CO2 Temperature-programmed Desorption Research Articles

Tuning the interfacial sites between copper and metal oxides (Zn, Zr, In) for CO2 hydrogenation to methanol

The influence of different metal oxides (ZnO, ZrO2, In2O3) in CO2 hydrogenation to methanol over Cu-based catalysts was studied. The catalysts were characterized using x-ray diffraction (XRD), thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), N2-physisorption, N2O chemisorption, H2 temperature-programmed reduction (H2-TPR), and CO2 temperature-programmed desorption (CO2-TPD). It was found that impregnating ZrO2 onto Cu/ZnO enhances the methanol formation rate from 14.7 mmol∙gcat−1∙h−1 to 15.6 mmol∙gcat−1∙h−1 (230 °C, 30 bar, 38 000 cm3/(gcat h)), which is attributed to the formation of Cu-ZrO2 sites. The results also indicate that In-doping of the Cu-based catalysts generates CuxIny alloys, which seems to inhibit the active sites on the Cu surface. However, new sites for methanol synthesis are present when Cu/ZrO2/In2O3 is prepared by co-precipitation. This is attributed to In-Zr mixed oxide species that increases the methanol formation rate from 53.2 mmol∙gcat−1∙h−1 to 60.5 mmol∙gcat−1∙h−1 (270 °C, 30 bar, 140 000 cm3/(gcat h)).

Interaction of CO with Pt nanoclusters on a graphene-covered Ru(0001) surface.

The adsorption of CO on Pt nanoclusters on a single layer of graphene epitaxially grown on the Ru(0001) surface [Gr/Ru(0001)] was studied with reflection absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD). The graphene layer was grown through exposure to ethylene using a method that has previously been shown to completely cover the surface. As CO adsorbs on Ru(0001) but not on graphene, the complete coverage of the Ru(0001) surface by graphene was verified with TPD as no CO adsorption was detectable. Previous work has demonstrated that Pt nanoclusters nucleate in the moiré unit cells of the Gr/Ru(0001) surface. Exposure of the Pt/Gr/Ru(0001) surface to CO gives rise to strong RAIRS peaks at 2065-2085 cm-1 assigned to CO at Pt atop sites and at 1848 cm-1 due to CO at Pt bridge sites. The CO TPD peak areas were used to quantify the CO coverage, which allowed for the determination of the RAIRS peak areas per CO molecule. It was found that the RAIRS intensity for CO on Pt/Gr/Ru(0001) is as much as nine times the intensity of CO on Ru(0001) on a per molecule basis. A more modest intensity enhancement was observed compared to CO on Pt islands on the Ru(0001) surface.

Easily Recycled CuMgFe Catalysts Derived from Layered Double Hydroxides for Hydrogenolysis of Glycerol

A series of CuMgFe catalysts with different (Cu + Mg)/Fe molar ratios derived from hydrotalcites were prepared by coprecipitation for the hydrogenolysis of glycerol to 1,2-propanediol (1,2-PDO). X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), vibrating sample magnetometer (VSM), hydrogen temperature-programmed reduction (H2-TPR), CO2-TPD, and H2-TPD (temperature-programmed desorption of CO2 and H2) were used to investigate the physicochemical properties of the catalysts. The CuMgFe-layered double oxides (CuMgFe-4LDO) catalyst with (Cu + Mg)/Fe molar ratio of 4 exhibited superior activity and stability. The high glycerol conversion and 1,2-propanediol selectivity over CuMgFe-4LDO catalyst were attributed to its strong basicity, excellent H2 activation ability, and an increase in the surface Cu content. The CuMgFe catalysts could be easily recycled with the assistance of an external magnetic field due to their magnetism.

Direct Conversion of Syngas to Light Olefins through Fischer-Tropsch Synthesis over Fe-Zr Catalysts Modified with Sodium.

