Temperature-programmed Oxidation Research Articles

Alkali/alkaline-earth metal-modified MnOx supported on three-dimensionally ordered macroporous–mesoporous TixSi1-xO2 catalysts: Preparation and catalytic performance for soot combustion

The performance of catalysts used in after-treatment systems is the key factor for the removal of diesel soot, which is an important component of atmospheric fine particle emissions. Herein, three-dimensionally ordered macroporous–mesoporous TixSi1-xO2 (3DOM-m TixSi1-xO2) and its supported MnOx catalysts doped with different alkali/alkaline-earth metals (AMnOx/3DOM-m Ti0.7Si0.3O2 (A: Li, Na, K, Ru, Cs, Mg, Ca, Sr, Ba)) were prepared by mesoporous template (P123)-assisted colloidal crystal template (CCT) and incipient wetness impregnation methods, respectively. Physicochemical characterizations of the catalysts were performed using scanning electron microscopy, X-ray diffraction, N2 adsorption–desorption, H2 temperature-programmed reduction, O2 temperature-programmed desorption, NO temperature-programmed oxidation, and Raman spectroscopy techniques; then, we evaluated their catalytic performances for the removal of diesel soot particles. The results show that the 3DOM-m Ti0.7Si0.3O2 supports exhibited a well-defined 3DOM-m nanostructure, and AMnOx nanoparticles with 10–50 nm were evenly dispersed on the inner walls of the uniform macropores. In addition, the as-prepared catalysts exhibited good catalytic performance for soot combustion. Among the prepared catalysts, CsMnOx/3DOM-m Ti0.7Si0.3O2 had the highest catalytic activity for soot combustion, with T10, T50, and T90 (the temperatures corresponding to soot conversion rates of 10%, 50%, and 90%) values of 285, 355, and 393°C, respectively. The high catalytic activity of the CsMnOx/3DOM-m Ti0.7Si0.3O2 catalysts was attributed to their excellent low-temperature reducibility and homogeneous macroporous–mesoporous structure, as well as to the synergistic effects between Cs and Mn species and between CsMnOx and the Ti0.7Si0.3O2 support.

Investigation of alkali metals addition on the catalytic activity of CuFe2O4 for soot oxidation

• The enhanced soot oxidation activity is ascribed to the formation of surface oxygen vacancies. • The low initial temperature (T ig = 308 °C) and the low temperature of maximum CO 2 emission (T max = 389 °C) were achieved. • DFT calculations were performed to correlate with the activity test results. Soot particle exhausted from diesel engines are causing severe health and environmental problems. Alkali metals (Li, Na, K, Cs) doped CuFe 2 O 4 catalysts were synthesized to eliminate soot residue. XRD, Raman, SEM, H 2 -TPR and temperature-programmed oxidation (TPO) were employed to investigate the effect of alkali metals addition on CuFe 2 O 4 . Density functional theory (DFT) calculations were used to explore the inner reaction mechanism. The results revealed that the doping of all alkali metals facilitated the formation of oxygen vacancies which are the main active sites for soot oxidation. The CuFe 2 O 4 doped by K showed smallest crystal size and the most oxygen vacancies. Therefore, Cu 0.9 K 0.1 Fe 2 O 4 catalyst performed best catalytic activity in soot oxidation with the T ig of 308 °C and T max of 389 °C.

Pentyl valerate biofuel from γ-valerolactone in one-pot process: Insights on the key role of acid sites of the catalytic support

