Effect of Cu promoter and alumina phases on Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> for propane dehydrogenation

We investigated the effects of different Cu weight ratio on θ or γ-Al₂O₃ which were impregnated with platinum in terms of catalytic activity for propane dehydrogenation and physicochemical properties. 1.5 wt% Pt, 0-10 wt% Cu catalyst supported on θ-Al₂O₃ or γ-Al₂O₃ was prepared by incipient wetness co-impregnation. Enhanced Pt dispersion by increasing Cu contents in γ-Al₂O₃ supported catalyst was confirmed via XRD and XPS. Pt and CuO was separated in Pt-Cu/θ-Al₂O₃, but Pt-Cu alloy was identified after reduction treatment. Also, adding Cu in Pt/Al₂O₃ makes catalyst’s acidity lower and this property led to increased propylene yield in propane dehydrogenation. However, Pt₃Cu was not good for yield of PDH, which was confirmed in Pt-10Cu/θ-Al₂O₃ through XRD.     

CO oxidation from syngas (CO and H<Subscript>2</Subscript>) using nanoporous Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

The concept of “waste-to-wealth” is spreading awareness to prevent global warming and recycle the restrictive resources. To contribute towards sustainable development, hydrogen energy is obtained from syngas (CO and H₂) generated from waste gasification, followed by CO oxidation and CO₂ removal. In H₂ generation, it is key to produce more purified H₂ from syngas using heterogeneous catalysts. In this respect, we prepared Pt/Al₂O₃ catalyst with nanoporous structure using precipitation method, and compared its catalytic activity with commercial alumina (Degussa). Based on the results of XRD and TEM, it was found that metal particles did not aggregate on the alumina surface and showed high dispersion. Optimum condition for CO conversion was 1.5 wt% Pt loaded on Al₂O₃ support, and pure hydrogen was obtained after removal of CO₂ gas.     

Catalytic cracking of isobutane over HZSM-5, FeHZSM-5 and CrHZSM-5 catalysts with different SiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ratios

Several systems of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolite catalysts with different ratios of SiO₂/Al₂O₃ (25,38,50,80, and 150) were prepared and they were characterized by means of X-ray diffraction (XRD), UV–Vis, NH₃-TPD and BET techniques. The results indicated that, compared with uncalcined HZSM-5 zeolites, the total acid amounts, acidic site density and acidic strength of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolite catalysts obviously decreased, while those of weak acid amounts obviously enhanced with the decrease of SiO₂/Al₂O₃ molar ratio. When the ratio of SiO₂/Al₂O₃ is less than 50, the three systems of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolite catalysts with same ratio of SiO₂/Al₂O₃ gave similar and high isobutane conversions. However, when the ratio of SiO₂/Al₂O₃ was equal to or greater than 80, these three systems of catalysts possessed different altering tendencies of isobutane conversions, thus their isobutene conversions were different. High yields of light olefins were obtained over the FeHZSM-5 and CrHZSM-5 zeolite catalysts with high ratio of SiO₂/Al₂O₃ (≥80). The ratio of SiO₂/Al₂O₃ has large effects on the surface area, and acidic characteristics of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolites catalysts, and thus further affect their catalytic performances for isobutane cracking. That is the nature of SiO₂/Al₂O₃ ratio effect on the catalytic performances.     

Direct conversion of cellulose into polyols or H2 over Pt/Na(H)-ZSM-5

The direct conversion of cellulose into polyols such as ethylene glycol and propylene glycol was examined over Pt catalysts supported on H-ZSM-5 with different SiO₂/Al₂O₃ molar ratios. The Pt dispersion, determined by CO chemisorption and transmission electron microscopy (TEM), as well as the surface acid concentration measured by the temperature-programmed desorption of ammonia (NH₃-TPD), increased with decreasing SiO₂/Al₂O₃ molar ratio for Pt/H-ZSM-5. The total yield of the polyols, i.e., sorbitol, manitol, ethylene glycol and propylene glycol, generally increased with increasing Pt dispersion in Pt/H-ZSM-5. The one-pot aqueous-phase reforming of cellulose into H₂ was also examined over the same catalysts. The Pt catalyst supported on H-ZSM-5 with a moderate SiO₂/Al₂O₃ molar ratio and a large external surface area showed the highest H₂ production rate. The Pt dispersion, surface acidity, external surface area and surface hydrophilicity appear to affect the catalytic activity for this reaction.     