Fe–Zr–Na catalysts synthesized by coprecipitation and impregnation methods were implemented to investigate the promoting effects of Na and Zr on the iron-based catalyst for high-temperature Fischer–Tropsch synthesis (HTFT). The catalysts were characterized by Ar adsorption–desorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, CO temperature-programmed desorption, H2 temperature-programmed desorption, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy (MES). The results indicated that Na changed the active sites on the catalyst surface for the CO and hydrogen adsorption, owing to the electron migration from Na to Fe atoms, which resulted in an enhanced CO dissociative adsorption and a decrease in hydrogen adsorption on the metallic Fe surface. The decreased H/C ratio on the catalyst surface accounted for the increased chain propagation and weakened hydrogenation of light olefins. Besides, Na could also facilitate the carbonization of catalysts and protect the iron carbide against oxidation, which provides more active sites for HTFT reaction and is beneficial to the C–C coupling. Zr could decrease the hematite crystallite size and stabilize the active phase to improve the HTFT activity. At an optimal Na loading of 1.0 wt %, the Fe–Zr–1.0Na catalyst exhibited the highest light olefin selectivity of 35.8% in the hydrocarbon distribution at a CO conversion of 95.2%.

Au-Modulated Z-Scheme CuPc/BiVO4 Nanosheet Heterojunctions toward Efficient CO2 Conversion under Wide-Visible-Light Irradiation

Unraveling the sluggish charge separation, insufficient catalytic sites, and limited visible-light absorption for Z-scheme heterojunction photocatalysts still remains a great challenge toward CO2 conversion. Herein, ultrafine Au-modulated copper phthalocyanine/BiVO4 nanosheet heterojunctions (CuPc/Au-BVNS) with wide-visible-light responses have been successfully fabricated as efficient photocatalysts for CO2 conversion to CO, achieving 9-time and 35-time photoactivity improvement compared to pristine BVNS (ca. 5 nm) and the previously reported BiVO4 nanoflake (ca. 15 nm), respectively. The exceptional photoactivity is mainly attributed to the ultrafine Au interfacial modulation, which is well capable of inducing the directional electron migration of BVNS and the highly dispersed CuPc assembly with the increased loading amount, synergistically strengthening the Z-scheme charge transfer and separation mainly based on the surface photovoltage spectroscopy assisted with the monochromatic beam and electron paramagnetic resonance technique. Moreover, the in situ diffuse reflectance infrared Fourier transform spectroscopy, CO2 temperature-programmed desorption measurement, and electrochemical results demonstrate that the central metal Cu2+ in the high-dispersion CuPc exhibits potential catalytic functions for CO2 reduction, much superior to other metals in MPc (M = Co and Ni)-modified ones. This work highlights the importance of strengthening artificial Z-scheme charge transfer and provides new strategies for designing BiVO4-based heterojunctions by controllably assembling MPc toward efficient solar-driven CO2 conversion.

Efficient Synthesis of Methyl Methacrylate by One Step Oxidative Esterification over Zn-Al-Mixed Oxides Supported Gold Nanocatalysts

Methyl methacrylate (MMA) is an important monomer in fine chemicals. The synthesis of MMA by one-step oxidative esterification from methacrolein with methanol over a heterogeneous catalyst with high activity, selectivity and stability is highly desirable. Herein, Zn-Al-hydrotalcites (HTs)-supported atomically precise Au25 nanoclusters with different molar ratios of Zn2+/Al3+ were prepared and used as the precursors for this reaction. They exhibited good performances in comparison with the gold catalysts prepared by the deposition precipitation method. The structural and electronic properties were evaluated by various characterization technologies, including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) of CO adsorption, X-ray photoelectron spectroscopy (XPS), and CO2 temperature-programmed desorption (TPD). The combined characterization results suggested that the adsorption property of gold and the basicity of the catalyst contributes to their high activities. Substrates extended experiments and stability tests implied the potential application of Zn-Al-mixed oxides supported gold catalysts, which paves a new way for supported gold catalyst in the one-step oxidation esterification reaction.

Carbon Monoxide Oxidation over Gold Nanoparticles Deposited onto Alumina Film Grown on Mo(110) Substrate: An Effect of Charge Tunneling through the Oxide Film.

Formation of gold nanosized particles supported by aluminum oxide film grown on Mo(110) substrate and oxidation of carbon monoxide molecules on their surface have been in-situ studied in ultra-high vacuum by means of Auger electron spectroscopy (AES), reflection-absorption infrared spectroscopy (RAIRS), low energy electron diffraction (LEED), atomic force microscopy (AFM), temperature-programmed desorption (TPD), and work function measurements. The main focus was to follow how the thickness of the alumina film influences the efficiency of CO oxidation in an attempt to find out evidence of the possible effect of electron tunneling between the metal substrate and the Au particle through the oxide interlayer. Providing the largest degree of surface identity of the studied metal/oxide system at different thicknesses of the alumina film (two, four, six, and eight monolayers), it was found that the CO oxidation efficiency, defined as CO2 to CO TPD peaks intensity ratio, exponentially decays with the oxide film thickness growth. Taking into account the known fact that the CO oxidation efficiency depends on the amount of excess charge acquired by Au particle, the latter suggests that electron tunneling adds efficiency to the oxidation process, although not significantly.

