Mehran Rezaei

CO2 reforming of methane over nickel catalysts supported on nanocrystalline MgAl2O4 with high surface area

Abstract In this paper dry reforming of methane (DRM) was carried out over nanocrystalline MgAl 2 O 4 -supported Ni catalysts with various Ni loadings. Nanocrystalline MgAl 2 O 4 spinel with high specific surface area was synthesized by a co-precipitation method with the addition of pluronic P123 triblock copolymer as surfactant, and employed as catalyst support. The prepared samples were characterized by X-ray diffraction (XRD), N 2 adsorption, H 2 chemisorption, temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), temperature-programmed desorption (TPD) and transmission and scanning electron microscopies (TEM, SEM) techniques. The obtained results showed that the catalyst support has a nanocrystalline structure (crystal size: about 5 nm) with a high specific surface area (175 m 2 ·g −1 ) and a mesoporous structure. Increasing in nickel content decreased the specific surface area and nickel dispersion. The prepared catalysts showed high catalytic activity and stability during the reaction. SEM analysis revealed that whisker type carbon deposited over the spent catalysts and increasing in nickel loading increased the amount of deposited carbon. The nickel catalyst with 7 wt% of nickel showed the highest catalytic activity.

Effect of Ni loadings on the activity and coke formation of MgO-modified Ni/Al2O3 nanocatalyst in dry reforming of methane

MgO-modified Ni/Al2O3 catalysts with different Ni loadings were prepared and employed in dry reforming of methane (DRM). The effect of Ni loadings on the activity and coke formation of Ni/MgO-Al2O3 catalysts were investigated. The synthesized catalysts were characterized by XRD, N2 adsorption-desorption, SEM, TPO and TPR techniques. The obtained results showed that increasing nickel loading decreased the BET surface area and increased the catalytic activity and amount of deposited carbon. In addition, the effect of gas hourly space velocity (GHSV) and feed ratio were studied.

Preparation of nanocrystalline γ-Al2O3 catalyst using different procedures for methanol dehydration to dimethyl ether

Abstract A series of nanocrystalline γ-alumina are synthesized by different procedures, namely, thermal decomposition method (sample A), precipitation method (sample B) and sol-gel method using sucrose and hexadecyltrimethyl ammonium bromide (CTAB) as templates (samples C and D, respectively). Textural and acidic properties of γ-alumina samples are characterized by XRD, N 2 adsorption-desorption and NH 3 -TPD techniques. Vapor-phase dehydration of methanol into dimethyl ether is carried out over these samples. Among them, sample C shows the highest catalytic activity. NH 3 -TPD analysis reveals that the sample with smaller crystallite size possesses higher concentration of medium acidic sites and consequently higher catalytic activity. Thermal decomposition method leads to decrease in both surface area and moderate acidity, therefore it is the cause of lower catalytic activity.

Ni catalysts supported on nanocrystalline magnesium oxide for syngas production by CO2 reforming of CH4

Abstract CO 2 reforming of methane (CDRM) was carried out over MgO supported Ni catalysts with various Ni loadings. The preparation of MgO supported Ni catalysts via surfactant-assisted precipitation method led to the formation of a nanocrystalline carrier for nickel catalysts. The synthesized samples were characterized by XRD, N 2 adsorption-desorption, H 2 chemisorption, TPR, TPO and SEM techniques. It was found that the high catalytic activity and stability of the prepared catalysts could be attributable to high dispersion of reduced Ni species and basicity of support surface. In addition, the effect of feed ratio, nickel loading and GHSV on the catalytic performance of CDRM over the catalysts were investigated.

Mesoporous MgO·Al2O3 nanopowder-supported meso–macroporous nickel catalysts: a new path to high-performance biogas reforming for syngas

Mesoporous nanocrystalline MgO·Al2O3 powders with different MgO/Al2O3 molar ratios were synthesized by a new and simple sol–gel route using C3H6O (propylene oxide) as a gelation agent. The prepared powders were employed as a support for preparation of 10 wt% Ni catalysts in biogas reforming, for the production of synthesis gas. This simple sol–gel method led to the preparation of powders with high BET surface area in the range of 252.8–301.6 m2 g−1 depending on the MgO/Al2O3 molar ratio after calcination at 700 °C. The samples also exhibited narrow single modal pore size distributions in the mesopore region. The H2-TPR analysis revealed that increasing the MgO/Al2O3 molar ratio shifted the Tmax of the reduction peaks to higher temperature, indicating the lower reducibility of the prepared catalysts with high MgO content. The NH3-TPD also confirmed the increase in basicity of the prepared samples with increasing MgO/Al2O3 molar ratio. The prepared catalysts exhibited high potential as catalysts for biogas reforming with high stability, and the catalysts with higher content of MgO showed higher resistance against carbon formation.

