Temperature-programmed Reduction Profiles Research Articles

PHYSICO-CHEMICAL PROPERTIES OF COMPOSITES ON THE BASE OF CERIA OBTAINED BY A CITRIC ACID METHOD

Composites with the formula nMOx–СеО2, where n is the mole part of copper or manganese oxide have been synthesized via citric acid aided route. Physico-chemical properties of materials obtained are investigated by XRD, low temperature desorption of nitrogen and by temperature-programmed reduction (TPR). It is defined that the composites with the n < 0.25 (for Cu) and < 0.75 (Mn) are the solid solutions obtained by the replacement of cerium ions in the structure of fluorite (СеО2) by copper or manganese ions. The existence of the separate phases of oxides such as CuO and Mn3O4 has been identified in the XRD patterns of composites with formula 0.25CuО–СеО2 and 0.75MnOx–СеО2. The parameters of cell and the particles size for all samples are calculated; decreasing these values occurs due to the solid solutions formation. Specific area of composites obtained is much bigger than specific area of individual oxides; the biggest values are determined for the samples containing the biggest part of copper or manganese oxide. According to TPR profiles of composites themaximal intensity of low temperature peak has the composite 0.25CuО–СеО2 that means the biggest part of the solid solution; so this material is the most active in CO and ethanol combustion. This fact can be explained by appearance of additional oxygen vacancies when ions Ce4+ are replacement by ions with the less oxidation state. The quantities of hydrogen used for reduction of samples with the copper oxide and samples with the manganese oxide with n < 0.5 are much bigger than the theoretical values; in this case the reduction of the part of ceria in the solid solution is happened. The composite 0.25MnOx–CeO2 is the most active in the ethanol combustion; full conversion to CO2 is finished at 205°С. The high activity of individual oxide MnOx and the composite 0.75MnOx–СеО2 in the reaction of toluene oxidation explains by the biggest part of Mn3+ ions in their structure among the all oxides investigated.

Studying Hydrotalcite-Like Compounds Isomorphically Substituted with Iron and Cobalt via Inverse Temperature-Programmed Reduction

The reducibility of multicomponent layered double hydrotalcite-like hydroxides containing Mg2+, Co2+, Al3+, and Fe3+ at different ratios of these metal cations and products of their thermal destruction in a hydrogen flow is studied via inverse temperature-programmed reduction (bTPD). It is shown that the temperature-programmed reduction profiles for layered double hydroxides (LDHs) contain signals corresponding not only to the reduction of iron and cobalt cations incorporated into the structure of brucite-like layers, but also ones corresponding to the reduction of cobalt and iron from the mixed oxides or spinel-like phases that appear due to the thermal destruction of LDHs occurring simultaneously with a reduction in iTPR measurements. Signals presumably corresponding to the reduction of residual nitrate anions are also revealed in iTPR profiles.

Preparation of Cu-Mn and Cu-Mn-Ce Oxide/Mesoporous Silica via Silicate Exfoliation for Removal of NO and Hg0

ABSTRACT Cu-Mn and Cu-Mn-Ce oxide-incorporated mesoporous silica was formed by hydrothermally exfoliating silicate, and the physicochemical properties and NO/Hg0 removal efficiency were investigated. The exfoliation induced structural reformation, resulting in a large specific surface area and the uniform dispersion of metal oxides on the surface. The transfer of valences between Cu2+ and Mn3+ in the Cu-Mn silica contributed to the single reduction peak displayed in the H2 temperature-programmed reduction profiles and the high Mn4+/Mn and Cu+/Cu ratios observed via X-ray photoelectron spectroscopy (XPS). The high oxygen lability of the Cu-Mn silica may have inhibited its ability to remove NO. By contrast, when SO2 was present, incorporating Ce enhanced the NO removal efficiency due to the increased number of Bronsted acid sites. Hg0 removal tests indicated that adsorption was the primary removal mechanism for both the Cu-Mn and the Cu-Mn-Ce silica samples. Cu2Mn8 exhibited the highest Hg removal efficiency, suggesting that Ce’s enhancing effect on Hg0 adsorption was diminished when a large amount of Mn was present. Of the gaseous components, the adsorbed HCl was mainly responsible for the oxidation and subsequent adsorption of Hg0. Furthermore, with the addition of SO2, the competitive adsorption of SO2 and the resulting HgCl2 did not decrease the Cu-Mn silica’s efficiency in oxidizing Hg0, but the oxidized Hg was less adsorptive.

