Activity and stability of Pd/MMnOx (M = Co,Ni, Fe and Cu) supported on cordierite as CO oxidation catalysts

Several catalysts of the general formula, MMnO_x (M = Co, Ni, Fe and Cu), were synthesised through the impregnation method; their activities were shown to be enhanced by the addition of a small amount of Pd (0.01–0.1 wt%). These catalysts exhibit different activities for the catalytic oxidation of CO, due to the different valence states of various transition metal oxides. The introduction of Pd prominently enhanced both the reduction and oxidation capabilities of the catalysts. These catalysts were optimised for oxidation activities by designing orthogonal experiments. Based upon the catalysts’ properties, the stability of these samples and their ability to resist steam over Pd/CoMnO_x/cordierite were investigated.     

Oxidation of alkylaromatics to benzylic ketones using TBHP as an oxidant over LaMO3 (M = Cr,Co, Fe,Mn, Ni) perovskites

A series of LaMO₃ (M = Cr, Co, Fe, Mn, Ni) perovskites were synthesized by citrate precursor decomposition method and characterized by XRD technique. The catalytic activity of the synthesized perovskites was investigated for the oxidative functionalization of alkylaromatics to benzylic ketones using TBHP as an oxidant. Of various perovskites screened, LaCrO₃ exhibited remarkable catalytic activity providing the oxidation of alkylarenes selectively at the benzylic position. The LaCrO₃/TBHP catalytic system provides excellent yields of the desired ketones under solvent-free conditions and the catalyst can be successfully used up to six consecutive cycles with no significant loss in activity.     

Oxidation of alkylaromatics to benzylic ketones using TBHP as an oxidant over LaMO3 (M = Cr, Co, Fe, Mn, Ni) perovskites

A series of LaMO₃ (M = Cr, Co, Fe, Mn, Ni) perovskites were synthesized by citrate precursor decomposition method and characterized by XRD technique. The catalytic activity of the synthesized perovskites was investigated for the oxidative functionalization of alkylaromatics to benzylic ketones using TBHP as an oxidant. Of various perovskites screened, LaCrO₃ exhibited remarkable catalytic activity providing the oxidation of alkylarenes selectively at the benzylic position. The LaCrO₃/TBHP catalytic system provides excellent yields of the desired ketones under solvent-free conditions and the catalyst can be successfully used up to six consecutive cycles with no significant loss in activity.     

Oxygen nonstoichiometry in Pr1−xSrxCo0.2B0.8O3−δ (B = Mn,Fe, x = 0.2, 0.4) perovskite oxides

Thermogravimetric analysis was applied to the study of oxygen nonstoichiometry of perovskite oxides of the compositions Pr_0.8Sr_0.2Co_0.2Mn_0.8O_3−δ and Pr_1−xSr_xCo_0.2Fe_0.8O_3−δ (x = 0.2, 0.4). The measurements were performed in the temperature range from room temperature to 1200 °C in various atmospheres: oxygen, air and argon. The recorded weight loss corresponds to the loss of lattice oxygen. The magnitude of oxygen loss increased and the temperature at which oxygen loss became significant decreased with increasing Sr content. The loss of lattice oxygen became more significant as the oxygen partial pressure decreased. For the same pO₂ and level of Sr doping, the Fe-containing composition became more easily oxygen deficient than the corresponding Mn-containing one, suggesting that Fe is more resistant to oxidation from the trivalent to the tetravalent state than Mn. Electrical conductivity measurements, performed in air, showed that the temperature ranges at which conductivity decrease was observed, correspond fairly well with those ranges where weight loss was detected.     

Intraligand fluorescence of M(III)(oxinate)3 under ambient conditions with M = Fe,Ru, Os and oxinate = 8-quinolinolate

The electronic spectra of the complexes M(III)(oxinate)₃ with M = Fe, Ru, Os and oxinate = 8-quinolinolate are dominated by oxinate to M(III) LMCT transitions. Nevertheless, these complexes are also characterized by a fluorescence at higher energies, which originates from the oxinate ligands. This green luminescence appears in solution as well as in the solid state under ambient conditions. The electronic coupling between the IL and the LMCT states is apparently not strong enough to lead to a complete quenching of the oxinate IL fluorescence.     

