Temperature-programmed Reduction Profiles Research Articles

Novel spinel based high entropy oxide as electrode for symmetric SOFCs

Fabrication of symmetric electrodes for intermediate temperature SOFCs can significantly reduce fuel cell production costs without compromising efficiency. Herein, we report a novel spinel based high entropy oxide (CuLiFeCoNi)1.4Mn1.6O4-δ (CM-HEO) that exhibit better symmetric electrode properties than the parent spinel oxide, Cu1.4Mn1.6O4-δ (CM). The prepared HEO exhibited good structural and thermal stability up to 800 °C as inferred from the XRD, Raman and TGA-DSC results. Temperature-programmed reduction and desorption profiles of CM-HEO outperformed CM by exhibiting hydrogen adsorption and lower CO2 desorption across different temperature ranges. The enhancement of Lewis acid-base sites is evident from the XPS analysis validating the observed increase in HOR and ORR activity. The high electrocatalytic activity of the material arise from its lower activation energies (0.27 eV in air, 0.09 eV in dry H2 and 0.03 eV in dry CH4) with a polarisation resistances of 0.152 Ωcm2 under ambient atmosphere and 0.044 Ωcm2 under dry H2. These findings exalt CM-HEO as an efficient symmetric SOFC electrode material.

Kinetic analysis of aerobic oxidation catalyzed by a hybrid heterogeneous-homogeneous system containing supported Mn and V oxides and N-hydroxyphthalimide

The activities of transition metal oxide (TMO) heterogeneous catalysts based on individual components such as VOX, and MnOX supported on TiO2 and TiO2-SiO2 as cocatalysts in catalytic systems complemented with N-hydroxyphthalimide (NHPI) in the processes of aerobic liquid-phase radical chain oxidation of alkylarenes (RH) was investigated. The mechanisms of catalysis by NHPI in a liquid phase and participation of TMO in the chain initiation stage were discussed. Catalytic activities of Mn- and V-oxide catalysts were compared with the results of molecular hydrogen temperature programmed reduction profiles (H2-TPR) of the catalysts, revealing correlation between them. Reaction enthalpies calculated via a semi-empirical method for model structures of catalytic centers explained the obtained experimental results. Finally, catalytic cumene oxidation was presented using a reactions scheme identifying the concomitant role of heterogeneous initiation and homogeneous propagation and termination steps for the oxidation process proceeding via a free-radical mechanism.

Hydrogen production from sorption enhanced steam reforming of ethanol using bifunctional Ni and Ca-based catalysts doped with Mg and Al

This work evaluated the performance of nickel-based catalysts supported on CaO and CaO–MgO–Al2O3 in the sorption enhanced steam reforming of ethanol (SESRE) aiming the production of high purity H2. The catalysts were prepared by sol-gel method and characterized by different methods: Temperature programmed reduction (TPR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) with chemical element mapping, N2 physisorption and CO2 capture capacity determined by thermogravimetric analysis (TGA). XRD analysis showed that the predominant phases were CaO, MgO, CaCO3, Ca(OH)2 and NiO in the calcined samples and Ni0 in the reduced and passivated samples. TPR profiles indicated that all catalysts presented a high degree of reduction (Ni/CaMgAl-68 > Ni/CaMgAl-79 > Ni/Ca), although Ni/CaMgAl-X samples presented high reduction temperatures indicating the formation of NiAl2O4. The addition of MgO and Al2O3 to CaO was very beneficial since the deactivation coefficients, calculated by the TGA data modeling, decreased by a factor of 3.8 for Ni/CaMgAl-79 and by a factor of 4.3 for Ni/CaMgAl-68 when compared to the Ni/Ca catalyst. The catalytic tests in the SESRE showed that Ni/CaMgAl-79 catalyst had the best performance since it had the longest high purity hydrogen production time. In the pre-breakthrough period, the H2 mole fractions were close to 90% for all samples during all reaction cycles. After the reaction-regeneration cycles, the average crystallite size of CaO estimated by XRD increased around 38, 6 and 35% for Ni/Ca, Ni/CaMgAl-79 and Ni/CaMgAl-68, respectively. Thus, adding a dopant to the sorbent material proved to be an effective strategy to obtain a more stable catalyst capable to produce hydrogen of high purity.

