Temperature-programmed Oxidation Research Articles

Nickel nanocatalyst on lanthanum aluminate: Optimizing preparation and evaluating performance in glycerol dry reforming for syngas production

In this study, mesoporous nanocrystalline Ni/La-Al catalysts with varying nickel (Ni) loadings (5, 10, 15, and 20 wt.%) were synthesized using a solid-state method for the glycerol dry reforming (GDR) reaction. The effects of different Ni loadings and the addition of steam on the structural and catalytic performance of the catalysts were investigated. Characterization techniques, including Brunauer-Emmett-Teller (BET) surface area analysis, temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), and X-ray diffraction (XRD) were employed to analyze the catalysts' properties. Results showed that increasing Ni loading to 10 wt.% improves the catalytic properties. However, by increasing the Ni loading, a decrease in catalytic properties due to increasing particle size, creating NiO bulk phase and surface pore blockage is obvious. A series of experiments were performed to investigate the effect of steam usage on catalytic properties. TPO analysis revealed that steam addition reduces the carbon deposition and shifts oxidation peaks to lower temperatures; consequently, the activity and stability of the catalyst will be enhanced. Although the 5 - 7.5 vol.% of steam in the feed composition significantly stabilizes the catalyst, it is possible to produce H2-rich synthesis gas, and conversely, increasing the temperature reduces the H2/CO ratio. Various examinations were conducted under different conditions, including varying gas hourly space velocity (GHSV), carbon-to-glycerol ratio (CGR), and temperature, to obtain more comprehensive data on the catalysts.

Real biofuel and fossil-fuel soot combustion activities in active and passive regeneration of diesel/gasoline particulate filters under different O2/NOx concentrations.

In this work, we aim to investigate and compare the combustion reactivities of real biofuel soot and fossil-fuel soot in the active and passive regeneration conditions of DPF and GPF through temperature-programmed oxidation (TPO). Higher reactivity of biofuel soot is achieved even under GPF conditions with extremely low oxygen concentration (~ 1%), which provides a great potential for low-temperature regeneration of GPF. Such a result is mainly attributed to the low graphitization and less surface C = C groups of biofuel soot. Unfortunately, the presence of high-content ashes (~ 47%) and P impurity in real biofuel soot hinder its combustion reactivity. TPO evidences that the O2/NOX-lacking conditions in GPF are key factors to impact the combustion of soot, especially fossil-fuel soot. This work provides some useful information for understanding real biofuel and fossil-fuel soot combustion in GPF and DPF regeneration and further improvement in filter regeneration process.

Biogas dry reforming over Li–Ni–Al LDH-derived catalysts

Biogas dry reforming or dry reforming of methane (DRM) is an alternative to produce hydrogen, in the context of development of sustainable routes for energy production, since this route uses CH4 and CO2, two greenhouse gases as reactants. However, the deactivation of catalysts due to carbon deposition and sintering is the main drawback of this reaction. In this work, with the aim of minimizing carbon formation and sintering during DRM, the effect of lithium as a promoter in catalysts Ni–Al derived from layered double hydroxides was investigated. The catalysts were prepared by co-precipitation and characterized by different techniques: BET surface area (SBET), X-ray diffraction (XRD), temperature-programmed reduction (TPR), CO2 and H2 temperature-programmed desorption (CO2-TPD and H2-TPD), Scanning Electron Microscopy (SEM-EDS), temperature-programmed oxidation (TPO). The catalytic tests were carried out in a fixed bed reactor using a synthetic biogas (60% CH4 and 40% CO2) in the temperature range of 500–750 °C. The incorporation of Li into the Ni–Al-LDH changed the reducibility and basicity of the catalysts. The Li2 sample containing an intermediary amount of Li (5 wt%) showed the highest reduction temperature and highest density of basic sites, which resulted in the smallest Ni crystallite size before and after the reactions. As a result, this catalyst presented the greater resistance to sintering and a lower rate of carbon produced. For the reaction carried out at 700 °C, only the Li2 catalyst remaining active during the test and reaching a maximum of 80% and a final CH4 conversion of 54% after 480 min of reaction, whereas CO2 conversion was higher than 90%. All other samples deactivated at different rates due to carbon deposition and sintering.

