La2O3 Catalyst Research Articles

Hydrogen Yield from CO2 Reforming of Methane: Impact of La2O3 Doping on Supported Ni Catalysts

Development of a transition metal based catalyst aiming at concomitant high activity and stability attributed to distinguished catalytic characteristics is considered as the bottleneck for dry reforming of methane (DRM). This work highlights the role of modifying zirconia (ZrO2) and alumina (Al2O3) supported nickel based catalysts using lanthanum oxide (La2O3) varying from 0 to 20 wt% during dry reforming of methane. The mesoporous catalysts with improved BET surface areas, improved dispersion, relatively lower reduction temperatures and enhanced surface basicity are identified after La2O3 doping. These factors have influenced the catalytic activity and higher hydrogen yields are found for La2O3 modified catalysts as compared to base catalysts (5 wt% Ni-ZrO2 and 5 wt% Ni-Al2O3). Post-reaction characterizations such as TGA have showed less coke formation over La2O3 modified samples. Raman spectra indicates decreased graphitization for La2O3 catalysts. The 5Ni-10La2O3-ZrO2 catalyst produced 80% hydrogen yields, 25% more than that of 5Ni-ZrO2. 5Ni-15La2O3-Al2O3 gave 84% hydrogen yields, 8% higher than that of 5Ni-Al2O3. Higher CO2 activity improved the surface carbon oxidation rate. From the study, the extent of La2O3 loading is dependent on the type of oxide support.

Highly Durable C2 Hydrocarbon Production via the Oxidative Coupling of Methane Using a BaFe0.9Zr0.1O3−δ Mixed Ionic and Electronic Conducting Membrane and La2O3 Catalyst

The oxidative coupling of methane (OCM) is an attractive technology for the production of ethane (C2H6) and ethylene (C2H4); and significant performance and efficiency gains as well as reduced carbon dioxide (CO2) emissions are expected when OCM takes place within mixed ionic and electronic conducting (MIEC) ceramic membrane reactors (CMRs). So far, research on OCM in CMRs has been limited to unstable and incompatible materials investigated under short-term measurements that hinder upscaling and commercial application. To this end, this work demonstrates long-term stable OCM performance enabled by a BaFe0.9Zr0.1O3−δ (BFZ91) perovskite utilized as the oxygen-ion MIEC membrane and lanthanum oxide (La2O3) used as the OCM catalyst. Experimental measurements conducted in the temperature (T) range of 750–900 °C and at inlet methane (CH4) mole fractions (XCH4in) of 0–30% revealed a highly stable performance during 23 days of continuous operation, which was further confirmed by material characterization. Under the aforementioned operating conditions, BFZ91 offers a high oxygen (O2) permeation flux (JO2) between 0.5−1.5 (μmol/cm2/s); CH4 conversion (CCH4) reached ∼35% while the selectivities to C2H6 (SC2H6) and C2H4 (SC2H4) were as high as ∼50% and ∼40%, respectively, showing a strong dependency on the operating conditions. Yields of C2H6 (YC2H6) and C2H4 (YC2H4) in the range of 1–5% and 1–7%, respectively, were measured, with more C2H4 being produced at higher T. In the absence of La2O3, CCH4 and C2 (C2H6 and C2H4) yields are lower confirming that BFZ91 does not promote CH4 oxidation, reforming, or coupling on its surface at high rates. The OCM performance of BFZ91 with La2O3 was also found to be stable under partial O2 consumption and pure CH4 conditions. Furthermore, a detailed analysis of the mixture composition allowed the identification of the primary reactions in the OCM chemistry. Our results reveal that within our reactor, CH4 full oxidation to CO2 and steam (H2O) happens simultaneously with CH4 oxidation to C2H6 and H2O (both on the La2O3 catalyst), but the production of the valuable C2H4 is primarily taking place through the C2H6 non-oxidative dehydrogenation in the gas phase; this reaction was not found to proceed on the La2O3 catalyst. Besides the promise of the investigated materials toward commercialization, the methods to study the OCM chemistry and the membrane catalyst coupling presented here are expected to promote further advances in the field of OCM.

