial titania P25 benchmark, the most used photocatalyst for this application. We used an innovative photoreactor operating at high pressures of up to 20 bar, which is unprecedented in photocatalytic applications where transparent windows are needed. This enabled a boost in the solubility of CO₂ in water when operating the reactor as a tri-phase liquid/gas/solid device and improved the surface adsorption over the catalyst. The best productivity for HCOOH so far achieved with these catalysts at 8 bar, pH = 14 and by using Na₂SO₃ as a hole scavenger was ca. 370 g/h kg_cat. Such productivity is several orders of magnitude higher than the literature values. Full article