Effects of La<Subscript>2</Subscript>O<Subscript>3</Subscript> on ZrO<Subscript>2</Subscript> supported Ni catalysts for autothermal reforming of CH<Subscript>4</Subscript>

The effect of La₂O₃ content in Ni-La-Zr catalyst was investigated for the autothermal reforming (ATR) of CH₄. The catalysts were prepared by the coprecipitation method and had a mesoporous structure. Temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) indicated that a strong interaction developed between Ni species and the support with the addition of La₂O₃. Thermogravimetric analysis (TGA) and H₂-pulse chemisorption showed that the addition of La₂O₃ led to well dispersed NiO molecules on the support. Ni-La-Zr catalysts gave much higher CH₄ conversion than Ni-Zr catalyst. The Ni-La-Zr containing 3.2 wt% La₂O₃ showed the highest activity. The optimum conditions for maximal CH₄ conversion and H₂ yield were H₂O/CH₄=1.00, O₂/CH₄=0.75. Under these conditions, CH₄ conversion of 83% was achieved at 700 °C. In excess O₂ (O₂/CH₄>0.88), the catalytic activity was decreased due to sintering of the catalyst.     

Ni-Co bimetallic catalyst for CH<Subscript>4</Subscript> reforming with CO<Subscript>2</Subscript>

A co-precipitation method was employed to prepare Ni/Al₂O₃-ZrO₂, Co/Al₂ O₃-ZrO₂ and Ni-Co/Al₂O₃-ZrO₂ catalysts. Their properties were characterized by N₂ adsorption (BET), thermogravimetric analysis (TGA), temperature-programmed reduction (TPR), temperature-programmed desorption (CO₂-TPD), and temperature-programmed surface reaction (CH₄-TPSR and CO₂-TPSR). Ni-Co/Al₂O₃-ZrO₂ bimetallic catalyst has good performance in the reduction of active components Ni, Co and CO₂ adsorption. Compared with mono-metallic catalyst, bimetallic catalyst could provide more active sites and CO₂ adsorption sites (C + CO₂ = 2CO) for the methane-reforming reaction, and a more appropriate force formed between active components and composite support (SMSI) for the catalytic reaction. According to the CH₄-CO₂-TPSR, there were 80.9% and 81.5% higher CH₄ and CO₂ conversion over Ni-Co/Al₂O₃-ZrO₂ catalyst, and its better resistance to carbon deposition, less than 0.5% of coke after 4 h reaction, was found by TGA. The high activity and excellent anti-coking of the Ni-Co/Al₂O₃-ZrO₂ catalyst were closely related to the synergy between Ni and Co active metal, the strong metal-support interaction and the use of composite support.     

Performance of Ni catalyst supported on La-hexaaluminate in CO<Subscript>2</Subscript> reforming of CH<Subscript>4</Subscript>

CO₂ reforming of CH₄ was performed using Ni catalyst supported on La-hexaaluminate which has been an well-known material for high-temperature combustion. La-hexaaluminate was synthesized by sol-gel method at various conditions where different amount of Ni (5–20 wt%) was loaded. Ni/La-hexaaluminate experienced 72 h reaction and its catalytic activity was compared with that of Ni/Al₂O₃, Ni/La-hexaaluminate shows higher reforming activity and resistance to coke deposition compared to the Ni/Al₂O₃ model catalyst. Coke deposition increases proportionally to Ni content. Consequently, Ni(5)/La-hexaaluminate(700) is the most efficient catalyst among various Ni/La-hexaaluminate catalysts regarding the cost of Ni in Ni(X)/La-hexaaluminate catalysts. BET surface area, XRD, EA, TGA and TPO were performed for surface characterization. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

CO<Subscript>2</Subscript> methanation and co-methanation of CO and CO<Subscript>2</Subscript> over Mn-promoted Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