Influence of particle size and metal-support interaction on the catalytic performance of Ni-Al2O3 catalysts for the dry and oxidative-dry reforming of methane

Dry reforming of methane (DRM) is a promising route for converting CH4 and CO2 to syngas. A Ni-Al2O3 catalyst was calcined at 500 and 850 °C to form NiAl-500 and NiAl-850. The oxidized nickel phase in both calcined catalysts are reduced to metallic nickel at conditions based on the temperature programmed reduction profile and found to be catalytically active for the DRM reaction with and without 7.5% v/v oxygen co-feed. Carbon deposition is most evident for DRM at 600 °C. Furthermore, after DRM the spent NiAl-500 shows detachment of nickel particles, whereas detachment was not readily seen in the spent NiAl-850 catalyst. By co-feeding oxygen, almost “carbon-free” operations were achieved even at 600 °C for both catalysts. The NiAl-500 catalyst possesses smaller particles due to lower reduction temperatures used. This catalyst shows higher CH4 and CO2 conversions, H2 and CO yields, and lower carbon formation for both reactions. At the same reduction temperature, the nickel particles in NiAl-500 were larger than those in NiAl-850 and the conversions and yields were smaller. Changes in the crystallite size and fraction of near-surface nickel were also detected in the catalysts after DRM and ODRM reactions.

Propane dehydrogenation over extra-framework In(i) in chabazite zeolites.

Indium on silica, alumina and zeolite chabazite (CHA), with a range of In/Al ratios and Si/Al ratios, have been investigated to understand the effect of the support on indium speciation and its corresponding influence on propane dehydrogenation (PDH). It is found that In2O3 is formed on the external surface of the zeolite crystal after the addition of In(NO3)3 to H-CHA by incipient wetness impregnation and calcination. Upon reduction in H2 gas (550 °C), indium displaces the proton in Brønsted acid sites (BASs), forming extra-framework In+ species (In-CHA). A stoichiometric ratio of 1.5 of formed H2O to consumed H2 during H2 pulsed reduction experiments confirms the indium oxidation state of +1. The reduced indium is different from the indium species observed on samples of 10In/SiO2, 10In/Al2O3 (i.e., 10 wt% indium) and bulk In2O3, in which In2O3 was reduced to In(0), as determined from the X-ray diffraction patterns of the product, H2 temperature-programmed reduction (H2-TPR) profiles, pulse reactor investigations and in situ transmission FTIR spectroscopy. The BASs in H-CHA facilitate the formation and stabilization of In+ cations in extra-framework positions, and prevent the deep reduction of In2O3 to In(0). In+ cations in the CHA zeolite can be oxidized with O2 to form indium oxide species and can be reduced again with H2 quantitatively. At comparable conversion, In-CHA shows better stability and C3H6 selectivity (∼85%) than In2O3, 10In/SiO2 and 10In/Al2O3, consistent with a low C3H8 dehydrogenation activation energy (94.3 kJ mol−1) and high C3H8 cracking activation energy (206 kJ mol−1) in the In-CHA catalyst. A high Si/Al ratio in CHA seems beneficial for PDH by decreasing the fraction of CHA cages containing multiple In+ cations. Other small-pore zeolite-stabilized metal cation sites could form highly stable and selective catalysts for this and facilitate other alkane dehydrogenation reactions.

In Situ Study of Reduction of MnxCo3-xO4 Mixed Oxides: The Role of Manganese Content.