Synergism Between Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Au/TiO<Subscript>2</Subscript> in the Low Temperature Oxidation of Propene

CO impedes the low temperature (<170 °C) oxidation of C₃H₆ on supported Pt. Supported Au catalysts are very effective in the removal of CO by oxidation, although it has little propene oxidation activity under these conditions. Addition of Au/TiO₂ to Pt/Al₂O₃ either as a physical mixture or as a pre-catalyst removes the CO and lowers the light-off temperature (T ₅₀) for C₃H₆ oxidation compared with Pt catalyst alone by ~54 °C in a feed of 1% CO, 400 ppm C₃H₆, 14% O₂, 2% H₂O.     

Aqueous-Phase Hydrogenolysis of Glycerol to 1,3-propanediol Over Pt-H<Subscript>4</Subscript>SiW<Subscript>12</Subscript>O<Subscript>40</Subscript>/SiO<Subscript>2</Subscript>

Abstract  

Hydrogenolysis of glycerol to 1,3-propanediol in aqueous-phase was investigated over Pt-H₄SiW₁₂O₄₀/SiO₂ bi-functional catalysts with different H₄SiW₁₂O₄₀ (HSiW) loading. Among them, Pt-15HSiW/SiO₂ showed superior performance due to the good dispersion of Pt and appropriate acidity. It is found that Br?nsted acid sites facilitate to produce 1,3-PDO selectively confirmed by Py-IR. The effects of weight hourly space velocity, reaction temperature and hydrogen pressure were also examined. The optimized Pt-HSiW/SiO₂ catalyst showed a 31.4% yield of 1,3-propanediol with glycerol conversion of 81.2% at 200 °C and 6 MPa.     

Characterization of Fischer–Tropsch Cobalt-Based Catalytic Systems (Co/SiO<Subscript>2</Subscript> and Co/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>) by X-ray Diffraction and Magnetic Measurements

Results of the characterization of six Co-based Fischer–Tropsch (FT) catalysts, with 15% Co loading and supported on SiO₂ and Al₂O₃, are presented. Room temperature X-ray diffraction (XRD), temperature and magnetic field (H) variation of the magnetization (M), and low-temperature (5 K) electron magnetic resonance (EMR) are used for determining the electronic states (Co⁰, CoO, Co₃O₄, Co²⁺) of cobalt. Performance of these catalysts for FT synthesis is tested at reaction temperature of 240 °C and pressure of 20 bars. Under these conditions, 15% Co/SiO₂ catalysts yield higher CO and syngas conversions with higher methane selectivity than 15% Co/Al₂O₃ catalysts. Conversely the Al₂O₃ supported catalysts gave much higher selectivity towards olefins than Co/SiO₂. These results yield the correlation that the presence of Co₃O₄ yield higher methane selectivity whereas the presence of Co²⁺ species yields lower methane selectivity but higher olefin selectivity. The activities and selectivities are found to be stable for 55 h on-stream.     

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).     

Synthesis of nickel catalysts supported on Zr-doped ordered mesoporous Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and their catalytic performance for low-temperature CO<Subscript>2</Subscript> reforming of CH<Subscript>4</Subscript>

A series of Zr-doped ordered mesoporous Al₂O₃ with various Zr contents were synthesized by evaporation-induced self-assembly strategy and the Ni-based catalysts supported on these Al₂O₃ materials were prepared by impregnation method. These catalysts with large specific surface area, big pore volume, uniform pore size possess excellent catalytic performance for the low-temperature carbon dioxide reforming of methane. The activities of these catalysts were tested in carbon dioxide reforming of methane reaction with temperature increasing from 500 to 650?°C and the stabilities of these catalysts were evaluated for long time reaction at 650?°C. It was found that when Zr/(Zr?+?Al) molar ratio?=?0.5%, the Ni/0.5ZrO₂–Al₂O₃ catalyst showed the highest activity, and exhibited superior stabilization compared to the Ni-based catalyst supported on traditional ordered mesoporous Al₂O₃. The “confinement effect” from mesoporous channels of alumina matrix is helpful to stabilize the Ni nanoparticles. As a promoter, Zr could stabilize the ordered mesoporous framework by reacting with Al₂O₃ to form ZrO₂–Al₂O₃ solid solution. Since ZrO₂ enhances the dissociation of carbon dioxide, more oxygen intermediates are given to remove the carbon formed during the reaction.     