In this work the acid-catalysed reactions involved in the one-pot production of pentyl valerate (PV) from γ-valerolactone (GVL) and pentanol in liquid phase at 523 K, 10 bar of N 2 over acidic catalysts was studied. Two consecutive acid-catalysed reactions must be performed: (1) nucleophilic addition of pentanol (PL) to GVL to form 4-hydroxy pentyl valerate (HPV) and (2) HPV dehydration into pentyl 2-pentenoate (PP), avoiding the undesirable formation of 4-pentoxy pentyl valerate (PPV). It was found that the support activity and selectivity strongly depended on: (i) the nature; (ii) strength; (iii) density of acid sites and (iv) the textural properties of the acid support. Solids containing predominantly Lewis acid sites, such as ZnO/SiO 2 , γ-Al 2 O 3 and NaY zeolite promote mainly a strong GVL adsorption leading to a relatively high missing carbon balance. Catalysts having mainly surface Brønsted acid sites of medium–high strength, such as HPA/SiO 2 , showed a very high activity and selectivity to PP but deactivated dramatically. Zeolites containing at least 40% of Brønsted acidity and strong acid sites promoted remarkably the undesirable intramolecular dehydration of pentanol into pentenes. SiO 2 -Al 2 O 3 , exhibiting a B/(L + B) ratio of 0.21 and a wide strength of acid sites, was more selective to PP than to PPV though the missing carbon balance was high. By calorimetric adsorption and temperature-programmed oxidation adsorption enthalpies of 61.9 and 59.1 Kcal/mol for GVL and PL were obtained, respectively. Besides, by temperature-programmed desorption experiments it was determined that GVL adsorption is irreversible on SiO 2 -Al 2 O 3 , whereas in the case of PL is partially reversible. The effect of the calcination temperature on the product distribution and evolution of the missing carbon balance was also studied over SiO 2 -Al 2 O 3 . These results contribute to the future design of more efficient bifunctional catalytic systems for biofuel production.

Novel CNT Supported Molybdenum Catalyst for Detection of L-Cysteine in Its Natural Environment

In this study, novel carbon nanotube-supported Mo (Mo/CNT) catalysts were prepared with the sodium borohydride reduction method for the detection of L-cysteine (L-Cys, L-C). Mo/CNT catalysts were characterized with scanning electron microscopy with elemental dispersion X-ray (EDX-SEM), X-ray diffraction (XRD), UV-vis diffuse reflectance spectrometry (UV-vis), temperature-programmed reduction (TPR), temperature programmed oxidation (TPO), and temperature-programmed desorption (TPD) techniques. The results of these advanced surface characterization techniques revealed that the catalysts were prepared successfully. Electrochemical measurements were employed to construct a voltammetric L-C sensor based on Mo/CNT catalyst by voltammetric techniques such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Further measurements were carried out with electrochemical impedance spectroscopy (EIS). Mo/CNT/GCE exhibited excellent performance for L-C detection with a linear response in the range of 0–150 µM, with a current sensitivity of 200 mA/μM cm2 (0.0142 μA/μM), the lowest detection limit of 0.25 μM, and signal-to-noise ratio (S/N = 3). Interference studies showed that the Mo/CNT/GCE electrode was not affected by D-glucose, uric acid, L-tyrosine, and L-trytophane, commonly interfering organic structures. Natural sample analysis was also accomplished with acetyl L-C. Mo/CNT catalyst is a promising material as a sensor for L-C detection.

Effect of Fe/Cu catalysts supported on zeolite/active carbon hybrid on bio-oil quality derived from catalytic pyrolysis of granular bacteria biomass

Catalytic conversion of granular bacteria biomass to biofuel through pyrolysis was thoroughly studied. The hybrid of beta zeolite and active carbon (ZAC) resulted a support of catalyst with the BET surface area of 302 cm2/g. The highly active bimetallic Fe/Cu catalysts were prepared using wetness incipient impregnation on ZAC hybrid support (Fe5CuXZAC, X = 0.5, 1 and 2). To compare the activity of catalysts, catalytic pyrolysis tests of granular bacteria was performed. The pyrolysis tests in presence of Fe5Cu2ZAC remarkably decreased nitrogen compounds and total oxygenates of the bio-oil from 41.6 and 24.7 to 30.0 and 15.6 area%, respectively. Also, good selectivity of bimetallic Fe/Cu catalysts supported on ZAC toward aromatization reactions with the maximum yield for Fe5Cu2ZAC has made it a novel catalyst for pyrolytic conversion of granular bacteria biomass to aromatic hydrocarbons.The synthesized samples were characterized by Fourier transform infrared (FTIR) spectrometer, field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy (ICP), BET (Brunauer–Emmett–Teller) and temperature-programmed desorption (TPD) techniques. The products were analyzed by a gas chromatography-thermal conductivity detector (GC-TCD), a gas chromatography-mass spectrometry (GC–MS) and CHNS. Temperature-programmed oxidation (TPO) analysis was performed to study probable deposited carbon on the used catalysts.

