Temperature-programmed Reduction Research Articles

The Effect of the Metal Oxide as the Support for Silver Nanoparticles on the Catalytic Activity for Ammonia Ozonation

Ammonia is one of the common inorganic pollutants in surface waters. It can come from a wide range of sources through the discharge of wastewater (industry, agriculture, and municipal waters). Catalytic ozonation reaction can efficiently remove ammonia nitrogen without introducing other pollutants and improve the nitrogen selectivity of reaction products by controlling the reaction conditions. Catalysts based on silver nanoparticles (Ag NPs) have shown excellent O3 decomposition performance; therefore, they are promising catalysts for catalytic ammonia ozonation due to their high reactivity, stability, and selectivity to N2. In this study, we synthesized well-defined silver nanoparticles (Ag NPs) using a modified alkaline polyol method and then dispersed them on solid oxide supports (Fe3O4, TiO2, and WO3). Before being deposited on the oxide support, the silver nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV-VIS spectroscopy. The obtained catalysts, Ag_Fe3O4, Ag_TiO2, and Ag_WO3 were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), BET surface area analysis, UV-VIS spectroscopy, temperature-programmed reduction (H2-TPR), and temperature-programmed desorption (TPD) of CO2 and NH3. It has been demonstrated that the nature of the support significantly influences the physicochemical properties of the catalysts, as well as their catalytic performance in ammonia ozonation reaction.

Synergetic effects of cerium and titanium on the catalytic performance of NiMn2O4 for selective catalytic reduction of NO by NH3.

In this work, NiMn2O4/TiO2-CeO2 (Ce = 1.15, 2.5, 5, 7.5%) nanocomposites were prepared by the co-precipitation method and evaluated for the selective catalytic reduction of NOx with NH3. The physical and chemical properties of the synthesized catalysts were examined using X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), Brunauer-Emmett-Teller (BET), temperature programmed desorption (TPD), temperature-programmed reduction of H2 (H2-TPR), and inductively coupled plasma optical emission spectrometry (ICP). The activity of NiMn2O4 catalysts was greatly enhanced by the addition of TiO2 and CeO2 in the temperature window of 200 to 400°C and the space velocity of 10,000 to 40,000h-1; NiMn2O4/TiO2-CeO2 (Ce = 5%) demonstrated the highest catalytic activity.

Development of supported nickel-containing catalysts for methane tri-reforming: influence of pretreatment conditions

To improve the efficiency of catalysts for methane tri-reforming, the effect of pretreatment conditions of the Ce0.2Ni0.8O1.2/Al2O3 catalyst on its physicochemical and functional properties was studied. A set of methods (thermal analysis, low-temperature nitrogen adsorption, X-ray phase analysis, electron microscopy, temperature-programmed reduction with hydrogen) has established that varying the composition of the gaseous medium (oxidizing, inert, reducing) used during pretreatment at 800 °C allows one to adjust the textural, structural and redox characteristics of the catalyst and, as a consequence, its functional properties. It has been shown that in the series of compositions of the gas environment used in the pretreatment of the catalyst, oxidative → inert → reducing, an increase in the specific surface area and dispersion of the active component is observed, but a decrease in the resistance of the sample to reoxidation and coking. It has been established that the highest and most stable performance of the methane tri-reforming process (H2 yield – 86 % at CH4 conversion – 95 %) is provided by the catalyst after pretreatment in an inert environment due to the implementation of the optimal degree of metal-support interaction and an increase in the concentration of centers involved in CO2 activation.

Enhancing the CO Oxidation Performance of Copper by Alloying with Immiscible Tantalum.

Copper-tantalum (Cu-Ta) immiscible alloy nanoparticles (NPs) have been the subject of extensive research in the field of structural materials, due to their exceptional nanostructural stability and high-temperature creep properties. However, Cu is also a highly active oxidation catalyst due to its abundant valence changes. In this study, we have for the first time obtained homogeneous CuxTa1-x (x = 0.5, 0.7, 0.9, 1) nanoparticles by wet coreduction with an average particle size of approximately 30 nm. Testing verified all the CuxTa1-x/TiO2 (x = 0.5, 0.7, 0.9) showed higher CO oxidation activity than Cu/TiO2, with Cu0.7Ta0.3/TiO2 exhibiting the most promising performance. The temperature-programmed reduction with hydrogen demonstrated that Cu0.7Ta0.3/TiO2 exhibits enhanced redox properties. While kinetic studies indicated that the reaction of the Cu0.7Ta0.3/TiO2 catalyst followed the Langmuir-Hinshelwood mechanism, in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) verified the introduction of Ta induced the generation of bicarbonate as an intermediate product and increased the adsorption capacity of Cu+ on CO in the catalyst, which facilitated the reaction of surface adsorbed CO with oxygen and led to the enhanced CO oxidation activity.

