High Surface Area MgO Research Articles

CO2 methanation using metals nanoparticles supported on high surface area MgO

This work shows that Ru nanoparticles supported on high surface area nano MgO is a highly active and selective catalyst for CO2 methanation, which is a promising method to store renewable energy and limit the emission of greenhouse gasses. We studied the effect of the Ru loading on MgO supports with different surface areas and compared the results to the corresponding Ni-based catalyst. Our results show that high surface area MgO containing 5 wt % Ru has the highest activity. This catalyst was stable for more than 50 h and resulted in 54 % conversion at 375 °C, which, under the given reaction conditions, corresponds to a site time yield of 520 molCH4 molRu−1 h−1. For comparison, the Ni-based catalyst only resulted in 45 % conversion at 450 °C with a low selectivity to CH4 (STY=263 molCH4 molNi−1 h−1). Furthermore, Ru on high surface area MgO catalyst was already active at low temperature of 250 °C due to chemisorption and activation of CO2 on the MgO support, which is promising for low-temperature CO2 methanation.

Synthesis and characterization of plate like high surface area MgO nanoparticles for their antibacterial activity against Bacillus cereus (MTCC 430) and Pseudomonas aeruginosa (MTCC 424) bacterias

• A high surface area and plate like MgO were synthesized by simple precipitation method. • MgO showed good antibacterial activity against both Bacillus cereus and Pseudomonas aeruginosa bacterias. • Pseudomonas aeruginosa (MTCC 424) was slightly resistant compared to Bacillus cereus (MTCC 430). • The effect of morphology, surface area, and particle size on antibacterial activity was analysed. In the present work high surface area MgO nanoparticles were synthesized by simple precipitation method without using any directing agent or capping agent. In this regard various experimental conditions required to achieve high surface area MgO nanoparticles have been addressed in this work. The experimental conditions namely, pH, calcination temperature, digestion temperature, digestion temperature and nature of precursor and precipitating agent, collectively produce high surface area MgO nanoparticles. The optical bandgap, functional group identification, the crystalline phase, surface morphology of MgO nanoparticles were obtained from UV– Vis, FTIR, XRD, SEM, and HRTEM techniques. The optical bandgap was found to be 5.8 eV. With the help of BET technique both specific surface area and the average pore diameter values were obtained and were found to be 246.95 g/m 2 and 6.721 nm respectively. The antibacterial activity of MgO nanoparticles was tested against Bacillus cereus (MTCC 430) and Pseudomonas aeruginosa (MTCC 424) bacterias. The material exhibited good antibacterial activity against both bacterias. A dosage concentration of 80 mg/ml concentration was sufficient to inhibit the bacterial growth. Further analysed the effect of particles size, surface area, optical bandgap, and morphology on antibacterial activity of MgO nanoparticles.

Co2 Methanation Using Metals Nanoparticles Supported on High Surface Area Mgo

Co2 Methanation Using Metals Nanoparticles Supported on High Surface Area Mgo

Ionic liquid-based controllable synthesis of MgO nanostructures for high specific surface area

Mesoporous MgO with nanoparticle morphology was synthesized via ionothermal, reflux and hydrothermal methods in the presence of 1-octyl-3-methylimidazolium bromide ionic liquid (IL) at a constant temperature. The analysis of structures and textural properties were carried out in the presence and lack of the IL. The results show that the IL and the method of synthesis influence the surface area and pore size of the product. It is shown that the reflux method, as a greener route, led to the highest surface area in comparison to other methods. The micelles formed in water by an ionic liquid at 80 °C, seem to have an important role in this regard. Hence, a special method producing high surface area MgO nanostructure is introduced. This successful method for the preparation of high surface area MgO can be applied for the production of effective adsorbents and catalysts in the reactions.