Highly active carbon nanotube–promoted Rh-Mn-Li/SiO2 catalysts for the synthesis of C2+ oxygenates from syngas

The effect of carbon nanotubes on the catalytic properties of Rh-Mn-Li/SiO2 catalysts was investigated for CO hydrogenation. The catalysts were comprehensively characterized by means of X-ray power diffraction, N2 sorption, transmission electron microscope, H2–temperature-programmed reduction, CO–temperature-programmed desorption, temperature-programmed surface reaction, and X-ray photoelectron spectroscopy. The results showed that an appropriate amount of carbon nanotubes can be attached to the surface of the SiO2 sphere and can improve the Rh dispersion. Moderate Rh-Mn interaction can be obtained by doping with the appropriate amount of carbon nanotubes, which promotes the formation of strongly adsorbed CO and facilitates the progress of CO insertion, resulting in the increase in the selectivity of C2+ oxygenate synthesis.

Oxygen vacancy enhancing CO2 electrochemical reduction to CO on Ce-doped ZnO catalysts

Oxygen vacancy defect engineering is currently an effective strategy to enhance the performance of electrocatalytic CO2 reduction to CO. In our work, ZnO with oxygen vacancies defects by Ce3+ doping were obtained through solvothermal method. The oxygen vacancies defects concentration could be controlled by varying the Ce3+ dopant concentration, which initially increased then decreased. And the CO2ER performance of as-prepared samples is found to be closely dependent with the concentration of oxygen vacancy in the as-prepared CexZn1-xO. The optimized CO2ER to CO performances can be obtained from Ce0.016Zn0.984O with the highest oxygen vacancy concentrations, which exhibited the highest performance (current density 24 mA cm−2 and Faradaic efficiency 88% for CO) at -1.0 V versus RHE. Through CO2 isotherm adsorption curve and CO2 temperature-programmed desorption (CO2-TPD) test, it was proved that the high concentration oxygen vacancy of Ce0.016Zn0.984O was beneficial to improve the CO2 adsorption and activation. This study proposes a strategy aimed at obtaining a high-performance catalyst for electrocatalytic CO2 reduction by adjusting the concentration of oxygen vacancies.

Screening of commercial catalysts for steam reforming of olive mill wastewater

Olive mill wastewater (OMW) is a pollutant effluent of the olive oil production. To reduce the environmental impact of this agro-industrial sector, with simultaneous valorization of such waste, the steam reforming of OMW was studied in this work. Besides the reduction of pollution resulting from OMW, the process allows producing “green” H2. In this study, several commercial catalysts (Ni-, Cu–Zn- and noble metal-based) were tested to compare their performances. A catalytic screening study with all the commercial catalysts was performed, and stability tests were conducted with the material that demonstrated higher activity (Rh-based catalyst). The physicochemical characterization of the fresh and spent materials was realized through several techniques (temperature-programmed reduction, temperature-programmed oxidation, transmission electron microscopy, temperature-programmed desorption of CO2, temperature-programmed desorption of NH3, chemisorption of H2, scanning electron microscopy with energy dispersive spectroscopy and physical adsorption of N2 at −196 °C). Although there are some materials with good catalytic performance, the Rh-based sample stood out during the tests, exhibiting high catalytic activity and high stability: at 400 °C the H2 yield (over 9 molH2·molOMW−1) and total organic carbon (TOC) conversion (>98%) were high along all the 24 h of the stability test.