A novel biomass sodium alginate gel foam to inhibit the spontaneous combustion of coal

In order to address the environmentally friendly issue of fire prevention and extinguishing materials in coal mines, A new biomass sodium alginate gel foam (SC-GF) was prepared by using sodium alginate (SA), calcium L-lactate (CL), alkyl glycoside (APG) and tea saponin (TS). The effect of different concentrations of CL on the properties of SC-GF was analyzed by studying the gelation time, foaming volume and half-life of the SC-GF. The results show that the gelation time of SC-GF is successfully controlled by using the weak electrolyte CL as the cross-linking agent. When SA: CL: APG: TS = 4 : 1 : 2 : 1, the gelation time of SC-GF is 10 min with half-life of 16 days. Furthermore, A metal coordination bond favorable to the stability of SC-GF is formed by the carboxylate ion of α-L-gulonic acid in SA and Ca2+ ionized by CL. SC-GF exhibits excellent fire prevention and extinguishing properties. The CO concentration of the coal sample treated with SC-GF decreases from 7556.8 to 34.92 ppm in the process of oxidation at room temperature for 48 h. The temperature-programmed oxidation test shows that SC-GF can delay the accelerated oxidation temperature from 120 to 160 °C, and the CO inhibition rate is as high as 60.5 % at 200 °C. The fire extinguishing test indicates that SC-GF can significantly reduce the temperature of the coal sample and extinguish the coal fire quickly. The study is useful to develop efficient and environmentally friendly coal mine fire prevention and extinguishing materials.

High Dispersion of CeO2 on CeO2/MgO Prepared under Dry Conditions and Its Improved Redox Properties

Suppressing the usage of rare-earth elements is crucial for making the catalysts sustainable. Preparing CeO2 nanoparticles is a common technique to reduce CeO2 consumption, but such nanoparticles are prone to sinter or react with the supports when subjected to heat treatments. This study demonstrated that stable CeO2 nanoparticles were deposited on MgO by the simple impregnation method. When CeO2/MgO was prepared under the dry atmosphere, the CeO2 nanoparticles remained ~3 nm in diameter even after being heated at 800 °C, which is much smaller than ~5 nm of CeO2/MgO prepared under ambient air. Temperature-programmed reduction, temperature-programmed oxidation, X-ray photoelectron spectroscopy, and in situ X-ray diffraction studies showed that CeO2/MgO exhibited higher oxygen mobility when prepared under the dry atmosphere. Dry reforming reaction demonstrated that CeO2/MgO prepared under the dry atmosphere exhibited higher activity than that prepared under ambient air and pure CeO2.

Cerium–zirconium mixed oxide synthesized by sol-gel method and its effect on the oxygen vacancy and specific surface area

In this study, cerium-zirconium mixed oxides were prepared using the sol-gel methodology with cetyltrimethylammonium bromide (CTAB) for tuning the specific surface area and pore volume. The composition of Ce0.8Zr0.2O2 (CZ) was selected as being one of the most active for soot oxidation, which is a concern as an environmental pollutant. The structural and morphological properties were investigated using EDXRF, XRD, SEM/EDS, Raman and N2 physisorption at low temperature. The catalytic test was evaluated by temperature-programmed oxidation coupled with mass spectrometry (TPO/MS). Any variation in the CTAB concentration during synthesis changed the particle size and surface area, indicating that the particle formation follows a mechanism in which the CTAB acts as capping agent. Additionally, the material synthesized with CTAB was found to have higher oxygen vacancy compared to the materials from the conventional sol-gel process. The catalytic test suggested that the material with the smallest surface area had the lowest temperature of oxidation (T50% ​= ​400 ​°C), which demonstrates that the oxygen vacancy parameter is essentially more important than the specific surface area itself.

