Powder Catalysts Research Articles

Boosting nitrogen adsorption for photocatalytic ammonia production via tuning electron distribution using zero valent iron as medium

Photocatalytic nitrogen reduction to ammonia plays an important role in agricultural production and now-generation hydrogen storage technology. However, the practicality is limited by low efficiency owing to the poor charge-transfer rate and slow ammonification reactions. Herein, a ternary Fe2O3-Fe-HCNS composite is reported with all-solid-state Z-scheme heterojunction, which zero valent iron (ZVI) with abundant electrons is employed as conductor between hollow g-C3N4 sphere (HCNS) and Fe2O3. ZVI facilitates photogenerated electrons transfer and changes charge distribution on the Fe2O3-Fe-HCNS surface, thus an electron-rich region is formed around HCNS, which improves N2 adsorption and ammonification reaction on the HCNS surface. Moreover, the dual interfacial electric fields are established in the heterojunction, which can promote efficient separation and migration of photo-induced electrons and holes in space, leading to the good photocatalytic performances with the higher ammonia yield (296.30 μmol g−1h−1) and apparent quantum yield (1.38%, 400 nm) in neutral electrolytes. In addition, compared with the catalyst powder, vertical carbon paper supporting Fe2O3-Fe-HCNS catalyst can reduce secondary pollution and facilitate recycling.

Nanometric Metal Overlayer Catalysts: Fundamental Aspects and Applications

Nanometric metal overlayer catalysts have been developed as novel catalyst structures with high three-way catalytic performance for practical applications. The metal overlayer is prepared via a dry process using pulsed arc plasma deposition, unlike wet coating processes for conventional powder catalysts containing nanoparticles. The key point to achieving high performance is the extremely high turnover frequencies for specific chemical reactions catalyzed by a large two-dimensional surface compared with metal nanoparticles. This overview study presents the preparation, structure, performance, reaction mechanism, and thermal stability of metal overlayer catalysts, focusing on rhodium (Rh) and catalytic conversion of nitric oxide (NO). Rh plays a pivotal role in the reduction of NO to N2 in automotive three-way catalytic converters. The potential benefit of the overlayer structure is the minimum loading of precious metal, such as Rh, which is limited and expensive.

Continuous catalytic pyrolysis of waste oil to aromatics: Exploring the structure-performance relations of ZSM-5 based on different scale-up forms

Waste oil, a byproduct of oil industry, holds significant potential to valuable aromatics through catalytic pyrolysis. However, there is a lack of research on catalysts suitable for large-scale production, which requires scaling up powder catalysts to meet industrial requirements. In this study, structure-performance relations of four different scale-up ZSM-5 in waste oil catalytic pyrolysis to aromatics was evaluated in a continuous system. Notably, ZSM-5/SiC ceramic foam catalyst exhibited the smallest pressure loss across the catalytic reactor, which was 6 times lower compared to the powder catalysts. ZSM-5/SiC ceramic foam catalyst has excellent initial activity, maintaining aromatics selectivity above 99% for the first 30 min time-on-stream and retaining 73.63% selectivity after 1 h. The pelletized ZSM-5 showed the longest lifetime during six reaction-regeneration cycles. The deactivation mechanism of ZSM-5 was deduced. This study helps to better understand the process at the molecular level and also contribute to research in large-scale production.

In-situ construction of Bi2WO6/BiOCl p-n heterojunction film for photocatalytic CO2 reduction

Heterojunction composite construction has been considered as a viable method to improve photocatalytic performance. In this study, a kind of highly efficient 2D/0D Bi2WO6/BiOCl p-n heterojunction film with boosted photocatalytic CO2 reduction performance was synthesized on Bi plate via in-situ electrochemical ion-exchange hydrothermal method. Furthermore, the XRD, XPS, SEM, TEM and other techniques were carried out to evaluate as-synthesized films. Our findings indicate that Bi2WO6/BiOCl composite film, with close border contact between Bi2WO6 and BiOCl surfaces, should be conducive to achieve excellent separation and migration of photogenerated charge carriers. Finally, the formation mechanism of p-n heterostructure is demonstrated using XPS core-level alignment method. This work should offer new perspectives into the immobilization method of efficient powder catalysts and the photocatalytic CO2 reduction mechanism of p-n heterojunction films.

