Effect of TiO2 on hydrodenitrogenation performances of MCM-41 supported molybdenum phosphides

The effect of TiO₂ on the hydrodenitrogenation (HDN) performance of MoP/MCM-41 was investigated using quinoline and decahydroquinoline as the model molecules. The catalysts were characterized by XRD, CO chemisorption, TEM, TPR and pyridine FT-IR. Addition of TiO₂ enhanced the C–N bond cleavage activity of MoP/MCM-41 but inhibited its dehydrogenation activity. A maximum HDN activity was observed when the TiO₂ loading was 5 wt%. The characterization results indicated that introduction of TiO₂ did not affect the formation of MoP phase. The TiO₂-containing catalysts possessed higher CO uptake than MoP/MCM-41, but no significant differences in the acid properties and particle size distributions were observed for all the catalysts. XPS results revealed a surface enrichment of TiO₂ in Ti-containing catalysts and small amount of these surface TiO₂ can be partially reduced to Tiⁿ⁺ (n < 4). It is suggested that these Tiⁿ⁺ (n < 4) species may be responsible for the promoting effect of TiO₂ on the HDN performance of MoP/MCM-41.     

Sulfidability and thiophene hydrodesulfurization activity of supported NiMo carbides

Ni–Mo carbides supported on activated carbon were synthesized by carbothermal hydrogen reduction and the effect of the sulfidability on the thiophene hydrodesulfurization catalytic activity was studied. The X-ray diffraction patterns of Ni–Mo carbides showed the presence of β-Mo₂C and NiC when the atomic ratio AR = Ni/(Ni + Mo) was between 0.25 and 0.75, while for AR = 1, it only was detected metallic Ni. The X-ray photoelectron spectroscopy results showed the distribution of different surface species in the passivated catalysts: Mo^δ + (0 ≤ δ ≤ 2), Mo^4 +, Mo^6 +, Ni^δ + and Ni^2 +. After sulfiding the carbides were modified in their surface and catalytic activity.     

Influence of reduction temperature and metal loading on the performance of molybdenum phosphide catalysts for dibenzothiophene hydrodesulfurization

Two series of alumina-supported molybdenum phosphide (MoP) catalysts with low and high metal loadings were prepared by temperature-programmed reduction of the oxidic catalyst precursors in hydrogen to different temperatures (823, 923, 1023 and 1123 K, respectively). Effects of reduction temperature and metal loading on the surface distribution and the type of species formed were studied by TPR, S_BET, XRD, HRTEM, ³¹P NMR, ²⁷Al NMR and in the reaction of dibenzothiophene (DBT) hydrodesulfurization (HDS) performed in a flow reactor at 553 K and total hydrogen pressure of 3.4 MPa. HRTEM and ³¹P NMR confirmed formation of MoP phase on all catalysts. The 9.9 wt% Mo catalyst activated at lowest reduction temperature (823 K) was found to be most active among the catalysts studied. The presence of a low amount of Mo⁰ species on the surface of this catalyst does not appear to be a drawback for the catalytic activity. The increase in both metal loading (from 9.9 to 15 wt% Mo and from 3.2 to 4.8 wt% P) and reduction temperature (from 823 to 1123 K) was found to be detrimental for HDS activity due to sintering of active phase, and also to decrease in specific area and formation of phosphate species.     

Catalytic removal of diesel soot particulates over K and Mg substituted La1 − xKxCo1 − yMgyO3 perovskite oxides

K and Mg substituted perovskite catalysts La_1 − xK_xCo_1 − yMg_yO₃ (x = 0–0.4, y = 0–0.2) for soot combustion were prepared by citric acid complexation and characterized by XRD, FT-IR, SEM, TEM, EDS, H₂-TPR, XPS and TG. Soot combustion was remarkably accelerated when K was introduced into LaCoO₃. Then Mg was doped into the K substituted LaCoO₃, soot combustion was further improved for the restrained growth of Co₃O₄ phase. K/Mg substitutions were responsible for enhancing activity of catalysts by improving reducibility as suggested by H₂-TPR studies. Among all the catalysts, La_0.6K_0.4Co_0.9Mg_0.1O₃ exhibited the highest activity.     

