Hydrogen Temperature-programmed Reduction Research Articles

Performance of NiO doped on alkaline sludge from waste photovoltaic industries for catalytic dry reforming of methane.

Alkali sludge (AS) is waste abundantly generated from solar photovoltaic (PV) solar cell industries. Since this potential basic material is still underutilized, a combination with NiO catalyst might greatly influence coke resentence, especially in high-temperature thermochemical reactions (Arora and Prasad, RSC Adv. 6:108,668-108688, 2016). This paper investigated alkaline sludge containing 3CaO-2SiO2 doped with well-known NiO to enhance the dry reforming of methane (DRM) reaction. The wet-impregnation method was used to prepare the xNiO/AS (x = 5-15%) catalysts. Subsequently, all catalysts were tested by using X-ray diffraction (XRD), nitrogen adsorption/desorption (BET), temperature-programmed reduction of hydrogen (H2-TPR), temperature-programmed desorption of carbon dioxide (TPD-CO2), field emission scanning electron microscopy (FESEM-EDX), and X-ray photoelectron spectroscopy (XPS). The spent catalysts were analyzed by thermogravimetric analysis (TGA/DTG), transmission electron microscopy (TEM), and temperature-programmed oxidation (TPO). The catalytic performance of xNiO/AS catalysts was investigated in a fixed bed reactor connected with gas chromatography thermal conductivity detector (GC-TCD) at a CH4:CO2 flow rate of 30 mL-1 during a 10-h reaction by following (Shamsuddin et al., Int. J. Energy Res. 45:15,463-15,480, 2021d). For optimization parameters, the effects of NiO concentration (5, 10, and 15%), reaction temperature (700, 750, 800, 850, and 900 °C), catalyst loading (0.1, 0.2, 0.3, 0.4, and 0.5 g), and gas hourly space velocity (GHSV) range from 3000, 6000, 9000, 12,000, and 15,000 h-1 were evaluated. The results showed that physical characteristics such as BET surface area and porosity do not significantly impact NiO percentages of dispersion, whereas chemical characteristics like reducibility are crucial for the catalysts' efficient catalytic activity. Due to the active sites on the catalyst surface being more accessible, increased NiO dispersion resulted in higher reactant conversion. The catalytic performance on various parameters that showed 15%NiO/AS exhibited high reactant conversion up to 98% and 40-60% product selectivity in 700 °C, 0.2 g catalyst loading, and 12,000 h-1 GHSV. According to spent catalyst analyses, the catalyst was stable even after the DRM reaction. Meanwhile, increased reducibility resulted in more and better active site formation on the catalyst. Synergetic effect of efficient NiO as active metal and medium basic sites from AS enhanced DRM catalytic activity and stability with low coke formation.

Investigating the Catalytic Influence of Boron on Ni-Co/Ca Catalysts for Improved Syngas Generation from Rice Straw Pyrolysis.

A series of boron-promoted Ni-Co/Ca catalysts were synthesized by the sol-gel method to enhance syngas generation from biomass pyrolysis. The efficiency of these catalysts was evaluated during the pyrolysis of rice straw in a fixed-bed reactor, varying the Ni/Co ratio, boron addition, calcination temperature, and residence time. The catalysts underwent comprehensive characterization using X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, scanning electron microscopy (SEM), and hydrogen temperature-programmed reduction (H2-TPR). The results indicated that the Ni-Co/Ca catalysts yielded superior syngas compared to singular Ni or Co catalysts, suggesting a synergistic interplay between nickel and cobalt. The incorporation of 4% boron significantly decreased the particle size of the active metals, enhancing both the catalytic activity and stability. Optimal syngas production was achieved under the following conditions: a biomass-to-catalyst mass ratio of 2:1, a Ni-Co ratio of 1:1, a calcination temperature of 400 °C, a pyrolysis temperature of 800 °C, and a 20 min residence time. These conditions led to a syngas yield of 431.8 mL/g, a 131.28% increase over the non-catalytic pyrolysis yield of 188.6 mL/g. This study not only demonstrates the potential of Ni-Co/Ca catalysts in biomass pyrolysis for syngas production but also provides a foundation for future catalyst performance optimization.

Enhancing CO and H2 Production in Propane Dry Reforming in Excess of CO2.