Magnesium borate whiskers/La2-XCeXZr2O7 catalysts preparation on cordierite honeycomb ceramic surfaces for soot catalytic oxidation͏

Magnesium borate whiskers were used to prepare a hierarchical microstructure on cordierite ceramic substrate through the precipitation-molten salt method. The La2-XCeXZr2O7 catalyst was then loaded onto the magnesium borate whiskers to form the hierarchical microstructure. The Ce-doped catalysts exhibited a significant improvement in the catalytic activity of soot combustion compared to the La2Zr2O7 catalyst. The study employed various techniques to characterize the structural morphology and phase composition, including scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform-infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). The growth of Magnesium borate whiskers (Mg2B2O5) with diameters of 100–200 nm and lengths of 2–5 μm were grown and tightly bonded to the cordierite ceramic substrate to mimic the structure of human respiratory system cilia. This could improve the filtration efficiency of soot in car exhaust. BET analysis showed that the specific surface area of cordierite increased from 0.684 m2/g to 1.363 m2/g after whisker growth. The study confirmed that the whiskers were firmly attached to the cordierite ceramic substrate, as demonstrated by the binding strength experiments. The addition of Ce metal has been found to significantly enhance soot combustion due to the presence of more active oxygen species and superior mobility of lattice oxygen species with more oxygen vacancies. The catalyst's intrinsic redox property was characterized using X-ray photoelectron spectroscopy (XPS) and H2 temperature-programmed reduction (H2-TPR). The semi-quantitative thermogravimetric analysis (TG-DTG) and the temperature-programmed oxidation (TPO) of catalysts showed that Z-La1.9Ce0·1Zr2O7 exhibited the highest catalytic activity for soot combustion, with an ignition temperature of 268 °C, a peak temperature of 418 °C, and a temperature of 90 % soot conversion of 464 °C. Furthermore, cyclic stability experiments demonstrate that the Z-La1.9Ce0·1Zr2O7 catalyst exhibits excellent structural stability and consistent catalytic performance. This distinctive microstructure holds great potential for applications in the field of DPF.

Optimization of syngas production via methane bi-reforming using CeO2 promoted Cu/MnO2 catalyst

Currently, syngas plays an important role in renewable and sustainable energy production. The idea of manufacturing syngas via bi-reforming methane, which involves the combination of methane (CH4), carbon dioxide (CO2), and steam, appears very promising. As a result, the goal of this research is to improve syngas output by improving process parameters in methane bi-reforming using a 3%Ce-15%Cu/MnO2 catalyst. Optimization analysis was performed using response surface methodology (RSM). The ultrasonic impregnation (UI) method was employed to synthesize the catalysts used in this study. Following that, the catalyst was characterized using several techniques such as Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption (TPD), and temperature programmed oxidation (TPO). The findings of the characterization show that the presence of CeO2 promoters has a dual effect on the size of CuO crystallites. Firstly, it reduces the size from 19.07 nm to 13.66 nm because to the dilutive effect generated by the inclusion of CeO2. Second, the presence of CeO2 promoter accelerates the transition from CuO to Cu0 metallic phase. Furthermore, the addition of CeO2 boosts the CH4 and CO2 conversion rates by 23.65% and 24.93%, respectively. As a result, the H2 yield increases significantly when compared to the unpromoted catalyst. The study investigates the influence of process parameters, specifically the reaction temperature (700–900℃), CO2 ratio (0.2–1), and gas hourly space velocity (GHSV) (16–36 L g cat−1 hr−1), on the conversion of CH4 and CO2, as well as the H2/CO ratio. The optimization study finds that the highest conversion rates for CH4 and CO2 are 78.32% and 72.45%, respectively, when the reaction temperature is 800 °C, the CO2 ratio is 0.6, and the gas hourly space velocity (GHSV) is 26 L g cat−1 hr−1. The optimum conditions result in the highest syngas ratio of 1.77. The results of the optimization are then assessed using the mean errors. The H2/CO ratio, as well as the average errors for CH4 and CO2 conversions, are discovered to be 0.15%, 0.95%, and 0%, respectively.

