Effect of alkaline earth promoters (MgO,CaO, and BaO) on the activity and coke formation of Ni catalysts supported on nanocrystalline Al2O3 in dry reforming of methane

Ni/Al₂O₃ promoted catalysts with alkaline earth metal oxides (MgO, CaO, and BaO) were prepared and employed in dry reforming of methane (DRM). The catalysts were prepared by impregnation method and characterized by XRD, BET, TPR, TPO, and SEM techniques. The obtained results showed that the addition of MgO, CaO, and BaO as promoter decreased the surface area of catalysts (S_BET). The catalysis results exhibited that adding alkaline earth promoters (MgO, CaO, and BaO) enhanced the catalytic activity and the highest activity was observed for the MgO promoted catalyst. TPR analysis showed that addition of MgO increased the reducibility of nickel catalyst and decreased the reduction temperature of NiO species. The TPO analysis revealed that addition of promoters decreased the amount of deposited coke; and among the studied promoters, MgO has the most promotional effect for suppressing the carbon formation. SEM analysis confirmed the formation of whisker type carbon over the spent catalysts.     

Surface Properties of CaO (or BaO)–La2O3–MgO Catalysts and Their Performance in Oxidative Coupling of Methane

CaO–La₂O₃–MgO and BaO–La₂O₃–MgO catalysts with different compositions have been studied for their bulk and surface properties (viz. crystal phases, surface area, acidity/acid strength distribution, basicity/base strength distribution, etc.) and catalytic activity/selectivity in the oxidative coupling of methane (OCM) at different processing conditions (reaction temperature, 700–850°C; CH₄/O₂ ratio in feed, 3·0, 4·0 and 8·0 and GHSV, 102000 and 204000 cm³ g⁻¹ h⁻¹). The surface acidity and strong basicity of La₂O₃–MgO are found to be increased due to the addition of a third component (CaO or BaO), depending upon its concentration in the catalyst. The addition of CaO or BaO to La₂O₃–MgO OCM catalyst causes a significant improvement in its performance. Both the CaO- and BaO-containing catalysts show a high activity and selectivity at 800°C, whereas, the activity and selectivity of BaO-containing catalysts at 700°C is lower than that of CaO-containing catalysts. © 1997 SCI.     

Effects of Ga doping on Pt/CeO2‐Al2O3 catalysts for propane dehydrogenation

This paper describes catalytic consequencesThis paper describes catalytic consequences of Pt/CeO₂‐Al₂O₃ catalysts promoted with Ga species for propane dehydrogenation. A series of PtGa/CeO₂‐Al₂O₃ catalysts were prepared by a sequential impregnation method. The as‐prepared catalysts were characterized employing N₂ adsorption‐desorption, X‐ray diffrtaction, temperature programmed reduction, O₂ volumetric chemisorption, H₂‐O₂ titration, and transmission electron microscopy. We have shown that Ga³⁺ cations are incorporated into the cubic fluorite structure of CeO₂, enhancing both lattice oxygen storage capacity and surface oxygen mobility. The enhanced reducibility of CeO₂ is indicative of higher capability to eliminate the coke deposition and thus is beneficial to the improvement of catalytic stability. Density functional theory calculations confirm that the addition of Ga is prone to improve propylene desorption and greatly suppress deep dehydrogenation and the following coke formation. The catalytic performance shows a strong dependence on the content of Ga addition. The optimal loading content of Ga is 3 wt %, which results in the maximal propylene selectivity together with the best catalytic stability against coke accumulation. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4365–4376, 2016     

Promoted Fe2O3‐Al2O3‐CuO Chromium‐Free Catalysts for High‐Temperature Water‐Gas Shift Reaction

Promoted Fe₂O₃‐Al₂O₃‐CuO (FAC) chromium‐free catalysts were prepared for high‐temperature water‐gas shift reactions and characterized by X‐ray diffraction (XRD), Brunauer‐Emmett‐Teller method (BET), temperature‐programmed reduction (TPR), and transmission electron microscopy (TEM) techniques. The catalytic results revealed that among the investigated promoted catalysts with Ce, La, Zn, Y, and Mn as promoters, the Mn‐promoted sample showed higher activity compared to the other promoted catalysts. Increasing the Mn content improved the surface area and catalytic activity. The FAC catalyst promoted with a high Mn content exhibited maximum activity and relatively high stability in high‐temperature water‐gas shift reaction.     