Physicochemical properties of rock salt-type ordered Sr2MMoO6 (M = Mg,Mn, Fe,Co, Ni) double perovskites

B-site rock salt-type ordered Sr₂MMoO₆ (M = Mg, Mn, Fe, Co, Ni) oxides have been systematically investigated in terms of their crystal structure, oxygen non-stoichiometry, transport properties, thermal expansion and chemical stability. Structural evolution on temperature of the studied materials was interpreted on a basis of octahedra rotation, with I4/m → Fm-3m phase transition. In the case of P2₁/n → I4/m transformation recorded for Sr₂MnMoO₆, a region of coexistence of two phases was observed. The Fe-containing compound was found to possess very high electrical conductivity, around 1000 S cm⁻¹ in 5 vol.% H₂ in Ar, and small negative Seebeck coefficient. Studies show that Mn- and Fe-containing compounds are stable only in reducing conditions, Co- and Ni-containing ones are stable only in oxidizing conditions, while Sr₂MgMoO₆ remains stable in a wide range of oxygen partial pressures. Recorded power density of a button-type SOFC with Sr₂FeMoO₆-based anode was 0.32 W cm⁻² at 900 °C.     

Lattice oxygen of La1−xSrxMO3 (M = Mn,Ni) and LaMnO3−αFβ perovskite oxides for the partial oxidation of methane to synthesis gas

The partial oxidation of methane to synthesis gas by using the lattice oxygen of La_1−xSr_xMO₃ (M = Mn, Ni; x = 0–0.4) and LaMnO_3−αF_β (β/(3 − α) = 0.1) perovskite oxides was explored. Approximately 75% CO selectivity at 16% CH₄ conversion with H₂/CO molar ratio of ca. 2.5 can be achieved at 800 °C. The stability of the perovskite structure and the reactivity/selectivity of lattice oxygen are found to be dependent on (i) B-site element, (ii) degree of substitution of La with Sr, and (iii) fluorination of the perovskite oxide.     

Electrochemical Properties of La0.5Sr0.5Co0.8M0.2O3–δ (M=Mn,Fe, Ni,Cu) Perovskite Cathodes for IT‐SOFCs

The electrochemical properties of La_0.5Sr_0.5Co_0.8M_0.2O_3–δ (M=Mn, Fe, Ni, Cu) cathodes are investigated with chemical bulk diffusion coefficients (D_chem) and polarization resistances. The electrochemical performance of long‐term testing for La_0.5Sr_0.5Co_0.8Cu_0.2O_3–δ cathode was carried out to investigate its electrochemical stability. In this work, an anode‐supported single cell with a thick‐film SDC electrolyte (30 μm), a Ni‐SDC cermet anode (1 mm), and a La_0.5Sr_0.5Co_0.8Cu_0.2O_3–δ cathode (10 μm) reaches a maximum peak power density of 983 mW/cm² at 700°C. Obviously, Cu substitution for B‐site of La_0.5Sr_0.5CoO_3–δ cathode reduced thermal expansion coefficient (TEC) value and enhanced oxygen bulk diffusion and electrochemical properties. La_0.5Sr_0.5Co_0.8Cu_0.2O_3–δ is a promising cathode material for intermediate temperature solid oxide fuel cells (IT‐SOFC).     

Catalytic activity of metal (M = Fe-, Cr-) loaded titania nanotubes

The catalytic activity of M-loaded titania nanotubes (M = Fe- and Cr-), prepared by hydrothermal treatment, was studied in the liquid-phase photodegradation of methyl orange. The prepared catalysts were characterized by various techniques. The optimum loading amounts of Fe and Cr were found to be at 2%, and 15%, respectively. When compared to unloaded and metal-loaded TNTs, the pure TNTs resulted in the best photocatalytic activity, giving complete degradation after 7 h, while 15% Cr-loaded TNTs calcined at 500 °C possessed the best absorption, about 80%, in the dark.     