Catalytic Hydrogenation of Nitrate over Immobilized Nanocatalysts in a Multi-Phase Continuous Reaction System: System Performance, Characterization and Optimization

Nitrate catalytic reduction in a continuous system was studied in the presence of Pd-Cu macrostructured catalysts synthesized through a novel washcoating methodology of the pre-formed bimetallic powder catalyst. The present work aims to understand the behavior of the macrostructured bimetallic catalyst in the presence of different reaction conditions in order to achieve the design of an optimized facility that can produce the best catalytic results: maximum NO3− conversion with enhanced N2 selectivity. The residence time of the inlet solution and the catalyst concentration in the reactor proved to be the parameters that most influenced the conversion and selectivity due to the important role that these parameters play in the hydrodynamic conditions of the reactor. A higher loading of catalyst and lower inlet flow rates allow promoting a higher contact time between the three phases that participate in the reaction (G-L-S). The most efficient reaction conditions (three pieces of the macrostructured catalyst, liquid flow rate of 10 mL min−1, and a total gas flow rate of 200 Ncm3 min−1 (1:1 H2:CO2)) allowed obtaining an NO3− conversion of 51% with a corresponding N2 selectivity of 23%. Also, the conversion results strongly depended on the total gas flow rate used during the reaction since this assists the mixing between the three phases and promotes a greater contact that will contribute to enhanced catalytic results.

Construction of continuous flow catalytic reactor-HPLC system with ultrahigh catalytic activity using 2D nanoflower MOF-derived Cu2O/Cu/PDA/CF catalyst

Currently, metal-organic frameworks (MOFs) derived materials have been widely concerned for the reduction of 4-nitrophenol (4-NP). However, complex recovery of powder catalysts and low utilization ratio of active sites make their application challenging. Herein, a novel Cu2O/Cu/PDA/CF catalyst has been developed for the rapid reduction of 4-NP to 4-aminophenol (4-AP). The catalyst was constructed by compositing a two-dimensional nanoflower MOF-derived nanoporous Cu2O/Cu network on a polydopamine (PDA)-modified porous copper foam by a mild and controllable in-situ reduction synthesis. Notably, an enhanced catalytic performance of Cu2O/Cu/PDA/CF was obtained for 4-NP reduction with a rate constant (k) of 0.8001 min−1, outperforming Cu/PDA/CF-X (X = 400, 500 and 600 ℃ pyrolysis temperature) catalysts (2.3–6.4 folds), and even many reported catalysts (2.3–46.5 folds). The ultrafast degradation of 4-NP was completed in 70 s. Moreover, an ingenious online continuous flow catalytic reactor (CFCR)-high performance liquid chromatography (HPLC) system was constructed for automatic and real-time monitoring of the reduction reaction. System stability experiments over 300 min revealed a surprisingly high reaction k value of 76.68 min−1 at low NaBH4 usage, significant increasing by 2–3 orders of magnitude compared with Cu2O/Cu/PDA/CF batch catalysis, due to the high aspect ratio of 2D nanoflower MOF and convection-accelerated mass transfer. This work offers new insights for the rational design of catalytic reactor and its potential application in wastewater treatment.

Fe and Zn Addition Effects of Ti Oxide-Based Electrocatalyst on Catalytic Activity for Oxygen Reduction Reaction