This study focuses on addressing the challenges in the dry reforming of propane, a process historically marked by low syngas yields and only moderate conversions of CO2 and propane. The primary objective was to enhance CO2 utilization and boost the selectivity of syngas (CO and H2) production using titania-based catalysts. For synthesizing these catalysts, an impregnation method was employed with subsequent characterization through X-ray diffraction (XRD), N2 adsorption-desorption, ammonia temperature-programmed desorption (TPD), and hydrogen temperature-programmed reduction (TPR). The titania-based catalysts generally possess weak acidic strength, with each catalyst displaying a unique reduction profile. The dry reforming process using these catalysts resulted in varying levels of propane conversion, with V/Ti, Ir/Ti, Al/Ti, and Zr/Ti catalysts showing distinct efficiencies. Notably, the Ir/Ti and V/Ti oxide catalysts achieved the lowest selectivity for generating intermediate byproducts such as methane, ethane, ethylene, and propylene while successfully promoting higher syngas CO and H2 production alongside stable propane conversion. When exposed to excess CO2, each catalyst consumed differing amounts of CO2 molecules. Particularly, the Ir/Ti and V/Ti oxide catalysts demonstrated enhanced activity in promoting CO2 reactions with intermediate radical species, facilitating carbon-carbon (C-C) bond dissociation and leading to increased syngas production. This study offers valuable insights into the potential of titania-based catalysts in improving the efficiency and selectivity of propane dry reforming processes for blue hydrogen.

Modeling the temperature-programmed reduction of metal oxide catalysts by considering the particle-size distribution effect

Hydrogen temperature-programmed reduction (H2-TPR) has become a very useful and common technique for the chemical characterization of solids as it is sensitive to the study of reducible species in catalysis and is considered to be a fingerprint for the reducibility of metal oxide catalysts. However, although modeling of H2-TPR patterns has been extensively studied, little attention has been paid to the effect of particle-size distribution (PSD). The complexity of modeling H2-TPR patterns arises from the fact that the chemistry of metal oxide reduction depends on several factors, including particle size, nature of the support material and confinement within the porous structure, amongst others. In order to identify the kinetic reaction model governing the reduction of certain metal oxides and to explore the effect of PSD, pure metal oxides that only exhibited the particle size difference effect were used to model the H2-TPR patterns. Kinetic and thermodynamic data, which are very useful for characterizing heterogeneous catalysts, were obtained from this study. This work presents a simple procedure for modeling H2-TPR patterns of various metal oxides (i.e., CuO, Ag2O, and NiO) used as active phases in several reactions of environmental and energetic interest using several solid-state reaction kinetic models and considering their PSDs. The results obtained show that modeling the H2-TPR profiles provides information regarding the PSD of metal oxide catalysts that undergo a single-step reduction and only present the particle size difference effect.

Ex situ and in situ studies on structural features of Pt/Ce0.75Zr0.25O2 catalyst for water gas shift reaction

Pt/Ce1-xZrxO2 catalysts have shown high activity in water gas shift (WGS) reaction, but their structural organization has been studied insufficiently. This work represents a detailed structural study on the supported Pt species and the metal/support interface in a 5 wt% Pt/Ce0.75Zr0.25O2 catalyst in the initial state, after reductive activation, and after WGS reaction in H2-enriched reformate-simulating mixture. A wide range of methods was used: ex situ and in situ X-ray diffraction (XRD) studies, high resolution transmission electron microscopy (HRTEM), X-ray atomic pair distribution function (PDF) method, pseudo in situ X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR). The Ce0.75Zr0.25O2 mixed oxide was shown to provide a highly dispersed state of Pt species. XPS revealed that the initial catalyst contains Pt2+species. PDF analysis allowed us to propose the structure of ultrafine PtO particles and to elucidate the metal-support interaction with fixation of Pt ions on the support surface. In situ XRD, pseudo in situ XPS, and H2-TPR studies revealed the reduction of ultrafine PtO particles in H2 atmosphere at low temperatures (20–90°С) with the formation of metallic Pt0 particles and simultaneous partial reduction of the support surface due to the hydrogen spillover. Catalytic tests of the as-prepared and poisoned with chlorine 5wt% Pt/Ce0.75Zr0.25O2 catalysts in the WGS reaction showed an important role of the oxygen vacancies in the oxide support as active sites. These findings contribute to the understanding catalytic performance of Pt/Ce1-xZrxO2 systems.