How CO2 poisons La2O3 in an OCM catalytic reaction: A study by in situ XRD-MS and DFT

Oxidative coupling of methane (OCM) is a catalytic partial oxidation process that converts methane directly into more valuable C2 products (ethane and ethylene). The mechanism related to selectivity and conversion is still not clear. Previous results suggested that the bulk structure change of the La2O3 catalyst is related to OCM activation performance. This work is focused on investigation of carbonates and the reaction products simultaneous formation over La2O3 catalyst utilizing coupled in situ XRD-MS. Semi quantitative analysis clearly reveals a positive dependence between CO2 and C2 products light-off temperature and the initial bulk La2O2CO3 concentration, indicating a strong correlation between carbonates and La2O3 catalyst poisoning. The activity of the La based catalyst is associated to its oxide form rather than to its oxycarbonate form. Based on operando results a two-step bulk La2O2CO3 decomposition model resulting in surface carbonates presenting on the catalyst surface between 500 °C and 800 °C is proposed. DFT calculations further confirm the proposed model and indicate surface carbonates do inhibit catalytic methane activation. It is concluded that CO32− species located in surface region of the catalyst operate as a direct La2O3 catalyst poison in the highly motivating OCM reaction.

Active oxygen center in oxidative coupling of methane on La2O3 catalyst

La2O3 catalyzed oxidative coupling of methane (OCM) is a promising process that converts methane directly to valuable C2 (ethylene and ethane) products. Our online MS transient study results indicate that pristine surface without carbonate species demonstrates a higher selectivity to C2 products, and a lower light-off temperature as well. Further study is focused on carbonate-free La2O3 catalyst surface for identification of active oxygen species associated with such products behavior. XPS reveals unique oxygen species with O 1 s binding energy of 531.5 eV correlated with OCM catalytic activity and carbonates removal. However, indicated thermal stability of this species is much higher than the surface peroxide or superoxide structures proposed by earlier computation models. Motivated by experimental results, DFT calculations reveal a new more stable peroxide structure, formed at the subsurface hexa-coordinate lattice oxygen sites, with energy 2.18 eV lower than the previous models. The new model of subsurface peroxide provides a perspective for understanding of methyl radicals formation and C2 products selectivity in OCM over La2O3 catalyst.

Heat treatment effect on nanostructured sol-gel derived lanthania doped with chromium

Chromium doped lanthanum oxide synthesized by glycerol-assisted sol-gel route was heat treated at different temperatures up to 860 °C in order to investigate the effect of treatment temperature on the atomic environment in these samples. The addition of Cr2O3 to La2O3 catalyst support and catalytic promoter was considered because chromium is an interesting catalyst dopant.As the temperature rises from 100 to 860 °C, nanostructured La(OH)CO3, La2O2CO3 and La(OH)3 phases are developed in the treated samples. The crystallites size increases with treatment temperature from about 10 nm up to 30 nm, and at the same time a higher surface basicity is obtained, that would imply an enhanced catalytic activity or an improved behavior as catalyst substrate. The La2O2CO3 stable phase against moisture was obtained by relative low temperature synthesis. The tendency to atmospheric CO2 adsorption was evidenced for La(OH)3 phase developed in the samples treated at 650 and 860 °C.The X-ray diffraction (XRD), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses were used to evidence structural changes with influence on sample properties.