The conventional catalyst of polymer electrolyte fuel cell (PEFC) is a platinum which is categorized as precious metal with very high-cost material, and its performance is limited in principal. From this point of view, the non-precious metal electrocatalyst should be required. We have focused and studied group 4 and 5 metal oxide-based electrocatalyst as non-platinum catalysts for the oxygen reduction reaction (ORR) because of low-cost, abundant reserves, and high stability in acidic electrolytes [1-2]. We found that titanium oxide prepared from TiOTPyzPz supported on multi-walled carbon nanotubes had superior ORR activity [3]. On the other hand, it was published as an international patent that the addition of other elements such as Fe and Ni is affected to enhance the ORR activity of Ti oxide-based electrocatalyst [4]. We have also applied for the TiOTPyzPz as a starting material with Fe, Ni, and Zn addition to enhance the ORR activity of Ti oxide-based electrocatalyst [5-6]. In this study, we have investigated the addition effects of Zn and Fe for Ti oxide-based electrocatalyst on the catalytic activity for the ORR.2,3-Dicyanopyrazine, urea, and Ti isopropoxide were dissolved in quinoline and refluxed to synthesize TiOTPyzPz. Iron acetate and zinc acetate were also added to dissolve in quinoline to obtain the Fe and Zn-added TiOTPyzPz as a starting material. These starting materials were mixed with carbon nanotube by ball-milling to prepare the precursors. These precursors were heat-treated under low oxygen partial pressure at 900 oC for 3 h to obtain the oxide-based electrocatalyst powder. The catalyst powder was dispersed into 1-propanol with Nafion solution to prepare a catalyst ink. The ink was dropped on a glassy carbon rod to use as a working electrode in electrochemical measurement.Electrochemical measurements were performed in 0.5 mol dm-3 H2SO4 at 30 oC with a conventional 3-electrode cell. A reversible hydrogen electrode (RHE) and a glassy carbon plate were used as used as a reference and counter electrode, respectively. Slow scan voltammetry (SSV) was performed at a scan rate of 5 mV s-1 from 0.2 V to 1.2 V vs. RHE under O2 and N2. The ORR current (i ORR) was determined by calculating the difference between the current under O2 and N2.Figure 1 shows the ORR polarization curves Fe and/or Zn addition to the Ti oxide-based electrocatalysts. The Fe and Zn added Ti oxide-based electrocatalyst (Fe,Zn-TiOx) was obviously the highest activity for the ORR, and it was higher ORR activity than Fe added Ti oxide-based electrocatalyst (Fe-TiOx), Zn added Ti oxide-based electrocatalyst (Zn-TiOx), and Ti oxide-based electrocatalyst (TiOx) without addition. It reveals that the addition of Fe and Zn was found to be effective for enhancing the ORR activity, and Fe addition was more effective than Zn addition for enhancing the ORR activity. XRD pattern of TiOx shows several peaks identified TiO2-Rutile and TiC0.3N0.7 while the XRD pattern of Fe-TiOx, Zn-TiOx, and Fe,Zn-TiOx also shows several peaks identified similar to TiOx. According to results from ICP analysis, the contain amount of Ti and Fe in Fe,Zn-TiOx was similar to preparation amount in precursor, but that of Zn showed below detection limit. From SEM images, Zn-TiOx and Fe,Zn-TiOx have more space in its powder than Fe-TiOx and TiOx. Based on above results, it is suggested that Zn addition affected to increased electrochemical surface area of TiOx, and Fe addition affected to form active site [7] in TiOx as similar case as Zr oxide-based electrocatalyst [8].Acknowledgement: The authors thank New Energy and Industrial Technology Development Organization (NEDO) and ENEOS Tonen General Research / Development Encouragement & Scholarship Foundation for financial support.Reference A. Ishihara, Y. Ohgi, K. Matsuzawa, S. Mitsushima, and K. Ota, Electrochim. Acta, 55, 8005 (2010).A. Ishihara, S. Tominaka, S. Mitsushima, H. Imai, H. Imai, O. Sugino, and K. Ota, Curr. Opin. Electrochem., 21 , 234 (2020).S. Tominaka, A. Ishihara, T. Nagai, and K. Ota, ACS Omega, 2, 5209 (2017).K. Takahashi, T. Imai, R. Monden, Y. Wakisaka, and S. Sato, Oxygen Reduction Catalyst, Process for Producing Same, and Polymer Electrolyte Membrane Fuel Cell, WO/2013/008501.K. Matsuzawa, M. Obata, Y. Takeuchi, Y. Ohgi, K. Ikegami, T. Nagai, R. Monden and A. Ishihara, ECS Trans., 108(7), 181 (2022).K. Matsuzawa, M. Obata, Y. Takeuchi, Y. Ohgi, K. Ikegami, T. Nagai, R. Monden and A. Ishihara, ECS Trans., 108(7), 189 (2022).J-H. Kim, A. Ishihara, S. Mitsushima, N. Kamiya, and K. Ota, Acta, 52, 2492 (2007).Y. Takeuchi, K. Watanabe, K. Matsuzawa, T. Nagai, K. Ikegami, R. Monden, and A. Ishihara, Chem. Lett., 51, 927 (2022). Figure 1