A series of Mn-promoted 15 wt-% Ni/Al₂O₃ catalysts were prepared by an incipient wetness impregnation method. The effect of the Mn content on the activity of the Ni/Al₂O₃ catalysts for CO₂ methanation and the comethanation of CO and CO₂ in a fixed-bed reactor was investigated. The catalysts were characterized by N2 physisorption, hydrogen temperature-programmed reduction and desorption, carbon dioxide temperature-programmed desorption, X-ray diffraction and highresolution transmission electron microscopy. The presence of Mn increased the number of CO₂ adsorption sites and inhibited Ni particle agglomeration due to improved Ni dispersion and weakened interactions between the nickel species and the support. The Mn-promoted 15 wt-% Ni/Al₂O₃ catalysts had improved CO₂ methanation activity especially at low temperatures (250 to 400 °C). The Mn content was varied from 0.86% to 2.54% and the best CO₂ conversion was achieved with the 1.71Mn-Ni/Al₂O₃ catalyst. The co-methanation tests on the 1.71Mn-Ni/Al₂O₃ catalyst indicated that adding Mn markedly enhanced the CO₂ methanation activity especially at low temperatures but it had little influence on the CO methanation performance. CO₂ methanation was more sensitive to the reaction temperature and the space velocity than the CO methanation in the co-methanation process.

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Effect of carbon deposition over carbonaceous catalysts on CH<Subscript>4</Subscript> decomposition and CH<Subscript>4</Subscript>-CO<Subscript>2</Subscript> reforming

An investigation was made using a continuous fixed bed reactor to understand the influence of carbon deposition obtained under different conditions on CH₄-CO₂ reforming. Thermogravimetry (TG) and X-ray diffraction (XRD) were employed to study the characteristics of carbon deposition. It was found that the carbonaceous catalyst is an efficient catalyst in methane decomposition and CH₄-CO₂ reforming. The trend of methane decomposition at lower temperatures is similar to that at higher temperatures. The methane conversion is high during the initial of stage of the reaction, and then decays to a relatively fixed value after about 30 min. With temperature increase, the methane decomposition rate increases quickly. The reaction temperature has significant influence on methane decomposition, whereas the carbon deposition does not affect methane decomposition significantly. Different types of carbon deposition were formed at different methane decomposition reaction temperatures. The carbon deposition Type I generated at 900°C has a minor effect on CH₄-CO₂ reforming and it easily reacts with carbon dioxide, but the carbon deposition Type II generated at 1000°C and 1100°C clearly inhibits CH₄-CO₂ reforming and it is difficult to react with carbon dioxide. The results of XRD showed that some graphite structures were found in carbon deposition Type II.     

Highly ordered mesoporous CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> and CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript> with crystalline walls

The highly ordered mesoporous CoFe₂O₄ and CuFe₂O₄ with crystalline walls can be synthesized by hard template with using mesoporous silica SBA-15 as hard template and using ferric nitrate, cobalt nitrate, and copper nitrate as metal precursors. These new mesoporous materials above have high surface areas, narrow pore size distribution, and large pore volumes, which are believed to be valuable for the potential application in the field of sensors, catalysis, message recording, magnetics, and biology. This work provides a method to fabricate the highly ordered mesoporous materials composed of multi-metal oxides with crystalline walls. The development of such versatile approach is of great significance in practical application. It can be envisaged that this established method is significantly expandable to the controlled synthesis of the mesoporous functional materials with diverse compositions.     

The effect of promoters on the CO<Subscript>2</Subscript> reforming activity and coke formation of nanocrystalline Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts prepared by microemulsion method

Mesoporous nanocrystalline nickel-alumina promoted catalysts with high surface area were prepared by microemulsion (ME) method and employed in dry reforming of methane reaction. The catalysts were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller surface area analysis (BET), temperature programmed reduction (TPR) and temperature programmed oxidation (TPO) techniques. The results showed that the prepared catalysts had high porosity with great surface area and small crystallite size. Among the K₂O, MgO, CaO and BaO promoters, the MgO promoter showed considerable effect on catalytic performance and coke suppression of catalyst.     

Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and CeO<Subscript>2</Subscript>-promoted MgO sorbents for CO<Subscript>2</Subscript> capture at moderate temperatures

A series of Al₂O₃ and CeO₂ modified MgO sorbents was prepared and studied for CO₂ sorption at moderate temperatures. The CO₂ sorption capacity of MgO was enhanced with the addition of either Al₂O₃ or CeO₂. Over Al₂O₃-MgO sorbents, the best capacity of 24.6 mg- CO₂/g-sorbent was attained at 100 °C, which was 61% higher than that of MgO (15.3 mg-CO₂/g-sorbent). The highest capacity of 35.3 mg-CO₂/g-sorbent was obtained over the CeO₂-MgO sorbents at the optimal temperature of 200 °C. Combining with the characterization results, we conclude that the promotion effect on CO₂ sorption with the addition of Al₂O₃ and CeO₂ can be attributed to the increased surface area with reduced MgO crystallite size. Moreover, the addition of CeO₂ increased the basicity of MgO phase, resulting in more increase in the CO₂ capacity than Al₂O₃ promoter. Both the Al₂O₃-MgO and CeO₂-MgO sorbents exhibited better cyclic stability than MgO over the course of fifteen CO₂ sorption-desorption cycles. Compared to Al₂O₃, CeO₂ is more effective for promoting the CO₂ capacity of MgO. To enhance the CO₂ capacity of MgO sorbent, increasing the basicity is more effective than the increase in the surface area.

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Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> xerogel support on hydrogen production by steam reforming of LNG over Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> catalyst

An Al₂O₃-ZrO₂ xerogel (AZ-SG) was prepared by a sol-gel method for use as a support for a nickel catalyst. The Ni/AZ-SG catalyst was then prepared by an impregnation method, and was applied to hydrogen production by steam reforming of LNG. A nickel catalyst supported on commercial alumina (A-C) was also prepared (Ni/A-C) for comparison. The hydroxyl-rich surface of the AZ-SG support increased the dispersion of nickel species on the support during the calcination step. The formation of a surface nickel aluminate-like phase in the Ni/AZ-SG catalyst greatly enhanced the reducibility of the Ni/AZ-SG catalyst. The ZrO₂ in the AZ-SG support increased the adsorption of steam onto the support and the subsequent spillover of steam from the support to the active nickel sites in the Ni/AZ-SG catalyst. Both the high surface area and the well-developed mesoporosity of the Ni/AZ-SG catalyst improved the gasification of adsorbed surface hydrocarbons in the reaction. In the steam reforming of LNG, the Ni/AZ-SG catalyst showed a better catalytic performance than the Ni/A-C catalyst. Moreover, the Ni/AZ-SG catalyst showed strong resistance toward catalyst deactivation.     

Synthesis and properties of flux-cast refractories in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-MgO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Details are given of the synthesis and testing of flux-cast refractory materials in the alumina-rich region of the Al₂O₃-MgO-B₂O₃ system; XRD and petrography indicate that the main structure-forming phases are corundum and magnesian spinel. In subordinate amounts there are the boroaluminate 9Al₂O₃·2B₂O₃ and the previously unknown compound 4Al₂O₃·MgO·2B₂O₃, whose composition has been established by microprobe analysis. Corrosion tests showed that three-component systems containing magnesium and boron oxides at levels of 5–10% do not increase the corrosion resistance of refractories in molten sodium-calcium-silicate glass and electrovacuum borosilicate glass. __________ Translated from Novye Ogneupory, No. 3, pp. 161–163, March, 2008.     