Thermodynamic analysis of combined reforming process using Gibbs energy minimization method： In view of solid carbon formation

Thermodynamic analysis was applied to study combined partial oxidation and carbon dioxide reforming of methane in view of carbon formation. The equilibrium calculations employing the Gibbs energy minimization were performed upon wide ranges of pressure (1–25 atm), temperature (600–1300 K), carbon dioxide to methane ratio (0–2) and oxygen to methane ratio (0–1). The thermodynamic results were compared with the results obtained over a Ru supported catalyst. The results revealed that by increasing the reaction pressure methane conversion decreased. Also it was found that the atmospheric pressure is the preferable pressure for both dry reforming and partial oxidation of methane and increasing the temperature caused increases in both activity of carbon and conversion of methane. The results clearly showed that the addition of O2 to the feed mixture could lead to a reduction of carbon deposition.

Selective methanation of carbon monoxide in hydrogen rich stream over Ni/CeO2 nanocatalysts

Abstract In the present work, selective methanation of carbon monoxide in hydrogen rich stream was investigated over Ni/CeO 2 nanocatalysts. The obtained results revealed that increasing in nickel loading decreased the BET surface area, pore volume and nickel dispersion. The 25%Ni/CeO 2 with a NiO crystal size of 12 nm exhibited the highest activity in CO methanation reaction and reached to maximum CO conversion and CH 4 selectivity at temperatures above 230 °C. The catalytic results revealed that CO selective methanation well progressed at lower temperatures while CO 2 methanation was completely suppressed until CO conversion reached to maximum value.

Effects of CO2 content on the activity and stability of nickel catalyst supported on mesoporous nanocrystalline zirconia

Abstract The effects of carbon dioxide content on the catalytic performance and coke formation of nickel catalyst supported on mesoporous nanocrystalline zirconia with high surface area and pure tetragonal crystalline phase were investigated in methane reforming with carbon dioxide. The samples were characterized by XRD, BET, TPR, TPO, TPH, TEM, and SEM techniques. The catalyst prepared showed high surface area and a mesoporous structure with a narrow pore size distribution. The obtained results revealed that the increase in CO2 content increased the methane conversion and stability of the catalyst and significantly reduced the coke deposition. The TPH analysis showed that several species of carbon with different reactivities toward hydrogenation were deposited on the spent catalysts employed under different CO2 contents.

CH4 reforming with CO2 for syngas production over La2O3 promoted Ni catalysts supported on mesoporous nanostructured γ-Al2O3

Abstract Nanostructured γ-Al 2 O 3 with high surface area and mesoporous structure was synthesized by sol-gel method and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by XRD, N 2 adsorption-desorption, TPR, TPO, TPH, NH 3 -TPD and SEM techniques. The BET analysis showed a high surface area of 204 m 2 ·g −1 and a narrow pore-size distribution centered at a diameter of 5.5 nm for catalyst support. The BET results revealed that addition of lanthanum oxide to aluminum oxide decreased the specific surface area. In addition, TPR results showed that addition of lanthanum oxide increased the reducibility of nickel catalyst. The catalytic evaluation results showed an increase in methane conversion with increasing lanthanum oxide to 3 mol% and further increase in lanthanum content decreased the catalytic activity. TPO analysis revealed that the coke deposition decreased with increasing lanthanum oxide to 3 mol%. SEM and TPH analyses confirmed the formation of whisker type carbon over the spent catalysts. Addition of steam and O 2 to dry reforming feed increased the methane conversion and led to carbon free operation in combined processes.

Ultrasound assisted co-precipitation synthesis and catalytic performance of mesoporous nanocrystalline NiO-Al2O3 powders

Mesoporous nanocrystalline NiO-Al2O3 powders with high surface area were synthesized via ultrasound assisted co-precipitation method and the potential of the selected samples as catalyst was investigated in dry reforming reaction for preparation of synthesis gas. The prepared samples were characterized by N2 adsorption (BET), X-ray diffraction (XRD), Temperature programmed reduction and oxidation (TPR, TPO) and scanning electron microscopy (SEM) techniques. The effects of pH, power of ultrasound irradiation, aging time and calcination temperature on the textural properties of the catalysts were studied. The sample prepared under specified conditions (pH10, 70W, without aging time and calcined at 600°C) exhibited the highest surface area (249.7m2g-1). This catalyst was calcined at different temperature and employed in dry reforming of methane and the catalytic results were compared with those obtained over the catalysts prepared by impregnation and co-precipitation methods. The results showed that the catalyst prepared by ultrasound assisted co-precipitation method exhibited higher activity and stability with lower degree of carbon formation compared to catalysts prepared by co-precipitation and impregnation methods.