The Effect of Strontium Content on the Activity and Selectivity of Sr-Doped La2O3 Catalysts in Oxidative Coupling of Methane

Thirty-five doped and undoped rare earth oxide catalysts were synthesized and tested under identical conditions for the oxidative coupling of methane. While La2O3 was found to be the most active, La2O3 doped with Sr was found to be the most selective. High resolution low energy ion scattering (HR-LEIS) showed that doping with Sr above 2 mole % led to migration of Sr to the surface of the catalyst producing surface (Sr/La) ratios of 2.7 – 4.4 from bulk (Sr/La) ratios of 0.053 and 0.13, respectively. Operando Raman analysis run under OCM conditions identified La2O3 and SrCO3 as the predominant lanthanum and strontium phases during reaction. A bilayer structure comprising a thermally stable Sr-doped La2O3 base covered with a mostly amorphous Sr phase containing SrCO3, SrO and SrO2 was proposed. Selectivity to C2+ for this structure increased with surface Sr content; and SrO2 is believed to be responsible for this effect.

Effect of the support composition on catalytic and physicochemical properties of Ni catalysts in oxy-steam reforming of methane

This work deals with Ni catalysts supported on both mono and binary oxide prepared by a conventional wet impregnation method. The catalytic properties of the material were investigated in oxy-steam reforming of methane (OSRM) process. The physicochemical properties of the catalysts were extensively studied using techniques such as Temperature Programmed Reduction (TPR-H2), Temperature Programmed Desorption of Ammonia (TPD-NH3), Brunauer Emmett Teller Method (BET), X-ray Diffraction studies (XRD), Thermal Analysis coupled with Mass Spectrometry (TG-DTA-MS), Time of Flight Secondary Ion Mass Spectrometer (ToF-SIMS), X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscope with EDX detector (SEM-EDX). The catalytic activity results showed that the Ni/CeO2∙La2O3 (2:1) catalyst exhibited superior activity and high selectivity towards hydrogen formation in the studied process due to the high content of Ni species present on the catalyst surface. The low activity of the Ni catalysts supported on La2O3 or binary oxide with high content of lanthanum oxide is related to the strong interaction of NiO with support.

Ni/La2O3 and Ni/MgO–La2O3 catalysts for the decomposition of NH3 into hydrogen

The decomposition of NH3 for hydrogen production was studied using Ni/La2O3 catalysts at varying compositions and temperatures prepared via surfactant-templated synthesis to elucidate the influence of catalyst active metal content, support composition and calcination temperature on the catalytic activity. The catalytic performance of all samples was studied between 300 and 600 °C under atmospheric pressure. The catalytic activity of the sample were as follows: 10Ni/La2O3-450 > 10Ni/La2O3-550 > 10Ni/La2O3-650 ≈ 10Ni/La2O3-750 ≈ 10Ni/La2O3-850. The excellent activity (100%) of 10Ni/La2O3-450 could be due to the high surface area, basicity strength and concentration of surface oxygen species of the catalyst as evidenced by BET, CO2-TPD and XPS. In addition, to adjust the activity of the catalyst support, the molar ratios of Mg and La were varied (1:1, 3:1, 5:1, 7:1 and 9:1). The 5Ni/5MgLa (5:1 M ratio) was found to be the most active (100%) relative to other Ni/MgLa formulations. Furthermore, the Ni content in the Ni/5MgLa sample was adjusted between 10 and 40 wt%. Increasing the Ni content of the catalysts increased NH3 conversion with the 40 wt% Ni formulation demonstrating complete NH3 conversion at 600 °C and a high gas hourly space velocities (GHSV) (30,000 mL∙h−1∙gcat−1).

Green synthesis of biodiesel from Ricinus communis oil (castor seed oil) using potassium promoted lanthanum oxide catalyst: kinetic, thermodynamic and environmental studies