Synthesis and characterization of rubbery/glassy blend membranes for CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> gas separation

A series of blend membranes made from the rubbery polyether block amide (Pebax®1657) and a glassy polymer, polyethersulfone (PES) or Matrimid 5218, were fabricated by solution casting with different ratios (10–40 %), in order to combine high permeability of the former with high selectivity of the latter polymer for CO₂/CH₄ gas separation. The membranes were characterized by scanning electron microscopy (SEM), differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), and stress–strain tests. These blend membranes showed two distinct T _g s, indicating their immiscible nature as confirmed by SEM images. However, weak intermolecular interaction between polymers, as illustrated by the FTIR results, corresponds to some degree to their compatibility and improved mechanical strength, compared to the pure Pebax®. TGA analysis revealed that addition of glassy polymer improved membranes’ thermal stability. Effect of feed pressure on membrane separation, investigated by three different pressures (4, 8, and 12 bar), indicated increased permeability for higher pressures for both CO₂ and CH₄. Gas separation tests also pointed to improved separation properties of the blend membranes compared to those of the neat polymers, prepared the same way.     

Reduced graphene oxide supported V<Subscript>2</Subscript>O<Subscript>5</Subscript>-WO<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> catalysts for selective catalytic reduction of NOx

We present a reduced-graphene-oxide (rGO)-supported V2O₅-WO₃-TiO₂ (VWTi) catalysts for the efficient selective catalytic reduction of NOx. The rGO support provides well-dispersed functional sites for the nucleation of nanoparticles, allowing the formation of VWTi catalysts with high specific surface areas. The dispersion of the nanoparticles, as observed by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS), confirmed the uniform dispersion of the particles on the rGO surface. Detailed Fourier-transform infrared (FT-IR) and NH₃ temperature-programmed desorption (NH₃-TPD) analyses indicated that the high density of acidic sites provided by the rGO is key to the observed enhancement of NOx removal efficiency, and the rGO-supported catalysts exhibit improved NOx removal efficiencies with smaller amounts of V₂O₅ and WO₃ compared with the commercially available V₂O₅-WO₃-TiO₂ catalysts.     

Reductive amination of ethanol to ethylamines over Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

Ni(x)/Al₂O₃ (x=wt%) catalysts with Ni loadings of 5–25 wt% were prepared via a wet impregnation method on an γ-Al₂O₃ support and subsequently applied in the reductive amination of ethanol to ethylamines. Among the various catalysts prepared, Ni(10)/Al₂O₃ exhibited the highest metal dispersion and the smallest Ni particle size, resulting in the highest catalytic performance. To reveal the effects of reaction parameters, a reductive amination process was performed by varying the reaction temperature (T), weight hourly space velocity (WHSV), and NH₃ and H₂ partial pressures in the reactions. In addition, on/off experiments for NH₃ and H₂ were also carried out. In the absence of NH₃ in the reactant stream, the ethanol conversion and selectivities towards the different ethylamine products were significantly reduced, while the selectivity to ethylene was dominant due to the dehydration of ethanol. In contrast, in the absence of H₂, the selectivity to acetonitrile significantly increased due to dehydrogenation of the imine intermediate. Although a small amount of catalyst deactivation was observed in the conversion of ethanol up to 10 h on stream due to the formation of nickel nitride, the Ni(10)/Al₂O₃ catalyst exhibited stable catalytic performance over 90 h under the optimized reaction conditions (i.e., T=190 °C, WHSV=0.9 h^?1, and EtOH/NH₃/H₂ molar ratio=1/1/6).     

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.     

Effect of CO<Subscript>2</Subscript> concentration on the performance of different thermodynamic models for prediction of CH<Subscript>4</Subscript>+CO<Subscript>2</Subscript>+H<Subscript>2</Subscript>O hydrate equilibrium conditions

Accurate prediction of phase equilibria regarding CH₄ replacement in hydrate phase with high pressure CO₂ is an important issue in modern reservoir engineering. In this work we investigate the possibility of establishing a thermodynamic framework for predicting the hydrate equilibrium conditions for evaluation of CO₂ injection scenarios. Different combinations of equations of state and mixing rules are applied and the most accurate thermodynamic models at different CO₂ concentration ranges are proposed.     

