115-10-6Relevant articles and documents
A Mechanistic Study of the Methanol Dehydration Reaction on γ-Alumina Catalyst
Schiffino, Rinaldo S.,Merrill, Robert P.
, p. 6425 - 6435 (1993)
The dehydration of methanol over a porous γ-Al2O3 catalyst was studied using periodic square-wave modulation of the feed to a microcatalytic reactor.Online mass spectrometry was used to obtain wave forms at the exit of the reactor for methanol, dimethyl ether, water, and a carrier gas.The reaction was studied over the temperature range of 230-350 deg C.At lower temperatures, the dimethyl ether wave form went first through a maximum, decreased to a constant level during the on cycle, and then went through a second maximum at the beginning of the off cycle.At higher temperatures where the conversions increased, the relative intensity of the maximum to the level part of the wave form continuously decreased until no maximum could be observed at temperatures above 280 deg C.Water was found to have a phase lag of about 4 s with respect to dimethyl ether over the studied temperature range.The shape of the wave forms was explained in terms of a reaction mechanism which involved reactions of surface species formed from the adsorption of methanol on the γ-Al2O3 surface.The species considered were molecularly adsorbed methanol, methoxy, and hydroxyl groups.The mechanism contained two parallel reaction pathways for the production of dimethyl ether.One pathway was the reaction between molecularly adsorbed methanol and methoxy species, and the other was the reaction between two methoxy species.For the production of water, only a single step of recombination of surface hydroxyls was considered in the mechanism.Equations for the material balances of the species considered in the mechanism were numerically integrated to generate wave forms with the same shape as observed in the experimental data.
Vapor-Phase Carbonylation of Methanol over Tin-on-Active Carbon Catalysts
Yagita, Hiroshi,Omata, Kohji,Shikada, Tsutomu,Fujimoto, Kaoru
, p. 2352 - 2357 (1990)
It was found that a number of metals or metal oxides showed catalytic activities for the vapor-phase carbonylation of methanol in the presence of methyl iodide (CH3I) promoter under the conditions of 250 deg C and 10 atm (1 atm = 1.01325x105 Pa), when they were supported on active carbon.Particularly, tin and lead showed high activities.The catalytic activity of the metallic tin increased with the process time over 5 h while that of the unreduced tin catalyst increased for more than 10 h to reach the same level.The catalytic performances of the tin on active carbon were similar to those of the nickel on active carbon which have been already reported.It was suggested that the active species of the tin catalyst was some kind of metal compounds which was highly dispersed on active carbon and was able to be incorporated in the redox cycle.
A novel sol-gel approach to highly condensed silicas at low temperature
Jorapur, Yogesh R.,Mizoshita, Norihiro,Maegawa, Yoshifumi,Nakagawa, Hiroki,Hasegawa, Takeru,Tani, Takao,Inagaki, Shinji,Shimada, Toyoshi
, p. 280 - 281 (2012)
We have discovered new Meerwein's reagent-catalyzed solgel polycondensations, which provide highly condensed silica Q4 and biphenylylene silica T3 as amorphous gels with marginal silanols starting from TEOS and 4,4′-bis(triethoxysilyl)biphenyl (BTEBph), respectively. We propose a plausible pathway for this protocol with possible silyloxonium intermediates.
Hydrogenation of CO2 to dimethyl ether on La-, Ce-modified Cu-Fe/HZSM-5 catalysts
Qin, Zu-Zeng,Zhou, Xin-Hui,Su, Tong-Ming,Jiang, Yue-Xiu,Ji, Hong-Bing
, p. 78 - 82 (2016)
Cu-Fe-La/HZSM-5 and Cu-Fe-Ce/HZSM-5 bifunctional catalysts were prepared and applied for the direct synthesis of dimethyl ether (DME) from CO2 and H2. The catalysts were characterized by X-ray diffraction (XRD), N2 adsorption-desorption, H2-temperature programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). The results showed that La and Ce significantly decreased the outer-shell electron density of Cu and improved the reduction ability of the Cu-Fe catalyst in comparison to the Cu-Fe-Zr catalyst, which may increase the selectivity for DME. The Cu-Fe-Ce catalyst had a greater specific surface area than the Cu-Fe-La catalyst. This promoted CuO dispersion and decreased CuO crystallite size, which increased both the DME selectivity and the CO2 conversion. The catalysts were stable for 15 h.
Fine Control of the Pore-opening Size of the Zeolite Mordenite by Chemical Vapour Deposition of Silicon Alkoxide
Niwa, Miki,Kato, Satoshi,Hattori, Tadashi,Murakami, Yuichi
, p. 3135 - 3146 (1984)
Chemical vapour deposition (c.v.d.) of Si(OCH3)4 on the H form of mordenite has been carried out in order to control the pore-opening size without affecting its acidic properties.It has been shown that Si(OCH3)4 is deposited irreversibly on the zeolite.Because the molecular size of the alkoxide is larger than the pore size, the alkoxide does not enter the pore and the silicon compound is deposited on the external surface.The alkoxide may be deposited by reaction with hydroxide, thus covering the external surface of zeolite crystal after subsequent reactions.Calcination with oxygen removes the hydrocarbon residue and produces silica-coated H-mordenite (SiHM).The SiHM thus obtained has been characterized by temperature-programmed desorption (t.p.d.) of NH3, adsorption experiments and X-ray photoelectron spectroscopy.The deposition of the alkoxide does not change the acidity but reduces the size of pore opening.Enrichment of Si on the external surface of the zeolite is confirmed.One can therefore conclude that SiO2 covers the external surface of the zeolite, thus reducing the effective size of the pore opening.The pore size is effectively reduced by ca. 0.1 and 0.2 nm upon formation of 1-2 and 3 molecular layers of silicon oxide, respectively.
