Characterization Of Catalysts Research Articles

ZrO2 promoted Ru/In2O3 catalyst for selective hydrogenation of CO2 to methanol

With the strong metal-support interaction, In2O3 supported Ru catalyst has been confirmed to be active for selective hydrogenation of CO2 to methanol. Herein, we report that the addition of ZrO2 into Ru/In2O3 further improves the catalytic activity for CO2 hydrogenation to methanol. The catalyst characterization shows a formation of In2O3-ZrO2 solid solution, which is an excellent support for the highly dispersed Ru catalyst. Compared to Ru/In2O3, a significantly higher methanol selectivity is achieved over the Ru/In2O3-ZrO2 catalyst with 1 wt% Ru loading. The methanol space–time yield (STY) reaches 0.685 gMeOH h−1 gcat−1 at 300 ℃, 5 MPa, and 21000 cm3 gcat−1h−1. It has more than 20% increase compared to Ru/In2O3. The addition of ZrO2 optimizes the oxygen vacancies of In2O3, improves the CO2 adsorption and enables a more stable catalyst architecture, while the hydrogen spillover by the highly dispersed ruthenium improves the hydrogen activation ability of the catalyst. All these results in a high level of methanol yield.

Surfactant-free synthesis of Ag@TiO2 and CuO@TiO2 photocatalyst: a comparative study of their photocatalytic activity for reduction of nitroaromatics in water

The reduction of harmful nitroaromatics to useful amino-aromatics have significant opportunities in synthetic chemistry. Here a visible-light-driven eco-friendly method for the selective reduction of aromatic nitro compounds to their corresponding amines in aqueous solution by using Ag@TiO2 and CuO@TiO2 is described. It was observed that both Ag@TiO2 and CuO@TiO2 are photo-catalytically more efficient compared to bare TiO2 and CuO@TiO2 has higher activity over Ag@TiO2 for the said conversion. The structural and morphological characterization of the as-synthesized catalysts has been done with SEM-EDX, TEM, powder XRD, ICP-AES, XPS, Photoluminescence, and UV-vis spectroscopic techniques. The nanocomposites Ag@TiO2 and CuO@TiO2 exhibit pure anatase phase with average crystallite size of 5.89 nm and 5.87 nm respectively as calculated from the Debye-Scherrer equation depending on the (101) plane. UV-visible results inferred enhanced optical properties of both the synthesized catalysts and revealed a reduced band gap (3.07 eV for Ag@ TiO2 and 2.5 eV for CuO@ TiO2) as compared to neat TiO2 (3.36 eV). Various nitro compounds were tolerated under 150 W LED as a light source (13.9 lumens for an area of 0.2 ft2) in an aqueous medium at room temperature (30 °C) using NaBH4 as a reducing agent to access corresponding amines in satisfying yields (78%–99%). The catalyst can be separated from the reaction mixture by simple centrifugal precipitation and reused for up to six consecutive cycles without apparent loss of its catalytic activity. The products were characterized by 1H-NMR spectroscopic techniques and compared with authentic samples.

Pengaruh Temperatur Kalsinasi Terhadap Kapasitas Ion Katalis Asam Heterogen Berbasis Silika dan Aplikasinya pada Sintesis Metil Oleat

Sulfated silica catalyst is a solid acid catalyst which in its application is used to accelerate esterification reactions. The purpose of this study was to determine the effect of calcination temperature and increasing the amount of catalyst on the effectiveness of silica as a catalyst in the formation of methyl oleate through esterification reactions. The synthesis of sulfuric acid catalyst from rice husk ash went through several stages, including preparation of raw material for rice husk ash, production of silica using the sol-gel method, manufacture of silica-based acid catalysts and characterization of the sulfated silica catalyst. The acid catalyst was prepared using impregnation method with sulfuric acid and calcined at various temperatures of 500, 600, 700 and 800oC. The characterization of the acid catalyst formed includes ionic capacity, catalyst performance in the esterification reaction, and the determination of the bond characteristic functional groups using FTIR. The results of ion capacity analysis showed that the highest acidity value was found in the sulfated silica catalyst calcined at 600oC of 0.372 mmol/gram. Testing the performance of the catalyst in the esterification reaction with a ratio of 4:1 (methanol:oleic acid) obtained an ester conversion of 38.89% using a catalyst of 30% of the amount of oleic acid. Identification results using FTIR show that sulfate ions have chemically interacted with silica at around 1103.28 cm-1