Synthesis of polyaniline/mesoporous carbon nanocomposites and their application for CO<Subscript>2</Subscript> sorption

Ordered mesoporous carbons (OMC), were synthesized by nanocasting using ordered mesoporous silica as hard templates. Ordered mesoporous carbons CMK-1 and CMK-3 were prepared from MCM-48 and SBA-15 materials with pore diameters of 3.4 nm and 4.2 nm, respectively. Mesoporous carbons can be effectively modified for CO₂ adsorption with amine functional groups due to their high affinity for CO₂. Polyaniline (PANI)/mesoporous carbon nanocomposites were synthesized from in-situ polymerization by dissolving OMC in aniline monomer. The polymerization of aniline molecules inside the mesochannels of mesoporous carbons has been performed by ammonium persulfate. The nanocomposition, morphology, and structure of the nanocomposite were investigated by nitrogen adsorption-desorption isotherms, Fourier Transform Infrared (FT–IR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and thermo gravimetric analysis (TGA). CO₂ uptake capacity of the mesoporous carbon materials was obtained by a gravimetric adsorption apparatus for the pressure range from 1 to 5 bar and in the temperature range of 298 to 348 K. CMK-3/PANI exhibited higher CO₂ capture capacity than CMK-1/PANI owing to its larger pore size that accommodates more amine groups inside the pore structure, and the mesoporosity also can facilitate dispersion of PANI molecules inside the pore channels. Moreover, the mechanism of CO₂ adsorption involving amine groups is investigated. The results show that at elevated temperature, PANI/mesoporous carbon nanocomposites have a negligible CO₂ adsorption capacity due to weak chemical interactions with the carbon nanocomposite surface.     

Effect of CeO<Subscript>2</Subscript>-addition sequence on the performance of CeO<Subscript>2</Subscript>-modified Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst in autothermal reforming of iso-octane

Two types of CeO₂-modified Ni/Al₂O₃ catalysts were prepared by a consecutive impregnation method with different sequences in the impregnation of Ni and CeO₂, and their performance in autothermal reforming (ATR) of isooctane was investigated. Catalysts prepared by adding CeO₂ prior to the addition of Ni, Ni/CeO₂-Al₂O₃, produced larger amounts of hydrogen than those obtained using catalysts prepared by adding the two components in an opposite sequence, Ni-CeO₂/Al₂O₃. The results of H₂ chemisorption and temperature-programmed reduction revealed that added CeO₂ increased the dispersion of the Ni species on Al₂O₃ and suppressed the formation of NiAl₂O₄ in the catalyst such that large amounts of Ni species were present as NiO, the active species for the ATR. The elemental and thermogravimetric analyses of deactivated catalysts indicated that Ni/CeO₂-Al₂O₃, which showed a longer lifetime than Ni-CeO₂/Al₂O₃, contained lesser amounts and different types of coke on the surface.     

Adsorption of CO<Subscript>2</Subscript> by iron-exchanged heteropolyacid Fe<Subscript>1.5</Subscript>PMo<Subscript>12</Subscript>O<Subscript>40</Subscript> supported on mesoporous cellular foams

Novel low-temperature swing adsorbents that preferably adsorb CO₂ were synthesized by varying loading of heteropolyacid Fe_1.5PMo₁₂O₄₀ (Fe–PMA) supporting on mesoporous cellular foams (MCFs) by wetting impregnation. The synthesized materials were characterized by various physicochemical, thermal and spectral techniques and the CO₂ adsorption capacity of the materials were evaluated. Solid adsorbents showed a significantly high adsorption capacity toward CO₂ due to the chemisorptions of CO₂. The CO₂ adsorption capacities of the materials decreased as the temperature increased. The results showed that the adsorption capacity reached a level of 81.8 mg CO₂/g-adsorbent at 25 °C for the 20 wt% Fe–PMA–MCFs. These results indicated that the iron (Fe²⁺) complexes acted as efficient catalysts for the separation of CO₂. The as-synthesized adsorbents were selective, thermally stable, long-lived, and could be recycled at a temperature of 110 °C.