Synthesis of Hydrocinnamaldehyde via Vapor Phase Dehydrogenation of Hydrocinnamyl alcohol over Rice‐Derived MgO‐Supported Copper Catalysts

AbstractGreen synthetic method for the production of hydrocinnamaldehyde via vapour phase dehydrogenation of hydrocinnnamyl alcohol over high surface area MgO (HSA‐MgO) supported Cu catalyst at atmospheric pressure without using any additives has been attempted. Cu/HSA‐MgO catalysts have been prepared by thermal decomposition of cooked rice grains mixed with magnesium acetate followed by wet impregnation by Cu. The prepared catalysts have been characterized by various physiochemical characterization techniques such as TGA, XRD, BET surface area, TPD of CO2, H2‐TPR, TEM, SEM, EDX and N2O pulse chemisorption. Among all the catalysts, 10%Cu/HSA‐MgO catalyst is found to be the best catalyst with 78% conversion of hydrocinnnamyl alcohol and 96% selectivity of hydrocinnamaldehyde. N2O pulse chemisorption and TPR analysis results divulge the high dispersion of smaller copper particles on the surface of HSA‐MgO support which is considered to be responsible for its superior catalytic activity.

Deactivation studies of bimetallic AuPd nanoparticles supported on MgO during selective aerobic oxidation of alcohols

Here we report the synthesis and characterisation of high surface area MgO prepared via the thermal decomposition of various magnesium precursors (MgCO3, Mg(OH)2 and MgC2O4). Bimetallic gold-palladium nanoalloy particles were supported on these MgO materials and were tested as catalysts for the solvent-free selective aerobic oxidation of benzyl alcohol to benzaldehyde. All these catalysts were found to be active and very selective (>97%) to the desired product (benzaldehyde). However, MgO prepared via the thermal decomposition of magnesium oxalate displayed the highest activity among all the magnesium oxide supports tested. Attempts were made to unravel the reasons for the deactivation of these catalysts using different characterisation techniques namely in situ XRD, XPS, ICP-MS, TEM, and TGA-MS. From the data obtained, it is clear that MgO undergoes phase changes from MgO to Mg(OH)2 and MgCO3 during catalyst preparation as well as during the catalytic reaction. Besides phase changes, strong adsorption of reactants and products on the catalyst surface, during the reaction, were also observed and washing the catalyst with organic solvents did not completely remove them. The phase change and catalyst poisoning were reversed through high temperature heat treatments. However, these processes led to the sintering of the metal nanoparticles. Moreover, substantial leaching of the support material (MgO) was also observed during the reaction. These latter two processes led to the irreversible deactivation of AuPd nanoparticles supported on MgO catalyst during the solvent-free selective aerobic oxidation of alcohols. Among the three different MgO supports studied in this article, an inverse correlation between the catalytic activity and Mg leaching has been observed. This article reports a deeper understanding of the mode of deactivation observed in metal nanoparticles supported on MgO during liquid phase reactions.

Thermal Stability Limits of Imidazolium Ionic Liquids Immobilized on Metal-Oxides.

Thermal stability limits of 33 imidazolium ionic liquids (ILs) immobilized on three of the most commonly used high surface area metal-oxides, SiO2, γ-Al2O3, and MgO, were investigated. ILs were chosen from a family of 13 cations and 18 anions. Results show that the acidity of C2H of an imidazolium ring is one of the key factors controlling the thermal stability. An increase in C2H bonding strength of ILs leads to an increase in their stability limits accompanied by a decrease in interionic energy. Systematic changes in IL structure, such as changes in electronic structure and size of anion/cation, methylation on C2 site, and substitution of alkyl groups on the imidazolium ring with functional groups have significant effects on thermal stability limits. Furthermore, thermal stability limits of ILs are influenced strongly by acidic character of the metal-oxide surface. Generally, as the point of zero charge (PZC) of the metal-oxide increases from SiO2 to MgO, the interactions of IL and metal-oxide dominate over interionic interactions, and metal-oxide becomes the significant factor controlling the stability limits. However, thermal stability limits of some ILs show the opposite trend, as the chemical activities of the cation functional group or the electron donating properties of the anion alter IL/metal-oxide interactions. Results presented here can help in choosing the most suitable ILs for materials involving ILs supported on metal-oxides, such as for supported ionic liquid membranes (SILM) in separation applications or for solid catalyst with ionic liquid layer (SCILL) and supported ionic liquid phase (SILP) catalysts in catalysis.