A novel composite inorganic retarding gel for preventing coal spontaneous combustion

In order to better control the fire problem due to coal oxidations, a novel composite inorganic retarding gel material processed from sodium-based bentonite junction and kaolin, silica, hydrogen peroxide and silicon oxide is developed. For studying the gel's properties the scanning electron microscopy (SEM) and the thermogravimetry (TG-DTG) are used to characterize microscopical structures and mass losses with the temperature change process, respectively. For quantifying the inhibitory effect of the novel gel on the spontaneous combustion process of coal oxidation, laboratory tests such as temperature-programmed oxidation and infrared spectroscopy are carried out. Changes of the gases generated from the treated coal sample by the novel gel under the temperature increasing are analyzed. The inhibitory effects of mud and MgCl2 solutions on coal spontaneous combustion are compared. The results show that the surface of the gel is flat and smooth in microscopic scale. Under the a high-temperature, the gel is stable and is not easy to decompose. In detail, the quality loss is within 10%. The novel gel with a concentration of 20% has a good inhibitory effect on CO release and spontaneous combustion in coal combustion. In addition, the novel gel can significantly reduce the consumption of –OH, –CH and other functional groups in the low-temperature oxidation reaction. Hence, the novel gel is a kind of Inhibitor material with a better comprehension performance. This study provides a novel gel for better preventing and controlling the coal spontaneous combustion hazard.

Dynamics of Reactive Oxygen Species on Cobalt-Containing Spinel Oxides in Cyclic CO Oxidation

Reactive oxygen species (ROS) are considered to be responsible for the high catalytic activity of transition metal oxides like Co3-xFexO4 in oxidation reactions, but the detailed influences of catalyst composition and morphology on the formation of these reactive oxygen species are not fully understood. In the presented study, Co3O4 spinels of different mesostructures, i.e., particle size, crystallinity, and specific surface area, are characterized by powder X-ray diffraction, scanning electron microscopy, and physisorption. The materials were tested in CO oxidation performed in consecutive runs and compared to a Co3-xFexO4 composition series with a similar mesostructure to study the effects of catalyst morphology and composition on ROS formation. In the first run, the CO conversion was observed to be dominated by the exposed surface area for the pure Co-spinels, while a negative effect of Fe content in the spinels was seen. In the following oxidation run, a U-shaped conversion curve was observed for materials with high surface area, which indicated the in situ formation of ROS on those materials that were responsible for the new activity at low temperature. This activation was not stable at the higher reaction temperature but was confirmed after temperature-programmed oxidation (TPO). However, no activation after the first run was observed for low-surface-area and highly crystalline materials, and the lowest surface-area material was not even activated after TPO. Among the catalyst series studied here, a correlation of small particle size and large surface area with the ability for ROS formation is presented, and the benefit of a nanoscaled catalyst is discussed. Despite the generally negative effect of Fe, the highest relative activation was observed at intermediate Fe contents suggesting that Fe may be involved in ROS formation.

Copper-iron mixed oxide supported onto cordierite honeycomb as a heterogeneous catalyst in the Kharasch-Sosnovsky oxidation of cyclohexene

A copper-iron mixed oxide was deposited by the washcoating procedure over cordierite honeycomb monoliths for its use as a heterogeneous catalyst in organic synthesis processes. In particular, the prepared catalyst, characterized by techniques such as X-ray fluorescence, X-ray diffraction, SEM-EDS, laser granulometry, adherence tests, Temperature-Programmed Oxidation and Temperature-Programmed Reduction, showed an excellent yield and stability in the selective production of the allylic ester derived from the Kharasch-Sosnovsky oxidation of cyclohexene with benzoic acid. The use of a structured catalyst here proposed opens up an interesting alternative to homogeneous catalysis in the field of synthetic chemistry.