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.

Calcium additives enhance coke migration and catalyst stability for Pt-based catalysts in ethane dehydrogenation

Understanding and mitigating catalyst deactivation in high-temperature alkane dehydrogenation reactions is critical toward improving their energy and atom efficiency. In this work, we show that a partial overcoat of calcium oxide on a Pt-In alloy catalyst reduces the rate of catalyst deactivation by 10-fold during the non-oxidative dehydrogenation of ethane to ethylene. During 20 h of time-on-stream at 600 °C in 5 % C2H6, the Ca-doped PtIn2 catalyst retains >85 % of its initial activity while the undoped PtIn2 deactivates to <20 %. Temperature-programmed oxidation and spatially-resolved Raman spectroscopy reveal that the improved catalyst stability stems from enhanced migration of coke precursors away from the catalytically-relevant Pt sites to the silica support. Strikingly, the Ca overcoat does not alter the inherent rate and selectivity of coke formation but rather its crystallinity and localization, which nonetheless has a dramatic impact on the long-term performance of the catalyst.

Interpretation of H2-TPR from Cu-CHA Using First-Principles Calculations.

Temperature-programmed reduction and oxidation are used to obtain information on the presence and abundance of different species in complex catalytic materials. The interpretation of the temperature-programmed reaction profiles is, however, often challenging. One example is H2 temperature-programmed reduction (H2-TPR) of Cu-chabazite (Cu-CHA), which is a material used for ammonia assisted selective catalytic reduction of NOx (NH3-SCR). The TPR profiles of Cu-CHA consist generally of three main peaks. A peak at 220 °C is commonly assigned to ZCuOH, whereas peaks at 360 and 500 °C generally are assigned to Z2Cu, where Z represents an Al site. Here, we analyze H2-TPR over Cu-CHA by density functional theory calculations, microkinetic modeling, and TPR measurements of samples pretreated to have a dominant Cu species. We find that H2 can react with Cu ions in oxidation state +2, whereas adsorption on Cu ions in +1 is endothermic. Kinetic modeling of the TPR profiles suggests that the 220 °C peak can be assigned to Z2CuOCu and ZCuOH, whereas the peaks at higher temperatures can be assigned to paired Z2Cu and Z2CuHOOHCu species (360 °C) or paired Z2Cu and Z2CuOOCu (500 °C). The results are in good agreement with the experiments and facilitate the interpretation of future TPR experiments.

Method of hydrothermal treatment for coal spontaneous combustion inhibition and its application

The use of coal combustion inhibitors, which are mostly sprayed on the surface of the coal that remains in the mining region (post-mining inhibition), has a significant effect on preventing spontaneous burning of coal, although their duration of action is limited. Pre-inhibition (pre-mining inhibition) prolong the inhibition duration and offers the chance to change the temperature of the inhibition fluid. This results in the suggestion of a hydrothermal inhibition strategy that emphasises the influence of inhibition fluid temperature on the inhibitory effect in order to achieve accelerated inhibition. Infrared tests and temperature-programmed oxidation are used to explore the inhibition law and mechanism of inhibition temperature on the spontaneous combustion of different coal orders. The findings demonstrated that when the inhibition temperature increased to 30 °C, 40 °C, 50 °C, 60 °C and 70 °C, the average inhibition rate and cross point temperature increased dramatically while the rates of oxygen consumption, exothermic rate, and CO production continuously dropped. Simultaneously, the coal's content of more reactive groups, such methyl and methylene, dropped, and the coal's risk to self-heat reduced. At the 70 °C inhibition temperature, the lignite coal showed the maximum inhibition rate (65.28%). This research is crucial to advancing the inhibitor's application technology and efficiency of inhibition.