Preparation of Ni-based egg-shell-type catalyst on cylinder-shaped alumina pellets and its application for hydrogen production via steam methane reforming

Nickel-based ‘egg-shell-type’ catalysts were prepared using cylinder-shaped alumina pellets as supports. In the egg-shell-type catalysts, nickel was selectively located in the outer region of the alumina pellets. Ethylene glycol or 1-octanol were used as hydrophobic solvents to retard internal penetration of the alumina pellets by the nickel nitrate solution. Without hydrophobic solvent, a ‘homo-type’ catalyst with even nickel distribution inside the alumina pellets was achieved. Cross-sectional images and SEM-EDS analysis of the cylinder-shaped alumina pellets showed that nickel concentration in the egg-shell-type catalyst was higher in the outer region and decreased towards the inner region of the alumina pellets. The egg-shell-type nickel distribution was maintained after subsequent magnesium impregnation and calcination processes. X-ray diffraction patterns and temperature programmed reduction profiles showed that the only difference between homo-type and egg-shell type catalysts, when their nickel loading was the same, was the nickel distribution inside pellets; and this was shown to cause significant difference in their catalytic activity in the steam methane reforming (SMR) reaction. For the homo-type catalyst, nickel loading of 3.5 wt% was insufficient for the SMR reaction, as metallic nickel particles were evenly distributed through the entire alumina pellet. However, nickel loading of 3.5 wt% was sufficient for the egg-shell-type catalyst, because active sites with metallic nickel particles were concentrated in the outer region of the pellets. These experimental results confirmed that the egg-shell-type nickel distribution is a favorable design for an SMR reaction catalyst.

A Non-Precious Metal Promoting the Synthesis of 5-Hydroxymethylfurfural

In this work, a new kind of catalyst was prepared for synthesis of 5-hydroxymethylfurfural. Copper ions were incorporated into manganese oxide octahedral molecular sieves (K-OMS-2). The catalysts Cu-K-OMS-2 were characterized by measuring FTIR spectra, scanning electron microscope images, X-ray diffraction patterns, and temperature-programmed desorption (TPD) and temperature-programmed reduction (TPR) profiles. Thermogravimetric analysis (TGA) demonstrated that the stability of Cu-K-OMS-2 is almost the same as that of K-OMS-2. XRD patterns showed that introducing copper ions did not change the structure of K-OMS-2, but copper ions had an effect on the morphology of K-OMS-2 as illustrated by SEM images. TPD profiles demonstrated that both K-OMS-2 and Cu-K-OMS-2 possess basic and acidic sites, and Cu-K-OMS-2 has weak acidic sites. One-pot synthesis of 2,5-diformylfuran (DFF) from fructose was investigated under the catalysis of Cu-K-OMS-2 together with a commercial catalyst Amberlyst 15. The effect of reaction time and temperature on the DFF yield was investigated, and reaction temperature had an effect on the DFF yield. The effect of atomic ratio of Cu to Mn of Cu-K-OMS-2 on the DFF yield was also investigated. The DFF yield was improved 34.7% by Cu-K-OMS-2 in comparison to K-OMS-2, indicating the promotion effect of copper on the DFF yield. Consecutive use of Cu-K-OMS-2 demonstrated that after 6 cycles, the loss of DFF yield was 6.3%, indicating a good reusability of Cu-K-OMS-2.