Physical–chemical property and activity evaluation of LaB0.5Co0.5O3 (B = Cr,Mn, Cu) and LaMnxCo1−xO3 (x = 0.1, 0.25, 0.5) nano perovskites in VOC combustion

The correlation between physical–chemical properties and activities of LaB_0.5Co_0.5O₃ (B = Cr, Mn, Cu) nano perovskites was studied in combustion of toluene. LaMn_0.5Co_0.5O₃ showed the highest activity among LaB_0.5Co_0.5O₃ catalysts and further optimization study was focused on LaMn_xCo_1?xO₃ (x = 0.1, 0.25, 0.5). The activity and reducibility of catalysts improved due to partial substitution of Co³⁺ by B cation. No direct relationship was between surface area and catalyst activity. T_50% of 2-propanol over LaMn_0.25Co_0.75O₃, LaMn_0.5Co_0.5O₃, LaMn_0.1Co_0.9O₃ and LaCoO₃ was 168, 200, 220 and 229 °C, respectively. LaMn_0.25Co_0.75O₃ was the optimum catalyst and showed robust stability in combustion of toluene and 2-propanol.     

Low temperature catalytic oxidation of nitric oxide over the Mn–CoOx catalyst modified by nonthermal plasma

Nonthermal plasma (NTP) treatment was investigated to modify the Mn–CoO_x catalyst for the low-temperature oxidation of nitric oxide. The catalysts were characterized by XRD, BET, TGA and XPS techniques. The results showed that the activity of NTP-treated catalysts improved significantly, and that NTP treatment has the advantage of changing the structural and morphological properties (higher surface areas and pore volume) and varying the relative surface concentration and oxidation states of surface species over catalysts. High surface areas and pore volume, high concentration of chemisorbed oxygen, Mn^4 + and Co^2 +, and the efficient synergetic catalytic effect between Co and Mn ions were thought to be the main reasons for the high activity of NTP-treated catalysts.     

Crystal structure,thermal expansion and electrical conductivity of perovskite oxides BaxSr1−xCo0.8Fe0.2O3−δ (0.3 ≤ x ≤ 0.7)

Ba_xSr_1−xCo_0.8Fe_0.2O_3−δ (0.3 ≤ x ≤ 0.7) composite oxides were prepared and characterized. The crystal structure, thermal expansion and electrical conductivity were studied by X-ray diffraction, dilatometer and four-point DC, respectively. For x ≤ 0.6 compositions, cubic perovskite structure was obtained and the lattice constant increased with increasing Ba content. Large amount of lattice oxygen was lost below 550 °C, which had significant effects on thermal and electrical properties. All the dilatometric curves had an inflection at about 350–500 °C, and thermal expansion coefficients were very high between 50 and 1000 °C with the value larger than 20 × 10⁻⁶ °C⁻¹. The conductivity were larger than 30 S cm⁻¹ above 500 °C except for x > 0.5 compositions. Furthermore, conductivity relaxation behaviors were also investigated at temperature 400–550 °C. Generally, Ba_0.4Sr_0.6Co_0.8Fe_0‘2O_3−δ and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ are potential cathode materials.     

Synthesis and negative thermal expansion properties of solid solutions Yb2−xLaxW3O12 (0 ≤ x ≤ 2)

A new series of rare earth solid solutions Yb_2?xLa_xW₃O₁₂ were successfully synthesized by the solid-state method. Effects of substituted ion lanthanum on the microstructures and thermal expansion properties in the resulting Yb_2?xLa_xW₃O₁₂ ceramics were investigated by X-ray diffraction (XRD), thermogravimetric analyzer (TGA), field emission scanning electron microscope (FESEM) and thermal mechanical analyzer (TMA). Results indicate that the structural phase transition of the Yb_2?xLa_xW₃O₁₂ changes from orthorhombic to monoclinic with increasing substituted content of lanthanum. The pure phases can form in the composition range of 0 ≤ x < 0.5 with orthorhombic structure and 1.5 < x ≤ 2 with monoclinic one. High lanthanum content leads to a low hygroscopicity of Yb_2?xLa_xW₃O₁₂. Negative thermal coefficients of the Yb_2?xLa_xW₃O₁₂ (0 ≤ x ≤ 2) also vary from ?7.78 × 10^?6 K^?1 to 2.06 × 10^?6 K^?1 with increasing substituted content of lanthanum.     