Electrochemical Characterization of Pd-Based Catalysts Deposited on Yittria Stabilized Zirconia Solid Electrolyte for Methane Oxidation Reaction

Methane, the main constituent of natural gas, has received increased attention since it has a higher energy density than other fossil fuels while producing less particulates containing sulphur and nitrogen. However, although methane emits less CO2 than other fossil fuels, it has 28 times more global warming potential [1]. Therefore, complete methane oxidation via heterogeneous catalysis that prevents escaping unburned methane from the engine exhaust is a key solution to this issue.Palladium is the most effective conventional noble metal for methane catalytic oxidation, which is susceptible to deactivation, especially in the presence of water. The stability and activity of a monometallic Pd catalyst could be improved upon adding a second less expensive and more abundant non-noble metal or metal oxide[2]. The interaction of Pd nanoparticles and the second metal can be characterized using electrochemical means to understand the catalytic and electrocatalytic activity of catalysts[3,4].In this work, the electrochemical behaviour of PdM (M= Co, Sn, Fe and ZnO) nanoparticles deposited on YSZ solid electrolyte was evaluated for complete methane oxidation and compared to free-standing Pd catalyst. To this end, the nanoparticles were synthesized via the polyol method and tested for their open circuit catalytic oxidation and electrochemical performance in a temperature range from 320 to 400 °C under reducing, stoichiometric and oxidizing reaction conditions.The light-off experiments in open circuit condition revealed that the presence of Sn increased the catalytic rate of the reaction more than two other metals, Co and Fe, which resulted in lowering the reaction rate per unit mass of active catalyst. Furthermore, ZnO-supported Pd demonstrated the highest catalytic reactivity due to metal-support interactions. Lastly, the results demonstrate a higher level of catalytic reactivity with higher temperatures and oxygen partial pressures (pO2).Using Tafel plot calculations from the linear sweep voltammetry measurements, the exchange current density (io) was obtained for each catalyst, as well as the apparent activation energy of the reaction in the individual condition. It was found that higher exchange current density corresponds to lower open circuit catalytic rates.The catalyst was characterized thoroughly by several physicochemical techniques, such as TEM, SEM, XRD and ICP-MS.

(Invited) Water Oxidation Catalysis with Atomically Defined Active Sites on Nanostructured Materials for Solar Energy Applications

Devising cost effective methods for efficiently capturing and storing solar energy is among the grand challenges of science (1). We are using insights from studies of natural photosynthetic systems (2) to develop bioinspired materials for photo-electrochemical water oxidation and solar fuel production by using molecular catalysts and dyes attached to mesoporous metal oxide photoanodes. Molecular catalysts are known for their high activity and tunability, but their solubility and limited stability often restrict their use in practical applications. We are developing anchoring chemistry to attach molecular water-oxidation catalysts to metal oxide surfaces (3), which not only greatly increases the stability of the molecular catalyst but also improves the catalytic performance of the oxide material. Our progress on the development and characterization of molecular iridium, copper and manganese water-oxidation catalysts (4-5), along with their application for photoelectrochemical water oxidation (6) and solar fuel production, will be discussed. Directing Matter and Energy: Five Challenges for Science and the Imagination, U.S. Department of Energy, Washington, DC, December 2007.D.J. Vinyard and G.W. Brudvig, Annu. Rev. Phys. Chem. (2017) 68, 101.J.L. Troiano, R.H. Crabtree and G.W. Brudvig, ACS Appl. Mater. Interfaces (2022) 14, 6582.S.W. Sheehan et al., Nature Comm. (2015) 6, 6469.K.J. Fisher et al., ACS Catalysis (2017) 7, 3384.Y. Zhao et al., Proc. Natl. Acad. Sci. U.S.A. (2018) 115, 2902.