Unexpected Support Effect in Hydrotreating: Evidence of a Metallic Character for ReS<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and ReS<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> Catalysts

Abstract  

Rhenium sulfide based catalysts were prepared by the incipient wetness impregnation method over alumina and silica supports and evaluated for 4,6-dimethyldibenzothiophene hydrodesulfurization in a high-pressure stirred-tank reactor. The catalyst prepared over silica was about six times more active for hydrodesulfurization than the corresponding catalyst prepared over alumina and a NiMo/Al₂O₃ industrial reference catalyst. This surprising and positive SiO₂ support effect was explained by a metallic character of the supported sulfide, which was demonstrated using a kinetic approach of competitive hydrogenations and by XPS characterization.     

The role of TiO<Subscript>2</Subscript> layers deposited on YSZ on the electrochemical promotion of C<Subscript>2</Subscript>H<Subscript>4</Subscript> oxidation on Pt

The electrochemical promotion of Pt/YSZ and Pt/TiO₂/YSZ catalyst-electrodes has been investigated for the model reaction of C₂H₄ oxidation in an atmospheric pressure single chamber reactor, under oxygen excess between 280 and 375 °C. It has been found that the presence of a dispersed TiO₂ thin layer between the catalyst electrode and the solid electrolyte (YSZ), results in a significant increase of the magnitude of the electrochemical promotion of catalysis (EPOC) effect. The rate enhancement ratio upon current application and the faradaic efficiency values, were found to be a factor of 2.5 and 4 respectively, higher than those in absence of TiO₂. This significantly enhanced EPOC effect via the addition of TiO₂ suggests that the presence of the porous TiO₂ layer enhances the transport of promoting O²⁻ species onto the Pt catalyst surface. This enhancement may be partly due to morphological factors, such as increased Pt dispersion and three-phase-boundary length in presence of the TiO₂ porous layer, but appears to be mainly caused by the mixed ionic-electronic conductivity of the TiO₂ layer which results to enhanced O²⁻ transport to the Pt surface via a self-driven electrochemical promotion O²⁻ transport mechanism.     

Sintering‐induced aromatization during n‐heptane reforming on Pt/Al2O3 catalysts

A platinum/alumina catalyst was sintered in oxygen and hydrogen atmospheres using two metal loadings of the catalyst: 0.3% Pt and 0.6% Pt. After sintering, the aromatization selectivity was investigated with the reforming of n‐heptane as the model reaction at a temperature of 500 °C and a pressure of 391.8 kPa. The primary products of n‐heptane reforming on the fresh platinum catalysts were methane and toluene, with subsequent conversion of benzene from toluene demethylation. To induce sintering, the catalysts were treated with oxygen at a flow rate of 60 mL min^?1, pressure of 195.9 kPa and temperatures between 500 and 800 °C. The 0.3% Pt/Al₂O₃ catalyst exhibited enhanced aromatization selectivity at various sintering temperatures while the 0.6% Pt/Al₂O₃ catalyst was inherently hydrogenolytic. The fact that aromatization was absent on the 0.6% Pt/Al₂O₃ catalyst was attributed to the presence of surface structures with dimensionality between two and three as opposed to essentially 2‐D structures on the 0.3% Pt/Al₂O₃ catalyst surface. On the 0.3% Pt/Al₂O₃ catalyst, the reaction product ranged from only toluene at a 500 °C sintering temperature to predominantly cracked product at a sintering temperature of 650 °C and no reaction at 800 °C. For sintering at about 650 °C, subsequent conversion of n‐heptane was complete and dropped thereafter. The turnover number was observed to change from 0.07 to 2.26 s^?1 as the dispersion changed from 0.33 to 0.09. The Koros–Nowark (K–N) test was used to check for the presence of internal diffusional incursions and Boudart's criterion was used for structural sensitivity determination. The K–N test indicated the absence of diffusional resistances while n‐heptane reforming was found to be structure sensitive on the Pt/Al₂O₃ catalyst. Copyright © 2006 Society of Chemical Industry     