Cascade Synthesis of Thieno[2,3-b]pyridines by Using Intramolecular Cyclization Reactions of 3-Cyano-2-(organylmethylthio)pyridines

2-Amino-4-aryl-6-mercaptopyridine-3,5-dicarbonitriles as starting materials have been prepared by reducing of 2-amino-4-aryl-6-(phenylthio)pyridine-3,5-dicarbonitrile derivatives which were synthesized on stepwise one-pot three component reaction of malononitrile, aldehydes and thiophenol in the presence of base catalysts such as triethylamine, high surface area (HSA) MgO or nanocrystalline magnesium oxide. Alkylation of 2-amino-4-aryl-6-mercaptopyridine-3,5-dicarbonitriles with α-halogen compounds in presence of sodium alkoxide as base catalyst followed with cyclization afforded the thieno[2,3-b]pyridine derivatives in excellent yields and in a short reaction time.

ChemInform Abstract: Three‐Component Synthesis of 4‐Amino‐2‐aryl‐2H‐pyrimido‐[1,2‐b][1,3]benzazole‐3‐carbonitriles and 4H‐Pyrimido‐[2,1‐b][1,3]benzazoles in the Presence of Magnesium Oxide and 12‐Tungstophosphoric Acid as Catalysts.

AbstractThe title compounds are obtained by three‐component reactions of 2‐aminobenzimidazole or 2‐aminobenzothiazole (I) with aldehydes and malononitrile or β‐ketoesters using high surface area MgO as catalyst.

Methanol as a clean and efficient H-transfer reactant for carbonyl reduction: Scope, limitations, and reaction mechanism

The previously unexplored use of methanol as a H-transfer agent for the Meerwein–Ponndorf–Verley reduction of aromatic aldehydes and aryl ketones is described. Furfural, 5-hydroxymethylfurfural, benzaldehyde, and acetophenone were selectively reduced to the corresponding alcohols in mild conditions. The reaction mechanism was elucidated by means of reactivity tests and DFT calculations. It was found to include the highly efficient H-transfer with the formation of formaldehyde, which further reacted with excess methanol to generate the adsorbed hemiacetal. In turn, the latter reduced carbonyl, with the formation of methylformate, which further decomposed into CO, CH4, and CO2. Compared to the alcohols typically used for carbonyl reductions, methanol showed the advantage of producing gaseous components as the only co-products, which are easily separated from the reaction medium. In the case of furfural, a 100% yield to furfuryl alcohol was obtained, using the high-surface area MgO as the easily recoverable and reusable catalyst.

Simple method to synthesize high surface area magnesium oxide and its use as a heterogeneous base catalyst

High surface area magnesium oxide (∼250–300m2g−1) was synthesized via the thermal decomposition of different precursors including (MgCO3)4Mg(OH)2, Mg(OH)2, MgCO3 and MgC2O4. The high surface area MgO displayed exceptionally high catalytic activity for the liquid phase Meerwein–Ponndorf–Verley (MPV) reaction of benzaldehyde with different alcohols. The effect of the calcination temperature and precursor source on the catalytic activity and morphology of MgO has been investigated in detail. It was found that the optimum calcination temperature was 450°C leading to a high surface area material containing no MgCO3 which is the key to obtaining high catalytic activity of MgO for the MPV reaction. The high area MgO catalyst could be reused without loss of catalyst activity. The simplicity of the synthesis method gives this methodology widespread applicability in countless applications that currently use homogeneous base catalysts or stoichiometric bases as reagents.

Characterization of Surface Acidity of Carbonated Materials by IR-Sensitive Molecular Probes: Advantages of Using tert-Butyl Cyanide

Bulk carbonates or carbonated surfaces are increasingly relevant materials applied to many base-catalyzed reactions. Various basic molecular probes were considered for the assessment of the surface acidity of a highly carbonated catalyst, namely a high surface area MgO prepared by sol–gel and activated at 240 °C. Using such a low activation temperature results in the presence of large amounts of residual superficial carbonates that hinders analysis with common IR acidity probes. Compared with pyridine, acetonitrile, and its deuterated counterpart CD3CN, tert-butyl cyanide (noted TBC, also known as pivalonitrile) appeared as the most appropriate probe to assess surface acidity at room temperature on this material. TBC did not lead to any measurable dissociative adsorption and easily enabled the differentiation between Lewis and Brønsted (i.e., surface hydroxyls) acid sites on carbonated solids on which the characteristic pyridine adsorption region (1700–1200 cm–1) is completely obscured by the signal of carbonates. The interpretation of the TBC-based spectra was also much more straightforward than those based on acetonitrile and deuterated acetonitrile, which both led to significant probe dissociation on the surface of the sample. TBC therefore appears as a suitable acidity probe for carbonated materials, opening the way to facile characterization of carbonate-rich base catalysts activated at low temperatures.