A series of Mn-Co mixed oxides with a gradual variation of the Mn/Co molar ratio were prepared by coprecipitation of cobalt and manganese nitrates. The structure, chemistry, and reducibility of the oxides were studied by X-ray diffraction (XRD), X-ray absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction (TPR). It was found that at concentrations of Mn below 37 atom %, a solid solution with a cubic spinel structure is formed. At concentrations above 63 atom %, a solid solution is formed on the basis of a tetragonal spinel, while at concentrations in a range of 37-63 atom %, a two-phase system, which contains tetragonal and cubic oxides, is formed. To elucidate the reduction route of mixed oxides, two approaches were used. The first was based on a gradual change in the chemical composition of Mn-Co oxides, illustrating slow changes in the TPR profiles. The second approach consisted in a combination of in situ XRD and pseudo-in situ XPS techniques, which made it possible to directly determine the structure and chemistry of the oxides under reductive conditions. It was shown that the reduction of Mn-Co mixed oxides proceeds via two stages. During the first stage, (Mn, Co)3O4 is reduced to (Mn, Co)O. During the second stage, the solid solution (Mn, Co)O is transformed into metallic cobalt and MnO. The introduction of manganese cations into the structure of cobalt oxide leads to a decrease in the rate of both reduction stages. However, the influence of additional cations on the second reduction stage is more noticeable. This is due to crystallographic peculiarities of the compounds: the conversion from the initial oxide (Mn, Co)3O4 into the intermediate oxide (Mn, Co)O requires only a small displacement of cations, whereas the formation of metallic cobalt from (Mn, Co)O requires a rearrangement of the entire structure.

In-situ reforming and combustion of liquid fuel using MnOx/Ce-γAl2O3 oxygen carrier in a chemical looping combustion process

A new MnOx/Ce-γAl2O3 oxygen carrier is developed for liquid fuel based fluidized chemical looping combustion (CLC) process. The developed material serves both as a catalyst and as a source of solid phase oxygen for gasification/reforming of liquid fuel followed by the combustion of the gasified products. The support γAl2O3 is modified with cerium, improved thermal stability and minimized the interaction with the main active component MnOx. In order to validate the desired properties, the prepared MnOx/Ce-γAl2O3 samples are characterized using various physicochemical characterizations, including X-ray fluorescence (XRF), nitrogen adsorption, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscope (SEM), temperature programmed reduction (TPR), and temperature programmed desorption (TPD). TPR, TGA and XRD analysis confirm that the Ce modification improves the thermal stability of γAl2O3 and hinders the formation of difficult reducing manganese aluminate. TPR profiles show excellent reduction and re-oxidation performances of the Ce modified samples. Based on characterizations, a selected sample is further evaluated in a fluidized CREC Riser Simulator (CREC: Chemical Reactor Engineering Centre) using n-hexane as a liquid fuel surrogate. Under the studied reaction conditions (500–650 C; 10–45 s reaction time), CO2 and CO are the main combustion products. At 650 °C, approximately 92% n-hexane combustion and 60% of CO2 selectivity was achieved, which is very encouraging, given the complexity of the interaction of liquid fuel with the solid metal oxides.

Influence of Zr Additive on the Chemical Reduction Behaviour of MoO<sub>3</sub> in Carbon Monoxide Atmosphere

Temperature-programmed reduction (TPR) was used to observe the chemical reduction behaviour of molybdenum trioxide (MoO3) and zirconia (Zr)-doped MoO3 catalyst by using carbon monoxide (CO) as the reductant. The characterisation of catalysts was performed by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and transmission electron microscopy (TEM) analyses. The reduction performance were examined up to 700°C and reduction was continued for 60 min at 700°C in a stream of 20 vol. % CO in nitrogen. The TPR profile showed that the doped MoO­3 catalyst was slightly moved to a higher temperature (580°C) as compared to the undoped MoO3 catalyst, which began at around 550°C. The interaction between zirconia and molybdenum ions in doped MoO3 catalyst led to an increase in the reduction temperature. According to characterisation of the reduction products by using XRD, it revealed that the reduction behaviour of pure MoO3 to MoO2 by CO reductant involved two reduction stages with the formation of Mo4O11 as the intermediate product. Meanwhile, MoO3 catalyst doped with zirconia caused a delay in the reduction process and was proven by the presence of Mo4O11 species at the end of reactions. Physical analysis by using BET showed a slight increase in surface area of 3% Zr-MoO3 from 6.85 m2/g to 7.24 m2/g. As for TEM analysis, black tiny spots located around MoO3 particles revealed that the zirconia was successfully intercalated into MoO3 particles. This confirmed that formation of intermetallic between Zr-MoO3 catalyst will give new chemical and physical properties which has a remarkable chemical effect by disturbing the reduction progression of MoO3 catalyst.