A Life-Cycle of Ni in Proton Exchange Membrane Fuel Cells

The usage of Proton Exchange Membrane Fuel Cells (PEMFCs) in the automotive industry is currently limited by the price, performance, and durability of a platinum catalyst. Alloying with nickel provides lower cost and enhances activity. However, the membrane electrode assembly (MEA) performance is, in practice, much lower than expected from liquid laboratory experiments on the catalyst layer. One of the identified issues is Ni leaching from nanoparticles (NPs) and subsequent Ni poisoning of the Nafion membrane.Here, we use Wide-Angle X-ray Scattering (WAXS) and X-ray Absorption Near-Edge Structure (XANES) to follow Ni dissolution from the catalyst layer and its movement in the MEA. We shine (synchrotron) light on the full life cycle of Ni, starting from (i) characterization of the catalyst powder, followed by (ii) the changes in catalyst composition during the ink-making process and (iii) membrane coating and finishing with (iv) NP characterization and Ni tracking during the operation of MEAs.Proper incorporation of PtNi catalyst requires modification of all the aforementioned steps that are otherwise well optimized for pure Pt catalyst. It is even more critical for shape-controlled octahedra (oh) PtNi NPs as their activity is closely related to their structure [1]. Highly active oh-PtNi NPs are usually made from precursors such as Nickel(II) bis(acetylacetonate). Using EDX, we find precursor residues in catalyst powders that dissolve upon further processing and add to membrane poisoning. We conclude that we need to develop a cleaning protocol that would remove all Ni residue while retaining the nanoparticle shape.During ink-making, high ionomer concentrations and elevated temperatures promote Ni dissolution from the catalyst, which can, in turn, poison the membrane even before the MEA is put in use. With the WAXS technique, we track the dissolution during ink-making and MEA operation by following changes in lattice parameter, showing the dynamics and the extent of Ni dissolution in each step of aging.Furthermore, we use angle-resolved XANES to track the movement of dissolved Ni. We show that Ni ions are getting reduced back to metallic form within the MEA, likely due to hydrogen crossover. The presence of such a metal band in the membrane blocks proton conductivity and decreases performance [2]. That is why it is crucial to set manufacturing and operational boundaries to prevent dissolution.For this reason, we follow WAXS total scattering intensity during oxidation and reduction cycles to understand the Ni dissolution dynamics during operation. We find that limiting both upper and lower potential cycling limits greatly reduces the redox extent and subsequent dissolution. It is, therefore, possible to find and understand the trade-off between high power density and dissolution in operational cells.Even though this work looks at the Ni life cycle, the presented techniques and conclusions are transferable to all multimetallic high-performance PEMFC catalysts.

(Invited) Overall Research on Electrode Coating Processes (OREO) - the Role of Imaging and Spectroscopy in Scale-up Fabrication of Low Temperature Water Electrolyzers

With the recent trends in hydrogen technologies, scale-up fabrication of membrane electrode assemblies (MEAs) for the electrochemical systems such as fuel cells and electrolyzers is gaining significant attention. Companies and researchers are focusing on diverse large-scale electrode fabrication processes, such as roll-to-roll and screen-printing. However, optimizing such processes is not trivial, and a number of parameters, including but not limited to catalyst type, solvent, ink mixing, electrode coating and drying, play a role in the quality of the final product. Correlations between the fabrication parameters and resulting electrode microstructure, properties and performance are important to understand, in order to better control the processes. Imaging and spectroscopy techniques play an important role in this understanding, starting from catalysts, inks and all the way to the electrodes. Information about catalyst distribution, composition, and surface chemistry can be correlated to ink characteristics, and finally to electrode structure, component distribution and properties, and their effect on MEA performance can be investigated.In this talk, a collaborative work between four institutions, University of Connecticut, Colorado School of Mines, National Renewable Energy Lab and Fraunhofer ISE, within a project on Overall Research on Electrode Coating Processes (OREO), is discussed, with the focus on low temperature water electrolyzers scale-up fabrication and characterization. The talk will especially focus on the role of advanced microcopy and spectroscopy in the characterization of catalyst powders, inks and electrodes.

