Kinetic Study of Dry Reforming of Methane Over Ni–Ce/Al2O3 Catalyst with Deactivation

Topics in Catalysis - A kinetic study for dry reforming of methane over Ni–Ce/Al2O3 catalyst was performed, taking into account both the main reactions and the catalyst deactivation. The...     

Catalytic Decomposition of Methane Over M–Co–Al Catalysts (M = Mg,Ni, Zn,Cu)

Abstract  

The catalytic decomposition of methane over M–Co–Al (M = Mg, Ni, Zn, Cu) was studied. The samples were prepared by co-precipitation and characterized by S_BET, TGA, DTA, TPR and XRD. The carbon produced in the reaction was characterized by SEM and TPO. Activity tests were carried out in a thermobalance between 500 and 750 °C. The results show that the textural properties of the calcined samples did not change significantly with the partial substitution of Co by Mg, Ni, Zn or Cu. On the other hand, there were marked differences in the reduced samples. There was a strong influence on the reducibility of cobalt oxides in the presence of Ni or Cu. Nickel promoted the reduction of Co₃O₄ at the same temperature as the NiO phase, whereas copper strongly decreased the reduction temperature of both Co₃O₄ and CoAl₂O₄ due to a synergistic effect between Cu and Co. The sample containing Cu resulted in low catalytic activity in the whole temperature range because the reduction conditions promoted the formation of a Cu–Co alloy. In the reaction carried out at 700 °C, the observed activity was Co–Al > Mg–Co–Al > Ni–Co–Al. All the samples were deactivated by encapsulation under these conditions due to high rates of carbon deposition. The carbon produced was mainly carbon nanotubes, except for the Cu–Co–Al sample, which produced mostly amorphous carbon.     

Reforming of Diesel Fuel for Hydrogen Production over Catalysts Derived from LaCo1−x M x O3 (M = Ru, Fe)

Catalysts derived from perovskite type oxides LaCo_1?x M _x O₃ (M = Ru or Fe, x = 0.2) synthesized by a modified citrate sol–gel method were tested in the oxidative reforming of diesel for hydrogen production. Physicochemical characterization of the samples revealed differences in the surface area, crystalline size, reducibility and relative distribution of the cobalt active phase on the surface of catalyst. These properties have important implications in the catalytic behaviour of the samples in the oxidative reforming of diesel. The increase in reducibility and metal exposition implies higher reforming activity as it was observed for the catalyst derived from LaCo_0.8Ru_0.2O₃.     

On-Board Hydrogen Production Through Catalytic Exhaust-Gas Reforming of Isooctane: Efficiency of Mixed Oxide Catalysts Ce2Zr1.5Me0.5O8 (Me = Co, Rh, or Co–Noble Metal)

Isooctane reforming under conditions which are set by exhaust gas can be built on to generate hydrogen on-board. Isooctane reforming reactivity tests have been performed with bimetallic catalysts Co–Noble Metal/ceria–zirconia. Variable activity of noble metals doped catalysts, depending on the nature of the noble metal, its loading, and affected by the activation process, is discussed.     

Methane steam reforming in the absence and presence of H2S over Ce0.8Pr0.2O2 − δ, Ce0.85Sm0.15O2 − δ and Ce0.9Gd0.1O2 − δ SOFCs anode materials

We report here on the activity and stability of low-content praseodymium–, samarium– and gadolinium–cerium oxide catalysts for the steam reforming of methane under water deficient conditions. These materials display different methane reforming activities, and remain free of praseodymium, samarium and gadolinium oxide phases respectively after use in a reaction gas stream composed of 50% CH₄–5% H₂O – (in the absence and presence of 50 or 200 ppm H₂S) – balance He at 740 °C. The results show that Ce_0.8Pr_0.2O_2 − δ, Ce_0.85Sm_0.15O_2 − δ and Ce_0.9Gd_0.1O_2 − δ are effective catalysts for reforming of methane and H₂S in the feed promotes the catalytic activity. Ce_0.8Pr_0.2O_2 − δ appeared to attain the highest activity for methane reforming, a feature that is associated with the ability of praseodymium to undergo a red–ox (Pr^4 +/Pr^3 +) and spreading action in the cerium oxide host structure, possibly resulting in a red–ox relationship between the components.     