β‐Nucleation of pimelic acid supported on metal oxides in isotactic polypropylene

To investigate the nucleation of metal pimelate for isotactic polypropylene (iPP) crystallization, iPP filled with a series of metal oxides with and without metal pimelate on their surface was prepared. There was a chemical reaction between pimelic acid (PA) and metal oxides MgO, CaO, BaO or ZnO, but not TiO₂. The corresponding metal pimelate formed by the chemical reaction between PA and MgO, CaO, BaO or ZnO had a different influence on the crystallization behavior and melting characteristics of iPP. Addition of metal oxides increased the crystallization temperature of iPP and mainly formed α‐phase due to the heterogeneous α‐nucleation of metal oxides. The α‐nucleation of CaO could be easily changed into β‐nucleation using CaO‐supported PA, and 90.1% β‐phase was obtained. The β‐nucleation of BaO could be markedly enhanced by barium pimelate formed using supported PA. However, no β‐phase was observed for iPP filled with MgO‐ or ZnO‐supported PA. The various metal oxides with supported PA had a different influence on the crystallization behavior and melting characteristics of iPP due to the different structure of metal pimelate formed by chemical reaction between PA and the metal oxides. Copyright © 2012 Society of Chemical Industry     

Oxidative reforming of methane on structured Ni-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/cordierite catalysts

The catalytic properties of Ni/Al₂O₃ composites supported on ceramic cordierite honeycomb monoliths in oxidative methane reforming are reported. The prereduced catalyst has been tested in a flow reactor using reaction mixtures of the following compositions: in methane oxidation, 2–6% CH₄, 2–9% O₂, Ar; in carbon dioxide and oxidative carbon dioxide reforming of methane, 2–6% CH₄, 6–12% CO₂, and 0–4% O₂, and Ar. Physicochemical studies include the monitoring of the formation and oxidation of carbon, the strength of the Ni-O bond, and the phase composition of the catalyst. The structured Ni-Al₂O₃ catalysts are much more productive in the carbon dioxide reforming of methane than conventional granular catalysts. The catalysts performance is made more stable by regulating the acid-base properties of their surface via the introduction of alkali metal (Na, K) oxides to retard the coking of the surface. Rare-earth metal oxides with a low redox potential (La₂O₃, CeO₂) enhance the activity and stability of Ni-Al₂O₃/cordierite catalysts in the deep and partial oxidation and carbon dioxide reforming of methane. The carbon dioxide reforming of methane on the (NiO + La₂O₃ + Al₂O₃)/cordierite catalyst can be intensified by adding oxygen to the gas feed. This reduces the temperature necessary to reach a high methane conversion and does not exert any significant effect on the selectivity with respect to H₂.     

Characterization of some perovskite oxides based on YBa2Cu3O7 − x in relation to their use in methanol production

The oxidized and weakly reducible perovskite oxide YBa₂Cu₃O_{7 − x} (YBCO) has been prepared as a catalyst, supported on γ‐Al₂O₃. It was further modified by (i) impregnation with Ru and Pd and (ii) cobalt incorporation via co‐precipitation. All the catalysts were either 20% (w/w) YBCO/γ‐Al₂O₃ or 2% (w/w) Ru, Pd or Co/20% (w/w) YBCO/γ‐Al₂O₃. The catalysts were characterized using temperature programmed reduction (TPR), surface area measurements and X‐ray diffraction (XRD) studies before and after various treatments. They were studied as catalysts in the pressure range 20–50 atmospheres and in the temperature range 523–573 K in an autoclave equipped with a spinning basket catalyst container. The Pd‐, Ru‐ and Co‐modified catalysts gave predominantly methanation products, along with some C₂–C₄ hydrocarbons. However the YBCO/γ‐Al₂O₃ catalyst exhibited significant methanol selectivity at 50 atmospheres and at 523 K X‐ray diffraction studies revealed the presence of Cu(0), Cu(I) and Cu(II) after reduction and the species Cu(0) and Cu(I) are probably essential to CH₃OH production. © 2000 Society of Chemical Industry     

The oxidative coupling of methane by sodium promoted lanthanide catalysts

The characteristics of La₂O₃ catalysts with three different supports (BaCO₃, MgO, and ZnO), two different alkaline metal promoters (Na₂O and Na₂CO₃), and a china clay have been investigated. The relationship of the surface basicity of the support to the activity and selectivity of the catalyst were studied by TPD. The results showed that the surface basicity of these three supports decreased in the following order: BaCO₃ > MgO > ZnO. The choice of Na₂O as a promoter in La₂O₃/(BaCO₃ or MgO) had a better effect than the choice of Na₂CO₃. The Na₂O promoter could increase not only the catalytic activity and the C₂ selectivity, but also lower the optimal reaction temperature. Addition of 15% clay into the La₂O₃–alkaline metal catalysts could increase the strength of the catalyst and lower the optimum reaction temperature.     