GaPt Supported Catalytically Active Liquid Metal Solution Catalysis for Propane Dehydrogenation-Support Influence and Coking Studies.

Supported catalytically active liquid metal solutions (SCALMS) of Pt in Ga (2 at.-% Pt) were studied in the temperature range of 500 to 600 °C for propane dehydrogenation. A facile synthesis procedure using ultrasonication was implemented and compared to a previously reported organo-chemical route for gallium deposition. The procedure was applied to synthesize GaPt-SCALMS catalyst on silica (SiO2), alumina (Al2O3), and silicon carbide (SiC) to investigate the effect of the support material on the catalytic performance. The SiC-based SCALMS catalyst showed the highest activity, while SiO2-based SCALMS showed the highest stability and lowest cracking tendency at higher temperatures. The selectivity toward propene for the SiO2-based catalyst remained above 93% at 600 °C. The catalysts were analyzed for coke content after use by temperature-programmed oxidation (TPO) and Raman spectroscopy. While the SiC- and SiO2-supported SCALMS systems showed hardly any coke formation, the Al2O3-supported systems suffered from pronounced coking. SEM-EDX analyses of the catalysts before and after reaction indicated that no perceivable morphological changes occur during reaction. The SCALMS catalysts under investigation are compared with supported Pt and supported GaPt solid-phase catalyst, and possible deactivation pathways are discussed.

Light-off Investigation of Oxymethylene Ether (OME) Considering the Presence of the Exhaust Components Heptane, Carbon, and Nitrogen Monoxide

Synthetic fuels and fuel blends like OMEs can contribute to tank-to-wheel CO2 emission savings. At the same time, it is known that these fuels have a lower exhaust temperature compared to conventional diesel. This effect has major impact on the exhaust after-treatment system, particularly in cold start conditions. This paper investigates the light-off behavior of exhaust gases containing OMEs by temperature-programmed oxidation experiments using a state-of-the-art oxidation catalyst. The main side product of catalytic oxidation of OMEs between 100 °C and the oxidation temperature T50, which was around 160 °C, was shown to be formaldehyde. While alkane oxidation, in this case heptane, was little influenced by OME oxidation, the oxidation temperature T50 of CO increases by more than 10 °C by OME addition. Nitrogen monoxide impeded the oxidation of OME in a similar way to the other components investigated. Due to the amount of FA produced and its toxicity, it could be concluded that it is necessary to heat up exhaust after-treatment systems of OME diesel engines even faster than conventional diesel exhaust after-treatment systems. The relatively high reactivity of OME on oxidation catalyst can be used by active thermal management approaches.

Substituent positions and types for the inhibitory effects of phenolic inhibitors in coal spontaneous combustion