Getting insight into the CO tolerance over Co-modified MnSm/Ti catalyst for NH3-SCR of NOx at low temperature: Experiments and DFT studies

The existence of carbon monoxide (CO) in industrial boilers flue gas can suppress the performance of the selective catalytic reduction with NH3 (NH3-SCR) for NOx removal at low temperatures over the Mn-based catalyst, and the related mechanism is needed to be revealed for improving the NH3-SCR performance. In this work, the effects of CO on the NH3-SCR performance over MnSm/Ti catalyst were studied, and the CO tolerance of the catalyst with cobalt (Co) modification at low temperatures was evaluated. The DFT calculations were performed to reveal the mechanism for the modification of Co over the MnSm/Ti catalyst. The NOx conversion for MnSm/Ti catalyst decreased by 15.2%-21.4% at 150–300 ℃ due to the presence of CO in the NH3-SCR reaction atmosphere. After introducing Co into MnSm/Ti catalyst, the NOx conversion for MnSmCo/Ti catalyst only decreased by 8.9%-13.8% at 150–300 ℃ with the presence of CO. It was evidenced that the CO tolerance of the MnSm/Ti catalyst was enhanced with the Co modification. The characterizations of catalysts revealed that the adsorptions of NH3 and NO over the MnSm/Ti catalyst were inhibited by the presence of CO in the mixed atmosphere. Furthermore, the presence of CO in the flue gas resulted in the formation of carbonates, bicarbonates, and bridging formate on the surface of the MnSm/Ti catalysts, which would cause a decrease in the content of Mn4+ and Oα on the surface of the catalyst surface. Introducing Co into MnSm/Ti catalyst could enhance the adsorption of NH3 by forming more Lewis acid sites over the MnSmCo/Ti catalyst. The contents of Mn4+ and Oα over MnSmCo/Ti catalyst were increased via the strong electronic interaction between Co ions and Mn ions. DFT calculations proved that the adsorption of CO over the catalyst was suppressed by the modification of Co with the change of the adsorption energy of CO from −167.25 kJ/mol to −53.82 kJ/mol. Additionally, the Co modification facilitated the decomposition of the carbonate formed over the catalyst with the energy barrier of related reactions decreasing from 214.67 kJ/mol to 24.45 kJ/mol, thus improving the CO tolerance of the catalyst.

Preparation and characterization of Cu-formate heterogeneous catalysts from ash of gelam wood (Melaleuca leucadendron) for glycerol oxidation

ABSTRACT The conversion of glycerol into high-value-added chemicals has begun to take the attention of researchers in recent years. Approximately 10% (w/w) of glycerol is produced as a by-product in the manufacture of biodiesel. Through a catalytic oxidation reaction, glycerol can be converted to formic acid. In this study, glycerol was converted to formic acid as the main product by involving a heterogeneous catalyst of Cu-formate which was embedded in the ash of gelam wood (Melaleuca leucadendron). The catalyst was made with variations in the ratio of Cu-formate to gelam wood ash (GWA) = 0.125; 0.25; 0.50; and 0.75 (w/w). The catalysts were characterized by FTIR, XRD, SEM-EDX, and SAA. The Cu-formate/GWA catalyst was then tested for its activity on glycerol oxidation with various catalyst ratios, amount of catalyst (0.5–3% (w/w)), reaction temperature (50°−90°C), and reaction time (1–11 hours). The results showed that the yield of the products increased with increase in catalyst ratio. The optimal amount of catalyst was used at a concentration of 2% (w/w), a reaction temperature of 70°C, and a reaction time of 3 hours.

Shaping Y-Zeolites using in situ formation of alumina and AlPO binders: Coke-resistant catalysts for the cracking of methylcyclohexane

Endothermic catalytic cracking of hydrocarbon fuels over solid acid catalysts has been considered a potential heat sink to offset the thermal loads on high-speed flight vehicles, thus maintaining their catalyst stability and activity. Which is essential as an effective heat sink and produce fuels for sustained flight. The present work demonstrates a novel approach of dispersing zeolite in a catalyst matrix containing inorganic binders such as alumina and aluminum phosphate (ALPO) to improve the thermal, mechanical stability as well as the coke-resistance of Y-zeolites during catalytic cracking of endothermic fuels. Synthesis of such binders modified zeolite was achieved by adding Y-zeolite to pseudo boehmite, an alumina precursor followed by its hydrolysis in the presence of either nitric acid or phosphoric acid, which led to the formation of Alumina or ALPO modified zeolites. During this process, partial removal of alumina from the zeolite framework functions as seed for the growth of alumina and AlPO binders which together form a catalyst matrix consisting of zeolite and binder. Three different Y-Zeolites of varying Si/Al ratios were modified with alumina and ALPO binders using the afore-mentioned process. N2 sorption isotherms, Ammonia TPD, Solid state NMR and SEM imaging showed that these two binders modified the textural, structural, and acidic sites of the zeolites. Catalytic cracking of methylcyclohexane (model endothermic fuel) over these binder modified zeolites was carried out to study their performance and determine the conversion of methylcyclohexane, catalyst stability, product selectivity and coke deposition. Alumina and AlPO binders were observed to have differential binding with the zeolite acid sites, therefore the resultant catalyst activity, product activity and coking behavior were also found to be different. The alumina modified zeolites showed a slight decrease in the catalytic activity but promoted the formation of coke which can be easily oxidized and the selectivity towards cracked products than their isomers. In contrast, AlPO modified zeolites exhibited decreased catalytic activity but also decreased the coking considerably. Spent catalysts characterization clearly demonstrated that the binder modification of zeolites improved the catalyst stability, products selectivity, coke deposition, nature of coke and the amount of coke deposition.