Effect of the zeolite modulus of Pt/MOR/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts on the <Emphasis Type="Italic">n</Emphasis>-heptane isomerization reaction

The effect of the mordenite acidic modulus (SiO₂/Al₂O₃, 20 and 30) of Pt/MOR/Al2O3 catalysts on the heptane isomerization reaction is investigated. The content of zeolite in the catalysts is varied from 10 to 50 wt %, with platinum applied to the samples from solutions of different precursors: H₂PtCl₆ and [Pt(NH₃)₄]Cl₂. It is established via the TPD of ammonia and FTIR spectroscopy (the adsorption of NH₃ and СО) that the total acidity of zeolite falls as the modulus grows: the number of Brønsted (BAC) and Lewis (LAC) acidic sites is reduced, accompanied by an increase in the strength of their acidity. The catalysts are tested in the n-heptane isomerization reaction. It is shown that the selectivity of n-heptane isomerization falls substantially when the acidic mordenite modulus is increased from 20 to 30.     

Reactions of methylcyclopentane on Rh–Pt catalyst prepared by underpotential deposition of Rh on Pt/SiO2

Rh was deposited on to a well-characterized 3.1% Pt/SiO₂ (InCat-1) parent catalyst by underpotential deposition method to obtain a model Rh–Pt bimetallic catalyst. TEM and EDS was used to determine its mean particle size and bulk composition: the particles of ca. 3 nm contained ca. 60% Pt and 40% Rh. The Rh–Pt catalyst was tested in methylcyclopentane (MCP) reaction between 513 K and 603 K and 60–480 Torr H₂ pressure (with 10 Torr MCP). The parent Pt/SiO₂ as well as a 5% Rh/SiO₂ catalyst were also studied for comparison. Four subsequent treatments with O₂ and H₂ up to T = 673 K were applied on the bimetallic catalyst before the catalytic runs. The overall activity showed positive hydrogen order on all samples, bimetallic Rh–Pt resulting in the lowest TOF values. Ring opening and hydrogenolysis products, as well as unsaturated hydrocarbons were formed from MCP. The selectivity of ring opening products and fragments over Rh–Pt catalyst was between the values observed on Pt and Rh, while the selectivity towards benzene formation was highest on the bimetallic sample, especially at higher temperatures. “Selective” ring opening occurred on all samples, resulting mostly in 2 and 3-methylpentane and less hexane. Different pretreatments with H₂ and O₂ affected slightly the dispersion values and the catalytic behavior of Rh–Pt sample. The selectivities of the Rh–Pt catalyst being between the values observed for Pt/SiO₂ and Rh/SiO₂ indicates that the sample studied represented a real bimetallic catalyst, resembling both components and exhibiting at the same time, new properties in addition to those, characteristic of Pt or Rh. Dedicated to Konrad Hayek.     

Influence of calcination temperature on the structure and properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> as support for Pd catalyst

We investigated the influence of the calcination temperature on the structural properties of Al₂O₃ and how the resultant Al₂O₃ support affects the characteristics of Pd/Al₂O₃ catalysts. Al₂O₃ pretreated at different calcination temperatures ranging from 500 °C to 1,150 °C, was used as catalyst supports. The Pd/Al₂O₃ catalysts were prepared by a deposition-precipitation method using a pH 7.5 precursor solution. Characterization of the prepared Pd/Al₂O₃ catalysts was performed by X-ray diffraction (XRD), N₂-physisorption, CO₂-temperature programmed desorption (TPD), CO-chemisorption, and field emission-transmission electron microscopic (FE-TEM) analyses. The CO-chemisorption results showed that the Pd catalyst with the Al₂O₃ support calcined at 900 °C, Pd/Al₂O₃ (900), had the highest and most uniformly dispersed Pd particles, with a Pd dispersion of 29.8%. The results suggest that the particle size and distribution of Pd are related to the phase transition of Al₂O₃ and the ratio of isolated tetrahedral to condensed octahedral coordination sites (i.e., functional groups), where the tetrahedral sites coordinate more favorably with Pd.     

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.     