The effect of hydrothermal impregnation of Ni, Co, and Cu on HZSM-5 in the nitrogen oxide removal

The selective catalytic reduction (SCR) of nitrogen oxides on M/ZSM-5 (M = Cu, Ni, Co) catalysts was investigated. The catalysts were prepared using hydrothermal impregnation of the metal chlorides and nitrates on ZSM-5. The catalysts were characterized by nitrogen absorption/desorption, X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible diffusion reflection spectroscopy (UV–Vis DRS), temperature-programmed reduction (TPR), N2O chemisorption and ammonia temperature-programmed desorption. The performance tests for SCR of NO were carried out in a fixed-bed reactor from 250 to 400 °C. During the impregnation, part of the aluminum was eliminated from the zeolite framework due to the acidity of the metal salt solution and heating process as indicated by the reduction in the intensity of XRD peaks and variations in the positions of the FTIR vibrational bands. The Cu(Cl)/ZSM-5 catalyst exhibited NO conversions over 90% over the entire temperature range. The other catalysts showed comparable activities, but the catalysts prepared with chloride salt precursors demonstrated higher activity than those based on nitrate as the precursor. Moreover, the TPR reduction peaks of the metal ion in catalysts prepared with chloride precursor were lower, and their UV–Vis absorption bands revealed bathochromic transfers with higher intensities. Concurrent with these changes, the activity of the catalyst increased. The TPR profiles indicated that Cu and Ni both had an oxidation number of +2, whereas Co was present in the oxidation number of +2 and +3. The mass transfer limitation analysis showed that for particles in millimeter size range or larger significant intra-particle mass transfer limitation would be expected.

Deposition of NiO on 3 mol% yttria-stabilized zirconia and Sr0.96Y0.04TiO3 materials by impregnation method

The main purpose of this work was the synthesis of composite materials by deposition of nickel oxide on 3 mol% yttria-stabilized zirconia (3 mol% Y2O3–97 mol% ZrO2–YSZ) and Sr0.96Y0.04TiO3 (4 mol% Y-doped strontium titanate—SYTO) supports. Yttria-stabilized zirconia and yttrium-doped strontium titanate were obtained by modified citrate method. The deposition of nickel oxide was performed by impregnation method. All materials were impregnated with proper amount of nickel(II) nitrate aqueous solution to receive the 1 and 5 mass% of nickel in the final composite. The temperature-programmed reduction (TPR) was applied to analyze the reduction mechanism of deposited NiO. Three forms of nickel oxide: non-stoichiometric NiO1+x, hexagonal and cubic are postulated on the base of the TPR profiles and analysis of bonds length in nickel oxides structures. Moreover, TPR analysis shows that support strongly affects the reduction mechanism as a consequence of various interactions between NiO and YSZ/SYTO. In the case of YSZ, the nickel oxide reveals the tendency to deposit on the support surface, while using SYTO as the support, nickel oxide exhibits significant ability to react with doped strontium titanate and what is more important nickel incorporates into Sr0.96Y0.04TiO3 structure.

Identification of Outer and Inner Nickel Particles in a Mesoporous Support: How the Channels Modify the Reducibility of Ni/SBA‐15 Catalysts

AbstractTwo different nickel supported on SBA‐15 catalytic systems have been prepared by means of impregnation (Ni/SBA‐15‐ImU) and deposition‐precipitation (Ni/SBA‐15‐DP) methodologies. Upon calcination, Ni/SBA‐15DP presents a well‐developed nickel phyllosilicate phase, which after reduction gives rise to a dispersed and homogeneous metallic phase, mainly located inside the 5 nm in diameter mesoporous structure of the support. On the contrary, as evidenced by XRD and a double temperature programmed reduction (TPR) peak, the Ni/SBA‐15‐ImU catalyst presents two different NiO phases, which after reduction in hydrogen generate nickel particles in a wide range of sizes. In situ XAS and XPS have unambiguously showed that the distinct TPR profiles obtained for each system are related with particles located in and out the mesoporous structure of the SBA‐15 channels. The particles inside the porous are more difficult to reduce, clearly showing a kind of confinement effect of the SBA‐15 mesostructure, modifying the reducibility of the NiO phase.

