Dimethyl Ether Synthesis over Novel Silicotungstic Acid Incorporated Nanostructured Catalysts

Materials Research Bulletin, 2019

Sulfonic acids grafted on inorganic support such as SiO 2 and MCM41 was used as catalysts for conversion of methanol to dimethyl ether. In this experimental work the catalysts were compared for their catalytic properties in a continuous flow fixed-bed reactor at temperatures between 180 and 320°C and 1 bar. It was found that all SO 3 H-functionalized materials in this study were active, selective and stable for DME synthesis. According to the experimental results MCM-41-(CH 2) 3-SO 3 H exhibited the best performance, related to its higher surface area and acidity.

Catalysts

MCM-41-type mesoporous silicas were modified with alumina by the impregnation, co-condensation, and template ion-exchange (TIE) methods. The obtained materials were characterized with respect to their chemical composition (ICP-OES), textural parameters (low-temperature N2 sorption), structure (XRD), and surface acidity (NH3-TPD) and tested as catalysts of methanol to dimethyl ether (DME) dehydration in a flow microreactor system. The catalytic performance of the studied materials was analyzed with respect to their porous structure, as well as their density and the strength of their acid sites. It was shown that the performance of the studied catalysts depends on the contribution of the surface exposed aluminum species, as well as their aggregation. For the most active catalyst, the study of its catalytic stability under rection conditions was performed. It was shown that the catalyst can be effectively regenerated by the incineration of carbon deposits under air flow at 550 °C for 1 h.

Catalysis Communications, 2005

A series of solid-acid catalysts with different content of components were prepared by co-precipitation (sol-gel) method. These samples comprised silica-titania and modified c-Al 2 O 3 with phosphorus. To determination of optimum ones, the effects of various contents of phosphorus have been investigated. Dehydration of methanol to dimethyl ether (DME) on solid-acid catalysts was studied in a fixed-bed reactor at a temperature of 300°C under atmospheric pressure and a GHSV of 15,600 h À1 . The catalysts have been characterized using BET, XRD, FT-IR, NH 3 -TPD and elemental analysis techniques and also the results were reported. According to the experimental results, silica-titania catalysts have exhibited low activity for DME synthesis. Phosphorus-modified catalysts have shown better performance compared to the untreated c-Al 2 O 3 . It was found that surface areas increase with increasing in the molar ratio of aluminium-to-phosphorus at aluminium phosphate catalysts. Also, by modifying alumina with phosphorus, it was observed that the surface acidity of aluminium phosphate catalysts decrease with increasing in the molar ratio of Al/P at aluminium phosphate catalysts. The sample of non-stoichiometric aluminium phosphate (molar ratio of Al/P = 2) have exhibited the best conversion without any by-product.

Catalysis Today, 2012

Nano-structured Pd catalysts with enhanced CH 3 OH synthesis activities for CO 2 hydrogenation were prepared by integrating two different effects, i.e., incorporation of uniform mesoporous support such as MCM-41 and SBA-15 leading to small Pd nanoparticles inside nano-sized pore channels, and promotion by alkali/alkaline earth metal additives. Pd supported on these mesoporous silica without any promoters exhibited only weak activities for CH 3 OH formation, while the addition of K, Mg and Ca significantly enhanced their activities. K(Ca)-promoted Pd supported on SBA-15 yielded CH 3 OH 2-5 times as much as amorphous SiO 2-supported Pd catalysts. The formation rate of CH 3 OH over the supported Ca/Pd varied as a function of average pore diameter of the support, and decreased in the order of MCM-41 > SBA-15 > MCM-48 > MSU-F ∼ amorphous SiO 2. In situ Pd K-edge EXAFS and H 2 chemisorption measurements of the reduced catalysts demonstrated that small mesopores of MCM-41 and SBA-15 worked as a template for the formation of small Pd 0 nanoparticles, leading to the higher activities for CH 3 OH formation compared to the conventional amorphous silica supported counterpart.