SrFe12O19/Zn0.65Ni0.25Cu0.1Fe2O4 Core–Shell Nanocomposite: Synthesis,Chracterization and Catalytic Activity in Aqueous Solution

SrFe₁₂O₁₉/Zn_0.65Ni_0.25Cu_0.1Fe₂O₄ core–shell nanocomposite has been successfully synthesized by sol–gel autocombustion (for SrFe₁₂O₁₉, core) and hydrothermal methods (for Zn_0.65Ni_0.25Cu_0.1Fe₂O₄, shell). The products were characterized by X-ray powder diffractometer, transmission electron microscopy, fourier transform infrared spectrsocopy, vibrating sample magnetometer, Ultraviolet–visible specroscopy and inductively coupled plasma. Both X-ray powder diffraction, transmission electron microscopy results showed that Zn_0.65Ni_0.25Cu_0.1Fe₂O₄ shell is on the surface of the SrFe₁₂O₁₉ core. The variations between the magnetic properties of the precursors and nanocomposite may be explained by interphase interactions at the surface of two ferrites. The properties of the SrFe₁₂O₁₉/Zn_0.65Ni_0.25Cu_0.1Fe₂O₄ core–shell nanocomposite were favourable in its separation, recycling and reuse after reaction. The catalytic activity of SrFe₁₂O₁₉/Zn_0.65Ni_0.25Cu_0.1Fe₂O₄ core–shell nanocomposite in the presence of NaBH₄ were tested against methyl violet.     

NO–H2–CO–O2 Reactions Over Pt Catalysts Supported on Ln-incorporated FSM-16 (Ln = La, Ce and Pr)

Catalytic NO–H₂–CO–O₂ reaction was studied over Pt-supported Ln-incorporated FSM-16 (Ln = La, Ce and Pr). Pr-FSM-16 exhibited the highest activity for NO _x reduction at ≤200 °C. Pr has an effect of increasing the basicity to promote the oxidative adsorption of NO, which is a key for efficient de-NO _x .     

Stability and electrical conductivity of BaCe0.85Tb0.05M0.1O3−δ (M=Co,Fe, Y,Zr, Mn) high temperature proton conductors

High temperature proton conductors (HTPCs) must possess both high electrical conductivity and good chemical and structural stability for practical applications. In this work, BaCe_0.85Tb_0.05M_0.1O_3−δ (BCTM) high temperature proton conductors doped with M=Co, Fe, Y, Zr, Mn were prepared by the sol-gel combustion method using EDTA and citric acid as the chelating agents. The structural and chemical stability, and electrical conductivity of the BCTM perovskites were measured in different atmospheres by the powder X-ray diffraction (XRD) and four-probe techniques. The results indicate that the perovskite phase formed in the BCTM oxides after calcination at 1000 °C can be preserved well in H₂ and water vapor-containing atmospheres, whereas the perovskites may be segregated into metal oxides and react with CO₂ into carbonates in the CO₂ environment due to the strong alkalinity of the BaCeO₃ composites. The electrical conductivity of the BCTM oxides in hydrogen atmosphere is noticeably higher than in the air atmosphere, confirming the dominant protonic conductivity in the BCTM perovskites. Doping with Mn or Co ions in the BCTb perovskite favors improving the electrical conductivity with lower activation energy. The BCTMn perovskite demonstrates an N-shaped variation trend in electrical conductivity with temperature due to the multi-valence states for Mn ions presented at different temperatures.     