Effects of metal doping agent on the properties of Nb2−xMxO5 (M = Mn,Fe, and Ni) system

In order to improve the behavior Niobium pentoxide on oxidation‐reductionreactions to degrade organic compounds in aqueous solutions, we developed the synthesis of Niobium pentoxide with the metal doping agents: manganese,iron, and nickel (Nb_2?xM_xO₅), respectively, and analyzing its effects on the structural and vibrational properties. The synthesis of the Nb_2?xM_xO₅ (M = Mn, Fe, and Ni; x = 0.02 and 0.05) was performed according the Pechini method, but before the annealing, the samples were submitted to Thermogravimetric analysis study showing better pre‐calcination annealing temperatures at 500 and 700°C for the materials. Then, we performed the crystal structural analysis by X‐ray Diffraction, obtaining crystallite sizes between 15 and 47 nm, the accurate size analysis was calculated by Scherrer equation. Structural analysis was also performed by IR spectroscopy to evaluate the vibrational modes of synthetized samples. The dopping effects were evaluated by UV‐Vis spectrophotometry through the energy band gap values, showing that doped samples with manganese and iron had lower values than undoped, except the sample doped with nickel. However, samples doped with iron at 2.5% showed better photocatalytic performance.     

Transformation of α-olefins over Pt–M (M = Re,Sn, Ge) supported chlorinated alumina

Three bimetallic catalysts, consisting of platinum and a second metal supported on chlorinated alumina, i.e. Pt–Re/Al₂O₃, Pt–Sn/Al₂O₃, and Pt–Ge/Al₂O₃, have been used in the transformation of two α-olefins, 1-pentene and 1-hexene. Their conversion to internal and branched olefins is highly interesting for their use in reformulated gasolines and as intermediate chemicals. The catalysts characterization has been accomplished by different techniques, such as elemental and XRD analysis, N₂ adsorption, TPD of ammonia and hydrogen chemisorption. Among the three catalysts, Pt–Sn/Al₂O₃ showed the highest hydrogenation activity, whereas Pt–Ge/Al₂O₃ was the less active towards the hydrogenation of the olefins, according to their H₂ adsorption abilities. The bimetallic catalysts were compared to the monometallic one (Pt/Al₂O₃), as well as to the support. The catalyst and reaction conditions significantly influenced the products distribution. Hydrogenation was dominant at low temperatures (up to 350–400 °C) while skeletal isomerization and double bond shift prevailed at higher temperatures.     

(MMgBO3)n (n = 1, M = Li,Na, K,Rb and n = 4, M = Cs): An investigation on the structure transition and optical properties

In crystal engineering, modification of the crystal structure by cation substitution is one of the most important and efficient methods. This paper reveals the origin of the structure transition of a series of (MMgBO₃)_n (n = 1, M = Li, Na, K, Rb and n = 4, M = Cs) compounds. A force-equilibrium model was established with the comparison of different structures of these compounds. After substituted by other alkali metal cations with different atomic radii, the changed bond between oxygen and cations leads to structural transition. The electronic and optical properties of NaMgBO₃, KMgBO₃ and RbMgBO₃ were also investigated by using DFT methods to give more comprehension of these compounds.     

Syntheses and structures of eight-semi-coordinate M(II) (M = Mn,Fe, Co,Ni, Cu,Zn) complexes and density functional theory study of bond dissociation energies for the MO semi coordinate bonds

Six new complexes 1–6 with the common formula [M(NiL)₄][M(NCS)₄] (M = Mn, Fe, Co, Ni, Cu and Zn for 1, 2, 3, 4, 5 and 6, respectively; the same below) were synthesised and structurally characterised by X-ray single crystal analysis. NiL acts as a complex ligand. L denotes the dianion of dimethyl 5,6,7,8,15,16-hexahydro-6,7-dioxodibenzo-[1,4,8,11]tetraazacyclotetradecine-13,18-dicarboxylate. Each M(II) centre of the [M(NiL)₄]^2 + complex cations in 1–6 adopts a distorted square-antiprism coordination geometry with a O₈ donor set. All the MO bonds in the six complexes are abnormally long (2.444–2.528 Å). M(II) complexes having such weak coordination environments have not been reported, and eight-coordinate M(II) complexes with all the eight oxygen donor atoms coming from metalloligands have also not been documented. Each M(II) centre of the [M(NCS)₄]^2 − anions in 1–6 has a distorted tetrahedral coordination environment with a N₄ donor set. Theoretical calculations for the bond dissociation energies (BDEs) of the MO semi coordinate bonds were performed using density functional theory at B3LYP level. The calculated BDE values are 23.8, 25.5, 20.0, 22.3, 19.8 and 18.2 kcal/mol for 1, 2, 3, 4, 5 and 6, respectively. The BDE values suggest that the long MnO bonds in 1 and the long CoO bonds in 3 are significantly weaker than their significantly shorter counterparts in the formerly reported [Mn(NiL)₂(NCS)₂] and [Co(NiL)₂(NCS)₂], respectively.     