This study is aimed at investigating the effects of substituent positions and types on the activities of phenolic inhibitors for inhibiting coal spontaneous combustion (CSC). To achieve this aim, six phenolic inhibitors with different substituent positions (ortho-, meta- and para-) and types (methyl, ethyl, isopropyl and tert butyl) were selected for testing their inhibitory effects on Xilinhe coal. First, the temperature-programmed oxidation experiment was performed on the raw coal sample and the inhibited coal samples to explore their CO generation volumes and crossing-point temperatures under low-temperature oxidation conditions. Meanwhile, the corresponding inhibition rates, oxygen consumption rates and apparent activation energy values were calculated. Furthermore, the weight loss processes, surface morphologies and active functional group variations of the raw coal sample and the inhibited coal samples were analyzed with the aid of a thermogravimetric analyzer, a scanning electron microscope and a Fourier transform infrared spectrometer. The test results showed that the phenolic inhibitors can not only infilter into coal but also accumulate on coal surface to form an inhibitor layer. Besides, they can inhibit CSC in both physical and chemical ways during low-temperature oxidation of coal, and their inhibitory effects exhibit varying characteristics in different stages. When the temperature is below 120 °C, the physical inhibitory effects of oxygen isolation and water retention dominate. When it exceeds 120 °C, the chemical inhibitory effect of capturing active free radicals in coal plays a dominant role. The types of substituents have a more notable effect on the activities of phenolic inhibitors than the positions of substituents. The inhibitor with smaller substituent steric hindrance and stronger infiltration ability is more capable of inhibiting CSC physically and chemically. Among the inhibitors with different substituent types, m-cresol boasts the optimal inhibitory effect. Its inhibition rate is 84.4% at 170 °C; the oxygen consumption rate is only 1/4 of that of raw coal; the crossing-point temperature is raised by 30.3 °C to 181.7 °C; and the apparent activation energy values are increased by 7.74 kJ/mol, 16.18 kJ/mol and 20.61 kJ/mol in the slow oxidation stage, the accelerated oxidation stage and the intense oxidation stage, respectively.

Valorization of fluid petroleum coke for efficient catalytic destruction of biomass gasification tar

Large volumes of waste petroleum coke stockpiled in open yard not only represent a huge loss of valuable material but also pose a significant risk to the environment. This work proposed an innovative strategy for waste petroleum coke valorization by exploring its catalytic performance of biomass gasification tar destruction. Waste petroleum coke was firstly activated by potassium hydroxide (KOH) to obtain high specific surface area as well as low sulfur and ash contents. Petroleum coke derived catalyst showed superior performance than a commercial activated carbon derived catalyst for destruction of naphthalene as the tar model compound. The petroleum coke derived catalyst exhibited 99.1% naphthalene destruction efficiency at 800 °C but deactivated quickly under N2 atmosphere. Under H2 and steam atmospheres, the catalytic activities were 98.6% and 96.5% for 8 h, respectively. To study the correlation between catalytic performance and the structure of carbon catalyst, elemental analysis, scanning electron microscope (SEM) analysis, transmission electron microscope (TEM) analysis, X-ray powder diffraction (XRD) analysis, Brunauer-Emmett-Teller method (BET) analysis, Fourier transform infrared (FTIR) spectroscopy, temperature programmed oxidation (TPO) analysis and Raman spectroscopy were performed on both fresh and spent catalysts. Results demonstrated that the hydrogen-rich groups (small rings and amorphous carbon) and oxygen-containing groups may account for the good resistance to coke deposition under H2 and steam atmospheres.

Catalytic Abatement of Volatile Organic Compounds and Soot over Manganese Oxide Catalysts.

A set of manganese oxide catalysts was synthesized via two preparation techniques: solution combustion synthesis (Mn3O4/Mn2O3-SCS and Mn2O3-SCS) and sol-gel synthesis (Mn2O3-SG550 and Mn2O3-SG650). The physicochemical properties of the catalysts were studied by means of N2-physisorption at −196 °C, X-ray powder diffraction, H2 temperature-programmed reduction (H2-TPR), soot-TPR, X-ray photoelectron spectroscopy (XPS) and field-emission scanning electron microscopy (FESEM). The high catalytic performance of the catalysts was verified in the oxidation of Volatile Organic Compounds (VOC) probe molecules (ethene and propene) and carbon soot in a temperature-programmed oxidation setup. The best catalytic performances in soot abatement were observed for the Mn2O3-SG550 and the Mn3O4/Mn2O3-SCS catalysts. The catalytic activity in VOC total oxidation was effectively correlated to the enhanced low-temperature reducibility of the catalysts and the abundant surface Oα-species. Likewise, low-temperature oxidation of soot in tight contact occurred over the Mn2O3-SG550 catalyst and was attributed to high amounts of surface Oα-species and better surface reducibility. For the soot oxidation in loose contact, the improved catalytic performance of the Mn3O4/Mn2O3-SCS catalyst was attributed to the beneficial effects of both the morphological structure that—like a filter—enhanced the capture of soot particles and to a probable high amount of surface acid-sites, which is characteristic of Mn3O4 catalysts.