Development and Up‐scaling of Iron‐based Catalysts for Fischer‐Tropsch Synthesis of Higher Alcohols

AbstractFor sustainable production of chemicals like hydrocarbons and oxygenates from renewable carbon sources and electricity Fischer‐Tropsch synthesis is focused in current research. Aiming for this purpose, the development of supported powdered and shaped catalysts for low‐temperature Fischer‐Tropsch synthesis of value‐added higher alcohols was addressed in this study. Promising support materials like α‐Al2O3, SiO2, ZrO2 and SiC were assessed and the influence of electrochemical promoters on product formation was investigated. The results show an outstanding promoting effect of lithium on conversion and alcohol selectivity. A beneficial synergistic effect occurred for the combination of 1 % Li and Cu each and could be exploited both for supported powdered and shaped catalysts. Furthermore, effects of surface, shape, porosity and Fe content on pellet catalysts were investigated. Exploiting the beneficial effects found, the first monometallic shaped Fe‐based catalyst – outperforming the state‐of‐the‐art monometallic Fe powder catalysts in conversion and selectivity – is presented.

Desain Dan Optimasi Proses Pirolisis Waste Oil Menggunakan Pendekatan RSM

The management of abundant oil waste in companies that are spread over tin mining operational locations is still not optimal. The waste oil comes from engine oil and hydraulic oil. With proper management, waste oil will become useful and have added value. This waste can be processed into HSD (High Speed ​​Diesel) fuel, so the company will get profit. The processing method used in waste treatment is the pyrolysis process. In this study, a pyrolysis tool was designed and built, and a test was carried out to obtain optimal parameters for the resulting fuel product using the Response Surface Methodology (RSM) method. The tests were carried out using activated Zeolite powder catalyst and 1000 ml of oil in each test. The indicators and parameters observed are the Quantity HSD and the percentage of Zeolite. The results of the optimization of the research process with the optimum formulation, namely setting temperature 285 oC, catalyst 109.8 gr, product yield 898.1 ml. Where as in the use of Raw Material Hydraulic Oil, the optimum formulation is a temperature of 325.8 oC, 118.6 gr catalyst, and a product yield of 920 ml with a duration of 60 minutes.

How Pt Influences H2 Reactions on High Surface-Area Pt/CeO2 Powder Catalyst Surfaces.

The addition of platinum-group metals (PGMs, e.g., Pt) to CeO2 is used in heterogeneous catalysis to promote the rate of redox surface reactions. Well-defined model system studies have shown that PGMs facilitate H2 dissociation, H-spillover onto CeO2 surfaces, and CeO2 surface reduction. However, it remains unclear how the heterogeneous structures and interfaces that exist on powder catalysts influence the mechanistic picture of PGM-promoted H2 reactions on CeO2 surfaces developed from model system studies. Here, controlled catalyst synthesis, temperature-programmed reduction (TPR), in situ infrared spectroscopy (IR), and in situ electron energy loss spectroscopy (EELS) were used to interrogate the mechanisms of how Pt nanoclusters and single atoms influence H2 reactions on high-surface area Pt/CeO2 powder catalysts. TPR showed that Pt promotes H2 consumption rates on Pt/CeO2 even when Pt exists on a small fraction of CeO2 particles, suggesting that H-spillover proceeds far from Pt-CeO2 interfaces and across CeO2-CeO2 particle interfaces. IR and EELS measurements provided evidence that Pt changes the mechanism of H2 activation and the rate limiting step for Ce3+, oxygen vacancy, and water formation as compared to pure CeO2. As a result, higher-saturation surface hydroxyl coverages can be achieved on Pt/CeO2 compared to pure CeO2. Further, Ce3+ formed by spillover-H from Pt is heterogeneously distributed and localized at and around interparticle CeO2-CeO2 boundaries, while activated H2 on pure CeO2 results in homogeneously distributed Ce3+. Ce3+ localization at and around CeO2-CeO2 boundaries for Pt/CeO2 is accompanied by surface reconstruction that enables faster rates of H2 consumption. This study reconciles the materials gap between model structures and powder catalysts for H2 reactions with Pt/CeO2 and highlights how the spatial heterogeneity of powder catalysts dictates the influence of Pt on H2 reactions at CeO2 surfaces.