High‐temperature calorimetric study of oxide component dissolution in a CaO–MgO–Al2O3–SiO2 slag at 1450°C

Blast‐furnace slags are formed, as iron ore is reduced to metal, as a molten a mixture of refractory and not easily reducible oxides, largely silica, alumina, lime, and magnesia. Their relatively low silica content makes them basic and poor glass formers. Their thermodynamic properties, though important for modeling their formation and reactivity, as well as furnace heat balance, are poorly known. Solution calorimetry of small amounts of solid oxides in a molten oxide solvent at high temperature (up to about 1500°C) permits direct assessment of energetics of dissolution. The enthalpies of solution of slag forming oxides: CaO, SiO₂, Al₂O₃, MgO, and Fe₂O₃ in a simplified model slag of composition: CaO (45.9 mol%), SiO₂ (35.1 mol%), Al₂O₃ (8.3 mol%), MgO (10.7 mol%) were measured by high‐temperature drop solution calorimetry at 1450°C. For this slag composition, enthalpies of solution become more exothermic in the order: Fe₂O₃ (279.3 ± 20.8 kJ/mol), MgO (56.7 ± 9.1 kJ/mol), Al₂O, (41.6 ± 11.3 kJ/mol), CaO (?4.3 ± 2.3 kJ/mol), and SiO₂, (?20.4 ± 4.4 kJ/mol), reflecting the relatively basic character of this low‐silica melt. Within these fairly large experimental errors, characteristic of calorimetry at this high temperature, there is little or no discernible concentration dependence for these heats of solution. The trends seen for these five solutes parallel those seen for heats of solution of the same oxides in other melts at various temperatures, with changes in magnitude reflecting the differences in acid‐base character of the melts. The new data for quartz show systematic behavior which extends the range of basicity studied for the enthalpy of dissolution of silica. The results provide reliable data for future modeling of the thermal balance of steel‐making furnaces and geologic and ceramic systems.     

Effect of promoters on catalytic performance of Cr/SiO2 catalysts in oxidative dehydrogenation of ethane with carbon dioxide

Several acidic and basic oxide promoted Cr/SiO₂ catalysts were prepared and investigated in oxidative dehydrogenation of ethane in the presence of carbon dioxide. The effects of SO₄ ^2–, WO₃ and alkali metal oxides (Li₂O, Na₂O, and K₂O) on the catalytic activity were studied. It is found that sulfation of silica produces a positive effect on ethane conversion and ethylene yield while tungstation and addition of strong basic promoters (alkali metal oxides) suppress the catalytic activity. Characterization indicates that the varying activity of the promoted catalysts can be attributed to the difference in acid/base property and redox potential.     

Oxidative coupling of methane over alkali metal oxide promoted La2O3/BaCO3 catalysts

The oxidative coupling of methane (OCM) over various alkali metal oxide promoted La₂O₃/BaCO₃ catalysts and the effects of Na₂O content on the performance of Na₂O–La₂O₃/BaCO₃ catalysts have been studied. It was found that Na₂O promoted La₂O₃/BaCO₃ catalysts had the advantages of high CH₄ conversion, C₂ selectivity and C₂H₄/C₂H₆ ratio. Na₂O might affect the properties of the catalysts through electronic and geometric effects. The highest C₂ yield (19·0–20·6%) was obtained with Na₂O–9 wt% La₂O₃/BaCO₃ catalysts of 1·0–3·0% Na₂O. The effects of reaction conditions on OCM over 3 wt% Na₂O–9 wt% La₂O₃/BaCO₃ catalysts have also been investigated. The catalysts were characterized by BET, TPD and XRD. TPD studies on 3 wt% Na₂O–9 wt% La₂O₃/BaCO₃ catalysts demonstrated that CO₂, CH₄ and O₂ could be adsorbed strongly on the catalyst. This might be related to the activation of CH₄ and the formation and regeneration of active oxygen species.     