Methane Decomposition over a Titanium-Alumina and Iron Catalyst Assisted by Lanthanides to Produce High-Performance COx-Free H2 and Carbon Nanotubes

COx-free H2, along with uniform carbon nanotubes, can be achieved together in high yield by CH4 decomposition. It only needs a proper catalyst and reaction condition. Herein, Fe-based catalyst dispersed over titania-incorporated-alumina (Fe/Ti-Al), with the promotional addition of lanthanides, like CeO2 and La2O3, over it, is investigated for a methane decomposition reaction at 800 °C with GHSV 6 L/(g·h) in a fixed-bed reactor. The catalysts are characterized by temperature-programmed reduction (TPR), powder X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). The promoted catalysts are facilitated with higher surface area and enhanced dispersion and concentration of active sites, resulting in higher H2 and carbon yields than unpromoted catalysts. Ceria-promoted 20Fe/Ti-Al catalyst had the highest concentration of active sites and always attained the highest activity in the initial hours. The 20Fe-2.5Ce/Ti-Al catalyst attains >90% CH4 conversion, >80% H2-yield, and 92% carbon yield up to 480 min time on stream. The carbon nanotube over this catalyst is highly uniform, consistent, and has the highest degree of crystallinity. The supremacy of ceria-promoted catalyst attained >90% CH4 conversion even after the second cycle of regeneration studies (against 87% in lanthanum-promoted catalyst), up to 240 min time on stream. This study plots the path of achieving catalytic and carbon excellence over Fe-based catalysts through CH4 decomposition.

Effect of Preparation Conditions of Fe@SiO2 Catalyst on Its Structure Using High-Pressure Activity Studies in a 3D-Printed SS Microreactor.

Fischer-Tropsch synthesis (FTS) in a 3D-printed stainless steel (SS) microchannel microreactor was investigated using Fe@SiO2 catalysts. The catalysts were prepared by two different techniques: one pot (OP) and autoclave (AC). The mesoporous structure of the two catalysts, Fe@SiO2 (OP) and Fe@SiO2 (AC), ensured a large contact area between the reactants and the catalyst. They were characterized by N2 physisorption, H2 temperature-programmed reduction (H2-TPR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron microscopy (XPS), and thermogravimetric analysis-differential scanning calorimetry (TGA-DSC) techniques. The AC catalyst had a clear core-shell structure and showed a much greater surface area than that prepared by the OP method. The activities of the catalysts in terms of FTS were studied in the 200-350 °C temperature range at 20-bar pressure with a H2/CO molar ratio of 2:1. The Fe@SiO2 (AC) catalyst showed higher selectivity and higher CO conversion to olefins than Fe@SiO2 (OP). Stability studies of both catalysts were carried out for 30 h at 320 °C at 20 bar with a feed gas molar ratio of 2:1. The Fe@SiO2 (AC) catalyst showed higher stability and yielded consistent CO conversion compared to the Fe@SiO2 (OP) catalyst.

Bimetallic Ruthenium‐Cobalt Catalyst Supported on Carbon Nanotubes: Synthesis, Characterization, and Application in Electrochemical Sensing of Isoleucine

AbstractIn this work, a bimetallic Ru‐Co catalyst based on carbon nanotubes (Ru‐Co/CNT) with a Ru to Co ratio of 95:5 is developed. The catalyst, featuring a total metal loading of 3% on the CNTs, is synthesized using the NaBH4 reduction method. Several analytical analyses are used to detect the properties of the Ru‐Co/CNT catalyst. X‐ray diffraction (XRD) provides information on crystal structures of the catalysts, high‐resolution transmission electron microscopy (HR‐TEM) reveals particle size and distribution, inductively coupled plasma mass spectrometry (ICP‐MS) measures the elemental composition, and X‐ray photoelectron spectroscopy (XPS) use to investigate the chemical oxidation states. In addition, thermal techniques including temperature‐programmed reduction (TPR), temperature‐programmed oxidation (TPO), and temperature‐programmed desorption (TPD) are used to recognize the active sites on the catalyst's surface and the acidity. Then, the Ru‐Co/CNT catalyst is applied as a sensor for isoleucine amino acid for the first time. It shows high performance with these parameters, sensitivity (0.002 mA cm−2 mm), LOD – limit of detection (0.04 µm), and LOQ – limit of quantification (0.12 µm). Moreover, the interferences of common serum blood including (D‐glucose, uric acid, ascorbic acid, and L‐tryptophan) are studied. The findings indicated that the sensor is applicable to work in complex biological systems.