Comptes Rendus Chimie, 2016

High surface area mesoporous silica based catalysts have been prepared by a simple hydrolysis/solegel process without using any organic template and hydrothermal treatment. A controlled hydrolysis of ethyl silicate-40, an industrial bulk chemical, as a silica precursor, resulted in the formation of very high surface area (719 m 2 /g) mesoporous (pore size 67 Å and pore volume 1.19 cc/g) silica. The formation of mesoporous silica has been correlated with the polymeric nature of the ethyl silicate-40 silica precursor which on hydrolysis and further condensation forms long chain silica species which hinders the formation of a close condensed structure thus creating larger pores resulting in the formation of high surface mesoporous silica. Ethyl silicate-40 was used further for preparing a solid acid catalyst by supporting molybdenum oxide nanoparticles on mesoporous silica by a simple hydrolysis solegel synthesis procedure. The catalysts showed very high acidity as determined by NH 3-TPD with the presence of Lewis as well as Brønsted acidity. These catalysts showed very high catalytic activity for esterification; a typical acid catalyzed organic transformation of various mono-and di-carboxylic acids with a range of alcohols. The in situ formed silicomolybdic acid heteropoly-anion species during the catalytic reactions were found to be catalytically active species for these reactions. Ethyl silicate-40, an industrial bulk silica precursor, has shown a good potential for its use as a silica precursor for the preparation of mesoporous silica based heterogeneous catalysts on a larger scale at a lower cost.

SBA-15 is an interesting mesoporous silica material having highly ordered nanopores and a large surface area, which is widely employed as catalyst supports, absorbents, drug delivery materials, etc. Since it has a lack of functionality, heteroatoms and organic functional groups have been incorporated by direct or post-synthesis methods in order to modify their functionality. The aim of this article is to review the state-of-the-art related to the use of SBA-15-based mesoporous systems as supports for hydrodesulfurization (HDS) catalysts.

Catalysts

Sulfated silica (SO4/SiO2) and nickel impregnated sulfated silica (Ni-SO4/SiO2) catalysts have been successfully carried out for the conversion of ethanol into diethyl ether (DEE) as a biofuel. The aims of this research were to study the effects of acidity on the SO4/SiO2 and Ni-SO4/SiO2 catalysts in the conversion of ethanol into diethyl ether. This study focuses on the increases in activity and selectivity of SiO2 with the impregnation of sulfate and Ni metal, which had good activity and acidity and were less expensive. The SO4/SiO2 catalysts were prepared using TEOS (Tetraethyl Orthosilicate) as a precursor and sulfuric acid with various concentrations (1, 2, 3, 4 M). The results showed that SO4/SiO2 acid catalyst treated with 2 M H2SO4 and calcined at 400 °C (SS-2-400) was the catalyst with highest total acidity (2.87 g/mmol), while the impregnation of Ni metal showed the highest acidity value at 3%/Ni-SS-2 catalyst (4.89 g/mmol). The SS-2-400 and 3%/Ni-SS-2 catalysts were selec...

Materials, 2013

SBA-15 is an interesting mesoporous silica material having highly ordered nanopores and a large surface area, which is widely employed as catalyst supports, absorbents, drug delivery materials, etc. Since it has a lack of functionality, heteroatoms and organic functional groups have been incorporated by direct or post-synthesis methods in order to modify their functionality. The aim of this article is to review the state-of-the-art related to the use of SBA-15-based mesoporous systems as supports for hydrodesulfurization (HDS) catalysts.

Microporous and Mesoporous Materials, 2010

a b s t r a c t SBA-15 mesoporous silica was modified with metal (Al, Ti, Cu, Fe) oxides by the molecular designed dispersion (MDD) method using acetylacetonate complexes of metals as precursors of the catalytically active components. The modified mesoporous silicas were characterized with respect to texture (BET), composition (EPMA), coordination and aggregation of transition metal species (UV-vis-DRS), reducibility of the deposited transition metals (TPRed) and surface acidity (FT-IR). Deposition of aluminium and titanium species on the SBA-15 surface significantly increased its acidity, mainly by generation of strong Lewis acid sites. Copper and iron deposited on the surface of pure SBA-15 were present nearly exclusively in the form of mononuclear cations. Deposition of Fe or Cu on the SBA-15 supports modified with alumina or titania resulted in a formation of significant amounts of oligomeric metal oxide clusters. The SBA-15 based samples have been found to be active and selective catalysts of the DeNO x process. The modification of the silica surface with titanium or aluminium prior to the deposition of iron or copper significantly improved the activity of the SBA-15 based catalysts.