Homogeneous-like Alkyne Selective Hydrogenation Catalyzed by Cationic Nickel Confined in Zeolite

The selective hydrogenation of alkynes to their corresponding alkenes is an important type of organic transformation, which is currently accomplished by modified palladium catalysts. Herein, we rep...

Study the hematite reduction kinetics by the magnetic method

This study is devoted to the reduction of Fe2O3 supported on silica gel in H2 in the temperature range of 290–600 °C. A continuous magnetization measurement method was used to obtain the temperature programmed reduction (TPR) profile. The influence of the external magnetic field on the dynamics of the process is investigated. It was shown that the TPR profile depends both on the magnitude of the applied field and on the particle size of hematite.

Influence of Pt/Ru anodic ratio on the valorization of ethanol by PEM electrocatalytic reforming towards value-added products

Abstract The ethanol electro-reforming process was studied over PtRu/C catalysts synthesized by the modified polyol method with different compositions. In particular, this work reports the influence of anodic Pt:Ru ratio (5:1, 2:1 and 1:2) on the organic product distribution (acetaldehyde, acetic acid and ethyl acetate) and pure hydrogen generation at different current densities operation levels. Physicochemical characterization of the catalysts was made by X-ray diffraction (XRD), temperature-programmed reduction (TPR) and N2 adsorption–desorption measurements. XRD patterns showed that Ru is introduced into the Pt structure, forming an alloy between both metals. Also, the degree of alloy was higher by increasing the Ru amounts. From TPR profiles Pt was found to be properly reduced while Ru was both in metallic state and forming RuO2. The electrochemical behaviour of each catalyst towards ethanol electro-reforming process was investigated through electrochemical techniques in a half cell and a single proton exchange membrane (PEM) cell systems. An intermediate Pt:Ru ratio was found to result in high current density and electrochemical surface area (ECSA) values along with lower amounts of adsorbed species. Also, Ru addition seems to diminish the degree of degradation of the catalyst. Based on characterization and in agreement with essays carried out in a PEM cell at mild conditions (80 °C and 1 atm), PtRu/C 2:1 anode provided the best electrocatalytic results in terms of current density (740 mA cm−2), hydrogen production and selectivity toward acetic acid (up to 15% apart from acetaldehyde and ethyl acetate) while requiring the lowest energy consumption.

BUTENEDIOLS PRODUCTION FROM ERYTHRITOL ON Rh PROMOTED CATALYST

The C-O hydrogenolysis of Erythritol to Butanodiols was studied in aqueous solution at 473 K and 25 bar of H2 using Rh/ReOx/TiO2 and the monometallic Rh/TiO2 and ReOx/TiO2 catalysts. The solids were characterized by temperature programmed reduction (TPR), TEM and XPS. TPR and XPS showed that ReOx species are close to Rh particles leading to reduction at lower temperature than Re on monometallic catalyst. However, some segregated Rhenium species were suspected by TPR profile for the bimetallic catalyst and detected by TEM. Re/TiO2 exhibited low activity forming only products from dehydration and epimerization. Although Rh/TiO2 showed high activity (total conversion at 14 h), was more selective to C-C cleavage leading to lower carbon products. Rh/ReOx/TiO2, showed instead, a good activity and selectivity towards C-O hydrogenolysis route yielding 37.5% of Butanodiols. Activation energy and reaction orders on ERY (0.58) and H2 (0.53) were estimated from experiences made at different reaction conditions

Enhanced Activity of Cu/ZnO/C Catalysts Prepared by Cold Plasma for CO2 Hydrogenation to Methanol