Large scale production of biodiesel from a lignocellulosic biomass using an efficient heterogeneous catalyst has several benefits like low production cost, reduction in CO2 emission along with other greenhouse gases, agricultural development and assurance of future energy supply. In present study, a solid base catalyst named as potassium (K) promoted lanthanum oxide (La2O3) has been synthesised by sol-gel auto-combustion method (Pechini's method) and introduced in transesterification of castor oil. Synthesized K promoted La2O3 catalyst was characterised by TGA-DTA, FT-IR, XRD, XPS, BET surface area analysis, HRSEM-EDX, Hammett indicator titration for basicity evaluation. Optimum K/La atomic ratio and catalyst activation temperature was investigated in terms of highest activity of the catalyst which was found at 1.5K/La atomic ratio and 900 °C calcination temperature for transesterification of castor oil. The following reaction influencing factors were optimised to be 1:16 oil to methanol molar ratio, 65 °C reaction temperature, 2 wt% catalyst loading, 500 rpm rotating speed of mechanical stirrer, 150 min reaction duration. Maximum 97.5% fatty acid methyl ester (FAME) conversion of castor oil was obtained under optimum circumstances. The product biodiesel was characterized by 1HNMR spectroscopy. Then reusability study and active metal leaching tests were performed simultaneously to find out the reason behind deterioration in activity of the catalyst during recycling process. It was found that the catalyst was efficient to produce 85.3% FAME conversion up to five reaction cycles at optimised reaction condition. The reaction activation energy (Ea) and pre-exponential factor (A) were estimated to be 47.13 kJ/mole and 9.93×105 per min respectively by the study of kinetics and thermodynamics regarding methyl esterification process of castor oil using K promoted lanthanum oxide catalyst. Additionally, the corresponding enthalpy of activation (ΔH#), entropy of activation (ΔS#) and Gibb’s free energy of activation (ΔG#) were evaluated to be 45.27 kJ.mol−1, −142.81 J.mol−1.K−1 and 93.53 kJ.mol−1 accordingly by the mean of Eyring-Polanyi’s plot. Turnover frequency and environmental studies implied that biodiesel production from castor oil using K promoted La2O3 is an efficient and green process.

LaCO3OH Nanoprisms and Their Luminescence and NO Reduction Properties

In this work, single-crystalline large-scale LaCO3OH nanoprism morphologies were synthesized by controlling La and Ca molar ratio and the hydrothermal reaction conditions. The nanoprism morphologies of LaCO3OH were unique in nature with a sharp corner and smooth surfaces. The hydrothermal reaction was carried out in the absence of organic additives or templates and (NH4)2CO3 was used as a precipitation agent. The molar ratio of La:Ca was varied over the following values (the sample shorthand is given in parentheses): 75:25 mol% (LC-1), 50:50 mol% (LC-2), and 25:75 mol% (LC-3). Phase-pure LaCO3OH nanoprisms formed at a La:Ca molar ratio of 75:25 mol% without any assistance of catalysts or template. The photoluminescence (PL) properties of the as-synthesized powders showed one broad emission band centered at 394 nm after excitation of the pure LC-3 LaCO3OH nanoprisms at λ = 280 nm. The PL intensities were decreased in the order of LC-1 < LC-2< LC-3. The LC-1 and LC-2 samples had almost the same PL intensities probably due to their unique and smooth particle morphology. The calcination result of three samples treated for two hours at 800 °C, shows a reduction in NO activities over highly distributed CaO comprising La2O3. Further, under the presence of H2O and O2 vapor, CaO comprising La2O3 catalysts shows higher stability for the reduction of NO with CH4.

Effect of microwave-assisted wet torrefaction on liquefaction of biomass from palm oil and sugarcane wastes to bio-oil and carbon nanodots/nanoflakes by hydrothermolysis and solvothermolysis

This study aimed to produce bio-oils from various lignocellulosic biomass, namely palm empty fruit bunch (EFB), palm fiber (PF), sugarcane bagasse (SB), and sugarcane leaves (SL). Hydrothermal liquefaction, an environmentally benign process, was applied for converting wet bio-resources to bio-oils. The effect of Na2CO3 and La2O3 catalysts were investigated at 300 °C, the results showed higher bio-oil yield from Na2CO3 compared to La2O3. The use of glycerol solvent as a hydrogen donor substantially enhanced bio-oil yield for 300% compared to aqueous solvent. Furthermore, the microwave-assisted wet torrefaction (800 W for 20 min) pretreatment employed for EFB helps to increase aliphatic and aromatic compounds and enhance the light and heavy bio-oils yields to 76.80 wt%. SB and EFB are promising biomass for solvothermolysis liquefaction giving the highest energy ratio. A substantial amount of carbon nanodots and nanoflakes were produced from hydrothermolysis and solvothermolysis liquefaction of EFB with average mean diameters of 49.5 and 100.4 nm, respectively.