Comparative Study of Exsolved and Impregnated Ni Nanoparticles Supported on Nanoporous Perovskites for Low-Temperature CO Oxidation.

This study investigated the redox exsolution of Ni nanoparticles from a nanoporous La0.52Sr0.28Ti0.94Ni0.06O3 perovskite. The characteristics of exsolved Ni nanoparticles including their size, population, and surface concentration were deeply analyzed by environmental scanning electron microscopy (ESEM), transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX) mapping, and hydrogen temperature-programmed reduction (H2-TPR). Ni exsolution was triggered in hydrogen as early as 400 °C, with the highest catalytic activity for low-temperature CO oxidation achieved after a reduction step at 500 °C, despite only a 10% fraction of Ni exsolved. The activity and stability of exsolved nanoparticles were compared with their impregnated counterparts on a perovskite material with a similar chemical composition (La0.65Sr0.35TiO3) and a comparable specific surface area and Ni loading. After an aging step at 800 °C, the catalytic activity of exsolved Ni nanoparticles at 300 °C was found to be 10 times higher than that of impregnated ones, emphasizing the thermal stability of Ni nanoparticles prepared by redox exsolution.

Simple and facile synthesis of single-crystal CeO2 abrasives and its highly efficient removal mechanism on SiO2 film

CeO2 nanoparticles are one of the key abrasives for chemical mechanical polishing (CMP) in advanced integrated circuits. However, synthesizing highly chemically reactive CeO2 often involves ion doping, high-temperature calcination or reduction, which increase cleaning challenges and risk scratching wafers. We developed a simple and facile method for synthesizing single-crystal CeO2. It exhibits superior polishing performance compared to commercial CeO2, with the material removal rate (MRR) increasing to 4141.45 from 3649.99 Å/min and the surface roughness (Sa) decreasing to 0.533 from 0.647 nm. The CeO2 abrasives were characterized by X-ray Diffraction (XRD), advanced microscopy techniques (SEM, TEM), X-ray Photoelectron Spectroscopy (XPS), and Hydrogen Temperature-Programmed Reduction (H2-TPR). It revealed that the synthesized CeO2 has a particle size of approximately 60 nm and its surface was covered with a uniform amorphous layer of ∼ 1 nm. XPS and H2-TPR revealed its high Ce3+ concentration and enhanced oxygen exchange capability. The polishing mechanism was investigated by XPS and High-Resolution TEM (HR-TEM). Under pressure, the CeO2 established Ce-O-Si bonds with the SiO2 surface. Ce3+ provided electrons to the antibonding orbitals of Si-O bonds, effectively breaking stable Si-O bonds and removed SiO2 film in the form of lump SiO2 through mechanical action.

Determination of characteristic properties of Co3O4 loaded LaFe x Al12−x O19 hexaaluminates

Abstract Hexaaluminates are drawing attention due to their exceptional mechanical and thermal stability. They can be proposed for applications as catalysts or catalyst support materials in high-temperature reactions. In this study, various LaFe x Al12−x O19 samples (x = 0.25, 0.5, 1, and 2) have been synthesized using the sol–gel method. Subsequently, these hexaaluminate samples were impregnated with cobalt oxide to form more active centers on the hexaaluminate support. The influence of the iron (Fe) content on the crystal structure, redox properties, and oxygen immobility has been investigated through X-ray diffraction, hydrogen temperature-programmed reduction, and oxygen temperature-programmed desorption techniques. Among the Co3O4@LaFe x Al12−x O19 samples, those with x ≥ 1 exhibited a hexaaluminate crystalline structure, demonstrating a higher lattice oxygen mobility.