An activated carbon-supported Cu/ZnO catalyst for CO2 hydrogenation to methanol has been prepared by the facile plasma decomposition of a Cu–Zn precursor at moderate temperature. The Cu/ZnO/C catalyst prepared by cold plasma featured smaller size and higher dispersion than that prepared by traditional calcination. The low operation temperature plays an important role in this. The catalysts are characterized using a multitechnique approach. X-ray photoelectron spectroscopy results indicate that cold plasma can introduce specific O-containing groups on the carbon surface. It also facilitates the dispersion of active components and H spillover. H2 temperature-programmed reduction profiles and transmission electron microscopy images show that the interaction between Cu, ZnO, and carbon in the Cu/ZnO/C catalyst prepared by cold plasma was stronger than that in the catalyst prepared by calcination. The properties are beneficial to the CO2 hydrogenation reaction. The catalytic performance of the catalysts was tested in a fixed-bed reactor. The Cu/ZnO/C catalyst prepared by cold plasma showed an obvious increase in CO2 conversion, methanol selectivity, and productivity in the catalytic evaluation of catalysts. Moreover, it obtained a remarkable space-time yield of 92.5 gmethanol·kgcat–1·h–1 at 260 °C that is approximately 1.5 times that of Cu/ZnO/C prepared by calcination.

Surface structure–activity relationships of Cu/ZnGaOX catalysts in low temperature water–gas shift (WGS) reaction for production of hydrogen fuel

A new species’ class of Cu-, Ga- and Zn-based rate catalysts was prepared by a systematic co-precipitation technique at the different related pH values (6.5–8.0) along with calcination functional conditions, influencing components’ physical properties, these were characterized, and their application performance for water–gas shift (WGS) reaction was researched. Substances were analysed by various experimental methods, namely chemisorption, temperature-programmed reduction (TPR) characterisation, diffraction, physisorption and microscopy. A homogenous size dispersion of the compounds with smaller granular particles was obtained for catalysis, implemented with high pH-resulting outputs. H2 TPR profiles revealed a tailored stronger effect of Cu–Zn on Ga for process, operated with low pH-conditioned forms. Over Cu/ZnGaOX, WGS was sensitive to Cu, which was primarily active. Catalytic chemical reactivity, activity and selectivity were also found to be critically dependent on material lattice structure, copper surface area and metal–support interaction phenomena. The temperature-programmed surface reaction with mass spectrometry (TPSR–MS) measurements showed that formulations, synthesised at the pH of 8.0, enabled reaching >99% of the equilibrium yield CO conversion at 260 °C. An increase in the converted CO, oxidation and H2 productivity with the integral steam content in gaseous feed flow was achieved. The heterogeneous phase processing at the correlated pH of 7.6 demonstrated the highest formed CO product at the temperature of 200 °C, compared with literature. This is particularly promising for reagent purity hydrogen-fed fuel cells. The kinetics for each co-precipitated solid was evaluated regarding the efficiency for the WGS in a fixed bed reactor.

Synthesis of Fe2SiO4-Fe7Co3 Nanocomposite Dispersed in the Mesoporous SBA-15: Application as Magnetically Separable Adsorbent.

The mixture containing alloy and oxide with iron-based phases has shown interesting properties compared to the isolated species and the synergy between the phases has shown positive effect on dye adsorption. This paper describes the synthesis of Fe2SiO4-Fe7Co3-based nanocomposite dispersed in Santa Barbara Amorphous (SBA)-15 and its application in dye adsorption followed by magnetic separation. Thus, it was studied the variation of reduction temperature and amount of hydrogen used in synthesis and the effect of these parameters on the physicochemical properties of the iron and cobalt based oxide/alloy mixture, as well as the methylene blue adsorption capacity. The XRD and Mössbauer results, along with the temperature-programmed reduction (TPR) profiles, confirmed the formation of Fe2SiO4-Fe7Co3-based nanocomposites. Low-angle XRD, N2 isotherms, and TEM images show the formation of the SBA-15 based mesoporous support with a high surface area (640 m2/g). Adsorption tests confirmed that the material reduced at 700 °C using 2% of H2 presented the highest adsorption capacity (49 mg/g). The nanocomposites can be easily separated from the dispersion by applying an external magnetic field. The interaction between the dye and the nanocomposite occurs mainly by π-π interactions and the mixture of the Fe2SiO4 and Fe7Co3 leads to a synergistic effect, which favor the adsorption.