Dry methane reforming with nickel–cobalt bimetallic catalysts based on halloysite nanoclay modified by alkaline melting method

AbstractCatalysts, including (10% Ni)/AMHA, (10% Ni + 5% Co)/AMHA, (5% Ni + 5% Co)/AMHA, and (5% Ni + 10% Co)/AMHA, were prepared by simultaneous impregnation of Ni and Co on alkaline molten halloysite (AMHA) and characterized by X‐ray diffraction (XRD), field diffusion scanning electron microscopy (FESEM), temperature‐programmed reduction (TPR), temperature‐programmed oxidation (TPO), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), atomic force microscopy (AFM), and Brunauer–Emmett–Teller (BET). The catalysts were evaluated in dry reforming of methane (DRM) at temperatures of 700 to 850°C and with a volumetric composition of a feed gas of 40% CH4, 40% CO2, and 20% Ar in a fixed bed reactor. Catalyst performance tests showed that the nickel catalyst based on milled and alkaline molten nano‐halloysite had a relatively poor performance. After impregnation of cobalt metal with different concentrations in the presence of nickel, the functional properties increased. Characteristic observations and experiments showed a very positive effect of cobalt metal on the catalyst performance. The presence of cobalt reinforcing metal along with nickel improves the activity and stability and reduces catalyst coking. Moreover, increasing cobalt along with nickel leads to better dispersion of the active phase of nickel, improved catalyst regeneration, and stable production of synthetic gas from methane and carbon dioxide. The effect of cobalt and nickel ratio on the catalyst structure, conversion rate of methane and carbon dioxide, stability, and carbon deposition rate were investigated. The conversion rate increases at high temperatures. Also, the resulting gas composition is suitable for Fischer–Tropsch reactions.

Redox catalysts based on amorphous porous carbons

A modular synthesis concept to prepare a library of mainly amorphous porous carbons has been developed. The carbons show – while keeping the textural properties nearly unchanged - systematically varied features such as the content of nitrogen, oxygen, iron and graphitic species, respectively. These individual features and the cross-relations between them were characterized with respect to applications of the carbons as reactants or catalysts in different test reactions, namely the temperature-programmed oxidation (TPO), the oxidation of sulphurous acid (OSA), the electrochemical oxygen reduction reaction (ORR) and the oxidative dehydrogenation of ethylbenzene (ODH), respectively. The carbon materials show striking similarities in terms of catalytic activity in TPO, OSA and ORR, respectively. The influence of individual nitrogen species and graphitic species on the catalytic behaviour was analyzed in detail. Pyrrole-like nitrogen species are obviously beneficial for the activation of molecular oxygen in different test reactions while pyridine-like species do not affect the catalytic behaviour. Graphitic species do not significantly influence the catalytic activity of otherwise amorphous carbons. For ODH, it was shown that nitrogen functionalities enhance the overall catalyst deactivation by catalysing the destruction of active sites. • A library of carbon catalysts with systematically varied features was developed. • The catalysts were used for comparative studies on different redox-reactions. • Carbon catalysts show striking similarities in terms of activity in TPO, OSA and ORR. • Pyrrole-like nitrogen is obviously beneficial for the activation of molecular oxygen. • Graphitic species do not significantly influence the catalytic activity of the carbons.