Chitosan –NH2 derived efficient Co3O4 catalyst for styrene catalytic oxidation: Simultaneously regulating particle size and Co valence

In this study, a Co3O4 catalyst is synthesised using the chitosan-assisted sol–gel method, which simultaneously regulates the grain size, Co valence and surface acidity of the catalyst through a chitosan functional group. The complexation of the free –NH2 complex inhibits particle agglomeration; thus, the average particle size of the catalyst decreases from 82 to 31 nm. Concurrently, Raman spectroscopy, hydrogen temperature-programmed reduction, electron paramagnetic resonance spectroscopy and X-ray photoelectron spectroscopy experiments demonstrate that doping with chitosan N sources effectively modulates Co2+ to promote the formation of oxygen vacancies. In addition, water washing after catalyst preparation can considerably improve the low-temperature (below 250 °C) activity of the catalyst and eliminate the side effects of alkali metal on catalyst activity. Moreover, the presence of Brønsted and Lewis acid sites promotes the adsorption of C8H8. Consequently, CS/Co3O4-W presents the highest catalytic oxidation activity for C8H8 at low temperatures (R250 °C = 8.33 μmol g−1 s−1, WHSV = 120,000 mL hr−1∙g−1). In situ DRIFTS and 18O2 isotope experiments demonstrate that the oxidation of the C8H8 reaction is primarily dominated by the Mars–van Krevelen mechanism. Furthermore, CS/Co3O4-W exhibits superior water resistance (1- and 2- vol% H2O), which has the potential to be implemented in industrial applications.

Efficient Synthesis of Nickel-Molybdenum/USY-Zeolite Catalyst for Eliminating Impurities (N, S, and Cl) in the Waste Plastic Pyrolysis Oil: Dispersion Effect of Active Sites by Surfactant-Assisted Melt-Infiltration

The upgrading of waste plastic pyrolysis oil (WPPO) through hydrotreating (HDT) is crucial for transforming plastic waste into chemical feedstock. The catalytic role of HDT is of paramount importance for this conversion procedure. In this study, bimetallic catalysts based on Ni and Mo were prepared using the surfactant-assisted melt-infiltration (SAMI) method, completely omitting the use of liquid solutions. Thorough analysis via X-ray diffraction, transmission electron microscopy, and hydrogen temperature-programmed reduction confirmed that the addition of Span60 surfactant effectively prevented the aggregation of Ni and Mo components, reduced the size of metal particles, and improved the dispersion of active sites on the zeolite supports. Consequently, NiMo-based catalysts incorporating Span60, synthesized using the SAMI method, exhibited a superior catalytic performance in the removal of nitrogen, sulfur, and chloride impurities from WPPO during HDT compared to those without surfactant. Specifically, the catalyst prepared with Span60 exhibited 15% higher nitrogen conversion compared to the catalyst prepared without Span60.

Thermally Inducing Viscous Fluids to Generate Co-Based Perovskites Enriched with Active Species for the Removal of VOCs.

Various Co-based perovskites are synthesized through thermally driving viscous fluids. In this process, rare earth salts, cobalt salts, and citric acid do not require homogeneous mixing but only need to be heated until they melt into a molten viscous slurry. The physicochemical properties of cobalt-based perovskites were examined using techniques such as X-ray diffraction (XRD), electron paramagnetic resonance (EPR), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-Mapping-EDS), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR), oxygen temperature-programmed desorption (O2-TPD), and N2 adsorption-desorption. The results indicate that the surface-active species can be controlled by altering the A-site elements of cobalt-based perovskites. All catalysts synthesized through the thermal treatment of viscous mixtures exhibited a low activation temperature and a low apparent activation energy for the catalytic oxidation of toluene. Among all cobalt-based perovskites, LaCoO3 demonstrated the most outstanding catalytic activity, primarily attributed to its capacity to expose a larger number of surface-active sites and oxygen species, as well as its superior reducibility. Furthermore, the formation process of optimal LaCoO3 was monitored using thermogravimetric analysis-differential scanning calorimetry (TGA-DSC), and the byproducts of the low-temperature catalytic oxidation of toluene by the catalyst were identified using gas chromatography-mass spectrometry (GC-MS). The possible mechanism of toluene oxidation was inferred by in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS). Moreover, LaCoO3 exhibits a predominant resistance to high-temperature hydrothermal conditions. This work provides a scalable and innovative approach to fabricating exceptionally effective catalysts for the efficient purification of VOCs.

Hydrodeoxygenation of Oxygenates Derived from Biomass Pyrolysis Using Titanium Dioxide-Supported Cobalt Catalysts.