Microwave dielectric properties of (Zn1/3B2/3)0.5(Ti0.8M0.2)0.5O2 (B = Nb5+, Ta5+, M = Sn4+, Ge4+) ceramics

Dielectric properties of (Zn_1/3Nb_(2?x)/3Ta_x/3)_0.5(Ti_0.8Sn_0.1Ge_0.1)_0.5O₂ (x = 0, 1, 2) and/or (Zn_1/3Nb_1/3Ta_l/3)_0.5(Ti_0.8Sn_0.2(l?y)Ge_0.2y)_0.5O₂ (y = 0, 0.5, 1) were investigated at the microwave frequencies. For the compositions with single phase of rutile structure, the dielectric constant (K) of specimens was not only dependent on the dielectric polarizabilities, but also on the bond length ratio of apical bond (d_apical) to equatorial bond (d_equatorial) of oxygen octahedron in the unit cell. Temperature coefficients of the resonant frequencies (TCF) of the specimens with B = Nb⁵⁺ and/or M = Sn⁴⁺ was larger than those with B = Ta⁵⁺ and/or M = Ge⁴⁺. These results could be attributed to the changes of the degree of oxygen octahedral distortion. Quality factors (Qf) of the specimens with B = Ta⁵⁺ and/or M = Sn⁴⁺ were larger than those with B = Nb⁵⁺ and/or M = Ge⁴⁺.     

Formation and properties of high entropy oxides in Co-Cr-Fe-Mg-Mn-Ni-O system: Novel (Cr,Fe,Mg,Mn,Ni)3O4 and (Co,Cr,Fe,Mg,Mn)3O4 high entropy spinels

Possibility of formation of quinary and senary equimolar high entropy oxides from the Co-Cr-Fe-Mg-Mn-Ni-O system is presented. Different proposed compositions are synthesized using the solid-state reaction route at high temperatures (900−1100 °C) and quenched to room temperature. Phase composition of the samples is studied, showing tendency toward formation of two main phases: rock salt-structured Fm-3 m and spinel-structured Fd-3 m. It is documented that the annealing temperature has a profound effect on stability of both structures, and at 1100 °C usually the highest content of Fm-3 m phase is usually observed. Three different oxides, namely, (Co,Cr,Fe,Mn,Ni)₃O₄, (Co,Cr,Fe,Mg,Mn)₃O₄ and (Cr,Fe,Mg,Mn,Ni)₃O₄ are obtained as single-phase materials, which structure can be described as the high entropy Fd-3 m spinel one. The latter two compounds have not been previously reported in the literature. Activated character of the electrical conductivity dependence on temperature is observed, with relatively high total conductivity at high temperatures and corresponding high absolute values of Seebeck coefficient.     

Two isomorphic hybrids M(en)3Ag2I4 (M = Zn and Ni) showing distinct dielectric feature

In this paper, the dielectric spectroscopy was studied for two isomorphic hybrids, Zn(en)₃Ag₂I₄ and Ni(en)₃Ag₂I₄. Two hybrids show temperature-independent dielectric permittivity and loss with εʹ ≈ 6.7 and εʺ ≈ 0.03 at temperatures below 200 K for Zn(en)₃Ag₂I₄ versus εʹ ≈ 1.24 and εʺ ≈ 0.01 at temperatures below 250 K for Ni(en)₃Ag₂I₄, as well as a dielectric anomaly and thermally assisted dielectric relaxation at elevated temperature. The anomaly peak temperature is ca. 300 K for Zn(en)₃Ag₂I₄ versus ca. 380 K for Ni(en)₃Ag₂I₄ in εʹ-T plots. Additionally, the εʹ value is < 2.6 at temperature below 360 K for Ni(en)₃Ag₂I₄, which is a low-κ material. The dielectric property distinction between two hybrids results from their different structural rigidity.     