Reverse water-gas shift reaction at the Cu/ZnO interface: Influence of the Cu/Zn ratio on structure-activity correlations

The physicochemical properties of hydroxycarbonate-based precipitates [zincian malachite (ZM) and aurichalcite precursors], calcined CuO/ZnO precatalysts and finally reduced Cu/ZnO catalysts, with several Cu-Zn ratios, have been investigated by different characterization techniques. Results from isothermal physisorption of N2 (BET), X-ray Diffraction (XRD), Temperature Programmed Reduction (TPR), N2O Reactive Frontal Chromatography (N2O-RFC), X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM) have been correlated with the catalytic activity for the reverse water-gas shift (rWGS) reaction in order to provide insight into the controversial nature of active species in carbon dioxide activation, respectively the role of Cu and ZnO. Average crystalline domain size of CuO and ZnO show a relationship with the amount of each phase in the calcined sample. This is in agreement with the TPR profiles, which indicate a better dispersion of Cu for the ZnO-rich samples and a shift for the first reduction step to higher temperatures (Tonset for CuII to CuI). XPS measurements point out the surface enrichment of ZnO is less pronounced with higher ZnO/(ZnO+Cu) ratios. Activity results show that catalysts derived from high surface area ex-aurichalcite (Zn content, 50–70% atom) catalysts are more active in rWGS with lower apparent activation energies than ex-ZM catalysts (Zn content, 15–30% atom) with comparable apparent Cu surface area/N2O capacity. Thus, the CO formation rate as function of the apparent Cu surface area indicates that the reaction rate is not dependent on the exposed apparent Cu surface, but from an adjusted interface composition predetermined by the precursor structure and its thermal post-treatment.

High catalytic activity and stability of ZnLaAlO4 supported Ni, Pt and Ru nanocatalysts applied in the dry, steam and combined dry-steam reforming of methane

Three novel M/ZnLaAlO4 (M=10%Ni, 3%Pt and 3%Ru) nanocatalysts as well as the common 10%Ni/γ-Al2O3 sample were synthesized by the wet impregnation method and characterized by XRD, FE-SEM, TEM, temperature-programmed reduction (TPR), N2 physisorption, FT-IR and TGA/DTA analyses. The catalytic activities of the four nanocatalysts were evaluated in dry (DRM), steam (SRM) and combined dry-steam (CRM) reforming of methane at atmospheric pressure, five various temperatures (600–800°C) and three different GHSV values (3500, 7000, 10,500h−1). Among the ZnLaAlO4 supported catalysts, the greatest and the least catalytic performances were measured for the 3%Ru/ZnLaAlO4 and the 3%Pt/ZnLaAlO4, respectively. Surprisingly, the TGA diagrams of the used nanocatalysts almost did not illustrated coke formation for the 3%Ru/ZnLaAlO4 and 3%Pt/ZnLaAlO4 (especially in the SRM process) that were supported by their FE-SEM images which did not display carbon deposition. All of the three ZnLaAlO4 supported catalysts revealed much higher catalytic activity and less coke content compared with the commercial 10%Ni/γ-Al2O3 catalyst. Thus, we believe that (to the best of our knowledge) this is the first time that such extremely active noble nanocatalysts are obtained with exceptionally high resistance against carbon deposition on their surfaces. The very low onset reduction temperatures in the TPR profiles of the 3%Ru/ZnLaAlO4, 3%Pt/ZnLaAlO4 and 10%Ni/ZnLaAlO4 at 230, 264, 333°C, respectively, reflected the convenient reducibility properties of these samples. Considering the catalytic efficiency and resistance against coke formation, the 3%Ru/ZnLaAlO4 was chosen as the best nanocatalyst for the DRM, SRM and CRM reactions among our four tested samples.

