Powder Catalysts Research Articles

Plasma catalysis: separating plasma and surface contributions for an Ar/N2/O2 atmospheric discharge interacting with a Pt catalyst

Atmospheric pressure non-equilibrium plasmas can form nitrogen oxide (NO x ) compounds directly from nitrogen and oxygen without a catalyst, and at lower catalyst temperatures than would be possible without plasma. In this work, the oxidation of plasma-produced NO from an Ar/N2/O2 non-equilibrium atmospheric-pressure plasma-jet (APPJ) over a platinum-on-alumina powder catalyst was investigated with in-situ infrared spectroscopy. Products downstream of the catalyst bed were analyzed along with catalyst surface species. The catalyst was exposed to plasma at both constant temperature and a cyclic temperature ramp in order to study long-lasting and transient surface changes. Primary incident reactive species to the catalyst were assessed to be NO and O3. Pt-Al2O3 at 350 °C increased oxidation of NO relative to Al2O3 or an empty chamber. The surface state of Pt-Al2O3 evolves during plasma-effluent exposure and requires upwards of 20 min exposure for stabilization compared to Al2O3. Once stable surface conditions are achieved, thermal cycling reveals a repeatable hysteresis pattern in downstream products. At low temperature, oxygen and NO x accumulate on the catalyst surface and react at elevated temperatures to form NO2. Increasing plasma power and O2:N2 ratio increases the hysteresis of the heating relative to the cooling curves in the pattern of NO2 formation. The limitation on NO oxidation at high temperatures was assessed to be Pt-O which is depleted as the catalyst is heated. Once stored species have been depleted, NO oxidation rates are determined by incoming reactants. Two overlapping NO oxidation patterns are identified, one determined by surface reactants formed at low temperature, and the other by reactants arriving at the surface at high temperature. The plasma is responsible for providing the reactants to the catalyst surface, while the catalyst enables reaction at high temperature or storage at low temperature for subsequent reaction.

Novel protonated LiCoO2 as a catalyst for the thermal decomposition of ammonium perchlorate

ABSTRACT LiCoO2 (LCO) powders were protonated and their catalytic activity on the thermal decomposition of ammonium perchlorate (AP) was tested using differential scanning calorimetry and thermogravimetric analysis. Powders were characterized using SEM, XRD, and BET surface area analysis to quantify the morphology and structure. The thermal analysis showed that protonated powders enhanced the catalytic activity in AP decomposition over commercial and unmodified LiCoO2, Fe2O3 and Co3O4 catalyst powders. The activation energies were investigated using the model-free Kissinger method, and the possible mechanisms governing the catalytic activity are discussed. The activation energies of AP thermal decomposition were decreased significantly by the use of these protonated catalysts. For neat AP, commercial LCO, and protonated LCO the activation energy for LTD and HTD were: 104 ± 5 kJ/mol and 143 ± 4 kJ/mol, 89 ± 4 kJ/mol and 92 ± 14 kJ/mol, and 76 ± 6 kJ/mol and 98 ± 7 kJ/mol respectively. We believe the hydrogen and vacancies in the protonated lattice act as reaction sites for the decomposition of AP.

Novel oxygen vacancy-rich Bi2MoO6-SOVs/MgFe2O4 S-scheme heterojunction piezo-photocatalytic for efficient degradation of norfloxacin and theoretical calculations

Magnetic materials introduced into semiconductor catalysts greatly compensate for the traditional powder catalysts’ disadvantages of difficult recovery and low reuse rate. A series of oxygen vacancy-rich Bi2MoO6-SOVs/MgFe2O4 nanomicrospheres are prepared by stepwise synthesis. By simulating visible light irradiation and ultrasonic co-illumination to degrade norfloxacin (NOR) to evaluate the piezo-photocatalytic performance of the samples, the Bi2MoO6-SOVs/MgFe2O4-15 % has a degradation efficiency of 96.8 % within 30 min and high chemical stability. This method not only improves the limitations of finite free electrons in piezoelectric catalysis but also effectively suppresses the rapid recombination of photogenerated electrons-holes in photocatalysis. To improve the practical application of this catalyst, we also consider the effects of pH, co-existing ions in water and different water matrices on NOR degradation. In situ X-ray photoelectron spectroscopy (ISI-XPS) and density functional theory (DFT) calculations further confirm the existence of an S-scheme charge transfer mechanism and oxygen vacancies (SOVs).