Development of Flowerlike Ce1-XZrxO2-δ-Dispersed Paper-Structured Catalyst for Direct-Biogas SOFC

Performance of direct internal reforming (DIR)-solid oxide fuel cell (SOFC) can be improved by the application of the paper-structured catalyst (PSC) on the anode material. In the ceramic fiber network of the PSC, any kinds of functional materials can be easily dispersed during paper-making process.The solid solution based on the equimolar mixture of ceria and zirconia (Ce0.5Zr0.5O2-δ), hereafter called CZ, is a promising oxide support of the Ni metal catalyst due to its high specific surface area and high oxygen storage capacity (OSC). By employing the two-step hydrothermal process developed in this study, we could successfully prepare the CZ with flowerlike geometry, which can prevent Ni from sintering under reducing atmosphere.Ni-loaded PSCs with and without the dispersion of CZ, Ni/CZ-PSC and Ni-PSC, respectively, were prepared. Structures of the PSCs were characterized by X-ray diffractometry (XRD), BET specific surface area measurement, field emission scanning electron microscopy (FESEM), inductively coupled plasma spectrometry (ICP) and thermogravimetric analysis (TG). Catalytic performances of these PSCs for the dry reforming of methane (DRM) in the feed of the equimolar mixture of CH4 and CO2 were evaluated by an automatic gas chromatograph (GC) with the posttest analysis by FESEM observation, temperature-programmed oxidation (TPO) and TG to estimate carbon deposition.In the durability (160 h) tests of the prepared-PSCs for DRM at 750oC under gas hourly space velocity (GHSV) of 2300 h-1 revealed that, for both cases with and without CZ dispersion, methane conversions were stable with the degradation rates (estimated after 10 h) of 13.7 and 21.8% 1000 h-1, respectively. TG measurements after the 160 h tests under oxidizing atmosphere in the range from 300 to 750oC revealed that the weights of the deposited carbon were 0.2 and 3.4 folds of those of PSCs for Ni/CZ-PSC and Ni-PSC, respectively. In the case without CZ dispersion (Ni-PSC), after the TG measurement to burn out the deposited carbon, Ni agglomeration and its detachment from the ceramic fiber could be clearly observed. On the other hand, for the Ni/CZ-PSC, these phenomena were considerably suppressed thanks to the flowerlike morphology for better dispersion of Ni metal particles and higher OSC of CZ solid solution to consume deposited carbon by the lattice oxygen.The developed PSCs will be applied on the anode of electrolyte-supported cell to demonstrate the stable operation of DIR-SOFC fueled by biogas (direct-biogas SOFC).

Role of Ba in low temperature thermochemical conversion of carbon dioxide with LaFeO3 perovskite oxides

Reverse water-gas shift chemical looping (RWGS-CL) is a low temperature thermochemical process to convert CO2 to CO by perovskite oxides. In this research, perovskite oxides of the form of La1-xBaxFeO3 (x = 0.25−0.75) are explored for enhancing CO yield while maintaining stability over multiple cycles. DFT was utilized to calculate the oxygen vacancy formation energies (Evac) identifying Evac of La0.75Ba0.25FeO3 (3.3 eV) and La0.5Ba0.5FeO3 (3.0 eV) are in the ideal range of 3.4 ± 0.5 eV. Additional Ba resulted in instability. XRD confirmed cubic perovskite structure and XRF analysis established the precise composition. XPS revealed that the materials had Ba enrichment at the surface, compared to the overall bulk. Temperature-programmed reduction (TPR) and oxidation (TPO) experiments determined that CO2 is converted to CO in the low temperature range of 400–600 °C for all compositions, which is lower than temperatures of many thermochemical CO2 processes. Isothermal cycling between hydrogen and CO2 at 600 °C indicated La0.5Ba0.5FeO3 and La0.4Ba0.6FeO3 were stable (verified by XRD and XPS) and produced CO at high yields of 200 and 500 μmol/gLBF, respectively. The CO2 conversion step fits to Langmuir–Hinshelwood type kinetics based on its partial pressure dependency and is consistent with DRIFTS studies. Therefore, multiple materials in this study enhance performance, indicating their suitability for industrial scale adaptation upon energy integration as a possible strategy for renewable energy storage in chemical form.