Basicity–FAME yield correlations in metal cation modified MgAl mixed oxides for biodiesel synthesis

In this paper Zn^2 +, Co^2 +, Fe^3 + and La^3 + were respectively introduced into Mg₃Al₁ mixed oxides to prepare Mg₁Zn₂Al₁, Mg₁Co₂Al₁, Mg₃Al_0.6Fe_0.4 and Mg₃Al_0.6La_0.4 oxides by calcinations at 773 K. The XRD, XPS, BET, ICP-AES and CO₂-TPD characterizations of samples exhibited that the effects of the substitution of trivalent cations (Fe^3 +, La^3 +) for Al^3 + on the basicity of samples were stronger than the substitution of divalent cations (Zn^2 +, Co^2 +) for Mg^2 + because of high O^2 − concentration which were coincident with the FAME yield for these catalysts. La^3 + modified catalyst exhibited highest activity in transesterification.     

Mesoporous CuO/TixZr1 − xO2 catalysts for low-temperature CO oxidation

Mesoporous CuO/Ti_xZr_1 − xO₂ catalysts were prepared by a surfactant-assisted method, and characterized by N₂ adsorption/desorption, TEM, XPS, in-situ FTIR and H₂-TPR. The catalysts exhibited high specific surface area (S_BET = 241 m²/g) and uniform pore size distribution. XPS and in-situ FTIR displayed that Cu⁺ and Cu²⁺ species coexisted in the catalysts. The CuO/Ti_xZr_1 − xO₂ catalysts presented obviously higher activity in CO oxidation reaction than the CuO/TiO₂ and CuO/ZrO₂ catalysts. Effect of molar ratios of Ti to Zr and calcination temperature on catalytic activity was investigated. The CuO/Ti_0.6Zr_0.4O₂ catalyst calcined at 400 °C exhibited excellent activity with 100% CO conversion at 140 °C.     

Catalytic properties in N2O decomposition of mixed cobalt–iron spinels

The effect of introduction of iron in the Co_3 − xFe_xO₄ on catalytic activity in N₂O decomposition was investigated. The spinel catalysts were characterized by XRD, SEM, RS, BET methods, work function measurements and Mössbauer spectroscopy. Introduction of iron in the Co_3 − xFe_xO₄ spinel catalysts at the level of x < 1 leads to preferential substitution of Fe³⁺ in tetrahedral sites, whereas for x > 1 also octahedral ones are substituted. A strong correlation between deN₂O activity (T_50%) and work function was observed showing that electronic factor controls the catalytic reactivity of Co–Fe spinels. The results revealed that the active centers for N₂O decomposition are cobalt ions and thus even a low level of their substitution by iron leads to substantial decrease of the deN₂O activity of the cobalt spinel.     

Redox behavior and oxidation catalysis of HnXW12O40 (X = Co2 +, B3 +, Si4 +, and P5 +) Keggin heteropolyacid catalysts

Redox behavior and oxidation catalysis of H_nXW₁₂O₄₀ (X = Co^2 +, B^3 +, Si^4 +, and P^5 +) Keggin heteropolyacid catalysts were investigated. Successful formation of H_nXW₁₂O₄₀ catalysts was confirmed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Reduction potentials of H_nXW₁₂O₄₀ catalysts were determined by electrochemical measurements. First electron reduction potential of H_nXW₁₂O₄₀ catalysts decreased with increasing overall negative charge of heteropolyanion. H_nXW₁₂O₄₀ catalysts were then applied to the liquid-phase oxidation of benzaldehyde to benzoic acid. Yield for benzoic acid increased with increasing first electron reduction potential.     

Electrical properties of [Li0.04(K0.5Na0.5)0.96−xAgx](Nb1−ySby)O3 ceramics

Dependence of electrical properties on the structural characteristics of Li_0.04(K_0.5Na_0.5)_0.96(Nb_1?ySb_y)O₃ (LKNNS (x = 0, 0.00 ≤ y ≤ 0.10)) and [Li_0.04(K_0.5Na_0.5)_0.96?xAg_x](Nb_0.925Sb_0.075)O₃ (LKNANS (0.01 ≤ x ≤ 0.05, y = 0.075)) were investigated. The oxygen octahedral distortion was dependent on Ag⁺ and/or Sb⁵⁺ content which affected to the phase transition temperature of LKNNS and LKNANS ceramics. The orthorhombic–tetragonal and tetragonal–cubic phase transition temperatures (T_O–T, T_C) of the specimens were decreased with increasing of average octahedral distortion. With increasing of Sb⁵⁺ content, the electromechanical coupling factor (k_p), piezoelectric constant (d₃₃) and dielectric constant (?_r) of the sintered specimens were increased up to y = 0.075, and then decreased. These results could be attributed to the shift of T_O–T to near room temperature for Li_0.04(K_0.5Na_0.5)_0.96(Nb_0.0925Sb_0.075)O₃.     