In-situ growth of Ni3S2@Mo2S3 catalyst on Mo-Ni foam for degradation of p-nitrophenol with a good synergetic effect by using ozone

In this study, Ni3S2@Mo2S3 composites were grown on the surface of molybdenum-nickel (Mo-Ni) foam in situ by a one-step hydrothermal method. With p-nitrophenol (PNP) as the target pollutant, the catalyst can produce a good synergistic effect with ozone, and the degradation rate of PNP is more than 96%. Even after five cycles, Ni3S2@Mo2S3-NF/O3 was able to degrade PNP efficiently and stably. In addition, the unique three-dimensional structure of Ni3S2@Mo2S3-NF solves the separation and recycling problem of traditional powder catalysts by maintaining the structural stability during the use process and thus, may reduce the cost of water treatment. The degradation process is mainly dominated by non-radical pathways, and the radical pathway, which work synergistically. This work reveals the influencing factors and degradation mechanism of Ni3S2@Mo2S3-NF/O3 system for PNP degradation, which provides a new idea for water treatment and broadens its potential application.

ZnCrXFe2-XO4 (X = 0–2) porous powder prepared through self-combustion glycine nitrate process and applied to methyl alcohol steam reforming for production of pure hydrogen

Climate change, global warming, and energy crisis have become an important problem due to the environmental impact of fossil fuels. Hence, alternate energy source is needed for environmental remediation. One such source could be hydrogen (H2). H2 is used as an alternate energy carrier due to it is non-toxic, clean, and efficient. Steam reforming of methyl alcohol (or) methanol (SRM) is a widely available and low-cost hydrogen production method. In this stream-reforming process, mostly commercial zinc-supported catalyst is used, these have some economic defect. Therefore, we need to find alternate suitable catalysts for the SRM process. In this study, ZnCrXFe2-XO4 (X = 0–2) porous catalyst powders of different ratios were synthesized by the glycine nitrate process (GNP) for hydrogen production by SRM. The specific surface areas of the ZnCrXFe2-XO4 powders ranged from 15.75 m2/g to 45.16 m2/g. The ZnCr0.4Fe1.6O4 powder had the highest H2 production without activation, reaching 6850.33 ml STP min−1 g-cat−1 at a reaction temperature of 450 °C. ZnCr0.4Fe1.6O4 porous powders prepared using the GNP method have simple, rapid process steps, low cost, high catalytic activity, and they can be applied to hydrogen fuel cells or other related catalysis applications in the future. The pure hydrogen production performance of these ZnCrXFe2-XO4 catalysts could be of great importance in industry and economic impact.

Porous organic semiconductor/PET composite fibre for the synergistic removal of hexavalent chromium and organic pollutants under sunlight

ABSTRACT In this study, the porous graphite phase carbon nitride photocatalyst (P-g-C3N4) is prepared by the CaCO3 template method, and then P-g-C3N4/T-polyethylene terephthalate (T-PET) catalytic fibre is prepared by the padding method. P-g-C3N4 can provide more active sites than g-C3N4 as proved by the Brunauer–Emmett–Teller and the UV–Visible diffuse reflectance test. P-g-C3N4 powder catalyst successfully supports PET fibre as proved by scanning electron microscope, Fourier infrared spectroscopy and X-ray diffraction spectroscopy. The photocatalytic performance of P-g-C3N4/T-PET catalytic fibre is tested by constructing a single hexavalent chromium or hexavalent chromium/organic pollutant binary pollution system. The potential application value of P-g-C3N4/T-PET catalytic fibre is further explored by simulating the complex actual water environment. After five recycles, P-g-C3N4/T-PET catalytic fibre shows good catalytic performance. The mechanism of P-g-C3N4/PET photocatalytic degradation of organic pollutants is proposed through the capture agent experiment and electron paramagnetic resonance spectroscopy. Among them, •O2 − is the most important active species of P-g-C3N4 catalytic fibre, which is used for the oxidation of organic pollutants. At the same time, photoelectrons generated by the catalytic fibre are used to reduce hexavalent chromium. The efficiency of P-g-C3N4 to remove pollutants is improved by using PET fibre as a carrier, which not only solves the problem of difficult recovery of powder catalysts but also provides more active sites.