Monodisperse mesoporous La2O3 flakes for the synthesis of glycerol carbonate by efficiently catalyzing the transesterification of dimethyl carbonate with glycerol

Monodisperse mesoporous La2O3 flakes were prepared by hydrothermal methods using polyethylene glycol as pore-expanding agent, the catalyst exhibited better catalytic activity than normal La2O3 in the reaction of glycerol and dimethyl carbonate to produce glycerol carbonate. The influence of the molecular weight of polyethylene glycol and the mass ratio of La(NO3)3·6H2O/polyethylene glycol on the catalyst was investigated. The results showed that the morphology of La2O3 was remolded to porous flakes interestingly by the suitable type and dosage of pore-expanding agent, this change made the La2O3 catalyst particles have higher alkalinity, better crystallinity, larger specific surface area and good dispersion, which greatly improved the catalytic performance of the catalyst. In addition, the optimal reaction conditions were studied. As a result, the as-prepared porous La2O3 modified by polyethylene glycol-20000 showed excellent catalytic performance with high glycerol carbonate yield of 99.4% under the optimal reaction conditions as follows: the glycerol/dimethyl carbonate molar ratio was 1:5, the catalyst dosage was 5.0 wt% to glycerol, the reaction temperature was 85 °C and the reaction time was 0.5 h. The catalyst had outstanding stability after six cycle reactions with almost no loss of catalytic activity. Thereby, the catalyst was considered to possess the promising potential in industrial production for catalyzing glycerol to the high value-added chemical glycerol carbonate.

Yttrium Oxide Supported La2O3 Nanomaterials for Catalytic Oxidative Cracking of n-Propane to Olefins

La2O3 nanorods were prepared by simple hydrothermal synthesis method. Yttrium oxide (1, 3, 5 and 7 wt%) supported La2O3 and SO42− incorporated La2O3 nanorods were prepared impregnation method and used as catalysts in oxidative cracking of n-propane. The pure La2O3 nanorods exhibited 15% n-propane conversion with 22% olefins (ethane and propene) selectivity. Considerable improvement in n-propane conversion was observed in case of 3 wt% yttrium oxide supported on La2O3 nanorods (25% conversion of n-propane and 36% selectivity to olefins) at reaction temperature of 550 °C. Interestingly, 5 wt% yttrium oxide supported 10 wt% SO42−/La2O3 nanorod sample exhibited superior performance in n-propane conversion (42%) and olefins selectivity (54%). The yttrium oxide loading and sulfation of La2O3 nanorods influenced the catalytic activity. The characterization of synthesized nanomaterials was performed using elemental analysis, XRD, FT-IR, N2-physisorption, SEM, XPS and H2-TPR techniques. The obtained results indicated that yttrium oxide was highly dispersed over the La2O3 nanorods because of strong interaction between the two rare earth metal oxides. Additionally, deposition of yttrium oxide to sulfated La2O3 nanorods increased the surface area and the amount of Lewis acid sites (for the activation of n-propane) on La2O3 nanorods. Yttrium oxide supported sulfated La2O3 catalyst showed no deactivation during the 24 h of reaction and without coke formation.