Structural and mechanical properties of La0.6Sr0.4M0.1Fe0.9O3-δ (M: Co,Ni and Cu) perovskites

La_0.6Sr_0.4M_0.1Fe_0.9O_3-δ (M: Co, Ni and Cu) perovskite nanostructures were synthesized using low frequency ultrasound assisted synthesis technique and effect of substitution of Fe by Co, Ni and Cu on crystal structure and mechanical properties in La_0.6Sr_0.4FeO_3-δ perovskite was studied. The HRTEM and Rietveld refinement analyses revealed the uniform equi-axial shape of the obtained nanostructures with the existence of La_0.6Sr_0.4M_0.1Fe_0.9O_3−δ with mixed rhombohedral and orthorhombic structures. Substitution by Cu decreases the melting point of La_0.6Sr_0.4FeO_3-δ. The results of mechanical characterizations show that La_0.6Sr_0.4Co_0.1Fe_0.9O_3−δ and La_0.6Sr_0.4Ni_0.1Fe_0.9O_3−δ have ferroelastic behavior and comparable elastic moduli, however, substitution by Ni shows higher hardness and lower fracture toughness than Co in B-site doping.     

Chemical compatibility of RE0.6M0.4Mn0.8Co0.2O3-δ (RE=La,Pr, Nd,Sm and Gd; M=Sr and Ca) with yttria stabilized zirconia

The chemical compatibility of one new series, RE_0.6M_0.4Mn_0.8Co_0.2O_3-δ (RE=La, Pr, Nd, Sm and Gd; M=Sr and Ca), with yttria stabilized zirconia (YSZ) has been examined. Powder mixtures of perovskites and YSZ were annealed at 1200° for 24h in air. RE_0.6M_0.4Mn_0.8Co_0.2O_3-δ showed different compatibility towards YSZ for M=Sr and Ca, respectively. The formation of SrZrO₃ was identified by X-ray diffraction analysis as a reaction product for RE_0.6Sr_0.4Mn_0.8Co_0.2O_3-δ. In contrary, there is no reaction product for RE_0.6Ca_0.4Mn_0.8Co_0.2O_3-δ. EDX analysis revealed that there is a larger difference between the solubility of Sr and Ca in YSZ. The bond-valence model was used to discuss the different compatibility of Sr and Ca series perovskites with YSZ. The present studies also showed that the formation of SrZrO₃ was favored for larger disorder effect due to size difference between A-site RE³⁺ and Sr²⁺ in RE_0.6Sr_0.4Mn_0.8Co_0.2O_3-δ.     

Influence of component manipulation on the structural,mechanical, thermophysical and electrical properties of La0·2Ce0.2Nd0.2(ZrxY1−x)0.4O2−δ high-entropy ceramics

A series of high-entropy ceramics (HECs) with compositions of La_0·2Ce_0.2Nd_0.2(Zr_xY_1−x)_0.4O_2−δ (x = 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0, the corresponding names being HEC(Zr_0·5/Y_0.5, Zr_0·6/Y_0.4, Zr_0·7/Y_0.3, Zr_0·8/Y_0.2, Zr_0·9/Y_0.1, Zr_1·0/Y₀)) were sintered in air at 1600 ^°C for 10 h. When x is in the range of 0.5–0.7, a fluorite phase is formed. Then, as x exceeds 0.7, a second pyrochlore-structured phase appears, and its content gradually increases with the increasing x. The grain growth of the samples is inhibited by increasing in the relative Zr content. The grain refinement and the formation of second phase reduce the thermal conductivity and reinforce the mechanical properties of the samples. HEC(Zr_0.9/Y_0.1) has the lowest thermal conductivity (50–500 °C) and brittleness index, as well as the highest fracture toughness among all samples. In addition, La_0·2Ce_0.2Nd_0.2(Zr_xY_1−x)_0.4O_2−δ ceramics have excellent thermal stability under Ar atmosphere in 50–1400 °C. The thermal expansion coefficients of the samples marginally change regardless of the variation in x. All samples show higher oxygen barrier property than Y₂O₃-stabilized ZrO₂.     