Perovskite Nano-Powder and Nano-Film Catalysts in Mineralization of Aqueous Organic Contaminants through Solar Simulated Radiation

Water contamination with various contaminants, including organic species, is a global concern. Reclamation through safe, economic and technically feasible methods is imperative. Two perovskites, zinc titanate (ZnTiO3) and manganese titanate (MnTiO3), mixed with TiO2 phases, were prepared as nano-powders and nano-films. The materials were characterized and used as catalysts in photodegradation of aqueous methylene blue, a hazardous model contaminant, using solar simulated radiation. The effects of various reaction conditions on the photodegradation were examined. The kinetics indicated the suitability of using the process at various contaminant concentrations and catalyst loadings. Both powder and film catalysts completely removed the contaminant in less than 6 h. Powder and film forms of the MnTiO3 mixture were more efficient than their ZnTiO3 counterparts. In both perovskite mixtures, the films exhibited higher catalytic efficiency than the powders. The film materials exhibited high catalytic efficiency in both the continuous flow and batch processes. Water contaminated with various methylene blue concentrations can be treated by the film catalysts that can be recovered and reused with no technical difficulties. The results open new horizons for larger-scale water purification processes.

Pt3Cu alloy anchored on nanoporous WO3 with high activity and stability in methanol oxidation

Designing highly efficient and durable electrode for methanol oxidation reaction (MOR) is crucial to commercializing direct methanol fuel cells (DMFCs). However, traditional Pt/C catalysts usually suffer from CO poisoning, and agglomeration of powder catalyst, which leads to rapid activity degradation. Herein, we have successfully fabricated self-supported Pt3Cu@3DP-WO3/W electrode via a facile and effective synthesis approach by combining anodic oxidation and electrodeposition method. Benefitting from the three dimensional nanoporous of WO3 with more surface area and strong adhesion, and Pt3Cu alloy synergism induced the lattice compressive strain, the Pt3Cu@3DP-WO3/W electrode achieved 2.77-fold and 4.8-fold enhancement in specific activity (2.15 mA cm−2) and mass activity (853 mA·mgPt−1) for MOR relative to Pt/C catalysts, respectively. Moreover, both the experiments and theoretical calculations revealed that the doping of Cu element weakened the chemisorption of CO-like intermediates by lowering the Pt d-band center through compressive lattice strain, which resulting in excellent catalytic stability. This binder-free self-supported electrode is a viable alternative for commercial application of DMFCs.

Unraveling surface structures of gallium promoted transition metal catalysts in CO2 hydrogenation

Gallium-containing alloys have recently been reported to hydrogenate CO2 to methanol at ambient pressures. However, a full understanding of the Ga-promoted catalysts is still missing due to the lack of information about the surface structures formed under reaction conditions. Here, we employed near ambient pressure scanning tunneling microscopy and x-ray photoelectron spectroscopy to monitor the evolution of well-defined Cu-Ga surfaces during CO2 hydrogenation. We show the formation of two-dimensional Ga(III) oxide islands embedded into the Cu surface in the reaction atmosphere. The islands are a few atomic layers in thickness and considerably differ from bulk Ga2O3 polymorphs. Such a complex structure, which could not be determined with conventional characterization methods on powder catalysts, should be used for elucidating the reaction mechanism on the Ga-promoted metal catalysts.

BiFeO3-PDMS hybrids: Development of visible-active floating photocatalysts with minimal catalyst loading.