Bio-oil upgrading to produce biofuels and chemicals has become an attractive topic over the past decade. However, the design of cost- and performance-effective catalysts for commercial-scale production remains a challenge. Herein, commercial titania (TiO2) was used as the support of cobalt (Co)-based catalysts (Co/TiO2) due to its low cost, high availability, and practicability for commercialization in the future. The Co/TiO2 catalysts were made with two different forms of TiO2 (anatase [TiO2-A] and rutile [TiO2-R]) and comparatively evaluated in the hydrodeoxygenation (HDO) of 4-propylguaicol (4PG), a lignin-derived model compound. Both Co/TiO2 catalysts promoted the HDO of 4PG following a similar pathway, but the Co/TiO2-R catalyst exhibited a higher activity in the early stages of the reaction due to the formation of abundant Ti3+ species, as detected by X-ray photoelectron spectroscopy (XPS) and hydrogen-temperature programed reduction (H2-TPR) analyses. On the other hand, the Co/TiO2-A catalyst possessed a higher acidity that enhanced propylcyclohexane production at prolonged reaction times. In terms of reusability, the Co/TiO2-A catalyst showed a higher stability (less Co leaching) and reusability compared to Co/TiO2-R, as confirmed by transmission electron microscopy (TEM) and inductively coupled plasma optical emission spectroscopy (ICP-OES) analyses. The HDO of the real bio-oil derived from pyrolysis of Leucaena leucocephala revealed that the Co/TiO2-A catalyst could convert high oxygenated aromatics (methoxyphenols, dimethoxyphenols, and benzenediols) to phenols and enhanced the phenols content, hinting at its potential to produce green chemicals from bio-feedstock.

Ni-Based Hydrotalcite (HT)-Derived Cu Catalysts for Catalytic Conversion of Bioethanol to Butanol.

Catalytic conversion of biomass-derived ethanol into n-butanol through Guerbet coupling reaction has become one of the key reactions in biomass valorization, thus attracting significant attention recently. Herein, a series of supported Cu catalysts derived from Ni-based hydrotalcite (HT) were prepared and performed in the continuous catalytic conversion of ethanol into butanol. Among the prepared catalysts, Cu/NiAlOx shows the best performance in terms of butanol selectivity and catalyst stability, with a sustained ethanol conversion of ~35% and butanol selectivity of 25% in a time-on-stream (TOS) of 110 h at 280 °C. While for the Cu/NiFeOx and Cu/NiCoOx, obvious catalyst deactivation and/or low butanol selectivity were obtained. Extensive characterization studies of the fresh and spent catalysts, i.e., X-ray diffraction (XRD), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Hydrogen temperature-programmed reduction (H2-TPR), reveal that the catalysts' deactivation is mainly caused by the support deconstruction during catalysis, which is highly dependent on the reducibility. Additionally, an appropriate acid-base property is pivotal for enhancing the product selectivity, which is beneficial for the key process of aldol-condensation to produce butanol.

Nanostructured Ru(2 wt%)/PrxCe1−xO2-δ (x = 0, 0.12 and 0.25) materials for hydrodeoxygenation of guaiacol: Influence of oxygen vacancies on reactivity

To assess the influence of catalyst morphology and dopant on catalytic activity for the hydrodeoxygenation (HDO) of guaiacol, four Ru catalysts—Ru(2 wt%)/CeO2 irregular nanoparticles (Ru-1), Ru(2 wt%)/CeO2 nanocubes (Ru-2), Ru(2 wt%)/Ce0.88Pr0.12O2-δ nanocubes (Ru-3) and Ru(2 wt%)/Ce0.75Pr0.25O2-δ nanocubes (Ru-4) were prepared and characterized using transmission electron microscopy, X-ray diffraction analysis, Raman spectroscopy, hydrogen temperature-programmed reduction, X-ray photoelectron spectroscopy, and volumetric oxygen titration. The shape-dependent catalytic activities for the HDO of guaiacol over Ru-1 and Ru-2 were initially determined, presenting that Ru-2 exhibited higher activity than Ru-1. In addition, the effect of Pr doping into CeO2 on the desired activity was examined using Ru-2, Ru-3 and Ru-4, demonstrating that there is an optimal Pr content that maximizes the activity. The results obtained by the analytical methods with additional oxygen vacancy titration indicate that the activities of the catalysts are strongly correlated with the normalized oxygen vacancy densities.