M_(0.5)Co_(2.5)O_4(M=La,Ce,Pr,Nd)尖晶石型复合氧化物催化剂催化分解N_2O性能

采用共沉淀法制备了M_(0.5)Co_(2.5)O_4(M=La,Ce,Pr,Nd)钴基尖晶石型复合氧化物催化剂,运用XRD、SEM、H_2-TPR和O_2-TPD-TG等对催化剂物化性能进行表征,并在固定床微型反应器中评价催化剂催化分解N_2O性能。结果表明,稀土金属掺杂改性的钴基尖晶石型复合氧化物催化剂粒径明显减小,比表面积增加,氧化还原性能得到改善,催化分解N_2O活性提高,其中,M_(0.5)Co_(2.5)O_4催化剂催化分解N2O温度低,T10和T95分别为342℃和499℃。     

Design of Efficient Ce<Subscript>x</Subscript>M<Subscript>1−x</Subscript>O<Subscript>2−δ</Subscript> (M = Zr,Hf, Tb and Pr) Nanosized Model Solid Solutions for CO Oxidation

Abstract  

Nanosized Ce_xM_1−xO_2−δ (M = Zr, Hf, Tb and Pr) solid solutions were prepared by a modified coprecipitation method and thermally treated at different temperatures from 773 to 1073 K in order to ascertain the thermal behavior. The structural and textural properties of the synthesized samples were investigated by means of X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), BET surface area, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy (RS) techniques. The catalytic efficiency has been performed towards oxygen storage/release capacity (OSC) and CO oxidation activity. The characterization results indicated that the obtained solid solutions exhibit defective cubic fluorite structure. The solid solutions of ceria–hafnia, ceria–terbia and ceria–praseodymium exhibited good thermal stability up to 1073 K. A new Ce_0.6Zr_0.4O₂ phase along with Ce_0.75Zr_0.25O₂ was observed in the case of ceria–zirconia solid solution due to more Zr⁴⁺ incorporation in the ceria lattice at higher calcination temperatures. The reducibility of ceria has been increased upon doping with Zr⁴⁺, Hf⁴⁺, Tb^3+/4+ and Pr^3+/4+ cations. This enhancement is more in case of Hf⁴⁺ doped ceria. Among various solid solutions investigated, the ceria–hafnia combination exhibited better OSC and CO oxidation activity. The high efficiency of Ce–Hf solid solution was correlated with its superior bulk oxygen mobility and other physicochemical characteristics.     

Preparation of new heteronuclear (NH4)RE[FeII(CN)6]·nH2O complexes (RE = La,Ce, Pr,Nd, Sm,Gd, Dy,Y, Er,Lu) and their low-temperature decomposition for perovskite-type oxide

New heteronuclear (NH₄)RE^III[Fe^II(CN)₆]·nH₂O complexes (RE = La, Ce, Pr, Nd, Sm, Gd, Dy, Y, Er, Lu) were synthesized and their thermal decomposition products were investigated. The crystal structure of (NH₄)RE[Fe^II(CN)₆]·nH₂O would be a hexagonal unit cell (space group: P6₃/m), which was the same as that of La[Fe^III(CN)₆]·5H₂O. The hydration number n = 4 was estimated by TG results for all the RE complexes. The lattice constants depended on the ionic radius of the RE³⁺ ion for the heteronuclear complexes. The single phase of the perovskite type materials was directly obtained by decomposition of the heteronuclear complexes for RE = La, Pr, Nd, Sm, and Gd. A mixture of CeO₂ and Fe₂O₃ was formed for RE = Ce because of its oxidation to Ce⁴⁺. In the case of RE = Dy, Y, Er, and Lu complexes, the perovskite type materials formed at higher temperature via. mixed oxides such as RE₂O₃ and RE₄Fe₅O₁₃ due to the small RE³⁺ ionic radius.