Nitrogen fixation as NOx using air plasma coupled with heterogeneous catalysis at atmospheric pressure

AbstractThis study presents insights into the use of activated catalysts to improve the energy efficiency of production in atmospheric pressure air plasma. The introduction of catalysts in the direct current glow discharge system reduces the energy cost of production by up to 45% at low gas flow rates. Notably, even when positioned away from the plasma zone, the catalyst enhanced production, suggesting a significant role for the catalytic activation of downstream neutral species. The study also introduced a novel approach involving an air plasma jet infused with floating catalyst powder. This method significantly increased energy efficiency at higher discharge currents, with an associated energy cost of 2.9 MJ/mol for production.

Evonik expanding production of nickel powder catalysts

Evonik expanding production of nickel powder catalysts

Powder properties of carbon-based solid acid catalyst for designing cellulose hydrolysis reactor with stirring apparatus

The powder properties of a carbon-based solid acid catalyst, an amorphous carbon material bearing SO3H, COOH and OH groups, were investigated for the hydrolysis of cellulose. The Carr flowability and floodability indices, the angle of internal friction (adherence), and the particle size distribution and shape for the powder catalyst were determined. The need to develop a special reactor with a stirring apparatus for the hydrolysis of cellulose was determined based on the Carr flowability index. Insight into the interaction or adherence between the catalyst and crystalline cellulose during the hydrolysis process was gained by measuring the internal friction angle. The optimum moisture content in the catalyst to achieve the maximum adherence was investigated.

Promoting photo-Fenton reactions by anchoring Fe doped g-C3N4 onto an amidoxime-functionalized fibrous support for organic contaminants removal

Fe-doped graphitic carbon nitride (g-C3N4) represents an attractive photo-Fenton catalyst for organic contaminants removal, but the practical performances still need to be improved for large-scale application. Herein, we developed a high-efficiency photo-Fenton catalyst by anchoring Fe-g-C3N4 onto an amidoxime-functionalized polyacrylonitrile fiber (AP) substrate through a simple hydrothermal approach. Comprehensive characterizations demonstrate the strong catalyst-support interaction via the axial coordination bonding between -OH groups and Fe3+, which could induce electric polarization of Fe-g-C3N4 to promote the H2O2 adsorption and activation. The fibrous support could also accelerate the photoelectrons transfer from g-C3N4 to Fe3+ by strengthening the d-π conjugated large π bond, as well as alleviate the backflow recombination from Fe3+ to g-C3N4 through the electron sink effect. These synergistic qualities resulted in superior photo-Fenton performance for organic contaminants removal, which delivered 4.0-fold higher degradation kinetics than that of the Fe doped g-C3N4 powder catalyst and exhibited unexpected high activity at strong basic environment (pH = 12). Our work demonstrates an ingenious and simple way to design exceptional photo-Fenton catalysts for environmental remediation.

Degradation of organic pollutants by floatable Fe-PAM hydrogel

The heterogeneous-Fenton process is a highly effective alternative technology for degrading pollutants in wastewater. To overcome the limitation of catalyst powders for practical use and to improve the reusability, polyacrylamide (PAM) hydrogel immobilized with iron (Fe-PAM) was prepared. The PAM hydrogel was synthesized at various amounts of N,N′-methylenebisacrylamide (MBA) as a crosslinker and then immersed in Fe3+ solution to obtain floatable Fe-PAM hydrogel after drying. The Fe-PAM hydrogel in the presence of H2O2 acted as an effective catalyst to degrade rhodamine B, reactive orange 16, and tetracycline hydrochloride in aqueous solutions via the heterogeneous-Fenton-like process. The degradation of pollutants was confirmed by mass spectrometry. The effects of H2O2, pollutant initial concentrations, and catalyst dosage, on the degradation performance were reported. The Fe-PAM hydrogel prepared with 3 % MBA exhibited favorable properties, including low iron leaching and high degradation activity. The developed materials could be reused for at least 10 cycles, highlighting its potential for wastewater treatment applications.

Electrochemically anodized solid and stable ZnO nanorods as an adsorbent/ nanophotocatalyst: ROS mediated degradation of azo dyes congo red and methyl orange

The fast industrial growth and discharge of industrial effluents into water bodies necessitate investigations of biocompatible and economically viable strategies to combat water pollution. This work presents the successful use of solid and stable ZnO nanorods fabricated by anodization as an adsorbent and photocatalyst for water treatment, circumventing the requirement of any post treatments currently needed with powder catalyst. The ZnO nanorods well- characterized structurally, morphologically and compositionally by a variety of methods manifest superior photocatalytic property than adsorption ability. Scavenger tests indicate that the photocatalytic action is controlled predominantly by superoxide (*O2−) radicals. Kinetic studies reveal that adsorption of MO as well as CR follow pseudo second order model favouring chemisorption, while adsorption isotherms correlate well with the Freundlich model suggesting heterogenous mode of dye adsorption. The photocatalyst manifests good cyclic stability with reduction in dye degradation efficiency by only 4–8 % in the fourth cycle of operation.