English

Temperature programmed reduction (TPR) is one of the techniques for obtaining information about phases or bulk species in heterogeneous catalysts. Information from TPR analysis can give insights about phase-support interaction and extent of reduction of the phases at different temperatures. TPR technique is a common tool in the characterisation of cobalt based Fischer-Tropsch (FT) catalysts. However, interpretation of TPR profiles of γ-alumina supported cobalt FT catalysts had been characterised with different views on the nature of phases and reduction processes involved. In this report, we use reduction behaviour of unsupported Co3O4 to gain insight for more explicit analysis of TPR profiles of γ-alumina supported Co3O4 catalysts. The transition Co3O4 → CoO → Co in γ-alumina supported catalysts prepared with wet impregnation with aqueous cobalt nitrate and calcined at temperatures ≤ 350°C gave reduction peaks at 300 to 350°C. Reduction peaks at 500 to 600°C were due to Co-Al mixed oxide phases; most likely Co2AlO4 and probably routes formation of the mixed oxide were also discussed. Consideration of tendency of dissolution of γ-alumina during the impregnation of metal salt is instructive toward achieving higher reducibility of Co3O4 in the design of cobalt based Fischer-Tropsch catalysts.   Key words: Temperature programmed reduction (TPR) profile, calcinations, Co3O4, γ-Al2O3, Fischer-Tropsch catalyst.

NiO–MgO Solid Solution Prepared by Sol–Gel Method as Precursor for Ni/MgO Methane Dry Reforming Catalyst: Effect of Calcination Temperature on Catalytic Performance

The influence of calcination temperature (500, 600 and 700 °C) on NiO–MgO solid solution formation and the performance of the resulting catalysts in CO2 reforming of methane was studied. The solid solutions and resulting catalysts were characterized by Brunauer–Emmett–Teller, XRD, temperature-programmed reduction (TPR), TEM and thermal gravimetric analysis techniques. Catalytic performance tests were carried out under 550–750 °C, 1 bar, CO2/CH4 = 1–3 mol/mol and space velocities of 30,000–120,000 ml/(h gcat). The catalyst calcined at 600 °C exhibited the best performance in terms of catalytic activity and stability and showed lowest amount of coke formation after 50 h-on-stream. The effect of calcination temperature on degree of NiO–MgO solid solution formation was demonstrated by both XRD and TPR profiles. The 600 °C calcination temperature was found to be an optimum as it caused modest NiO–MgO interaction, which is responsible for complete formation of the NiO–MgO solid solution with high nickel dispersion and resistant to coke formation.

Synthesis of a novel 3 %Ru/CeZr0.5GdO4 nanocatalyst and its application in the dry and steam reforming of methane

A novel 3 %Ru/CeZr0.5GdO4 nanocatalyst was synthesized by the wet impregnation method and evaluated for its catalytic activity in dry and steam reforming of methane at atmospheric pressure, seven various temperatures (from 500 to 800 °C) and two different gas hourly space velocity values (7000, 10,500 h−1). The thermogravimetric diagrams of the used catalysts did not illustrate any carbon deposition on the catalysts applied in both the dry and steam reforming processes and this valuable phenomenon was supported by the scanning electron microscopy images. The low onset reduction temperature in the temperature-programmed reduction profile of the 3 %Ru/CeZr0.5GdO4 at 183.21 °C reflected much convenient reducibility/oxygen mobility property of the catalyst. Comparing the CH4 conversions in the dry reforming (92 %) and steam reforming (97 %) reactions using the gas hourly space velocity = 10,500 h−1 at 800 °C indicated higher efficiency of the steam reforming process. The time on stream experiments for the dry and steam reforming reactions exhibited that the CH4 and CO2 conversions are almost constant (and even they are slightly increased in the dry reforming) after 30 h reflecting the catalyst outstanding stability with time, absence of coke deposition and catalyst very high activity.