Recent advances in photocatalysis include the development of floating catalysts since they assure efficient and rapid recollection of the catalysts from the purified liquid, besides enhancing the availability of photons at the catalytic surface. Bismuth ferrite (BiFeO3 and BFO) is a multifunctional perovskite material renowned for its excellent photocatalytic properties. Since bandgap of BFO falls in the visible spectrum, BFO nanoparticles could be combined with a suitable floating substrate to develop efficient visible light photocatalysts. Here, we report the synthesis of BFO-polydimethylsiloxane (PDMS) hybrids for photocatalytic applications, where sol-gel-synthesized BFO nanoparticles are immobilized on a floating porous PDMS sponge. The successful incorporation of the nanoparticles on PDMS is confirmed using Raman spectroscopy, scanning electron microscopy, and energy dispersive x-ray spectroscopy. The photocatalytic activity of the floating catalysts was studied by monitoring the degradation of malachite green dye under visible light irradiation. The effect of the amount of BFO immobilized, and the area and thickness of the PDMS sponge on the photocatalytic activity of the floating catalysts were investigated. An efficiency of 80.5% was obtained when the weight of BFO immobilized on the PDMS sponge was 5 mg. The method yields degradation efficiencies comparable with or higher than that of conventional BFO powder catalysts, even with 6-18 times less catalyst loading. The method introduces the fabrication of recyclable floating photocatalysts of notable efficiency using significantly less amount of BFO nanoparticles, which could be further modified by approaches such as doping, functionalization, or composite formation.

Photocatalytic fuel cell based on integrated silicon nanowire arrays/zinc oxide heterojunction anode for simultaneous wastewater treatment and electricity production

Photocatalytic fuel cells (PFCs) convert organic waste into electricity, thereby providing a potential solution for remediating environmental pollution and solving energy crises. Most PFCs for energy generation applications use powder photocatalysts, which have poor mechanical stability, high internal resistance, and may detach from the substrate during reactions, leading to unstable performance. Integrated photoelectrodes can overcome the drawbacks of powder catalysts. In this study, an integrated photoanode was prepared based on a silicon nanowire arrays/zinc oxide (Si NWs/ZnO) heterojunction by combining metal-assisted chemical etching (MACE) and hydrothermal methods. The resulting photoanode was used to assemble a PFC for simultaneous electricity generation and Rhodamine (RhB) dye wastewater degradation. This PFC showed excellent cell performance under irradiation, with a short-circuit current density of 0.183 Am−2, an open-circuit voltage (OCV) of 0.72 V, and a maximum power density of 0.87 W m−2. It could also be used continuously 20 times while degrading > 90% of RhB. This performance was ascribed to the three-dimensional (3D) structure and large surface area of Si NWs, as well as the matched band structure of ZnO, which facilitated the efficient separation and transport of photogenerated carriers in Si NWs/ZnO. The integrated structure also shortened the carrier transport pathways and suppressed carrier recombination. This research provides a foundation for the development of efficient, stable, low-cost, small-scale PFCs.

Polyurethane sponge assisted recoverable photocatalyst for outdoor weak sunlight-driven efficient water purification

Photocatalysis is an effective technology to address wastewater issue. However, the difficult recoverability of sample powders and poor degradation performance of catalysts under weak sunlight irradiation restrict the commercialization applications. In this work, the Bi2WO6/g-C3N4 heterojunction is synthesized by hydrothermal and calcination techniques, and a three-dimensional polyurethane sponge is introduced to assist the catalyst powder. On the one hand, weather variations produce less affection for Bi2WO6 sample, which exhibits the efficient photocatalytic activity driven by weak sunlight. The construction of Bi2WO6/g-C3N4 heterojunction speeds up separation and transfer of photogenerated carriers, further improving the catalytic performances of pristine Bi2WO6. Under cloudy (solar power density 21.93–52.97 mW/cm2) and overcast (solar power density 3.66–18.99 mW/cm2) weathers, tetracycline degradation efficiencies of Bi2WO6/g-C3N4 reach 64.66% and 55.19% after 150 min of sunlight irradiation, respectively. On the other hand, catalyst powder is tightly loaded onto the surface of polyurethane sponge via polyurethane waterproof coating, which is convenient for material recovery and reuse. After 4 cycles, tetracycline degradation efficiencies of Bi2WO6/g-C3N4 present no significant decrease, saving reaction cost and causing no secondary pollution to water environment. This work provides a promising candidate for large-scale commercialization applications of wastewater treatment.