Surface modification strategies for nanoparticles based on chitosan and titanium dioxide: Catalytic properties and mechanism for sodium borohydride dehydrogenation in methanol

Chitosan, which has important functional groups such as amino and hydroxyl, is effectively preferred for application areas. Due to its low cost and high chemical stability, titanium dioxide (TiO2) attracts great attention especially in the fields of environment and energy. Here, the green fabrication of two-stage catalyst particles by facile surface modification strategies was performed. In the first step, a hybrid material was fabricated by dispersing TiO2 nanoparticles on the chitosan polymer matrix by the calcination method. The catalytic performance can be further improved by changing the surface properties and additional defect sites by doping with green non-metallic heteroatoms. In the second stage, protonation with hydrochloric acid, nitrogen doping with ammonia and nitrogen and oxygen doping with nitric acid were applied to improve the surface properties of the hybrid material obtained by the hydrothermal method. These hybrid particles were performed for dehydrogenation (H2) in methanol of sodium borohydride. The most effective results were obtained with chitosan-TiO2 treated with nitric acid with an HGR value of 10118 mol g(cat)−1 min−1. The activation energy (Ea) value was calculated as 39.25 kJmol−1. XRD, XPS, SEM, EDS, TEM and FTIR analyses were used for the characterization of hybrid catalysts. Besides, the mechanism of H2 release in methanol using N, O-doped chitosan-TiO2 has been proposed.

Multielectrode electrochemical cell for in situ structural characterization of amorphous thin-film catalysts using high-energy X-ray scattering

A multielectrode-based electrochemical cell allows the structural characterization of an amorphous thin-film water oxidation catalyst under various electrochemical potentials using high-energy X-ray scattering and atomic pair distribution function (PDF) techniques. A multielectrode with five electrodes provides a sufficiently low background signal to enable high-energy X-ray scattering (HEXS) measurements and amplifies the extremely low HEXS signals from samples for high-resolution PDF analysis of in situ data from thin-film catalysts. Glassy carbon (GC) creates a relatively low intensity HEXS pattern and is used as a working electrode. Instead of a three-dimensional (3D) porous electrode architecture, the flat geometry of the electrode enables various deposition techniques to be used for the preparation of a highly conductive metal oxide layer. PDF analysis demonstrates high spatial resolution for a 230 nm thick amorphous iridium oxide film deposited on two roughened 60 µm thick GC electrodes. The PDF analysis resolves the domain size and distinguishes changes in fine structure which are directly correlated with the structure and function of the catalysts. The results bring the opportunity to analyze the structure of nanometre-scale amorphous thin-film catalysts in an electrolyte-compatible and compact 3D-printed electrochemical cell in a three-electrode configuration.

Enhanced performance and stability of Cu/ZnO catalyst by hydrophobic treatment for low-temperature methanol synthesis from CO2

