La Mixed Oxide Research Articles

Co supported on Mg–La mixed oxides as an efficient catalyst for ammonia synthesis

Ammonia presents a promising hydrogen source and energy carrier for mobile and stationary applications. The development of new and cheaper catalysts for ammonia synthesis is thus of great importance in improving the efficiency of the Haber-Bosch process. Here we report the investigation of ammonia synthesis on cobalt catalysts supported on magnesium–lanthanum mixed oxides with varying Mg/La molar ratios. Our studies revealed that the catalyst's activity is tuneable by varying the support composition, allowing an adjustment of the surface adsorption properties. Owing to the increased basicity of the support and weaker interactions between cobalt and hydrogen atoms, the catalyst supported on mixed MgO–La2O3 oxide with Mg/La molar ratio of 7 demonstrated the highest activity and stability for ammonia synthesis as compared to other reported cobalt catalysts.

Continuous Synthesis of Glycerol Carbonate by Transesterification of Glycerol with Dimethyl Carbonate Over Fe–La Mixed Oxide Catalysts

Transesterification of glycerol with dimethyl carbonate to produce glycerol carbonate was studied under continuous reaction over Fe–La mixed oxide catalysts. A series of Fe–La oxide catalysts with different molar compositions were synthesized by co-precipitation method. Surface and structural investigations of the catalysts were carried using N2 physisorption, powder X-ray diffraction, temperature-programmed desorption, X-ray photoelectron spectroscopy, FT-infra red spectroscopy, scanning electron microscopy and Laser Raman spectroscopy. Glycerol carbonate yield was influenced by the molar ratios of Fe/La and catalyst calcination temperature, which are responsible for the variation in acid–base properties of the catalysts. The catalyst with a molar ratio of 1:1 calcined at 550 °C exhibited superior activity with 71% yield of glycerol carbonate. The synergistic effect between Fe–La oxides and the formation of LaFeO3 perovskite structure are responsible for the high activity of the catalyst. The catalyst exhibited unprecedented stability over 100 h during the time on stream analysis.

Effect of lanthanum loading on nanosized CeO2-ZnO solid catalysts supported on cordierite for diesel soot oxidation

We report the application of a solid lanthanum–ceria–zinc catalyst in the catalytic regeneration of diesel particulate filters (DPF) in diesel engines. We synthesized a CeO2–ZnO–La2O3 (Ce–Zn–La) mixed oxide by a lactic acid-mediated sol–gel method, which efficiently coated cordierite substrates for soot capture and combustion. We studied the effects of La loading on the physicochemical and catalytic properties of Ce–Zn mixed oxide during low-temperature soot combustion processes. We characterized the synthesized catalysts by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), N2 adsorption, Raman spectroscopy, oxygen storage capacity (OSC), and scanning and transmission electron microscopy (SEM and TEM). Thermogravimetric and differential thermal analysis (TGA/DTA) confirmed that the catalysts effectively reduced the soot oxidation temperature. The ternary Ce–Zn–La mixed oxide catalyst with Ce/Zn/La atomic ratio of 2:1:0.5 had the highest catalytic activity and promoted soot oxidation at temperatures below 390°C. This indicated that the large number of oxygen vacancies in the catalyst structure generated oxygen species at low temperatures. Raman spectroscopy measurements revealed the presence of oxygen vacancies and lattice defects in Ce–Zn–La samples, which were key parameters concerning the stability and redox properties of the prepared catalysts.

Active oxygen species on Mg–La mixed oxides: the effect of Mg and La oxide interactions

Mg–La mixed oxide catalysts with a strong interaction between Mg and La oxides had higher amounts of oxygen vacancies and surface adsorbed oxygen species, resulting in a better performance in H2 oxidation and CH4 oxidative reactions.

Hydrogen production by ammonia decomposition using Co catalyst supported on Mg mixed oxide systems