Applied Catalysis A: General, 2017

The effects of catalyst matrix porosity composition on the catalytic performance have been studied using sulfonated mesoporous SBA-15 silica. The matrix was sulfonated with three different methods: grafting, in situ oxidation, and carbon infiltration. Additionally, unordered sulfonated mesoporous carbon, and the commercial catalysts Amberlite IR-120 and Nafion 117 were tested. The catalytic performance was evaluated in a Fischer esterification using acetic acid and ethanol, as well as in a transesterification of triglycerides (sunflower oil) and ethanol to produce biodiesel. The study shows that for long carbon chains, the effective wetting of the porous catalyst matrix by the reactants is most important for the catalytic efficiency, while for shorter carbon chain, the mass transport of the reagents trough the porous structure is more important. The catalysts were analysed using electron microscopy and physisorption. The study shows that the reactions are faster with carbon infiltrated materials than the silica materials due to a higher concentration of sulfonic groups linked to the carbon. The in situ functionalized SBA-15 is a more efficient catalyst compared to the post grafted one. All the synthesized catalysts outperform the commercial ones in both reactions in terms of conversion.

Turkish Journal of Chemistry, 2007

Pd-Si-structured novel mesoporous nanocomposite catalytic materials, having quite high Pd/Si ratios, were synthesized by an acidic direct hydrothermal synthesis route. The nanocomposite catalytic materials were then characterized by XRD, XPS, EDS, nitrogen adsorption, and SEM techniques. Unlike MCM-41, the XRD patterns indicated a rather wide d (100) band at a 2θ value of about 1.9. The materials, with very high Pd/Si wt ratios between 1.43 and 2.66, were synthesized and had BJH surface area values between 600 and 200 m 2 /g. The pore size distributions of these materials were also quite narrow, indicating pores between 2 and 7 nm.

Microporous and Mesoporous Materials, 2013

Sulfonic acid-functionalized mesoporous silica nanoparticles (SAMS-Ns) have been used as a highly efficient and recoverable heterogeneous acid catalyst for green synthesis of dicoumarols by reaction of different aldehydes with 4-hydroxycoumarin in aqueous media. High to excellent yields were obtained. This mesoporous catalyst is readily recovered and can be reused at least six times without significant loss of its catalytic activity.

A series of sulfoorganosilica (vinyl-containing) catalysts based on MSM-41 mesoporous molecular sieves were prepared by template synthesis. The structure and properties of these catalysts and their catalytic characteristics in synthesis of ethyl tert-butyl ether were examined

Chemical Engineering Journal, 2012

Tungstophosphoric acid (TPA) incorporated silicate structured new mesoporous catalysts were synthesized following one-pot hydrothermal and impregnation procedures. Surface area of TPA@MCM-41, which was prepared by impregnating TPA into MCM-41, was two orders of magnitude higher than the surface area of pure TPA and this catalyst showed very high activity in dehydration reactions of both ethanol and methanol. Ethanol fractional conversion values reaching to 1.0 was obtained at 300°C at a space time of 0.27 s.g/cm 3 , over TPA@MCM-41. Diethyl ether selectivity showed a decreasing trend by increasing temperature from 180 to 400°C in ethanol dehydration reaction. Ethylene yield values approaching to 100% were obtained at temperatures over 250°C. DME yield passed through a maximum at about 200°C with this catalyst, over which coke formation caused catalyst deactivation. One-pot hydrothermal synthesis procedure was very successful to synthesize a catalyst (TRC-W40) which did not lose any activity after repeated washing steps. This catalyst gave highly stable catalytic performance in dehydration of both ethanol and methanol. Well dispersed WO x clusters were formed within the mesoporous silicate matrix of this material. This catalyst showed very good activity in dehydration reactions of alcohols, giving 100% conversion in ethanol dehydration at 400°C and 100% DME selectivity in methanol dehydration at temperatures less than 300°C.

2009

Dimethyl ether (DME) is a substitute of LNG and light oil. DME burns without particulate matters and SOx, so DME is a clean fuel. DME is a storage and carrier of hydrogen. For these usages, useful catalysts such as DME steam reforming catalysts and DME synthesis catalysts should be developed. I have developed those new effective Cu-Zn/Al2O3 catalysts. The catalysts prepared by a sol-gel method produce DME faster than usual mixed catalysts of methanol synthesis catalysts and methanol dehydration catalysts. The sol-gel Cu-Zn/Al2O3 catalysts also produce hydrogen faster than usual mixed catalysts of DME hydrolysis catalysts and methanol steam reforming catalysts. It is the reason why that alumina sites (working for dehydration and hydrolysis) and copper sites (working for methanol synthesis and methanol steam reforming) are co-existing and distributing well on the surfaces of the catalysts prepared by the sol-gel method. Therefore, the consecutive reactions (methanol synthesis, methano...