CO2 hydrogenation to methanol is an efficient way to utilize CO2 and store hydrogen. However, realizing high activity and methanol selectivity as well as excellent stability are still challenges due to the competitive reverse water-gas shift (RWGS) reaction and the accumulation of water on the catalyst surface. Herein, Cu/ZnO catalyst was prepared by oxalic acid-assisted solid-state grinding method and then was subjected to hydrophobic treatment using stearic acid as a functionalization agent. The effect of stearic acid concentration on the physicochemical properties of Cu/ZnO catalysts and the catalytic activity for low-temperature CO2 hydrogenation to methanol was investigated and discussed in detail. Detailed catalyst characterizations disclosed that hydrophobic treatment using suitable concentration of stearic acid removed residues from the decomposition of oxalic acid and also increased specific surface area, surface basicity, reducibility and hydrogen adsorption strength on Cu/ZnO catalysts, leading to the enhanced catalytic performance and methanol selectivity. Among all the catalysts, Cu/Zn-2 mM catalyst exhibited methanol selectivity and methanol space time yield (STY) of 78.8% and 87.17 g/kg·h−1 at 200 ℃, much higher than those of untreated Cu/ZnO catalyst (71.7% and 68.93 g/kg·h−1). The hydrophobic Cu/Zn-2 mM catalyst also exhibited outstanding stability for low-temperature CO2 hydrogenation to methanol, keeping its activity for 100 h without obvious deactivation when compared to untreated Cu/ZnO catalyst. This facile hydrophobic treatment using stearic acid not also enhanced catalytic activity, methanol selectivity and stability of Cu/ZnO catalysts for low-temperature methanol synthesis, but also enlightened the invention of more hydrophobic materials in the near future.

Construction of microwave/PMS combined dual responsive perovskite-MXene system for antibiotic degradation: Synergistic effects of thermal and non-thermal

A series of two-dimensional catalysts (LFCO/Ti3C2-x) were prepared by dispersing perovskite on layered Ti3C2 for microwave-combined PMS catalyzed degradation of ciprofloxacin (CIP). Under the optimal treatment conditions (10% Ti3C2 composite, 1.5 g·L−1 catalyst dosage, 1 mM PMS concentration and initial pH = 7.0), the catalyst achieved 96.49% CIP removal efficiency within 14 min. The addition of Ti3C2 contributed to the granulation and homogeneous dispersion of perovskite, which facilitated charge transfer and generation of active species. The catalyst characterization before and after the reaction and experiments related to the quenching of the active species confirmed that the thermal effect of MW irradiation promoted the generation of ROS. The non-thermal effect of MW enhanced the electron transfer ability of the catalytic system and accelerated the oxidation of metal sites, which indirectly promoted the generation of ROS. Combined with LC-MS and DFT calculations, the degradation pathway and mechanism of CIP were revealed. Meanwhile, the ecotoxicity of CIP intermediates calculated using ecological structure–activity relationship software indicates that they are much less harmful or not toxic. This work opens new perspectives for the application of perovskite-MXene based catalysts in the rapid and efficient catalytic activation of MW combined AOPs for antibiotic degradation.

Enhanced catalytic stability and structural evolution of Rh-BN interface in dry reforming of methane under intensified CO2 partial pressure

Strong metal-support interaction (SMSI) is a crucial factor that determines the structure and performance of a supported metal catalyst. Herein, the SMSI effect of Rh nanoparticle catalyst supported on h-BN is investigated in the dry reforming of methane (DRM) reactions with different CO2/CH4 ratios. The catalyst characterization results demonstrate that the SMSI effect allows the Rh nanoparticles to be encapsulated by BOx overlayers under DRM reaction conditions (CO2/CH4 = 1/1), which prevents the interaction between the reactants and metal centers for causing rapid deactivation. By increasing the partial pressure of CO2 (CO2/CH4 = 3/1), Rh/BN exhibits significantly enhanced activity and long-term stability in the DRM reaction. CO2 or H2O in the reactive atmosphere can effectively etch the BOx overlayers for steadily exposing the active Rh-BN interface sites, as evidenced by the characterization. This observation extends the understanding of the SMSI effect at the interfaces between metal and non-oxide support.

Small Angle Scattering Techniques for the Study of Catalysts and Catalytic Processes

AbstractSmall‐Angle Scattering (SAS) techniques are essential tools for the characterization of catalysts before, during and after catalytic reactions. Either based on X‐Rays (SAXS) or neutrons (SANS), they provide unique structural information that helps to understand catalytic processes at the nanoscale level, allowing a rational improvement of the catalysts design. In this review, we present the key aspects involved in the use of these techniques in the catalysis field. Firstly, we introduce some of the fundamentals of the techniques and describe their main features and their impact in the catalyst design. Then, we analyze key examples of the use of SAS to study catalysts’ structure through ex situ analysis, focusing on examples involving different porous materials and metallic nanoparticles. Afterwards, we discuss in situ and operando approaches for studying catalytical processes monitored using SAS. Finally, we present perspectives and challenges for the future use of SAS in the catalysis field.