Enhancing catalytic performance, coke resistance, and stability with strontium-promoted Ni/WO3-ZrO2 catalysts for methane dry reforming

The first step of the DRM reaction is just the decomposition of CH4 into CH4−x (x = 1–4). The next step comprises two steps, namely the oxidation of CH4−x into syngas (by CO2) and the self-polymerization of CH4−x species. The earlier one is known as dry reforming of methane (DRM), and the latter one generates carbon deposits over the catalyst surface. In this study, we investigated the impact of 1–3 wt% Sr over Ni-based catalysts on a ZrO2-WO3 support on the catalytic activity and coke deposit. Various characterization techniques such as thermogravimetric analysis, X-ray diffraction, Raman spectroscopy, temperature-programed oxidation, temperature-programed reduction, and temperature-programed desorption were used to assess the physicochemical properties of the fresh and spent catalysts. The addition of 2wt% Sr promoter significantly improves the catalyst’s basicity in strong basic sites region through Sr2+ mediated interaction of CO2 species as well as inhibits the deposition of carbyne type carbon. Enhanced CO2 interaction results into the potential oxidation of carbon deposit and the highest CH4 conversion, reaching 60% up to 470 min TOS at a reaction temperature of 700 ℃.Graphical abstract

Nickel catalyst supported on SiC incorporated SiO2 for CO2 methanation: Positive effects of dysprosium promoter and microwaves heating method

In this work, Dy-promoted Ni/SiC-SiO2 catalysts with varied Dy loadings (0–1 %) were developed using the wet impregnation method and evaluated for their effectiveness in CO2 methanation. The characterization results reveal that Dy addition can reduce the Ni crystallite size, enhance the dispersion of active phase and increase the catalyst’s reducibility. Among the prepared catalysts, the 0.5 %Dy-10 %Ni/SiC-SiO2 demonstrated the highest CH4 selectivity (100 %) and CO2 conversion (73.9 %) at 350 °C owing to its highest basic sites and H2 chemisorption capacity. The performance of this Dy-promoted catalyst diluted with different amounts of SiC, which was employed as a microwave susceptor and high thermal conductive dilution material, was also investigated in both microwave and electric reactor. Microwave heating leads to higher CO2 conversion compared to electric heating, regardless of reaction temperature and dilution factor due to selective heating and the random occurrence of hot spots, which are usually considered as micro-plasmas in the catalyst bed. However, further increase quantity of SiC decreased both CO2 conversion and CH4 selectivity regardless of heating method. This may be attributed to the appearance of extreme overheating and the absence of gentle overheating with increased amount of SiC in the microwave and electric reactors, respectively. The temperature-programmed oxidation results demonstrated that carbon deposition on the 0.5 %Dy-10 %Ni/SiC-SiO2 catalyst during 30 h of reaction can be significantly suppressed by microwave.

Selective Electrochemical Determination of L-Cysteine by a Cobalt Carbon Nanotube (CNT)-Modified Glassy Carbon Electrode (GCE)