Promotion effects of alkali metals on iron molybdate catalysts for CO2 catalytic hydrogenation

CO2 hydrogenation is an attractive way to store and utilize carbon dioxide generated by industrial processes, as well as to produce valuable chemicals from renewable and abundant resources. Iron catalysts are commonly used for the hydrogenation of carbon oxides to hydrocarbons. Iron-molybdenum catalysts have found numerous applications in catalysis, but have been never evaluated in the CO2 hydrogenation. In this work, the structural properties of iron-molybdenum catalysts without and with a promoting alkali metal (Li, Na, K, Rb, or Cs) were characterized using X-ray diffraction, hydrogen temperature-programmed reduction, CO2 temperature-programmed desorption, in-situ 57Fe Mossbauer spectroscopy and operando X-ray adsorption spectroscopy. Their catalytic performance was evaluated in the CO2 hydrogenation. During the reaction conditions, the catalysts undergo the formation of an iron (II) molybdate structure, accompanied by a partial reduction of molybdenum and carbidization of iron. The rate of CO2 conversion and product selectivity strongly depend on the promoting alkali metals, and electronegativity was identified as an important factor affecting the catalytic performance. Higher CO2 conversion rates were observed with the promoters having higher electronegativity, while low electronegativity of alkali metals favors higher light olefin selectivity.

Synthesis of Ni-Cu-CNF Composite Materials via Carbon Erosion of Ni-Cu Bulk Alloys Prepared by Mechanochemical Alloying

The unique physical and chemical properties of composite materials based on carbon nanofibers (CNFs) makes them attractive to scientists and manufacturers. One promising method to produce CNFs is catalytic chemical vapor deposition (CCVD). In the present work, a method based on carbon erosion (CE) of bulk microdispersed Ni-Cu alloys has been proposed to prepare efficient catalysts for the synthesis of CNF-based composites. The initial Ni-Cu alloys were obtained by mechanochemical alloying (MCA) of metallic powders in a planetary mill. The effect of MCA duration on the phase composition of Ni-Cu samples was studied by X-ray diffraction analysis and temperature-programmed reduction in hydrogen. It has been also revealed that, during such stages as heating, reduction, and short-term exposure to the reaction mixture (C2H4/H2/Ar) at 550 °C, the formation of a Ni-based solid solution from the initial Ni-Cu alloys takes place. The early stages of the CE process were monitored by transmission electron microscopy combined with energy-dispersive X-Ray analysis. It was found that the composition of the catalytic particles is identical to that of the initial alloy. The morphological and structural features of the prepared Ni-Cu-CNF composites were studied by scanning and transmission electron microscopies. The textural characteristics of the composites were found to be dependent on the reaction time.

Catalytic oxidation of Benzene with manganese oxide supported on Cordierite

Volatile organic compounds (VOCs) are one of the principal causes of air pollution, posing a grave danger to the environment and human health due to their toxicity. In the presence of heat or light, catalytic oxidation has been recognized as a viable and efficient approach for VOCs remediation. Manganese-based oxides are one of the most environmentally benign and cost-effective choices for the catalytic destruction of volatile organic compounds in thermocatalysis. That is the reason why this article focused on catalytic oxidation to control benzene (a VOCs component). The wet impregnation process was used to produce manganese oxide supported on cordierites. Scanning electron microscopy (SEM), energy dispersive spectrometer mapping (EDS mapping), X-ray diffraction (XRD), and Hydrogen Temperature-programmed reduction (TPR-H2) were used to characterize the catalysts. When using the TCD-FID detector, catalytic activity measurements were done on a micro-flow reactor system coupled online to GC. The results showed that MnO2-Cor potential catalyst for completely oxidizing benzene with a 100% benzene conversion temperature of 350 C to CO2 and H2O. This catalyst provides high thermal stability and good reusability due to being carried on cordierite.