Catalytic microwave-assisted pyrolysis of plastic waste to produce naphtha for a circular economy

Catalytic cracking of plastics into naphtha as a substitute for new plastic production has the potential to contribute to the plastic circular economy. However, mitigating catalyst deactivation in large-scale processes poses a significant challenge. Here, we demonstrate a remarkable improvement (4.3 × to 12.3 ×) in catalyst lifetime by utilizing hierarchical ZSM-5 catalysts compared to conventional analogues. Increasing the Brønsted acid concentration from 0 to 302 µmol/g enhances catalyst lifetime by over 46 × and boosts cumulative aromatic selectivity from 6 to 73%. Catalyst characterization reveals the development of significant voids after modification, enhancing molecular transport within the hierarchical ZSM-5. Economic analysis shows a pilot system with a 10 ton/day capacity yielding an annual profit of $344,999 and an 11.5% return on investment. Life cycle assessment indicates a reduction of 817.6 kg CO2 eq compared to traditional plastic-to-fuels technology. These findings advance the plastic circular economy and bring us closer to commercial implementation.

Catalytic fast pyrolysis of waste truck-tire to aromatics production over metal-modified USY catalysts

This work aimed to investigate the effect of several metal-modified (Fe, Co, Ni, Cu, Zn) USY catalysts on the high-value aromatic production from fast pyrolysis of waste truck-tire in an infrared-heated fixed-bed reactor. The relationship between the physical and chemical properties of the catalyst and the production of light aromatic hydrocarbons was revealed based on comprehensive catalyst characterization and catalytic reaction test results, guiding the selection of the optimal modified metal and loading amount. Among all the investigated metal-modified USY catalysts, 1%Cu/USY catalyst exhibited the best aromatics production capacity, with a relative content of monoaromatics of 63.70% and a yield of specific aromatics of 42.92 mg/g, both of which were significantly greater than those obtained over the parent USY catalyst (58.73% and 27.23 mg/g). The introduced copper species provided abundant Lewis acid sites and cooperated with Brønsted acid sites to promote the cracking, dehydrogenation, and aromatization reactions to reach a specific balance, thus enhancing catalytic performance. However, when the loading amount exceeded 1 wt%, Cu species aggregate on the surface of the zeolite, leading to pore blockage and surface area reduction. High Cu loading amounts could also result in excessive acidity, which could cause excessive cracking of volatiles and lower aromatics selectivity. In addition, the 1%Cu/USY catalyst exhibited excellent reusability in the reaction/regeneration cycles. This work demonstrates the feasibility of producing light aromatics via WTT catalytic fast pyrolysis over Cu-modified USY catalyst, which provides new ideas for the chemical recovery of waste tires.

Boosting toluene mineralization and ozone decomposition in plasma catalytic system by regulating the oxygen vacancy over Ag-based catalyst

Incomplete mineralization and high outlet ozone concentration are two urgent issues that need to be overcome in plasma catalytic systems for the purification of volatile organic compounds (VOCs). Herein, we attempted to address these issues by coupling Ag/ZSM-5 catalyst reduced by hydrogen at different temperatures with a dielectric barrier discharge (DBD) reactor during toluene degradation. The catalyst characterization (including XRD, UV–vis, XPS, XAFS, Raman, EPR) combined with density functional theory (DFT) calculations indicated that hydrogen reduction lowered the energy between metal ions and oxygen, generating more oxygen vacancies and facilitating the transition from Ag ions to Ag0. The abundant vacancies influenced the electron properties in the adjacent atoms, making them catalytically active and thereby promoting the adsorption and activation of CO and O3. Thus, the mineralization rate and O3 decomposition performance were significantly enhanced for the hydrogen-reduced Ag/ZSM-5 catalysts. Moreover, the L-H, E-R and MVK mechanisms were first experimentally verified in plasma catalytic system by changing the background atmosphere during toluene adsorption and discharge degradation stages. This study provides insights into the rational design of highly effective catalysts in a plasma catalytic system for the removal of VOCs.