L-Cysteine is a semi-essential and proteinogenic amino acid, with the formula HO2CCH (NH2) CH2SH. L-cysteine is mostly found in protein-rich foods. In this study, catalysts consisting of cobalt (Co) supported on carbon nanotubes (CNTs) were prepared using the sodium borohydride (NaBH4) reduction method. These catalysts were characterized by means of energy-dispersive x-ray (EDX) with scanning electron microscopy (SEM), temperature-programmed reduction (TPR), and temperature-programmed oxidation (TPO) techniques. Characterization results confirmed the successful preparation of the desired catalyst. After preparing the Co/CNT catalysts, a highly efficient and sensitive electrochemical sensor was developed using a glassy carbon electrode (GCE) modified with the Co/CNT catalysts. The electrochemical behavior of the bare GCE and Co/CNT-modified GCE electrodes was investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) in 0.1 M phosphate buffer solution (PBS) + L-cysteine. Electrochemical results showed that the Co/CNT-modified GCE electrode exhibited high sensitivity and selectivity compared to the bare GCE, with sensitivity of 0.0046 µA/µM, limit of detection of 0.2 µM, and limit of quantification of 0.6 µM. Furthermore, this electrode showed higher sensitivity values than those reported in the literature. Further interference studies were performed using CV and EIS to investigate interfering species in the serum environment, such as D-glucose, uric acid, L-tyrosine, and L-tryptophan. In conclusion, the results suggest that the Co/CNT-modified GCE electrode is a promising catalyst for the sensitive detection of L-cysteine.

Performance Study of Ni/Si-MCM-41 Catalysts, Synthesized with Different Silica Sources, and their Application on Methane Dry Reform to Produce Green Hydrogen

The present work carried out an extensive and deepened study regarding the physicochemical characteristics of two Si-MCM-41-type supports, synthesized employing two distinct silica precursors, tetraethyl orthosilicate (TEOS) and rice husk ash (RHS), with the dispersion of nickel on the surface of the catalytic support. The direct influence of the active phase dispersion was analyzed, making a relationship with the formation of coke and with its performance on methane dry reform (DRM). The catalysts were prepared with 5, 10, and 20% (m/m) of Ni by wet impregnation method (with excess solvent), calcined at 800 ºC for 6 h, and characterized by the techniques of scanning electron microscopy and energy dispersive spectroscopy (SEM/ EDS), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET)/Barret-JoyerHalenda (BJH), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), temperature-programmed ammonia desorption (TPD-NH3), and H2-temperature-programmed reduction (TPR). The DRM experiments were carried out at 800 °C for 24 h with a 1:1 CH4:CO2 molar ratio. Analyzes of gaseous products were performed in gas chromatography (GC) and the coke produced was estimated by temperature-programmed oxidation (TPO). The best reaction results were obtained for catalysts with 20% nickel, which were selective and stable within 24 h of reaction. Comparing the TEOS and RHS catalysts for 20% Ni, the DRM results were very similar. The catalysts on RHS support demonstrated a significant low formation of coke, which can be considered negligible in a 24 h reaction.

Exploring the oxidation behavior of undiluted and diluted iron particles for energy storage: Mössbauer spectroscopic analysis and kinetic modeling.

Iron is an abundant and non-toxic element that holds great potential as energy carrier for large-scale and long-term energy storage. While from a general viewpoint iron oxidation is well-known, the detailed kinetics of oxidation for micrometer sized particles are missing, but required to enable large-scale utilization for energy production. In this work, iron particles are subjected to temperature-programmed oxidation. By dilution with boron nitride a sintering of the particles is prevented enabling to follow single particle effects. The mass fractions of iron and its oxides are determined for different oxidation times using Mössbauer spectroscopy. On the basis of the extracted phase compositions obtained at different times and temperatures (600-700 °C), it can be concluded that also for particles the oxidation follows a parabolic rate law. The parabolic rate constants are determined in this transition region. Knowledge of the particle size distribution and its consideration in modeling the oxidation kinetics of iron powder has proven to be crucial.