Effect of Gallium Loading on Reducibility and Dispersion of Copper-Based Catalyst

The effect of gallium-promoted copper-based catalysts has been investigated in connection with the characteristic of the active copper phase. CuO-ZnO-Ga2O3catalysts with different gallium loadings were prepared using oxalate co-precipitation method. The effects of gallium loading on the properties of catalysts were studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and temperature-programmed reduction (TPR). The dispersion and metal area of copper were also determined by dissociative nitrous (N2O) adsorption technique conducted on a metal dispersion analyzer (BELCAT). The TPR profiles showed that the presence of two different reduction regions in the CuO-ZnO catalysts can be attributed to the reduction of highly dispersed copper oxide species (reduced at 246 °C) and bulk-like CuO (reduced at above 390 °C). By contrast, the only low-temperature reduction peak was presented in the TPR profiles after the Ga2O3loading was higher than 4 wt%. With the same molar ratio (Cu/Zn = 2:1), the reducibility of CuO-ZnO-Ga2O3was found to be more facile than CuO-ZnO due to the lower copper oxide crystallite sizes of gallium-promoted catalysts. Higher Ga2O3loadings resulted in an increase in both copper dispersion and metal surface area of all the catalysts studied in good agreement with the reduction behaviors in the TPR profiles, although all the gallium-promoted catalysts were slightly different for the reducibility.

Bimetallic Catalyst of Co and Ni for Fischer-Tropsch Synthesis Supported on Alumina

Bimetallic catalysts of cobalt and nickel supported over alumina were studied through Fischer-Tropsch synthesis aiming to achieve the co-production of methane and synthetic oil. Temperature-programmed reduction profiles suggested that 10Co-10Ni/Al2O3 had a relatively lower reducing temperature at 383°C compared with monometallic catalysts. Bimetallic catalysts showed higher selectivity towards light hydrocarbons compared with Co catalysts. 10Co-10Ni/Al2O3 possessed the lowest CO2 selectivity and a relatively high C5+ fraction, and it exhibited distinct behaviors in comparison with the physical mixture of 20Co/Al2O3 and 20Ni/Al2O3. Reaction temperature played an obvious role in product distribution while selectivity towards CH4 would achieve 15.96% at 250°C.

Preparation and characterization of Pt-dealuminated Y zeolite by TG/DTA and TPR

Monometallic catalysts containing Pt supported on dealuminated Y zeolite were prepared by impregnation with a solution containing H2PtCl6·6H2O cationic complexes. The catalysts were calcined and characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), simultaneous thermogravimetry/differential thermal analysis (TG/DTA), temperature programmed reduction, physisorption of nitrogen, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). The XRD results showed that zeolite Y maintained its crystalline structure throughout the dealumination and metal incorporation processes. However, the relative crystallinity of the various samples was reduced upon impregnation. Furthermore, the XRD diffractograms, the SEM and TEM micrographs, and EDX spectra for the impregnated samples presented evidence for the presence of Pt oxides. The adsorption isotherms of the nitrogen physisorption showed the existence of micropores and mesopores within the Pt/Y zeolite. Temperature programmed reduction profiles suggest that the reduction temperature of Pt depends on the location of the metal within the zeolitic structure. The reduction peaks can be attributed to cations located in the large cavities, sodalite cages, or hexagonal prisms. The TG/DTA analyses showed the endothermic decomposition of the Pt complexes deposited on the zeolite during impregnation.

Influence of magnetic field on the adsorption of organic compound by clays modified with iron

Insertion of iron into montmorillonite (Mt) resulted in two modified materials, when different treatments were used: i) pillared clay (FePILC) and ii) magnetic clay (FeMAG). The ability of the modified clays to remove the organic dye methylene blue (MB) by adsorption was tested. Additionally, we evaluated the effects of adsorption after exposure to a pulsed magnetic field, the results were monitored by UV–vis spectroscopy and chemical analysis of total organic carbon. All materials were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), temperature-programmed reduction (TPR), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS) and specific surface area measurements. The catalytic activity of the clays modified with iron was evaluated in hydrogen peroxide decomposition reaction. The XRD patterns show the formation of crystalline iron phases on the surface of the clays, besides confirming the pillaring procedure for FePILC with a basal spacing of 1.79nm, an increase of 0.53nm over the montmorillonite. The specific surface area of FePILC was 210.9m2/g. FeMAG had part of this original structure broken, with an area of 177.1m2/g and magnetic properties demonstrated by the attraction to a permanent magnet. The TPR profiles and EDS indicated that the different heat treatments exerted great influence on the amount and phases of iron formed. The materials showed high capacity for removal of the MB dye, and the isotherms fit the Langmuir model. Adsorption of the dye significantly increased in the presence of a magnetic field, changing the Langmuir parameters and especially the maximum adsorption capacity for all materials. The best results were observed for FeMAG.