Efficient degradation of thiamethoxam pesticide in water by iron and manganese oxide composite biochar activated persulfate

Neonicotinoid pesticides in aquatic environments pose a risk to the sustainability of ecosystems and human health. However, there is limited research on the removal of these pesticides from aquatic systems. In this study, biochar doped with different Fe/Mn ratios (FeMn­BC) were prepared at various pyrolysis temperatures and used for the degradation of a typical neonicotinoid pesticide, thiamethoxam (TMX), by activated persulfate (PS). From the experimental results, it is known that the biochar with a Fe/Mn ratio of 3/1 prepared at 600 °C has the most excellent removal efficiency. Optimal degradation conditions were investigated, and under these conditions, TMX removal rates of up to 99.0 % in 90 min were achieved. The applicability of this system in natural surroundings were tested by investigating the effects of inorganic anions and humic acid and in real water samples on TMX removal. In addition, the TMX removal remainly reach to 90.0 % by FeMn-BC activated PS and basically no change after five reuse cycles. Free radical quenching experiments and electron paramagnetic resonance analysis revealed that SO4− and OH radicals on the catalyst surface were the main radicals promoting TMX degradation. Combining the catalyst characterization and experimental results, the possible mechanisms were proposed: the interaction of iron and manganese ions and the oxygen-containing functional groups on the catalyst surface together promote the generation of reactive radicals. This study provides a novel approach for removing neonicotinoid pesticides using modified biochar.

Morphology effect of Pd/In2O3/CeO2 catalysts on methanol steam reforming for hydrogen production

Catalyst support morphology strongly influences its surface and structural properties, therefore, may have a significant impact on their reactivity in heterogeneous catalysis. Herein, the Pd/In2O3/CeO2-x (loaded with 1 wt% Pd and In2O3) catalysts with different morphologies of rods(r), cubes(c) and irregularity(w) shapes were prepared by hydrothermal method and impregnation method. At temperature of 275–425 °C, as-prepared catalysts were evaluated for hydrogen production from methanol steam reforming (MSR). The activity data showed the outstanding performance of the rod-shaped Pd/In2O3/CeO2 catalysts, exhibiting the complete conversion of methanol and particularly low CO (1.3%) at 375 °C. The structural properties and physicochemical of Pd/In2O3/CeO2-x with different morphologies were characterized by means of X-ray diffraction (XRD), high resolution transmission microscopy (HR-TEM), CO pulse chemisorption, X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption of methanol (CH3OH-TPD). Activity data and catalyst characterization results correlated, and indicated that the excellent reactivity for the rod-shaped Pd/In2O3/CeO2 catalysts in MSR is ascribed to the large particle size of palladium nanoparticles and the abundant oxygen vacancies induced by the strong interaction between Pd, In and Ce. HR-TEM results revealed that rod-like CeO2 mainly expose (110) crystalline surface with high mobility of surface oxygen and possess the most abundant surface oxygen vacancies with the low formation energy, facilitating the formation of active species of Pd0 on catalyst surface, and promoting the activation and adsorption of methanol and water molecules. Furthermore, the rod-shaped Pd/In2O3/CeO2 catalysts showed excellent reactivity and stability in MSR for 30 h, demonstrating its potential of being used as catalysts in methanol steam reforming in PEMFC systems.

Copper Oxide Supported on Silica (CuO/SiO2): A Highly Efficient Heterogeneous Catalyst for the Synthesis of 1,2-Dihydroquinazolines at Room Temperature

Abstract: A copper oxide supported on silica (CuO/SiO2) catalyst has been prepared which catalyzes a three-component reaction between 2-aminobenzopenone, benzaldehyde, and ammonium hydroxide leading to a convenient synthesis of 1,2-dihydroquinazoline. The main advantages of the process over the previous reports are room temperature reaction, selective formation of 1,2-dihydroquinazoline as a sole product, and recyclability of the catalyst. Seventeen derivatives with various substituents are prepared. The catalyst (fresh and recovered) has been fully characterized using HR-TEM, BET Surface area, XPS, FTIR, and XRD. The enhanced activity and selectivity of the catalyst (towards 1,2-dihydroquinazoline) is attributed to the formation of Cu-O-Si type surface structure which is also explained by the help of different analytical techniques. Further, the reaction was performed without a catalyst, with CuO and SiO2 separately. Based on catalyst characterization and experimental results a possible mechanism has been proposed and discussed thoroughly. Recovery and reusability of the catalyst have also been studied.