Boroaluminosilicate Catalysts with the ZSM-5 Structure Synthesized in Nonalkaline Media
Sulikowski, Bogdan,Klinowski, Jacek
, p. 5030 - 5035 (1992)
Aluminosilicate and borosilicate (containing up to 3.80 B atoms per unit cell) zeolites with the ZSM-5 structure have been prepared by the "fluoride route" and studied by a range of techniques.Contrary to numerous studies (which investigated the conversion of methanol at much higher temperatures), trans-but-2-ene and not ethylene is the first hydrocarbon desorbed from the catalyst at temperatures below 200 deg C.We propose a mechanism for this reaction which does not require the formation and desorption of ethylene to the gas phase.The reaction of the methoxy intermediate formed on an acid site with the CH3OH molecule gives surface ethoxy groups, which are alkylated by further methanol molecules to give propoxy and butoxy groups.
An intermetallic Pd2Ga nanoparticle catalyst for the single-step conversion of CO-rich synthesis gas to dimethyl ether
Gentzen, Manuel,Doronkin, Dmitry E.,Sheppard, Thomas L.,Grunwaldt, Jan-Dierk,Sauer, J?rg,Behrens, Silke
, p. 206 - 214 (2018)
Well-defined Pd/Ga-nanoparticles were prepared and used as a precursor for the methanol active component in a bifunctional syngas-to-dimethyl ether catalyst. In situ X-ray absorption spectroscopy experiments were employed both to unravel the initial formation of the active catalyst phase in reductive H2 atmosphere and to further monitor changes of the nanoparticles under conditions of dimethyl ether synthesis at a pressure up to 20 bar (250 °C). The catalytic studies were conducted using simulated biomass-derived, CO-rich syngas in a continuous-flow reactor, with the bifunctional catalyst offering the two types of active sites, i.e. for methanol synthesis (Pd/Ga nanoparticles) and its subsequent dehydration (γ-Al2O3), in close proximity. As compared to the conventional Cu/Zn-based reference catalyst prepared via a similar procedure, the Pd/Ga-based catalyst showed a promising activity together with a notable stability with time on stream and a high temperature tolerance (up to 300 °C). A kinetic model which considers the individual reactions involved in direct DME synthesis based on power law equations was used to fit the experimental data, and the apparent activation energies were compared to the Cu/Zn-based catalyst.
SYNERGISTIC EFFECT OF HOMOGENEOUS RUTHENIUM-RHODIUM CATALYSTS FOR METHANOL HOMOLOGATION
Pursiainen, Jouni,Karjalainen, Kauko,Pakkanen, Tapani A.
, p. 227 - 230 (1986)
Homogeneous solutions containing both ruthenium and rhodium complexes and methyl iodine are shown to exhibit a synergistic effect for the homologation of methanol to ethanol.Reactions were studied at pressures from 100 to 175 atm and at temperatures from 160 to 240 deg C.The highest selectivities were obtained with excess of ruthenium complexes present.Under these reaction conditions no evidence for cluster catalysis was found.
Influence of metal oxide modification of alumina on the dispersion and activity of vanadia catalysts
Lakshmi, L. Jhansi,Alyea, Elmer C.,Srinivas,Kanta Rao
, p. 3324 - 3328 (1997)
Alumina was modified with 10 wt % MOx (MOx = TiO2, ZrO2, La2O3, or MgO) prior to its impregnation with 12 wt % vanadia. The catalysts VTiAl, VZrAl, VLaAl, and VMgAl were characterized by X-ray diffraction (XRD), electron spin resonance (ESR), FT-Raman spectroscopy, 51V solid state nuclear magnetic resonance (51V NMR), and oxygen chemisorption. The activities of the catalysts were determined by methanol partial oxidation and their acid-base properties were evaluated for the decomposition of 2-propanol. XRD and FT-Raman spectroscopy indicated the formation of bulk TiO2 and ZrO2 on the titania and zirconia modified alumina. 51V solid state NMR results suggest the presence of both octahedrally and tertrahedrally coordinated vanadia species in the catalysts VTiAl, VZrAl, and VAl and the presence of tetrahedrally coordinated vanadia species in the catalysts VLaAl and VMgAl. ESR spectra recorded at ambient temperature showed the presence of V4+ ions having axial symmetry. Oxygen chemisorption results indicated an enhanced number of reducible vanadia sites, i.e., redox sites in the modified catalysts. Metal oxide modification is found to influence significantly the surface coverage and the methanol partial oxidation activity of vanadia supported on alumina. With proper MOx modification enhanced reducibility of vanadia could be attained, which in turn makes the partial oxidation reaction of methanol more facile.
Synthesis of lower olefins from dimethyl ether in the presence of zeolite catalysts modified with rhodium compounds
Kolesnichenko,Goryainova,Biryukova,Yashina,Khadzhiev
, p. 55 - 60 (2011)
The catalytic properties of zeolite catalysts modified with rhodium compounds in the synthesis of olefins from dimethyl ether (DME) and methanol (MeOH) have been studied. The optimum concentration of rhodium in the composition of a zeolite catalyst has been determined. It has been shown that one of the possible precursors of ethylene in the conversion of DME is ethanol, which, under reaction conditions, can be formed through both the DME isomerization and methanol homologation stages.