NO Oxidation on Lanthanum-Doped Ceria Nanoparticles with Controlled Morphology

The present work aims to assess the impact of morphology and reducibility on lanthanum-doped ceria nanocatalysts with controlled morphology on the NO oxidation reaction. Specifically, samples were prepared using a hydrothermal method incorporating lanthanum at varying molar concentrations (0, 5, 10, and 15 mol.%) into ceria with a controlled morphology (nanocubes and nanorods). The structural, compositional, and redox characterization of these catalysts has been performed via scanning transmission electron microscopy (STEM), X-ray diffraction (XRD), X-ray energy dispersive spectroscopy (X-EDS), inductively coupled plasma (ICP), hydrogen temperature-programmed reduction (H2-TPR), and oxygen storage capacity (OSC). NO oxidation catalytic tests were conducted, and the results were compared with estimated curves (obtained by considering the proportions of the corresponding components), which revealed the presence of a synergistic effect between lanthanum and ceria. The degree of enhancement was found to depend on both the morphology and the amount of lanthanum incorporated into CeO2. These findings may facilitate the optimization of features concerning ceria-based nanocatalysts for the removal of NOx emissions from exhaust gases.

Variation in Metal-Support Interaction with TiO2 Loading and Synthesis Conditions for Pt-Ti/SBA-15 Active Catalysts in Methane Combustion.

The control of catalytic performance using synthesis conditions is one of the main goals of catalytic research. Two series of Pt-Ti/SBA-15 catalysts with different TiO2 percentages (n = 1, 5, 10, 30 wt.%) were obtained from tetrabutylorthotitanate (TBOT) and peroxotitanate (PT), as titania precursors and Pt impregnation. The obtained catalysts were characterized using X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), N2 sorption, Raman, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), hydrogen temperature-programmed reduction (H2-TPR) and H2-chemisorption measurements. Raman spectroscopy showed framework titanium species in low TiO2 loading samples. The anatase phase was evidenced for samples with higher titania loading, obtained from TBOT, and a mixture of rutile and anatase for those synthesized by PT. The rutile phase prevails in rich TiO2 catalysts obtained from PT. Variable concentrations of Pt0 as a result of the stronger interaction of PtO with anatase and the weaker interaction with rutile were depicted using XPS. TiO2 loading and precursors influenced the concentration of Pt species, while the effect on Pt nanoparticles' size and uniform distribution on support was insignificant. The Pt/PtO ratio and their concentration on the surface were the result of strong metal-support interaction, and this influenced catalytic performance in the complete oxidation of methane at a low temperature. The highest conversion was obtained for sample prepared from PT with 30% TiO2.

Vapor-phase hydrodeoxygenation of guaiacol for phenol production using bifunctional Ni/Cu-Beta zeolite catalysts

A series of bifunctional catalysts based on beta zeolite were prepared though co-impregnation and tested for vapor-phase hydrodeoxygenation (VHDO) reaction to form phenol. Among the catalysts tested, 10Ni/Cu-Beta exhibited the highest stability, catalytic activity, and selectivity for phenol. Under the optimal conditions of a contact time (W/F) of 1.5 h, a molar flow of hydrogen to guaiacol (H/G) of 24, a time of stream (TOS) of 40min. A temperature of 450 °C, and a molar flow of stream to guaiacol (S/G) of 3, complete conversion was achieved, with a phenol yield of 63.95% and a sum yield of phenolic compounds of 96.89%. The beta zeolite support provided an adequate specific surface area and initial acid sites for the VHDO process. In the absence of water, the addition of Cu metal improved catalytic performance of the catalyst. However, the increase in temperature could result in more severe deactivation. The addition of water had little effect on the catalyst activity and helped to improve its stability to a certain extent. The loading of Ni metal contributed to an increased selectivity for phenol. The characterization results from X-ray diffraction (XRD) and hydrogen temperature-programed reduction (H2-TPR) showed that reduced and oxidized metals are finely dispersed on the catalyst surface. NH3 temperature-programed desorption and pyridine infrared resonance (Py-IR) characterizations revealed that the addition of Cu and Ni metal adjusts the type and amount of acid sites. A small part of Cu2+ and Ni2+ could be bound simultaneously to the surface of beta support, of which Cu2+ forms new metal-induced L-sites while Ni2+ does not, resulting in a lower concentration of L-sites on Ni/Cu-based catalysts compared to that on Cu-based catalysts and weakening the transmethylation reaction of phenolic compounds. The combination of metal sites and acid sites enabled the VHDO reaction of guaiacol to produce more phenol in the products.