Elucidating the reaction kinetics of hydrogen generation via ethanol steam reforming using a nickel-based catalyst

Abstract The continuous rise in CO2 emissions from fossil fuel consumption has intensified the search for alternative clean energy sources. Hydrogen produced from renewable sources like ethanol offers a promising alternative to fossil fuels, mitigating CO2 emissions. This study investigates the kinetics of hydrogen production via ethanol steam reforming using a nickel-based catalyst, specifically the Ar-401 catalyst. Characterization techniques, including scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, transmission electron microscopy, Brunauer–Emmett–Teller method, temperature-programmed reduction, and powder X-ray diffraction, were used to analyze the catalyst properties. Under optimal conditions of 973 K, atmospheric pressure, and a steam-to-ethanol ratio of 9, we achieved 100% ethanol conversion, 74.8% hydrogen selectivity, and 85% hydrogen yield. Kinetic experiments were conducted under kinetically controlled conditions, examining the effects of temperature (473–673 K) and weight hourly space velocity ranging from 1 to 15 (g·h/mol). A power law kinetic model was developed, yielding an activation energy of 11.17 kJ/mol and a reaction order of 0.46, with an absolute average deviation of 3.23% between predicted and experimental rates. This study provides key insights into the reaction mechanisms and highlights the effectiveness of the nickel-based catalyst, providing valuable insights for the design of efficient chemical reactors for sustainable hydrogen production.

Alkali-Boosted Catalytic Activity of Co-Based Catalysts Supported by Nanoporous Carbon in the Hydrodeoxygenation of Guaiacol

The catalytic activity and selectivity of Co-based catalysts supported on home-made nanoporous carbon was studied as a function of the type of alkali promoter (Ca and Mg). The catalysts were characterized by N2 adsorption/desorption isotherms, temperature-programmed reduction, CO chemisorption, and X-ray diffraction patterns. The catalysts were compared against carbon-supported alkali-promoted Ni-based catalysts and Re-containing catalysts. The catalytic activity of the Co-based catalyst was clearly enhanced in the presence of Ca and Mg, and it was higher than the Ni-based catalysts and comparable to that obtained using an ReC catalyst. The initial activity of the Mg-promoted catalyst increased by a factor of up to 2.5 times higher compared to the non-promoted catalyst. Moreover, this catalyst showed a turnover frequency of up to 5 times higher than equivalent carbon-supported Re-based catalysts. Significant changes were not observed in the selectivity of products after the incorporation of alkali, with cyclohexane being the main product. However, it was demonstrated that the presence of alkali led to a faster and higher production of cyclohexane from the demethoxylation of phenol and the dehydrogenation of cyclohexanol. The present results suggest that Co-based catalysts are an economical alternative for the catalytic conversion of representative target molecules from bio-oil feed.

Influence of palladium state on the efficiency of hexane isomerization catalysts

In this work, the catalytic properties of palladium catalysts based on Al2O3, SiO2, their mechanical mixtures with SO4-ZrO2 and the Pd/SO4-ZrO2-Al2O3 catalyst in the hexane isomerization reaction were studied. The catalysts were characterized by low-temperature nitrogen adsorption, X-ray diffraction, transmission electron microscopy, temperature-programmed reduction, IR spectroscopy of adsorbed CO, and XPS. It has been shown that the nature of the palladium support and precursor influences the size and charge state of palladium particles in catalysts. It has been established that the most active in the hexane isomerization reaction are catalytic systems in which positively charged forms of palladium are present.

On the Surface Compositions of Molybdenum Carbide Nanoparticles for Electrocatalytic Applications

Perspective On the Surface Compositions of Molybdenum Carbide Nanoparticles for Electrocatalytic Applications Siying Yu and Hong Yang * Department of Chemical and Biomolecular Engineering, University of Illinois Urbana-Champaign, 600 S. Mathews, Urbana, IL 61801, USA * Correspondence: hy66@illinois.edu Received: 28 November 2024; Accepted: 2 December 2024; Published: 6 December 2024 Abstract: Molybdenum carbide has attracted much research attention for its precious metal-like catalytic properties, especially in hydrogen-involved reactions. It possesses rich crystal and surface structures leading to different activity and product selectivity. With advances in nanoengineering and new understanding of their surfaces and interfaces, one can control the transition between different phases and surface structures for molybdenum carbide nanoparticles. In this context, it is essential to understand their surface compositions and structures under operating conditions in addition to their intrinsic ones under ambient conditions without external cues. The necessity of surface study also comes from the mild oxidation brought by passivation in carbide nanoparticles. made using the bottom-up synthesis or solid-gas phase temperature-programmed reduction. In this perspective, we first introduce the relevant crystal structures of molybdenum carbides and highlight the features of the three types of chemical bonding within. We then briefly review the studies of thermodynamically favored surface components and nanostructures for partially oxidized molybdenum carbide nanoparticles based on both experimental and theoretical data. An electrochemical oxidation method is used to illustrate the feasibility in controlling and understanding the surface oxidation. Finally, structure-property relationship is discussed with several recent examples, focusing on the effect of phase dependency on the adsorption energy of reaction intermediates.