SO42−/ZrO2 supported on γ‐Al2O3 as a catalyst for CO2 desorption from CO2‐loaded monoethanolamine solutions

In this work, the composite catalysts, SO₄²/ZrO₂/γ‐Al₂O₃ (SZA), with different ZrO₂ and γ‐Al₂O₃ mass ratios were prepared and used for the first time for the carbon dioxide (CO₂)‐loaded monoethanolamine (MEA) solvent regeneration process to reduce the heat duty. The regeneration characteristics with five catalysts (three SZA catalysts and two parent catalysts) of a 5 M MEA solution with an initial CO₂ loading of 0.5 mol CO₂/mol amine at 98°C were investigated in terms of CO₂ desorption performance and compared with those of a blank test. All the catalysts were characterized using X‐ray diffraction, Fourier transform infrared spectroscopy, N₂ adsorption–desorption experiment, ammonia temperature programmed desorption, and pyridine‐adsorption infrared spectroscopy. The results indicate that the SZA catalysts exhibited superior catalytic activity to the parent catalysts. A possible catalytic mechanism for the CO₂ desorption process over SZA catalyst was proposed. The results reveal that SZA1/1, which possesses the highest joint value of Brφnsted acid sites (BASs) and mesopore surface area (MSA), presented the highest catalytic performance, decreasing the heat duty by 36.9% as compared to the catalyst‐free run. The SZA1/1 catalyst shows the best catalytic performance as compared with the reported catalyst for this purpose. Moreover, the SZA catalyst has advantages of low cost, good cyclic stability, easy regeneration and has no effect on the CO₂ absorption performance of MEA. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3988–4001, 2018     

Selective catalytic reduction by urea in a fluidized‐bed reactor

The selective catalytic reduction (SCR) of NO_x by urea as a reducing agent was carried out over fresh and sulfated CuO/γ‐Al₂O₃ catalysts in a fluidized‐bed reactor. The optimum temperature ranges for NO reduction on the fresh and sulfated CuO/γ‐Al₂O₃ catalysts were 300–350 °C and 400–450 °C, respectively. NO reduction with the sulfated CuO/γ‐Al₂O₃ catalyst was somewhat higher than that with the fresh CuO/γ‐Al₂O₃ catalyst. N₂O formation increased with increasing reaction temperature. Ammonia (NH₃) slip increased with increasing gas velocity and decreased with increasing reaction temperature. Copyright © 2003 Society of Chemical Industry     

Treatment of Volatile Organic Compounds with a Pt/Co3O4‐CeO2 Catalyst

For emission control of volatile organic compounds (VOC), e.g., in the painting and printing industries, conventional Pt/Al₂O₃ and Co₃O₄‐CeO₂ catalysts are used. On the Pt/Al₂O₃ catalyst, aromatic hydrocarbons containing a benzene ring such as toluene can be oxidized at a lower complete oxidation temperature than on Co₃O₄‐CeO₂, under typical treatment conditions. However, ethyl acetate and isopropyl alcohol can be oxidized at a lower complete oxidation temperature on Co₃O₄‐CeO₂ than on Pt/Al₂O₃. In this study, platinum was directly supported on Co₃O₄‐CeO₂. Using chloroplatinic acid, the platinum cohered and the catalytic activity did not improve. But when the platinum was supported using platinum colloid coated with dispersant, high‐dispersion support of the platinum on the Co₃O₄‐CeO₂ surface was achieved, and toluene, ethyl acetate, and isopropyl alcohol could be oxidized at less than 250 °C.     

Raman and X-ray photoelectron spectroscopy study on the influence of La2O3 on the melt structure of SiO2–CaO–Al2O3–MgO

In order to gain more insights into the influence of rare earth elements on the melt structure of SiO₂–CaO–Al₂O₃–MgO glass ceramics, Raman and X-ray photoelectron spectroscopy techniques were used to study the influence of La₂O₃ on the Si–O/Al–O tetrahedron structure within SiO₂–CaO–Al₂O₃–MgO–quenched glass samples in this study. Results showed that some Raman peak shapes at low frequencies (200–840 cm^?1) changed significantly after the addition of La₂O₃, compared to the high frequency (840–1200 cm^?1) region that corresponds to the [SiO₄] structure, suggesting that the depolymerization of the low-frequency T–O–T (T=Si or Al) structure was more prevalent with La³⁺ addition. Besides, the depolymerization extent of the Si–O/Al–O tetrahedral network varied when the melt composition altered. Most notably, depolymerization is the most significant at a low CaO/SiO₂ ratio (0.25) and a high Al₂O₃ content (8%). Meanwhile, La³⁺ can promote the transformation of Si–O–Si and Al–O–Al bonds to the Si–O–Al ones, thereby forming a complex ionic cluster network interwoven with Si–O and Al–O tetrahedrons.     