Chemical Reduction Behavior of Zirconia Doped to Nickel at Different Temperature in Carbon Monoxide Atmosphere

The reduction behavior of nickel oxide (NiO) and zirconia (Zr) doped NiO (Zr/NiO) was investigated using temperature programmed reduction (TPR) using carbon monoxide (CO) as a reductant and then characterized using X-ray diffraction (XRD), nitrogen absorption isotherm using BET technique and FESEM-EDX. The reduction characteristics of NiO to Ni were examined up to temperature 700 °C and continued with isothermal reduction by 40 vol. % CO in nitrogen. The studies show that the TPR profile of doped NiO slightly shifts to a higher temperature as compared to the undoped NiO which begins at 387 °C and maximum at 461 °C. The interaction between ZrO2 with Ni leads to this slightly increase by 21 to 56 °C of the reduction temperature. Analysis using XRD confirmed, the increasing percentage of Zr from 5 to 15% speed up the reducibility of NiO to Ni at temperature 550 °C. At this temperature, undoped NiO and 5% Zr/NiO still show some crystallinity present of NiO, but 15% Zr/NiO shows no NiO in crystalline form. Based on the results of physical properties, the surface area for 5% Zr/NiO and 15% Zr/NiO was slightly increased from 6.6 to 16.7 m2/g compared to undoped NiO and for FESEM-EDX, the particles size also increased after doped with Zr on to NiO where 5% Zr/NiO particles were 110 ± 5 nm and 15% Zr/NiO 140 ± 2 nm. This confirmed that the addition of Zr to NiO has a remarkable chemical effect on complete reduction NiO to Ni at low reduction temperature (550 °C). This might be due to the formation of intermetallic between Zr/NiO which have new chemical and physical properties.

Kinetics of Fischer–Tropsch Synthesis in a 3-D Printed Stainless Steel Microreactor Using Different Mesoporous Silica Supported Co-Ru Catalysts

Fischer–Tropsch (FT) synthesis was carried out in a 3D printed stainless steel (SS) microchannel microreactor using bimetallic Co-Ru catalysts on three different mesoporous silica supports. CoRu-MCM-41, CoRu-SBA-15, and CoRu-KIT-6 were synthesized using a one-pot hydrothermal method and characterized by Brunner–Emmett–Teller (BET), temperature programmed reduction (TPR), SEM-EDX, TEM, and X-ray photoelectron spectroscopy (XPS) techniques. The mesoporous catalysts show the long-range ordered structure as supported by BET and low-angle XRD studies. The TPR profiles of metal oxides with H2 varied significantly depending on the support. These catalysts were coated inside the microchannels using polyvinyl alcohol and kinetic performance was evaluated at three different temperatures, in the low-temperature FT regime (210–270 °C), at different Weight Hourly Space Velocity (WHSV) in the range of 3.15–25.2 kgcat.h/kmol using a syngas ratio of H2/CO = 2. The mesoporous supports have a significant effect on the FT kinetics and stability of the catalyst. The kinetic models (FT-3, FT-6), based on the Langmuir–Hinshelwood mechanism, were found to be statistically and physically relevant for FT synthesis using CoRu-MCM-41 and CoRu-KIT-6. The kinetic model equation (FT-2), derived using Eley–Rideal mechanism, is found to be relevant for CoRu-SBA-15 in the SS microchannel microreactor. CoRu-KIT-6 was found to be 2.5 times more active than Co-Ru-MCM-41 and slightly more active than CoRu-SBA-15, based on activation energy calculations. CoRu-KIT-6 was ~3 and ~1.5 times more stable than CoRu-SBA-15 and CoRu-MCM-41, respectively, based on CO conversion in the deactivation studies.