Unravel the surface active sites on Cu/MgLaO solid base catalyst by DRIFT spectroscopy and adsorption techniques for the synthesis of triazoles by click reaction

Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy explored the surface basicity of Cu supported on MgO, La2O3 and MgLaO catalysts in the Click reaction of aryl alkyne and aryl azide for the synthesis of substituted triazoles by using formic acid as a probe. Ionic copper in combination with surface basic sites played a prominent role for a high rate of the desired product over 5 wt%Cu/MgLaO catalyst at 70 °C and water as solvent in the absence of a base. A structure-activity correlation established for the Click reaction using in situ DRIFT spectroscopy and based on the Brunauer–Emmett–Teller (BET) surface area, X-ray diffraction (XRD), H2- temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), N2O titration and temperature programmed desorption (TPD) of CO2 analyses plausible reaction mechanism was established. The bulk and surface properties of the recovered 5 wt%Cu/MgLaO revealed that the catalyst was stable even after 4 recycles.

Highly Loaded Mesoporous Ni–La2O3 Catalyst Prepared by Colloidal Solution Combustion Method for CO2 Methanation

Highly dispersed Ni-based catalysts for CO2 methanation have been extensively studied over the last decade. However, a highly loaded Ni-based catalyst always results in a large Ni particle size and poor CO2 methanation activity. In this work, a colloidal solution combustion method was used to prepare a highly loaded Ni–La2O3 catalyst (50 wt % Ni) with a small Ni particle size and abundant metal–support interface. The characterizations demonstrated that a Ni–La2O3 catalyst prepared in this way has a mesoporous structure and a small Ni particle size. Due to the small Ni particle size and abundant metal–support interface, the highly loaded mesoporous Ni–La2O3 catalyst exhibits higher activity and selectivity in CO2 methanation compared to the Ni–La2O3 catalyst prepared by a conventional solution combustion method.

Uncertainty analysis of environmental sustainability of biodiesel production using Thai domestic rare earth oxide solid catalysts

Life Cycle Assessment (LCA) is increasingly used as a valuable tool to evaluate and assess the environmental profile of rare earth element (REE) production due to rapid growth in the application of these elements. Rare earth elements including cerium (CeO2), lanthanum (La2O3) and neodymium (Nd2O3) oxides were synthesized by the decomposition of Thai monazite ore using the alkali method following the solvent extraction process. The rare earth oxides (REOs) were utilized as catalysts for biodiesel production of palm oil with methanol. LCA methodology is applied to evaluate the environmental impact of biodiesel production using REO catalysts in terms of the potential for global warming, abiotic deletion, acidification, human toxicity, and eutrophication. This study applied statistical methods to LCA models to analyse uncertainty in the production system. The LCA results show that La2O3 catalyst production has lower environmental impact than the production of the other synthesized catalysts. The environmental impact from cradle-to-gate biodiesel production using the La2O3 catalyst is better than the other options in terms of all impact categories. In cradle-to-grave, the global warming potential of the studied biodiesel process is lower than that of conventional diesel by 1.22–1.67 times due to its lower CO2 emissions. The effect of key environmental benefit obtained from biodiesel production using the REO catalysts is avoidance of CO2 emissions from combustion because of its biogenic origin. Uncertainty analysis of the LCIA showed that the biodiesel–La2O3 has 100% probability of lower environmental values than the biodiesel–CeO2 and biodiesel–Nd2O3. The LCA results are expected to aid the improvement of the environmental performance of REE production and the biodiesel process using the catalysts in Thailand and provide transparent data for government plans.

Understanding of binding energy calibration in XPS of lanthanum oxide by in situ treatment.