Raman spectra and extended X-ray absorption fine structure characterization of La(2−x)/3NaxTiO3 and Nd(2−x)/3LixTiO3 microwave ceramics

A-site deficient perovskite compounds, La_(2?x)/3Na_xTiO₃ (0.02 ≤ x ≤ 0.5) and Nd_(2?x)/3Li_xTiO₃ (0.1 ≤ x ≤ 0.5) microwave ceramics, were investigated by Raman scattering. Nd_(2?x)/3Li_xTiO₃ (0.1 ≤ x ≤ 0.5) was also investigated by extended X-ray absorption fine structure (EXAFS) measurement. The Raman shifts of the E (239 cm^?1) and A₁ (322 cm^?1) modes of La_(2?x)/3Na_xTiO₃ were found to decrease with x. However, the E (254 cm^?1) and A₁ (338 cm^?1) of Nd_(2?x)/3Li_xTiO₃ were found to blueshift with x, which was caused by Li substitution. The redshift of the A₁ (471 cm^?1) phonon of Nd_(2?x)/3Li_xTiO₃ (0.1 ≤ x ≤ 0.3) indicates that O–Ti–O bonding forces lessen with Li concentration, which is consistent with the EXAFS result that Ti–O bond lengths increase for 0.1 ≤ x ≤ 0.3. For x > 0.3, the EXAFS result shows that Ti–O bond lengths decrease. Moreover, Ti–O bond lengths show strong correlation with the microwave dielectric constants of Nd_(2?x)/3Li_xTiO₃.     

Phase evolution and chemical durability of Zr1-xNd xO2-x/2 (0 ≤ x ≤ 1) ceramics

A series of Zr_1-xNd _xO_2-x/2 (0 ≤ x ≤ 1) ceramics was prepared by solid-state reaction method. The effects of Nd content on the phase evolution were investigated. The chemical durability of resulting waste forms was also examined. The results show that the ceramics with x < 0.1 show monoclinic and cubic zirconia phase, with 0.2 ≤ x < 0.4 exhibit a single cubic phase, with 0.4 ≤ x ≤ 0.6 exhibit a single pyrochlore phase, with 0.6 < x < 0.8 exhibit a single cubic phase and remain cubic phases and hexagonal Nd₂O₃ when 0.8 ≤ x ≤ 1. The unit cell parameters of the Nd-doped zirconia samples increase as the Nd content increases. Moreover, the normalized element release rates of Nd element in Nd-doped zirconia ceramics firstly decrease with leaching time and almost no change after 21 days (∼0⁻⁶ g m⁻² d⁻¹), demonstrating its good chemical durability.     

Structure and thermal expansion of (Crx,V1−x)n+1AlCn phases measured by X-ray diffraction

MAX phases in the (Cr_x,V_1−x)_n+1AlC_n system were synthesized by reactive sintering or hot isostatic pressing of elemental powders at temperatures between 1400 °C and 1600 °C. For n = 1, a complete range (0 ≤ x ≤ 1) of solid solutions was found; for n = 2 and 3 the solubility ranges were 0.25 ≤ x ≤ 0.75 and 0 ≤ x ≤ 0.5, respectively. Powder X-ray diffraction revealed that the lattice parameters of all (Cr_x,V_1−x)_n+1AlC_n solid solutions followed Vegard’s law. The thermal expansion coefficients of the various compounds were determined from Rietveld refinements of X-Ray patterns obtained at temperatures between ambient and 800 °C. For the n = 1 and 3 phases the thermal expansion coefficients were almost isotropic; those for the n = 2, however, were quite anisotropic with the expansion along the a-axis being significantly larger than along the c-axis. As a general trend, vanadium rich compounds have smaller thermal expansion coefficients than their Cr-rich counterparts.     