Influence of structure water on crystal structure of hydrated molybdenum oxide and its interesting photothermal catalytic performances under indoor ambient conditions

From the viewpoint of engineering application, it is highly desirable to develop a low-cost, fossil energy–saving degradation technology. In this work, hydrated molybdenum oxide (MoO3·0.55H2O) is prepared by a simple chemical method. It is interesting that under indoor natural ambient conditions, 79% of methylene blue is degraded by hydrated molybdenum oxide after 150 min, but under the same conditions, anhydrous molybdenum oxide does not have any degradation activity. It is found that the outstanding ambient activity of hydrated molybdenum oxide is mainly attributed to the photothermal synergistic effect caused by structure water. On one hand, the coordination of structure water with molybdenum brings about the Jahn–Teller distortion of MoO6 octahedron, giving rise to Lewis acid sites that promote the adsorption and activation of oxygen. O2–temperature-programmed desorption and H2–temperature-programmed reduction profiles show that compared with MoO3, MoO3·0.55H2O has a higher oxygen adsorption ability and a higher oxidation ability. Jahn–Teller effect is mainly responsible for the thermocatalytic activity. On the other hand, the ligand-to-metal charge transfer (LMCT) transfer from structure water to molybdenum obviously increases the light absorption, thus LMCT is mainly responsible for the photocatalytic activity The most important is that compared with conventional photocatalysis, no artificial light source equipment is required; compared with thermocatalysis, no extra heating equipment is needed. Thus, this mild degradation process is low-cost, energy-saving and space-saving, which is very promising for indoor or limited space cleaning.

Influence of Calcination Conditions on Structural and Solid-State Kinetic Properties of Iron Oxidic Species Supported on SBA-15.

Iron oxidic species supported on silica SBA‐15 were synthesized with various iron loadings using two different FeIII precursors. The effect of varying powder layer thickness during calcination on structural and solid‐state kinetic properties of FexOy/SBA‐15 samples was investigated. Calcination was conducted in thin (0.3 cm) or thick (1.3 cm) powder layer. Structural characterization of resulting FexOy/SBA‐15 samples was performed by nitrogen physisorption, X‐ray diffraction, and DR‐UV/Vis spectroscopy. Thick powder layer during calcination induced an increased species size independent of the precursor. However, a significantly more pronounced influence of calcination mode on species size was observed for the FeIII nitrate precursor compared to the FeIII citrate precursor. Temperature‐programmed reduction (TPR) experiments revealed distinct differences in reducibility and reduction mechanism dependent on calcination mode. Thick layer calcination of the samples obtained from FeIII nitrate precursor resulted in more pronounced changes in TPR profiles compared to samples obtained from FeIII citrate precursor. TPR traces were analyzed by model‐dependent Coats‐Redfern method and model‐independent Kissinger method. Differences in solid‐state kinetic properties of FexOy/SBA‐15 samples dependent on powder layer thickness during calcination correlated with differences in iron oxidic species size.

Increasing the catalytic stability by optimizing the formation of zeolite-supported Mo carbide species ex situ for methane dehydroaromatization

The synthesis of zeolite-supported Mo carbide species was studied by testing different reduction/carburization conditions applied to a zeolite-supported Mo oxide catalyst, with the aim to find the optimized treatment conditions necessary to form stable supported Mo carbide catalysts ex situ for application in methane dehydroaromatization reaction. Four types of treatment were performed and studied using temperature-programmed reduction and carburization profiles: (1) heating the catalyst in a reducing gas, H2, up to reaction temperature and switching to CH4; (2) heating the catalyst in a reducing gas, H2, mixed with dilute CH4; (3) heating the catalyst in CH4 up to reaction temperature; and (4) heating the catalyst in an inert gas (commonly He) up to reaction temperature and then switching to CH4 or to H2 followed by CH4 or to H2/CH4 mixture. Each of these processes were stopped at intermediate points to analyze the phases that were present in order to identify the structural evolution of the supported Mo carbides that originate from the supported Mo oxides. Once the supported carbides were formed, they were quenched under the same gas mixture, and then they were each tested in methane dehydroaromatization via previous heating to reaction temperature in He flow. Despite all of them showing only presence of Mo2C species on HZSM-5, the catalytic properties were dramatically different. Catalysts treated in H2 or CH4/H2 showed remarkably higher stability. These catalysts exhibited a higher Mo dispersion and thus exposure on the active surface.