Combined Steam and Carbon Dioxide Reforming of Methane on Ni/MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript>: Effect of CeO<Subscript>2</Subscript> Promoter to Catalytic Performance

Abstract  

The catalytic performance during combined steam and carbon dioxide reforming of methane (SCR) was investigated on Ni/MgAl₂O₄ catalyst promoted with CeO₂. The SCR catalyst was prepared by co-impregnation method using nickel and cerium metal precursors on hydrotalcite-like MgAl₂O₄ support. In terms of catalytic activity and stability, CeO₂-promoted Ni/MgAl₂O₄ catalyst is superior to Ni–CeO₂/Al₂O₃ or Ni/MgAl₂O₄ catalysts because of high resistance to coke formation and suppressed aggregation of nickel particles. The role of CeO₂ on Ni/MgAl₂O₄ catalyst was elucidated by carrying out the various characterization methods in the viewpoint of the aggregation of nickel particles and metal-support interactions. The observed superior catalytic performance on CeO₂-promoted Ni/MgAl₂O₄ catalyst at the weight ratio of MgO/Al₂O₃ of 3/7 seems to be closely related to high dispersion and low aggregation of active metals due to their strong interaction with the MgAl₂O₄ support and the adjacent contact of Ni and CeO₂ species. The CeO₂ promoter also plays an important role to suppress particle aggregation by forming an appropriate interaction of NiO–CeO₂ as well as Ni–MgAl₂O₄ with the concomitant enhancement of mobile oxygen content.     

Controllable synthesis of EU-1 molecular sieve with high SiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ratios in thermodynamic stable sol system

A new green chemical route was designed in this paper for the synthesis of high-silica EU-1 molecular sieve in TEAOH–SiO₂–Al₂O₃–HMBr₂–H₂O system in which tetraethylammonium hydroxide (TEAOH) substituted for sodium hydroxide (NaOH) as an alkali source. The physicochemical properties of the synthesized samples characterized by such means as X-ray powder diffraction (XRD), electrophoresis apparatus, precise pH meter, scanning electron microscope, Fourier infrared spectrometer (FT-IR), thermo gravimetric analyzer (TG) and temperature programmed desorption (NH₃-TPD). The research results showed that the SiO₂/Al₂O₃ ratio of EU-1 molecular sieve could reach 706 with TEAOH as an alkali source. The SiO₂/Al₂O₃ ratio of the product was improved greatly to 1046 with the template agent increasing. The new synthetic route has also significantly expanded the synthetic phase region. The absolute value of zeta potential of the TEAOH sol system was obviously higher than that of the NaOH sol system, indicating the thermodynamic stability of the former sol system was higher and better for the synthesis of pure high-silica EU-1 molecular sieve. The FT-IR spectra and TG/DTG diagrams of products indicated that TEA⁺ occluded in the final products could balance electronegative framework. The amount of strong, weak and the total acidity reduced with the increase of SiO₂/Al₂O₃ ratio. The catalytic results of methanol-to-hydrocarbon demonstrated that the molecular sieve prepared by the new method has better catalytic performance.     

Modification of Cu/Zn/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalyst by Activated Carbon Based Metal Organic Frameworks as Precursor for Hydrogen Production

In this study, Cu/Zn/Al₂O₃-AC (AC?=?activated carbon) catalyst was synthesized and evaluated for dimethoxymethane (DMM) reformation to hydrogen. The Cu/Zn/Al₂O₃-AC catalyst was prepared using high surface area metal organic frameworks (MOFs) consisting of Cu₃(BTC)₂ (MOF-199) and Zn₄O(BDC)₃ (MOF-5) for Cu(II) and Zn(II) sources respectively, as precursors while γ-Al₂O₃ was applied as support. The synthesized catalyst was investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Brunauer–Emmett–Teller analysis (BET), Temperature programmed desorption (NH₃-TPD) and Energy-dispersive X-ray spectroscopy (EDX) techniques. Complete DMM conversion was observed over Cu/Zn/Al₂O₃-AC catalyst (Cu:Zn:Al mole ratio of 6:3:2) under atmospheric pressure, T?=?533 K, GHSV?=?20 NL h^?1 g_cat^?1, N₂/H₂O/DMM?=?24/5/1 volume percent (vol%) with hydrogen productivity of 12.8 L H₂ h^?1 g_cat^?1 and 64% hydrogen concentration. Application of MOFs as precursors and modified activated carbon as an acidic component provided the catalyst with the porous structure and high specific surface area for the hydrolysis of DMM, subsequently, high selectivity and productivity of hydrogen was obtained.     

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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