Cerium Doping Effect in 3DOM Perovskite-Type La2−xCexCoNiO6 Catalysts for Boosting Soot Oxidation

Herein, we present an in-depth investigation into the enhancement of catalytic soot oxidation through cerium-doped three-dimensional ordered macroporous (3DOM) La-Co-Ni-based perovskites synthesized with the colloidal crystal template (CCT) method. The 3DOM structure significantly contributes to the accessibility and interaction efficiency between soot and catalyst. Based on the results of powder X-ray diffraction (XRD), N2 adsorption-desorption measurements, scanning electron microscopy (SEM), temperature-programmed oxidation of NO (NO-TPO), temperature-programmed reduction of H2 (H2-TPR), in situ infrared Fourier transform spectroscopy (In-situ DRIFTS), and temperature-programmed oxidation (TPO) reactions, the role of cerium doping in modifying the structural and catalytic properties of 3DOM perovskite-type La2−xCexCoNiO6 catalysts was investigated systematically. The optimized cerium doping ratio in La2−xCexCoNiO6 catalysts can improve the microenvironment for efficient soot-catalyst contact, enhancing the catalytic activity of soot oxidation. Among the catalysts, the 3DOM La0.8Ce1.2CoNiO6 catalyst shows the highest catalytic activity for soot oxidation, whose T10, T50, and T90 values are 306 °C, 356 °C, and 402 °C, respectively. The mechanism of the cerium doping effect for boosting soot oxidation is proposed: The doping of Ce ions can increase the surface oxygen species, which is the main active species for promoting the key step of NO oxidation to NO2 in catalyzing soot oxidation. This research provides a new strategy to develop high-efficient non-noble metal catalysts for soot oxidation in pollution control and sustainable environmental practices.

Low temperature oxidation of diesel soot particles over one-dimensional 2 × 3 tunnel-structured Na2Mn5O10 catalysts

Tunnel-structured manganese oxides have drawn widespread research attention due to their excellent oxidation properties for the soot oxidation reaction. In this study, a series of romanechite Na2Mn5O10 catalysts with a 2 × 3 tunnel structure were synthesized via a facile hydrothermal method. The as-synthesized catalysts were investigated using X-ray diffraction, scanning and transmission electron microscopy, H2 and soot temperature-programmed reduction, O2 temperature-programmed desorption, NO temperature-programmed oxidation, X-ray photoelectron spectroscopy, and other measurements. Among all the catalysts, the Na1MnyOδ-120 catalyst exhibited the best catalytic performance for soot combustion, with T10, T50, and T90 values of 281 ℃, 317 ℃, and 343 ℃, respectively, which were considerably reduced to 271 ℃, 310 ℃, and 335 ℃ in the existence of 10% H2O. The results of multiple characterization methods indicated that the Na2Mn5O10 catalysts exhibit good reducibility, strong oxygen adsorption and activation capacity, and NO to NO2 oxidation ability. Moreover, the active sites (Mn and oxygen vacancies) and reaction mechanism (Langmuir–Hinshelwood) were also revealed by in-situ DRIFT and density functional theory calculations results. This study details a new strategy for the design and synthesis of efficient soot oxidation catalysts with practical application prospects.

Numerical investigation on the effects of axial-stress loads on the temperature-programmed oxidation characteristics of loose broken coal

This work innovatively explored the qualitative and quantitative effect of axial stress loads on the low-temperature oxidation behaviors of loose broken coal using a multi-field coupled numerical simulation. To achieve this purpose, a global numerical model for simulating the multi-field coupling temperature-programmed oxidation behavior of coal subjected to axial stress was established. We first acquired the evolution of the temperature, gas concentrations, axial-deformation behaviors, and seepage-heat transfer parameters of coal oxidation under axial stress loads based on the numerical model validation. Subsequently, the influence of various axial stress loads on the temperature-programmed oxidation behaviors was qualitatively and quantitatively evaluated. Results indicate that the numerical model exhibited excellent reliability. In addition, the entire oxidation process comprised temperature-dominated, temperature- and oxygen-dominated, and oxygen-consumption-dominated stages. Moreover, under axial stress conditions, both the porosity and permeability of coal samples decreased, whereas the heat conductivity coefficient increased, indicating an intensifying trend in oxidation reactions. Additionally, there was a critical stress that promoted the coal oxidation process; both the permeability and temperature of the coal demonstrated significant differences as the axial stress reached this critical point. The axial stress affected the oxidation behavior by changing the permeability and heat-transfer characteristics of the coal. This study is significant for predicting, preventing, and mitigating spontaneous fire disasters of stress-loaded coal.