Design and fabrication of the alumina nanofibers decorated with isolated ZSM-5 using electrospinning method: A novel catalyst for methanol conversion to light olefins

ZSM-5 nanoparticles are widely used as the catalyst in the methanol conversion to olefins (MTO) process due to their high surface area and short diffusion path length. However, agglomerate formation is a challenge for this catalyst. To address this issue, in this study, electrospinning was used for the first time to synthesize fibrous catalysts comprised of ZSM-5 nanoparticles embedded in the alumina nanofibers. The catalysts were characterized using XRD, FTIR, SEM, TEM, EDX-map, BET, and NH3-TPD analyses. In the synthesized samples, ZSM-5 nanoparticles with an average particle size of 683 nm are uniformly and homogeneously dispersed over alumina nanofibers with a 300 nm diameter. These composites form core-shell structures and have a reactor porosity of 0.85, which is higher than that of parent ZSM-5. In the MTO process, electrospun catalysts demonstrate superior catalytic activity and a longer lifespan than powder catalysts. 80 wt% ZSM-5- 20 wt% Al2O3 with 47.76 % light olefin selectivity and complete methanol conversion after 321min on stream performed better than 50 wt% ZSM-5-50 wt% Al2O3. Moreover, a lower coke formation of about 3.28 % was achieved for the 80 wt% ZSM-5- 20 wt% Al2O3 sample. The reduced bulk density of the electrospun samples increases the probability of reactant and catalyst contact. Additionally, electrospinning is an effective method for reducing particle aggregation and improving catalytic process efficiency.

Phosphorus vacancy-rich FeP@Al2O3 catalyze hydrogen peroxide decomposition for wastewater purification: Catalytic mechanism and performance evaluation

In this work, phosphorus vacancies-rich (PV-rich) FeP@Al2O3 spheres with 4–6 mm were prepared by FeSO4 as initial material and porous Al2O3 as carrier. The formation of FeP@Al2O3 experienced oxidation, polymerization, load, transformation and phosphorization processes. PV-rich FeP@Al2O3 catalyst not only overcame the shortcomings of powder catalyst, such as easy loss and difficult recovery after reaction, but also exhibited high catalytic activity for the activation of H2O2 and the degradation of antibiotics and dyes. The high removal efficiencies were remained over 9 cycles. Mechanism research indicated that both Fe and P could activate H2O2 to generate •OH. Experimental and density functional theory calculation results showed that the formation of PVs allowed more electrons to be transferred to O2 to produce O2•−. The •OH and O2•− can effectively degrade pollutants in a batch reactor and a continuous degradation reactor. This study provided an essential reference for the rational design of high-performance Fenton-like catalyst to degrade organic wastewaters.

Designing hierarchically porous zero-valent iron via 3D printing to degrade organic pollutants by activating peroxymonosulfate using high-valent iron-oxo species

Zero-valent iron (ZVI) has emerged as an efficient catalyst for facilitating the decomposition of organic pollutants. However, practical applications of ZVI remain limited owing to its susceptibility towards oxidation and agglomeration. Herein, we utilize 3D printing to fabricate hierarchically porous ZVI (3D-ZVI), which displays a high level of printing precision and superb compression resistance. The 3D-ZVI catalyst can effectively activate peroxymonosulfate (PMS) to degrade a diverse selection of organic contaminants. Notably, while the catalytic activity of 3D-ZVI is comparable to that of Fe powder under similar conditions, the concentration of leached Fe ions of the former is 6.3 times lower than that of the latter. Moreover, 3D-ZVI is capable of maintaining an efficient catalytic performance throughout 45 continuous reactions, which is significantly superior to most previously reported powder catalysts. The high-valent iron-oxo species generated in the 3D-ZVI/PMS system are primarily responsible for contaminant removal, while hydroxyl and sulfate radicals play a lesser role. Additionally, the degradation intermediates and their toxicity levels are investigated. This work provides insight into the practical applications of the ZVI/PMS system, and it also serves as a guide for the rational design of efficient and stable catalysts that can be conveniently recovered from aqueous environments.

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.