Rare earth oxides have seen increased usage over the years in batteries and catalysts. Due to their unique electronic properties, they are the subject of fundamental and practical interest. However, the complexity in their electronic structures makes unambiguous characterization, such as X-ray photoelectron spectroscopy (XPS), very challenging. Lanthanum oxide (La2O3) has attracted special attention as a promising catalyst for the oxidative coupling of methane (OCM) reaction. In this work, a new and reliable way of XPS calibration is developed by applying various in situ preparations for a nanorod La2O3 catalyst to intentionally form different lanthanum compounds, followed by XPS characterization and corroboration with first principles calculations. To form different compounds, five sample treatments were performed including heating in vacuum and treatment with O2, CH4, CO2, and H2O, which are all relevant to OCM reaction conditions. Adventitious carbon or lattice oxygen, as conventional calibration standard species for energy scale, is only suitable for one or few in situ prepared surfaces. Our results also clearly demonstrate the vital difference between performing the ex situ analysis after exposure of the sample to the atmosphere and the in situ analysis. By carefully comparing the spectra of various photoemission peaks of different compounds, we conclude that the binding energy of 102.2 eV for the La 4d7/2 peak can be used as the internal calibration standard for all considered samples. Furthermore, different oxygen species were unambiguously identified by matching the oxygen 1s binding energies from the in situ measurements and first principles predictions.

Ir-Based Bimetallic Catalysts for Hydrogen Production through Glycerol Aqueous-Phase Reforming

Iridium, Iridium-Nickel and Iridium-Copper catalysts were prepared by incipient wetness impregnation and evaluated in the aqueous-phase reforming of glycerol using La2O3 or CeO2 as supports. The catalysts were characterized by N2 physisorption, XRD, H2-TPR, XPS, and EDS. The reactions were carried out in a fixed bed reactor feeding a solution of glycerol (10 wt %) in water, at 270 °C and 58 bar. All IrNi catalysts showed higher activity than Ir and IrCu, and in general, La2O3 catalysts showed a better performance when compared to CeO2 catalysts. The highest hydrogen production yield was reached by bimetallic IrNi catalysts with over 250 µmol min−1 gcat−1 for La2O3 and 150 µmol min−1 gcat−1 for CeO2.

Online Kinetics Study of Oxidative Coupling of Methane over La2O3 for Methane Activation: What Is Behind the Distinguished Light-off Temperatures?

Oxidative coupling of methane (OCM) is a catalytic partial oxidation process that converts methane directly to valuable C-2 products (ethane and ethylene). The main difficulties from further investigation of this reaction are due to the nature of its high operating temperature and the severe reaction exothermicity. In this work, an especially designed online characterization setup is applied for this reaction, which achieved both precise bed temperature control and real-time product measurement. High-resolution temperature-dependent product rates of OCM (CO2, ethane, and ethylene) were obtained, and their behavior vs reaction conditions as well as the activation energy barriers above their onset temperatures are clearly differentiated over a recently reported high performance nanorod La2O3 catalyst. Different from general expectation, CO2, resulting from full methane oxidation, dominates all the products in the lower temperature region, whereas the C-2 species are only formed at much higher temperatures. Further analysis indicates that the selectivity and apparent activation energy for both COx and C-2 products are strongly influenced by the oxygen concentration and temperature. In combination with density functional theory calculations and additional experimental measurements, significant insights are brought to this high-temperature reaction of wide interest.

Synthesis, characterization and catalytic activity studies of lanthanum oxide from Thai monazite ore for biodiesel production

Abstract Rare earths in Thai monazite ore were separated by chemical process following purification by an ion exchange process technique. They were utilized as raw materials to synthesize solid catalysts for the production of biodiesel. The novel solid catalysts were prepared by the simple oxalic acid precipitation method. The prepared CeO2, La2O3 and Nd2O3 catalysts were employed to catalyze transesterification of palm oil and methanol. They showed high catalytic activity with FAME content over 95%. The catalytic performance of the best available La2O3 catalyst was additionally investigated. It was found that the initial transesterification rate catalyzed by the synthesized La2O3 catalyst was three times higher than its commercial counterpart, which related to its basic strength, high crystallinity, large pore volume and great crystallite size. The highest FAME content of 95% was achieved within 45 min under the optimal conditions of 200 °C reaction temperature, 39 bar reaction pressure, 1:30 molar ratio of oil to methanol, 10 wt% catalyst loading and 600 rpm stirring rate. In addition, the novel La2O3 catalyst was observed to be stable even after four recycle runs with insignificant loss of catalytic activity.