Use of Ni-Containing Catalysts for the Olive Mill Wastewater Steam Reforming

The olive oil mill wastewater (OMW) is a by-product (with a high organic load) derived from the production of the olive oil. The OMW steam reforming (OMWSR) process was studied herein, aiming to decrease the environmental damage of such effluents; simultaneously, the waste is economically and energetically valorized with the H2 production. Several Ni-containing catalysts were prepared and tested to compare their performances for the OMWSR using a synthetic OMW effluent; still, stability tests were also carried out. The materials were extensively characterized: thermogravimetric analysis, temperature-programmed oxidation/reduction, temperature-programmed desorption of CO2 /NH3, chemisorption of H2, inductively coupled plasma optical emission spectrometry and physical adsorption-desorption of N2 at -196 oC. Amongst the materials tested, the Ni-Ru/SiO2 sample stood out, exhibiting high catalytic performance: at 400 oC, the H2 yield (> 8 molH2·molOMW) and conversion of total organic carbon (≈ 75 %) were high during all the 24 h of the long-term test, with only a small deactivation being noticed.

Effect of alkali (Cs) doping on the surface chemistry and CO2 hydrogenation performance of CuO/CeO2 catalysts

The reaction of captured carbon dioxide with renewable hydrogen towards the eventual indirect production of liquid hydrocarbons via CO2 reduction to CO (reverse water-gas shift reaction, rWGS) is a promising pathway in the general scheme of worldwide CO2 valorization. Copper-ceria oxides have been largely employed as rWGS catalysts owing to their unique properties linked to copper-ceria interactions. Here, we report on the fine-tuning of CuO/CeO2 composites by means of alkali promotion. In particular, this work aims at exploring the effect of cesium doping (0–4 atoms Cs per nm2) on co-precipitated CuO/CeO2 catalysts under CO2 hydrogenation conditions. The as-prepared samples were characterized by N2 physisorption, X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), CO2-temperature programmed desorption (CO2-TPD), Fourier-transform infrared spectroscopy (FTIR) of pyridine adsorption and CO-diffuse reflectance Fourier-transform infrared spectroscopy (CO-DRIFTS). The results demonstrated that a low amount of Cs exerted a beneficial effect on CO selectivity, inhibiting, however, CO2 conversion. Specifically, a doping of 2 atoms Cs per nm2 offers > 96 % CO selectivity and equilibrium CO2 conversion at temperatures as low as 430 °C, whereas further increase in cesium loading had no additional impact. The present findings can be mainly interpreted on a basis of the alkali effect on the textural and acid/base properties; Cs doping results in a significant reduction of the surface area and thus to a lower population of active sites for CO2 conversion, whereas it enhances the formation of basic sites and the stabilization of partially reduced Cu+ species, favoring CO selectivity.

Sol-gel synthesis of nanocrystalline MgO and its application as support in Ni/MgO catalysts for ethanol steam reforming

This work reports the improved catalytic activity of nickel catalysts supported on nanocrystalline magnesium oxide prepared by a sol–gel method, using Pluronic P123 as a structure-directing agent for pore formation. The presence of Pluronic also provided a reduction of the magnesium oxide crystallite size from 54 to 18 nm, as well as the attainment of small supported metallic nickel particles. In situ X-ray diffraction was used to assess the structural evolution of the materials during activation, followed by X-ray absorption spectroscopy, N2 physisorption isotherms, transmission electron microscopy, and temperature-programmed CO2 desorption. The materials synthesized with the surfactant presented heightened activity in the ethanol steam reforming reaction. The long-term stability of the catalysts was improved, due to the decrease the coke formation, with the catalyst prepared using surfactant developing less deactivating coke.

Effect of EDTA-2Na modification on Fe-Co/Al2O3 for hydrogenation of carbon dioxide to lower olefins and gasoline

Capturing and utilization of carbon dioxide (CO2) not only leads to effective use of carbon resources, but also alleviates environmental pollution caused by increasing concentration of CO2, thus making it a hot research topic in recent years. In this study, a series of highly dispersed iron-cobalt (Fe-Co) catalysts was prepared by ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) modification, which could efficiently convert CO2 into high value-added chemicals (C2-C4= and C5-C11). X-ray diffraction (XRD) analysis showed that the addition of a small amount of Co and EDTA-2Na contributed to enhance the sintering resistance of Fe species. During the calcination process, EDTA4− can be decomposed into small organic molecules with reducibility, thus promoting the reduction of iron species. The CO temperature-programmed desorption (CO-TPD) results showed that cobalt enhanced the adsorption and activation of intermediate CO on NaxFe-Co catalyst, thereby promoting the catalytic conversion of CO2. The complexation of EDTA promotes the synergistic effect of Fe-Co bimetals, enhances the chemical adsorption of CO2. Sodium in EDTA-2Na promotes the surface basicity of the catalysts, which is favored for improving the product distribution of hydrocarbons. At lower H2/CO2 (1/1) ratio, the EDTA-2Na modified Fe-Co/Al2O3 catalyst exhibited high conversion of CO2 (32.8 %) and excellent selectivity toward high value-added chemicals. The selectivity of by-product CO was only 8.1 %; and C2-C4= (32.5 %) and C5-C11 (46.3 %) accounted for ∼79 % selectivity among the hydrocarbons generated.