Ammonia decomposition for hydrogen production was studied using cobalt catalysts supported on different Mg mixed oxide systems (MgAl, MgCe and MgLa) to elucidate the influence of support composition on the activity of these catalysts. For this purpose three supports of Mg to X ratio (X = Al, Ce or La) equal to two were prepared. These supports were applied to synthesis 5 wt% cobalt samples by impregnation. The catalytic performance was evaluated in the temperature range of 300–550 °C at atmospheric pressure. It was found that 5CMLa-2 (5 wt% Co impregnated on MgLa support with Mg:La = 2:1) has the highest activity among the other catalysts and the decreasing order of NH3 conversion as follows: 5CMLa-2 > 5CMCe-2 >> 5CMAl-2. Another series of mixed Mg–La oxide supports with different Mg/La molar ratios (Mg/La = 1, 2,3,5,9 and 14) were prepared and impregnated with 5 wt% cobalt. The prepared catalysts were characterized by BET, XRD, TPR, XPS and CO chemisorptions techniques. Investigation of the effect of La content in the mixed oxide support showed that the 5 wt% cobalt with Mg/La ratio 5 catalyst was the most active. This could be attributed to enhance the interaction between Mg and La which leads to suitable basicity for ammonia decomposition reaction. The increase of MgO content creates high surface area, high active metal area and high surface lattice oxygen (i.e. O2−). From TPD data the basic sites become stronger in the Mg–La mixed oxide at Mg/La = 5 ratio. 5CMLa-5 (5 wt% Co on MgLa with ratio 5:1) is showing highest activity among all catalysts with other Mg/La ratios. The enrichment in activity of 5CMLa-5 catalyst could be attributed to increase in surface area, metal dispersion, easily reducible Co species and high basicity.

Biodiesel production from Jatropha curcas L. oil with Ca and La mixed oxide catalyst in near supercritical methanol conditions

The catalytic transesterification of crude Jatropha curcus oil (JCO) with supercritical methanol (scMeOH), in the presence of calcium lanthanum mixed oxide (CaLaO) heterogeneous base catalyst was carried out using a batch reactor at near critical temperatures and pressures. The performance of synthesized CaLaO mixed oxide catalysts was examined by characterizing it through instruments such as XRD, BET and CO2-TPD, revealed that the Ca/La atomic ratio strongly affects the phase structure, catalyst basic sites, and thus the catalytic reactivity. The reaction parameters including Ca/La atomic molar ratio in the mixed metal oxide catalyst, molar ratio of methanol to oil, catalyst concentration, reaction pressure, temperature and time were varied one at a time and optimized based on the content of fatty acid methyl esters (FAMEs). The highest FAME yield for supercritical methanolysis reached 93% under the optimum reaction conditions: 240°C, 8.2MPa, a molar ratio of methanol to oil of 21:1, and reaction time of 10min in the presence of 1wt.% catalyst. The results demonstrated that the presence of CaLaO mixed oxide catalyst in the reaction system effectively reduced reaction temperature, time and pressure of supercritical conditions. It required a very low concentration to mitigate the harsh operation conditions (290°C, 15MPa, 60min) of the scMeOH process. On the other hand, supercritical reaction compensated for low conversion rate of solid catalytic transesterification whereby, it takes one step further by improving the role of catalyst with supercritical conditions to achieve higher yield and shorter processing time. The reusability of CaLaO mixed oxide catalyst for repeated use was tested, the catalytic activity was >80% when the catalyst was employed for fourth time. The study concluded that slight leaching of Ca2+ (0.52–6.07ppm) and La3+ (0.34–2.33ppm) occurred during transesterification reaction, however it is below acceptable levels of metals as ASTM D6751 (United State) and in Europe, EN 14214 (Europe) standards. This proved that heterogeneous catalytic supercritical reaction process is more promising than non-catalytic processes and it can be turned to practical use in the near future.

Influence of La on reduction behaviour and Ni metal surface area of Ni–Al2O3 catalysts for COx free H2 by catalytic decomposition of methane

A series of Ni:Al:La mixed oxides derived from hydrotalcite precursors with varying La/Al mole ratio were examined for COx free H2 production by catalytic decomposition of CH4. The physico-chemical characteristics of Ni:Al:La were determined by XRD, UV-DRS, SEM, TEM, Raman spectroscopy, BET-surface area, TPR and O2 pulse chemisorption measurements. Addition of La to Ni–Al improved the Ni metal surface area and the reduction behaviour of NiO particles is dramatically changed. Particle size of Ni was similar to the size of carbon nano fibre in the deactivated catalyst. A direct correlation between Ni metal surface area and the CH4 decomposition activity was observed.

Synthesis of fluorenones by using Pd(ii)/Mg–La mixed oxide catalyst

Palladium(ii)/magnesium–lanthanum mixed oxide (Pd(ii)/Mg–La mixed oxide) catalyst was used in the dehydrogenative cyclization of benzophenones to afford fluorenones.