Structure and lithium-ion mobility in Li1.5M0.5Ge1.5(PO4)3 (M = Ga,Sc, Y) NASICON glass-ceramics

This work reports structural and lithium-ion mobility studies in NASICON single- or multiple phase Li_1+xM_xGe_2−x(PO₄)₃ (M = Ga³⁺, Sc³⁺, Y³⁺) glass-ceramics using solid-state NMR techniques, X-ray powder diffraction, and impedance spectroscopy. X-ray powder diffraction data show the successful incorporation of Ga³⁺ and Sc³⁺ into the Ge⁴⁺ octahedral sites of the NASICON structure at the levels of x = 0.5 and 0.4, respectively. The glass-to-crystal transition was further characterized by multinuclear NMR and electrical conductivity measurements. Among the studied samples, the gallium-containing glass-ceramic presented the highest DC conductivity, 1.1 × 10⁻⁴ S/cm at room temperature, whereas for the Sc-containing samples, the maximum room temperature conductivity that could be reached was 4.8 × 10⁻⁶ S/cm. No indications of any substitution of Ge⁴⁺ by Y³⁺ could be found.     

Comparison of H2 production from ethanol and ethylene glycol on M/Pt(1 1 1) (M = Ni, Fe, Ti) bimetallic surfaces

The reactions of ethylene glycol and ethanol have been studied on Fe/Pt(1 1 1) and Ti/Pt(1 1 1) bimetallic surfaces utilizing temperature programmed desorption (TPD). These results are compared to our previous studies on Ni/Pt(1 1 1) to illustrate the trend in the reforming activity on 3d-Pt bimetallic surfaces. The oxygenates decomposed on these surfaces to produce mainly H₂ and CO. The bimetallic surfaces were prepared by thermal evaporation of Fe or Ti onto Pt(1 1 1), using Auger electron spectroscopy (AES) to monitor surface compositions. Surfaces prepared by deposition of a monolayer of Fe or Ti on Pt(1 1 1), designated Fe–Pt–Pt(1 1 1) or Ti–Pt–Pt(1 1 1), displayed higher reforming activity for both ethylene glycol and ethanol than the corresponding subsurface monolayer Pt–Fe–Pt(1 1 1) and Pt–Ti–Pt(1 1 1) structures or clean Pt(1 1 1). The reforming yield increased as the surface d-band center, calculated from density functional theory (DFT), shifted closer to the Fermi level. The reforming selectivity of oxygenates, especially ethanol, began to decrease as the d-band center shifted closer to the Fermi level. Combining results in the current work with previous studies on Ni/Pt(1 1 1), a general criterion can be formulated for selecting 3d-Pt bimetallic surfaces with desirable reforming activity and selectivity.     

Environmental-friendly yellow pigment based on Tb and M (M = Ca or Ba) co-doped Y2O3

A yellow inorganic ceramic pigment with general formula Y_1.86?xM_xTb_0.14O_3?x/2 (M = Ca and/or Zn) with x = 0.06, 0.32 and 0.64 were synthesized by a modified Pechini method. XRD, SEM and HRTEM/EDX analysis showed the formation of solid solution at 1300 °C when x = 0.06 and 0.32. The best b* yellow coordinates were obtained for Ca and Zn co-doped Y_1.86Tb_0.14O₃ samples. The intensity of the yellow colour in the samples is related to the presence of Tb⁴⁺ ions. Samples with higher concentration of Tb⁴⁺ ions lead to a better yellow colour. The chemical stability of these pigments was determinate in an industrial glaze. The glazing tests indicated that the powder samples with x = 0.06 and 0.32 fired at 1300 °C were stable in the glaze. These results make it a potential candidate for environmental friendly yellow ceramic pigment to be used in applications such as pigment for glazes or inkjet printers.