Optimal mixing method of ZnZrOx and MOR-type zeolite to prepare a bifunctional catalyst for CO2 hydrogenation to lower olefins

In recent years, the issue of global warming caused by CO2 emissions has become a critical problem and poses a worldwide challenge. To address this issue, we have developed a bifunctional catalyst that can convert CO2 to lower olefins in a single stage. Our bifunctional catalysts are a combination of two catalysts, a CO2-to-methanol hydrogenation catalyst (Zn-doped ZrO2, named ZnZrOx) and a methanol-to-olefin catalyst (MOR-type zeolite, named MOR104). In this research, we examined the impact of various mixing modes of the two catalysts on product distribution. We tested four different mixing modes using a down-flow fixed bed reactor: (a) ZnZrOx in the upper layer and MOR104 in the lower layer, (b) catalysts were mixed randomly after being pelletized separately, (c) MOR104 in the upper layer and ZnZrOx in the lower layer, and (d) granulated catalyst produced by physically mixing both catalyst powders. Our findings indicated that the best performance was achieved with catalyst (d), where the two catalysts were mixed in close proximity. This proximity resulted in efficient supply of methanol produced on ZnZrOx to MOR104. In other words, the MTO reaction in MOR104 efficiently consumed methanol molecules produced via equilibrium-limited CO2-to-methanol hydrogenation. When ZnZrOx and MOR104 were thoroughly mixed, the conversion of CO2 to methanol shifted towards the product side, resulting in a greater overall utilization of CO2. Furthermore, the bifunctional catalyst we developed was stable for six hours. Since there have been few studies of bifunctional catalysts containing zeolites other than ZSM-5 and SAPO-34, this study opens up new opportunities for bifunctional catalysts specialized for one-pass hydrocarbon synthesis through CO2 hydrogenation.

Ultrahigh-flux 2D CoO@MoS2 composite membrane activated peroxymonosulfate through enhanced electron transfer for rapid degradation of refractory benzotriazole

The application of heterogeneous advanced oxidation processes (AOPs) in the removal of refractory pollutants has been hindered by several drawbacks, such as difficult recovery of the powder catalyst, the low yields and inefficient utilization of reactive oxygen species (ROS). We developed a novel catalytic membrane named 2D CoO@MoS2 membrane, its catalytic active layer was a composite material formed by MoS2 nanosheets wrapped and intercalated between 2D CoO porous nanoplates, providing abundant active sites and oxygen vacancies (Ov). 2D CoO@MoS2 membrane was applied to activate peroxymonosulfate (PMS) for benzotriazole (BTA) degradation. DFT calculations and series characterizations demonstrated that electron transfer occurred at the contact interface between 2D CoO and MoS2 phase, while the 2D CoO@MoS2 composite could act as an effective electron donor for PMS. The redox cycles of Mo(IV)/Mo(VI) and Ov/O2− could synergistically enhance the regeneration of Co(II), thereby maintaining the cycle of catalytic active center, which facilitated the spontaneous dissociation of PMS to generate various ROS, including SO4− (30.2 μM), 1O2 (8.6 μM) and OH (5.8 μM). These ROS rapidly degraded 99.7% of BTA (20 mg/L) through the nanoconfined layer of hydrophilic membrane with an ultra-high flux of 2172 L m−2h−1 in a super-fast time (∼195 ms). Surprisingly, the degradation rate constant k exhibited 3 to 5 orders of magnitude higher compared to conventional heterogeneous AOPs. Furthermore, the catalytic stability, degradation pathways and biological toxicity of BTA degradation were also evaluated. This membrane-based AOPs technique provides a new approach to overcome the limitations of conventional heterogeneous catalysis.