Exploring the impact of Nickel on ceria doped Cobalt catalysts for low-temperature catalytic combustion of methane

Exploring the impact of Nickel on ceria doped Cobalt catalysts for low-temperature catalytic combustion of methane

Hydrotalcite-derived well-dispersed and thermally stable cobalt nanoparticle catalyst for ammonia decomposition

Hydrotalcite-derived well-dispersed and thermally stable cobalt nanoparticle catalyst for ammonia decomposition

Aspects of Fe-Incorporation into CaTiO3-SrTiO3 Perovskites and Their Catalytic Application for Ammonia SCO/SCR.

Perovskite materials in the CaTiO3-SrTiO3 system doped with different amounts of iron (1, 2 and 5 mol.%) and various Ca/Sr ratios were prepared by the modified citrate method. Additionally, the materials with 0.05 deficiency in strontium/calcium sublattice and 5 mol.% of Fe were also synthesised. The materials were subjected to structural (XRD, XANES) and microstructural (SEM) characterisation, as well as the analysis of susceptibility to reduction/oxidation processes. The structural analysis indicates a lack of iron-containing phases; thus, an incorporation of Fe into the perovskite structure was postulated. Additionally, the oxidation state of iron in the perovskite structure changes with the dopant amount. The temperature-programmed reduction measurements showed partial reversibility of the reduction processes. For the materials with the highest iron amount, the catalytic tests in NH3-SCO and NH3-SCR reactions were carried out. The materials showed high catalytic activity and high selectivity to N2 in the NH3-SCR process; however, they were inactive in NH3-SCO.

CO Oxidation over Cu/Ce Binary Oxide Prepared via the Solvothermal Method: Effects of Cerium Precursors on Properties and Catalytic Behavior

Cu/Ce binary oxides were prepared via the one-pot solvothermal method, and the effects of different cerium precursors (cerium nitrate and cerium ammonium nitrate) on the catalytic activity and resistance to water vapor or CO2 of the prepared samples for low-temperature CO oxidation reaction were investigated. The physicochemical characteristics of the catalysts were characterized via thermal analyses (TG-DSC), X-ray diffraction (XRD), Raman spectroscopy, N2 adsorption/desorption, inductively coupled plasma-atomic emission spectrometry (ICP-AES), X-ray photoelectron spectroscopy (XPS), in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTs), and temperature-programmed reduction with H2 (H2-TPR). The results indicated that the CuO/CeO2 catalyst (CC-N) prepared with cerium nitrate showed higher activity for low-temperature CO oxidation, which can be ascribed to its larger specific surface area and pore volume, higher amounts of highly dispersed CuO species with strong interaction with CeO2, Cu+ species, and more active surface oxygen species, compared with the counterpart prepared with cerium ammonium nitrate (CC-NH). Furthermore, the CC-N catalyst also exhibited better resistance to CO2 poisoning than CC-NH.

Cu-Doped La0.3Sr1.7Fe1.5Mo0.5O6-σ Decorated with Exsolved Nanoparticles for the Improvement of Syngas Production in Solid Oxide Electrolysers