A convenient one-pot synthesis and anxietic activity of 3-cyano-2(1H)-iminopyridines and halogen derivatives of benzo[h]chromenes

A general and easy method for the synthesis of 4,6-disubstituted-3-cyano-2(1H)-iminopyridine or 3-amino-6-chloro-1-aryl-1H-benzo[h]chromen-2-yl cyanide derivatives in the presence of high surface area MgO as a highly effective heterogeneous base catalyst is described. These compounds were synthesized using one-pot multicomponent reactions of the properly substituted acetophenone, appropriate aldehyde, ammonium acetate and malononitrile or three component reactions of 4-chloro-2-naphthol, aldehydes and malononitrile, respectively, in DMF. The compound of 7c was evaluated for its anxiolytic activities.

Chirality-enriched semiconducting carbon nanotubes synthesized on high surface area MgO-supported catalyst

Single-walled carbon nanotubes (SWCNTs) with a narrow diameter distribution were synthesized by radio frequency-Catalytic Chemical Vapor Deposition (RF-CCVD) through the pyrolysis of CH4. Fe–Co bimetallic catalytic nanoclusters were supported on high-surface area MgO nanopowders and used in the nanotube synthesis process. Nanolog absorption fluorescence analysis was used to characterize the chiralities of the as-produced SWCNTs over this nanostructural catalyst. In the final SWCNT sample, the (7,5) semiconducting carbon nanotube species were found to be dominant, with a low chirality variation.

Properties of alkali-promoted Cu–MgO catalysts and their activity for methanol decomposition and C 2-oxygenate formation

The decomposition of CH 3OH in the presence of CO has been investigated over high surface area MgO, Cu–MgO, K–Cu–MgO and Cs–Cu–MgO catalysts. The catalysts were prepared by thermal decomposition of metal salts mixed with palmitic acid. The reduced catalysts had surface areas of 18–74 m 2 g −1 and intrinsic basicities of 4–17 μmol CO 2 m −2. Results revealed that methyl formate was a primary product of CH 3OH decomposition, whereas CO was a secondary product. Although selectivity to C 2 species (ethanol and acetic acid) was low (<5 C-atom %) at the low pressure (101 kPa) conditions of the present study, there was an optimum intrinsic basicity (9.5 μmol CO 2 m −2) at which the selectivity to C 2 species and methyl formate reached a maximum. The role of catalyst basic properties in the formation of C 2 species from CH 3OH is discussed.

Heterogeneously-Catalyzed Glycerolysis of Fatty Acid Methyl Esters: Reaction Parameter Optimization

The synthesis of monoglycerides by glycerolysis of methyl oleate, an unsaturated fatty acid methyl ester, was studied on strongly basic high surface area MgO as an alternative to the current commercial technology that uses liquid base catalysts. Initially, the reaction conditions such as catalyst particle size and stirring rate required for operating the four-phase reactor under a kinetically controlled regime were determined. Then, the optimization of the reaction parameters for achieving high monoglyceride yields was performed. Results showed that glycerolysis of methyl oleate on MgO compares favorably with the corresponding homogeneously catalyzed process. In fact, when using high reaction temperatures (493−523 K), glycerol/methyl oleate molar ratios between 2 and 6, and catalyst/reactant ratios of about 30 g/mol, glycerolysis of methyl oleate on MgO yields up to 77% monoglycerides in 2 h, a much higher value than those usually obtained via the liquid-base-catalyzed homogeneous process (40−60%).