Investigation of Sm2O3 additive on mechanical and electrical properties of Li2O‐ stabilized β″‐alumina electrolyte

Li₂O‐ stabilized β″‐alumina was synthesized by the double zeta process. The effect of Sm₂O₃ additive as the sintering aid, on microstructure, mechanical and electrical properties of Li₂O‐ stabilized β″‐alumina ceramics was studied by means of X‐ray diffraction, field emission scanning electron microscope, biaxial flexure test and ionic conductivity measurement. The results indicated that both the fracture strength and the ionic conductivity of the sample containing 0.2 wt% Sm₂O₃ improved approximately 52% and 54%, respectively, that can be attributed to its higher density, higher amount of β″‐Al₂O₃ phase and more uniform microstructure.     

Co–Pd/γ‐Al2O3 catalyst for heavy oil upgrading: Desorption kinetics,reducibility and catalytic activity

The influence of Pd on a Co–Pd/γ‐Al₂O₃ heavy oil upgrading catalyst is investigated using different physicochemical and reactive Characterization techniques. Nitrogen adsorption isotherm analysis shows that the specific surface area and porosity of the support alumina is significantly decreased due to the blockage of the pores by the loaded cobalt species. The estimated activation energy of NH₃ desorption is found to be less for Co–Pd/γ‐Al₂O₃ sample, which confirms improved acidity due to Pd. TPR experiments show that the reducibility of the catalyst is significantly improved with the presence of Pd. Higher metal dispersion and hydrogen spillover effects are the main reasons for the enhanced reducibility of the Pd promoted catalyst as revealed by the H₂‐pulse chemisorptions study. When evaluated using VGO as feed stock, the Co–Pd/γ‐Al₂O₃ displayed superiority both in hydrodesulphurisation (HDS) and hydrocracking (HC) activities as compared to the unpromoted Co/γ‐Al₂O₃ catalyst. The coke deposition on the spent catalyst is also found to be low due to the Pd promotional effects. This is an encouraging result, given that higher hydrogenation activity of the catalyst can be achieved without compromising the cracking activity and sustained activity of the catalyst.     

Large enhancement in methane-to-syngas conversion activity of supported Ni catalysts due to precoating of catalyst supports with MgO,CaO or rare-earth oxide

Supported nickel catalysts prepared using commercial sintered low surface area porous catalyst carriers (containing SiO₂ and/or Al₂O₃) precoated with MgO, CaO or rare-earth oxide show very much higher activity, selectivity and productivity in methane-to-syngas conversion reactions, than the catalysts prepared using catalyst carriers without any precoating. Among the precoating metal oxides, the best performance is observed for MgO.     

Phase evolution mechanism of non‐oxide bonded Al–Al2O3–MgO–ZrO2 composites at 1873 K in flowing nitrogen

In flowing nitrogen, non‐oxides such as Al₄O₄C, Al₂OC, Zr₂Al₃C₄, and MgAlON bonded Al₂O₃‐based composites were successfully prepared by a gaseous phase mass transfer pathway using aluminum, zirconia, alumina, and magnesia as raw materials at 1873 K, after an Al–AlN core‐shell structure was formed at 853 K. Resin bonded Al–Al₂O₃–MgO–ZrO₂ composites after sintering were characterized and analyzed by X‐ray diffraction (XRD), scanning electron microscope (SEM) and, energy dispersive spectrometer (EDS), and the influence of the MgO content on the sintered composites was studied. The results show that after sintering, the phase composition of the Al–Al₂O₃–ZrO₂ composite is Al₂O₃, Al₄O₄C, Al₂OC, and Zr₂Al₃C₄, while the phase composition of the Al–Al₂O₃–ZrO₂ composite with the addition of MgO 6 wt% and MgO 12 wt% is Al₂O₃, MgAlON, Al₄O₄C, Al₂OC, and Zr₂Al₃C₄ as well as Al₂O₃, MgAlON, Al₂OC, and Zr₂Al₃C₄, respectively. The addition of MgO changed the phase composition and distribution for the resin bonded Al–Al₂O₃–MgO–ZrO₂ system composites after sintering. When the added MgO content is equal to or more than 12 wt%, the Al₄O₄C in the resin bonded Al–Al₂O₃–MgO–ZrO₂ system composites is unable to exist in a stable phase.     

Investigation of La3+-modified Al2O3supported CeO2

X-ray photoelectron spectroscopy measurements indicate that the Ce³⁺ fraction in Al₂O₃-supported CeO₂ can be decreased by the incorporation of La³⁺. If La³⁺ is incorporated into the Al₂O₃ before CeO₂ is added, a higher CeO₂ dispersion and a greater range of reversible reducibility of the CeO₂ may also be obtained. These changes offer potential for improvement in the oxygen storage capacity provided by CeO₂ in three-way catalysts.