Effects of Ti-based catalysts and synergistic effect of SWCNTs-TiF3 on hydrogen uptake and release from MgH2

The present investigations are focused on the effect of different Ti-based catalysts (Ti, TiO2, TiCl3 and TiF3) on de/re-hydrogenation characteristics of nanocrystalline MgH2. Desorption temperature of milled MgH2 lowers from 380 to 350, 340, 310 and 260 °C with the addition of Ti, TiO2, TiCl3 and TiF3 respectively. The rehydrogenation characteristics are also improved through the deployment of Ti-based catalysts. Among all Ti based additives, TiF3 is found to be the most effective catalyst for hydrogen sorption from nano MgH2. The better catalytic effect of TiF3 over other Ti-based catalyst can be explained on the basis of temperature programmed reduction (TPR) studies. TPR experiments performed for different Ti additives, reveals that there is no oxidation/reduction reaction below 400 °C except for TiF3. The TPR profile of TiF3 shows some oxidation/reduction reaction exhibits at 200 °C. In order to further improve the sorption characteristics and cyclability of TiF3 catalyzed nano MgH2, we have investigated the effect of SWCNTs in MgH2+TiF3 sample. De/rehydrogenation characteristics reveal the synergistic effect of SWCNTs and TiF3 in MgH2+TiF3 sample. The details of the improvement in sorption behavior of MgH2–TiF3 in presence of SWCNTs are described and discussed.

A new insight to the physical interpretation of activated carbon and iron doped carbon material: Sorption affinity towards organic dye

To enhance the potential of activated carbon (AC), iron incorporation into the AC surface was examined in the present investigations. Iron doped activated carbon (FeAC) material was synthesized and characterized by using surface area analysis, energy dispersive X-ray (EDX), temperature programmed reduction (TPR) and temperature programmed desorption (TPD). The surface area of FeAC (543 m(2)/g) was found to be lower than AC (1043 m(2)/g) as a result of the pores widening due to diffusion of iron particles into the porous AC. Iron uploading on AC surface was confirmed through EDX analysis, showing up to 13.75 wt.% iron on FeAC surface. TPR and TPD profiles revealed the presence of more active sites on FeAC surface. FeAC have shown up to 98% methylene blue (MB) removal from the aqueous media. Thermodynamic parameters indicated the spontaneous and exothermic nature of the sorption processes.

TPR, XRD and XPS characterisation of ceria-based materials synthesized by freeze-drying precursor method

A freeze-drying precursor method was used to obtain submicrometric powders of ceria-based materials such as Ce1−xGdxO2−δ (x=0, 0.01, 0.05, 0.10 and 0.20), 80%CeO2–20%ZrO2, 80%CeO2–20%Al2O3 and (1−y)Ce0.99Gd0.01O2−δ–(y)Al2O3 (y=0.01, 0.02, 0.05, 0.10 and 0.30) at temperatures as low as 400°C. The phase formation and evolution with the temperature was studied by X-ray diffraction (XRD). Also, temperature programmed reduction (TPR) was performed to investigate the reducibility of the ceramic powders. It was observed that after reduction of the ceria-based materials the fluorite structure of the samples was retained. The TPR profiles showed two peaks which are associated to the surface and bulk ceria reduction processes. Likewise, after the TPR measurements the resulting powders have showed high phase stability and reproducibility. XPS results confirmed the reduction of Ce4+ to (Ce3++Ce4+) ratio with alumina doping.