Steam reforming of ethanol over copper-zirconia based catalysts doped with Mn, Ni, Ga

The activity toward hydrogen production in steam reforming of ethanol (SRE) reaction has been evaluated for CuO/ZrO2 catalysts doped with Mn, Ni, Ga at 350 °C. The copper based catalysts were synthesised by co-precipitation method at constant pH = 7 and fixed (wt.%) CuO/ZrO = 2.3. The catalysts were characterised by means of N2 adsorption, temperature programmed reduction (H2-TPR), N2O dissociative chemisorption, X-ray diffraction (XRD), CO2 temperature programmed desorption (CO2-TPD), and temperature programmed oxidation (TPO). It has been found that copper based catalysts exhibit high ethanol conversion in SRE (>86%) at 350 °C. Due to basic character of catalysts, the formation of acetaldehyde is observed. The CuO/ZrO2 catalyst modification with dopants increases the hydrogen yield with maximum (52%) for CuO/ZrO2/NiO. The addition of Ni changes the distribution of carbon-containing products. In this case, the increase in selectivity to CO, CO2 and CH4 is observed whereas selectivity to acetaldehyde is significantly decreased. This shows that presence of Ni facilities the C–C bond cleavage. On the other hand, the formation of acetic acid is limited upon addition of Mn and Ga. For all modified catalysts, decrease in carbon deposition rate during SRE is pronounced according to TPO experiments. The modification of Cu/Zr with Mn, Ni and Ga causes the decrease in copper particle size, which hinders the carbon deposit formation.

K-Modified Co–Mn–Al Mixed Oxide—Effect of Calcination Temperature on N2O Conversion in the Presence of H2O and NOx

The effect of calcination temperature (500–700 °C) on physico-chemical properties and catalytic activity of 2 wt. % K/Co-Mn-Al mixed oxide for N2O decomposition was investigated. Catalysts were characterized by inductively coupled plasma spectroscopy (ICP), X-ray powder diffraction (XRD), temperature-programmed reduction by hydrogen (TPR-H2), temperature-programmed desorption of CO2 (TPD-CO2), temperature-programmed desorption of NO (TPD-NO), X-ray photoelectron spectrometry (XPS) and N2 physisorption. It was found that the increase in calcination temperature caused gradual crystallization of Co-Mn-Al mixed oxide, which manifested itself in the decrease in Co2+/Co3+ and Mn3+/Mn4+ surface molar ratio, the increase in mean crystallite size leading to lowering of specific surface area and poorer reducibility. Higher surface K content normalized per unit surface led to the increase in surface basicity and adsorbed NO per unit surface. The effect of calcination temperature on catalytic activity was significant mainly in the presence of NOx, as the optimal calcination temperature of 500 °C is necessary to ensure sufficient low surface basicity, leading to the highest catalytic activity. Observed NO inhibition was caused by the formation of surface mononitrosyl species bonded to tetrahedral metal sites or nitrite species, which are stable at reaction temperatures up to 450 °C and block active sites for N2O decomposition.

Methane dry reforming over nickel-based catalysts: insight into the support effect and reaction kinetics

The nickel-based catalysts supported on MgO-modified α-Al2O3, CeO2, and SBA-15 were prepared by impregnation method and investigated by N2 physisorption measurements, powder X-ray diffraction, Raman spectroscopy, H2 temperature-programmed reduction, CO2 temperature-programmed desorption, and transmission electron microscopy. Investigation of the kinetics of the dry reforming of methane (DRM) was carried out in gradientless circulating micro-flow system at atmospheric pressure and temperature range of 600–800 °C. The results showed that carriers have a prominent role in characterising the physico-chemical properties of catalysts such as specific surface area, dispersity of active metal, reducibility and basicity that greatly affect the adsorption feature and activity of NiO catalyst. However, the kinetic equation of DRM on three catalysts was found to be written by a common fractional equation, following a dual-site Langmuir–Hinshelwood Hougen Watson model. The order in the catalyst reducibility and apparent rate constant was observed as follows: NiMg/Al<Ni/Ce<Ni/SBA, while the apparent activation energy (E) is in the opposite order. The highest activity was observed on the catalyst containing 31.2 wt% Ni supported on SBA-15.