A major concern within modern society is the need to substitute the fossil fuels with more renewable sources of the energy. Chemical industry is one of major players in the field of the usage of the crude oil to produce more complex chemicals. Despite of being good source of carbon species, a dropping amount of the coal and oil is raising the questions for future solutions. Carbon dioxide can be promising and sustainable source of carbon, but its high C-O bond energy (806 kJmol-1) poses general problems in efficient utilization. The most common feedstock in chemical synthesis is the syngas, a mixture of H2 and CO, which can be simply processed into more complex molecules like e.g., methanol, dimethyl ether, or methane.Highly inert CO2 can be transformed into more valuable CO via, so called, Reverse Water-Gas Shift Reaction (RWGS). Even though there are couple proposed CO2 activation mechanisms, and knowledge on the reaction is quite high, the common issue is still proper selection of the catalyst for the reaction. In the surface redox mechanism Cu metal is being oxidized by CO2 to form Cu2O with the release of CO. After that, Cu+ ions are getting reduced back to metallic copper using surrounding H2. Solid Oxide Cells can become good source of ‘green’ hydrogen and, at the same time, perform direct electrolysis or chemical reduction of CO2. High temperature, at which SOECs are working, is beneficial from the point of Faradaic efficiency and CO2 conversion rate. Steam electrode of SOEC contains copious amount of nickel. It is also a well-known catalyst for many reactions, but in this case the electrodes are struggling under carbon-rich atmosphere. Therefore, an addition of different catalytic materials is needed. Commonly used are mixed catalytic heterogenous systems composed of Cu supported on oxide materials e.g., FexOy, MoO3, La2O3, and many more.In this study a series of catalysts for SOECs were fabricated based on the Cu-doped double perovskite structure able to exsolve intermixed Cu or Cu-Fe nanoparticles supported on the matrix lattice of La0.3Sr1.7Fe1.5Mo0.5O6-σdenoted as LSFM. The usage of LSFM compound as a matrix for Cu exsolution was based on the idea that it already consists of the oxides, which are currently utilized as the catalysts in RWGS. On the other hand, quite high mixed ionic-electronic conductivity may lead to even more enhanced electrochemical activity of the compound.The samples with varying Cu dopant level (5-20 mol.%) were synthesized via modified Pechini method maintaining fixed Fe:Mo ratio. Selected powders were processed into inks and screenprinted onto Ni-YSZ electrode. During the startup procedure of the SOEC, the catalysts were activated and the exsolution of metallic nanoparticles occurred. The powders and catalytic layers were characterized using XRD, SEM, and XPS techniques in both oxidized and reduced states. Doped compounds were able to exsolve metallic nanoparticles with the coverage density and size depending on the initial Cu amount in the lattice and the temperature of the reduction. Additional Temperature-Programmed Reduction and Oxidation (TPR/TPO) tests were performed to better understand the formation mechanism of surficial nanoparticles.SOECs equipped with additional layer of LSFM-Cu on the fuel electrode were examined for the performance in coelectrolysis mode under flowing H2O-CO2 with subsequent measurement of the outlet gases concentration using GC-MS. New layer altered the production of syngas concerning H2:CO ratio, yield, selectivity and conversion rates. The anchoring effect of the exsolution process causes higher integration of the nanoparticles compared to conventional catalysts produced via simple deposition and most likely limits the evaporation and surface diffusion of copper. LSFM-Cu can be promising material for increasing the efficiency of the SOECs. Acknowledgements This work was supported by a project funded by National Science Centre Poland, based on decision UMO-2021/43/B/ST8/01831 (OPUS 22).

Does the active surface area determine the activity of silica supported nickel catalysts in CO2 methanation reaction?

Does the active surface area determine the activity of silica supported nickel catalysts in CO2 methanation reaction?

Bio-templated Ni/MgO-Al2O3 as an efficient catalyst toward methane dry reforming

Bio-templated Ni/MgO-Al2O3 as an efficient catalyst toward methane dry reforming

Comprehensive performance investigation of inexpensive oxygen carrier in chemical looping gasification of coal

Comprehensive performance investigation of inexpensive oxygen carrier in chemical looping gasification of coal

Cu-Based Praseodymium-Modified γ-Al2O3 Oxygen Carrier for Chemical Looping Combustion Process Optimization

Chemical looping combustion (CLC) emerges as a cost-effective CO2 capture technology, demonstrating high competitiveness for both industrial and energy applications. This study explores the synthesis of a Cu-based, praseodymium (Pr)-modified gamma-alumina-supported (20CuPA) oxygen carrier (OC) through the wet impregnation method and investigates its performance in CLC. The characteristics of the synthesized OC were investigated using field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, temperature-programmed reduction analysis, and X-ray diffraction analysis. The CLC of methane gas was performed in a thermogravimetric analyzer (TA-Q50). The oxygen transport capacity (OTC) of the 20CuPA-based OC was investigated for 10 redox cycles. The impact of temperature and time as process variables in determining the OTC of OCs was studied. The TGA results indicated that the most important factor influencing the optimization of the OTC of OCs was time. In comparison to time, temperature had less of an impact on the OTC of 20CuPA-OC. The maximum OTC of 20CuPA-OC, which was 0.0546 mg of O2/mg of OC, was reached using optimized process variables, including a temperature of 800 °C and a time of 3 min.