The role of various preparation techniques and nickel loadings in ethanol steam reforming over mesoporous nanostructured Ni–Al2O3 catalysts

This study involved the preparation of Al2O3 support and Ni/Al2O3 catalysts through different methods such as mechanochemical, impregnation, and co-precipitation. These prepared samples were then assessed for their performance in the ethanol steam reforming (ESR) process. The results indicated that the 10Ni/Al2O3 catalyst, which was created using the impregnation method and exhibited a high BET surface area of 200.8 m2/g along with well-dispersed nickel, displayed exceptional performance in the ethanol steam reforming reaction. When compared to other catalysts, it exhibited greater activity and stability. A series of Ni/Al2O3 catalysts were prepared with nickel contents ranging from 2.5 to 20 wt%. The study showed that increasing the amount of nickel from 2.5 to 12.5 wt% led to a boost in the catalysts' ability to be reduced, which in turn resulted in improved catalytic performance. However, increasing the nickel content beyond 12.5 wt% led to a decline in catalytic performance. This decrease could be attributed to weaker Ni–Al2O3 interactions, an increase in particle size from 2.7 to 7.8 nm, and a significant reduction in the BET surface area from 198.3 m2/g to 166.4 m2/g. Temperature-programmed oxidation (TPO) profiles revealed that the carbon deposits on the catalyst's surface exhibited a whisker-like structure, and higher nickel contents correlated with increased oxidation peak temperatures and intensities. Moreover, the 12.5Ni/Al2O3 catalyst demonstrated remarkable stability over a 550-min reaction period. The study's findings indicated that as the Tcal. rose from 500 to 700 °C, the catalytic activity gradually lessened. The 12.5Ni/Al2O3 catalyst calcined at 500 °C, characterized by a small particle size and moderate Ni–Al2O3 interaction, exhibited the most favorable catalytic activity.

Sr Promoted Ni/W-Zr Catalysts for Highly Efficient CO2 Methanation: Unveiling the Role of Surface Basicity.

This study explores the employment of CO2 methanation for carbon dioxide utilization and global warming mitigation. For the first time, in this work, we combine the interesting properties of the WO3-ZrO2 support and the benefits of Sr to improve the performance of Ni-based catalysts in this reaction. Sr loading on 5Ni/W-Zr samples is increased to 3 wt %, resulting in improved surface basicity through strong basic site formation. After 300 min, the 5Ni + 3Sr/W-Zr catalyst exhibits high activity and stability, achieving 90% CO2 conversion and 82% CH4 yield compared to 62 and 57% on 5Ni/W-Zr. Limited sintering and absence of carbon deposits are confirmed by temperature-programmed oxidation, XRD, Raman, and TEM analyses at 350 °C for 300 min. Sr promotion creates additional CO2 adsorption and conversion sites, enhancing the catalytic performance.

Cobalt aluminate spinel-derived catalysts for glycerol steam reforming

Steam reforming of glycerol presents a promising possibility for the production of clean hydrogen. The steam reforming of glycerol (10 wt%) utilizing catalysts derived from cobalt aluminate spinel was examined at 550 °C, while the space–time covered 3.76–37.60 g·h/mol. Among the characterization techniques, glycerol desorption tests (glycerol-TPD) were conducted to assess the feasibility of the catalytic system for dehydration/dehydrogenation activity. The 0.625CoAl catalyst displayed the highest conversion of carbon to gas and selectivity to H2, which corresponds to the higher H2 desorption at lower temperature levels observed in the glycerol-TPD experiments. The catalyst's deactivation and regeneration were studied on 0.25CoAl catalyst under severe operation conditions and resulted in cobalt leaching detection. Raman spectroscopy and temperature programmed oxidation (TPO) revealed the formation of predominantly amorphous carbon on the surface of the catalyst.