Zn-Al Mixed Oxides Decorated with Potassium as Catalysts for HT-WGS: Preparation and Properties

A set of ex-ZnAl-LDHs catalysts with a molar ratio of Zn/Al in the range of 0.3–1.0 was prepared using co-precipitation and thermal treatment. The samples were characterized using various methods, including X-ray fluorescence spectroscopy (XRF), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy FT-IR, N2 adsorption, Temperature-programmed desorption of CO2 (TPD-CO2) as well as Scanning electron microscopy (SEM-EDS). Catalyst activity and long-term stability measurements were carried out in a high-temperature water–gas shift (HT-WGS) reaction. Mixed oxide catalysts with various Zn/Al molar ratios decorated with potassium showed high activity in the HT-WGS reaction within the temperature range of 330–400 °C. The highest activity was found for the Zn/Al molar ratio of 0.5 corresponding to spinel stoichiometry. However, the catalyst with a stoichiometric spinel molar ratio of Zn/Al (ZnAl_0.5_K) revealed a higher tendency for surface migration and/or vaporization of potassium during overheating at 450 °C. The correlation of the activity results and TPD-CO2 data show that medium basic sites enhance the progress of the HT-WGS reaction.

Hydrogen production over Fe enriched porous clay-based nanocomposites and mesoporous silica in bio-ethanol reforming – The role of the clay component

Embedded catalysts, featuring Fe species on the surface of Porous Clay derived Heterostructures (PCH) and mesoporous silica (SBA-15 or MMS type) were developed. Two different methods of iron deposition were applied, affecting different activity in steam reforming of ethanol. The nature and distribution of nanostructured Fe-O moieties formed on the surface of porous supports and the role of clay component in H2 production were investigated by X-ray diffraction (XRD) method, scanning electron microscopy (SEM), temperature-programmed reduction with the hydrogen (H2-TPR), CO2 temperature-programmed desorption (CO2-TPD), and advanced X-ray photoelectron spectroscopy (XPS) and 57Fe Mössbauer spectroscopy (MS). The speciation of Fe moieties in the function of Fe interaction with the support entailed the creation of nanostructured catalysts active in H2 production. Dispersion of the Fe species on the surface of mesoporous silica promoted the dehydration of ethanol to ethylene occurring on the developed acidic sites. The formation of iron oxide nanocrystals was beneficial for H2 production. The introduction of amorphous silica between the layers of Laponite (Lap) in PCH composite resulted in the developing of a flexible base for the embedding of active centres, available to reagents and highly selective to H2. The composition and the basic nature of the Lap in Fe-PCH composites contributed to the increase of H2 content in the reaction products. The applied treatment forced the migration of MgII from the octahedral sheet of Laponite to the PCH surface. The developed Mg entities influenced the basicity of the PCH surface shifting the reaction balance towards hydrogen formation, limiting the dehydration of ethanol to ethylene – the precursor of coke deposits.

Ammonia synthesis over lanthanoid oxide–supported ruthenium catalysts

Ammonia synthesis catalysts with high activity under mild reaction conditions for use in synthetic chemical processes powered by renewable energy are needed. Here, we investigated the physicochemical properties and ammonia synthesis activity of lanthanoid oxide–supported Ru catalysts. The basicity of the Ru/lanthanoid oxide catalysts, as estimated by CO2 temperature-programmed desorption, was higher than that of Ru/MgO, a representative catalyst with high ammonia synthesis activity, and a positive relationship was observed between basicity and turnover frequency. The turnover frequency of Ru/Pr2O3 and Ru/La2O3 (both 0.24 s−1) was eight times that of Ru/MgO (0.03 s−1). A kinetic analysis revealed that hydrogen poisoning, which is a typical drawback of oxide-supported Ru catalysts, was markedly retarded in the Ru/lanthanoid oxide catalysts. As a result, the ammonia synthesis rate of the Ru/Pr2O3 catalyst increased with increasing reaction pressure, reaching 49 mmol g−1 h−1 at 400 °C and 1.0 MPa, which was 12 times that of Ru/MgO under the same conditions.