A Pd(ii)/Mg–La mixed oxide catalyst for cyanation of aryl C–H bonds and tandem Suzuki–cyanation reactions

We report direct cyanation of aromatic C–H bonds and tandem Suzuki–cyanation reactions catalyzed by a heterogeneous palladium impregnated magnesium–lanthanum mixed oxide catalyst.

High performance of Mg–La mixed oxides supported Ni catalysts for dry reforming of methane: The effect of crystal structure

A series of mixed Mg–La oxide supports with various Mg2+/La3+ mole ratios were prepared via co-precipitation of Mg and La nitrates, and then impregnated to form 5 wt.% Ni catalysts. The as-prepared catalysts were evaluated in DRM reaction for 200 h and characterized by means of in situ DRIFTS, XRD, TEM, CO2-TPD, XPS, and TGA. It was found that the interaction of suitable amount of MgO with La2O3 stabilized cubic La2O3 species in catalysts, which has high basicity to adsorb CO2 forming monoclinic La2O2CO3 (Ia) species in DRM reaction. The introduction of MgO also created surface oxygen ions (i.e. O–). Both monoclinic La2O2CO3 (Ia) and surface oxygen species are able to oxidize and remove deposited carbon, keeping the Ni catalyst at high activity and stability. Low Mg2+/La3+ ratios generated hexagonal La2O3 and La2O2CO3 (II) in DRM reaction. The hexagonal La2O2CO3 (II) did not play significant role in carbon removal so that the catalysts deactivated fast.

Pd/Mg–La mixed oxide catalyzed oxidative sp2 C[sbnd]H bond acylation with alcohols

Pd/Mg–La mixed oxide is used as an efficient catalyst for the oxidative direct acylation of arene sp2 CH bonds with alcohols. TBHP was used for in situ oxidation of the alcohols to aldehydes which after coupling with 2-aryl pyridines forms aryl ketones. The catalyst is recovered and used for four cycles.

Partial oxidation of methane over Ni/Mg/Al/La mixed oxides prepared from layered double hydrotalcites

A series of Ni/Mg/Al/La mixed oxides prepared by thermal decomposition of layered double hydrotalcites (HT) were characterized by XRD, ICP, EXAFS, TGA, TPR-H 2, SEM, and N 2 adsorption/desorption technique. The results revealed the formation of periclase-type catalysts with mesoporous structure, and the addition of La 3+ lowered the phase crystallization with the formation of small oxide particles. Such catalysts had both high activities and stabilities toward partial oxidation of methane (POM). The catalyst containing 6.5 mol.% La 3+ showed the highest performance at 1053 K with CH 4 conversion of 99%, CO selectivity of 93% and H 2 selectivity of 96%, which could be attributed to the presence of highly dispersed nickel and then the resistance to coke formation due to the promotion effect of lanthanum.

Microstructural characterization of the fluorite phase in the ULaO system. I. Rhombohedral microdomain formation in (U 1− yLa y)O 2± x, 0.56 ≤ y ≤ 0.67

A series of hyperstoichiometric, stoichiometric, and hypostoichiometric ULa mixed oxides with fluorite-type structures has been prepared in air at 1673 K in the composition range (U 1− y La y )O 2± x , 0.33 ≤ y ≤ 0.67, by a mixed organic precursor/ceramic procedure. The oxidation state of uranium in these materials has been examined by XPS and near FT-IR spectroscopy, uranium ions existing within each sample either as U 5+ and U 6+ (0.33 ≤ y ≤ 0.50) or U 6+ and U 4+ (0.56 ≤ y ≤ 0.67). Electron diffraction studies reveal two sets of patterns with diffuse scattering phenomena depending on composition. The diffuse scattering for specimens with 0.56 ≤ y ≤ 0.67 is discussed in terms of microdomain formation of a rhombohedral R III phase, that is obtained as a single phase when samples with these compositions were annealed at 1373 K for 100 hr.

XPS study of β-carbon hydrogenation on nickel(111) surface

A series of Ni:Al:La mixed oxides derived from hydrotalcite precursors with varying La/Al mole ratio were examined for COx free H2 production by catalytic decomposition of CH4. The physico-chemical characteristics of Ni:Al:La were determined by XRD, UV-DRS, SEM, TEM, Raman spectroscopy, BET-surface area, TPR and O2 pulse chemisorption measurements. Addition of La to Ni–Al improved the Ni metal surface area and the reduction behaviour of NiO particles is dramatically changed. Particle size of Ni was similar to the size of carbon nano fibre in the deactivated catalyst. A direct correlation between Ni metal surface area and the CH4 decomposition activity was observed.