Synthesis of porous, high surface area MgO microspheres

Porous MgO microspheres with nanocrystallites have been prepared by a wet precipitation process using ammonium hydrogen carbonate and ammonium hydroxide as precipitants. The as-precipitated powders are composed of crystalline Mg 5(OH) 2(CO 3) 4.4H 2O microspheres with porous and hollow microstructure and are decomposed and transformed to nanocrystalline cubic MgO after being calcined at 500 °C. The average crystallite size of MgO microspheres increases from 10 nm to 31.6 nm with increasing temperature from 500 °C to 1100 °C. The surface area of the MgO powder decreases from 90.7 m 2/g to 31.5 m 2/g with increasing temperature from 500 °C to 1100 °C.

Surface area and thermal stability effect of the MgO supported catalysts for the synthesis of carbon nanotubes

Surface area (SA) of the oxide support was found to play a major role on the morphology, quality of the single wall carbon nanotubes (SWNTs) growth. Fe–Co bimetal was supported onto MgO powders with different surface areas, and used for the SWNTs synthesis from the pyrolysis of CH4 through radio frequency catalytic chemical vapor deposition (RF-CCVD). The high surface area MgO showed specificity towards the growth of SWNTs even at the very high metal loadings of 17.4%. As the MgO surface areas decreased, the agglomeration of the active metal species on the support, nanotubes with wider diameter distributions and more graphitic walls were obtained. This surface area effect suggested that the high surface area networks were responsible for a more effective confinement of the active metal nanoparticles that impeded their migration during the SWNTs thermal growth process. Therefore, by adjusting the surface area or chemical morphology of the catalyst systems, SWNTs with narrower diameter distribution and specific chiralities can be grown.

Pd catalysts supported on MgO, ZrO2 or MgO-ZrO2: Preparation, characterization and study in hexane conversion

Abstract High surface area zirconia and MgO–ZrO2 composites are prepared and used as supports of Pd catalysts. Amorphous zirconia is prepared via precipitation and digestion of zirconium oxyhydroxide in hydrazine. Composite MgO–ZrO2 oxides are obtained by (i) grafting of zirconium acetylacetonate on MgO and (ii) coprecipitation of a mixed gel of zirconium oxyhydroxide and magnesium hydroxide. Several methods of palladium deposition are investigated: multi-step processes such as anchoring and impregnation of Pd acetylacetonate, single-step processes such as electroless and photodeposition in acidic or basic medium (for zirconia only). These catalysts are tested in hexane conversion at 753 K. In continuous flow reactor measurements, only aromatic, cracking and isomerization products are detected, with only very low amounts of methylcyclopentane. Deposition of Pd via anchoring of Pd(acac)2 leads to the smallest metal particle size (4–5 nm) whatever the support. The basic MgO support favours strongly aromatization (near 90% selectivity) but limits conversion (around 12%). Introduction of small quantities of zirconia on MgO increases the conversion without loss of aromatization selectivity. Conversely, zirconia-rich supports favour isomerization at the expense of aromatization but increase the conversion (around 22%). With pure zirconia, the conversion suffers a marked decrease with time. The cracking selectivity is low (≤10%) for all anchored catalysts. The method of palladium deposition on zirconia has a marked influence on the catalytic performances. The significant differences in conversion at stationary state (electroless ≪ photodeposition in acidic medium

Carbon nanotube and nanofiber syntheses by the decomposition of methane on group 8–10 metal-loaded MgO catalysts

We have found that several precious metal-loaded MgO catalysts are active in the formation of carbon nanotube (CNT) by the chemical vapor deposition (CVD) of methane. The catalysts were prepared with nine metals (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt) by impregnation onto a high surface area MgO. CNT synthesis was carried out in the temperature range from 600 °C to 1000 °C after reduction with H 2 at 800 °C. The amount of carbon deposited and crystallinity in the produced CNT on nine metals showed interesting tendencies: (i) The amount of carbon formed increased in the following transition series metals: first < second < third row transition elements, and (ii) the index of crystallinity I G/ I D in Raman-bands of the CNTs decreased in the following order: 8 > 9 > 10 in the Periodic Table. Group 8 and 9 metals produced tube type fibers composed of the graphite layers arranged parallel to the fiber axis. On the other hand, carbon nanofibers (CNFs) grown on group 10 metals had herringbone type graphene sheets.