Synthesis of monoclinic Celsian from Coal Fly Ash by using a one-step solid-state reaction process

Monoclinic (Celsian) and hexagonal (Hexacelsian) Ba_1?xSr_xAl₂Si₂O₈ solid solutions, where x = 0, 0.25, 0.375, 0.5, 0.75 or 1, were synthesized by using Coal Fly Ash (CFA) as main raw material, employing a simple one-step solid-state reaction process involving thermal treatment for 5 h at 850–1300 °C. Fully monoclinic Celsian was obtained at 1200 °C/5 h, for SrO contents of 0.25 ≤ x ≤ 0.75. However, an optimum SrO level of 0.25 ≤ x ≤ 0.375 was recommended for the stabilization of Celsian. These synthesis conditions represent a significant improvement over the higher temperatures, longer times and/or multi-step processes needed to obtain fully monoclinic Celsian, when other raw materials are used for this purpose, according to previous literature. These results were attributed to the role of the chemical and phase constitution of CFA as well as to a likely mineralizing effect of CaO and TiO₂ present in it, which enhanced the Hexacelsian to Celsian conversion.     

Fischer–Tropsch synthesis over a Co/SiO2 catalyst modified with Mn- and Zr under practical conditions

Fischer–Tropsch (FT) synthesis activity and the stability of a Co/SiO₂ catalyst modified with Mn- and Zr were examined under various practical conditions. Dependence of FT synthesis on reaction pressure and bench-scale FT synthesis were investigated. Evaluating catalyst lifetime during continuous FT reactions was conducted. The Co + Mn + Zr/SiO₂ catalyst exhibited relatively greater activity and stable reactivity for 168 h. Sulfur resistance of catalysts were investigated and results showed that the presence of 4 ppm H₂S drastically affected catalytic activity. The Co + Mn + Zr/SiO₂ catalyst exhibited greater activity even with H₂ presence and the sulfur poisoning rate was almost similar on both Co + Mn + Zr/SiO₂ and Co/SiO₂ catalysts.     

Effect of CaO addition on the structure and electrical conductivity of the pyrochlore-type GdSmZr2O7

Polycrystalline GdSm_1?xCa_xZr₂O_7?x/2 (0 ≤ x ≤ 0.20) ceramics have been prepared by the solid-state reaction method. The effects of CaO addition on the microstructure and electrical properties of the pyrochlore-type GdSmZr₂O₇ ceramic were investigated. GdSm_1?xCa_xZr₂O_7?x/2 (x ≤ 0.05) ceramics exhibit a pyrochlore-type structure; however, GdSm_1?xCa_xZr₂O_7?x/2 (0.10 ≤ x ≤ 0.20) ceramics consist of the pyrochlore-type structure and a small amount of CaZrO₃. The total conductivity of GdSm_1?xCa_xZr₂O_7?x/2 ceramics follows the Arrhenius relation, and gradually increases with increasing temperature from 723 to 1173 K. GdSm_1?xCa_xZr₂O_7?x/2 ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10^?4–1.0 atm at each test temperature. The highest total conductivity is about 1.20 × 10^?2 S cm^?1 at 1173 K for the GdSm_0.9Ca_0.1Zr₂O_6.95 ceramic.     

A DFT study of methanol oxidation on Co3O4

By means of spin polarized density functional theory with the GGA + U framework, the reaction mechanism of CH₃OH oxidation on the Co₃O₄ (110)-B and (111)-B surfaces has been investigated. Adsorption situation and a part of reaction cycle for CH₃OH oxidation are clarified. Our results indicated that: i) U value can affect the calculated energetic result significantly; ii) CH₃OH can adsorb with surface lattice oxygen atom (O_2f/O_3f) to form CoO bond directly, and the adsorption of CH₃OH and its decomposition products on (110)-B is more stable than on (111)-B, which means CH₃OH prefers Co^3 + better than Co^2 +; iii) on the (110)-B surface, CH₃OH can form CO₂, H₂O and adsorbed H atom. But on the (111)-B surface, CH₃OH can just form formaldehyde (CH₂O) and adsorbed H atom, this means oxidative capacity of (110)-B (Co^3 +) is higher than (111)-B (Co^2 +). The possible reasons corresponding to the high oxidative of (110)-B come from both Co^3 + and O_2f: Co^3 + tends to bind adsorbed species for further decomposition and O_2f tends to bind more hydrogenation atom involved in methanol due to its low-coordinates number compared to that of O_3f.