Dimethyl Ether Selectivity Research Articles

Influence of acidic and alkaline silica sols on the performance of Cu/Zn/Al slurry catalysts

A series of Cu/Zn/Al/Si slurry catalysts were prepared using acidic and alkaline silica sols by the complete liquid-phase technology. The samples were characterized with XRD, H2-TPR, FT-IR, BET, NH3-TPD, XPS and TEM techniques. Addition of acidic silica sol to the catalyst gave the highest CO conversion and dimethyl ether (DME) selectivity, being 65.38% and 76.26% respectively. The acidic silica sol weakens the interaction between Cu and other components, resulting in a rapid reduction of Cu species and exposure of more active lattice planes of Cu0. In addition, the acidic/alkaline properties of silica sol also influence the number and the strength of acid sites in the sample. It was found that both the strong and the weak acid sites decreased in the strength. The acidic silica sol significantly increased the weak acid sites, mesopores and specific surface area, consequently promoting the methanol dehydration and increasing the DME selectivity.

An experimental study on single-step dimethyl ether (DME) synthesis from hydrogen and carbon monoxide under various catalysts

Dimethyl ether (DME) is a potential and green substitute to diesel and liquefied petroleum gas. In this study, DME synthesized from hydrogen and carbon monoxide (i.e. syngas) through a single step process is investigated to figure out the reaction characteristics. The influences of reaction temperature, H2/CO molar ratio, and prepared catalyst on DME synthesis are investigated, while the space velocity is fixed at 15,000 mL (gcat h)−1. The results indicate that the optimal reaction temperature for DME synthesis develops at 220 °C where the chemical kinetics and thermodynamic equilibrium are in a comparable state. Increasing H2/CO ratio increases the CO conversion but lowers the H2 conversion. The maximum DME yield is 2.3 g (gcat h)−1 which occurs at H2/CO = 1. The addition of palladium (Pd) into a Cu–ZnO–Al2O3 catalyst intensifies the CO conversion and DME yield of a gas mixture with syngas and 10 vol% of CO2. This is the consequence of hydrogen spillover which is able to increase the stability of active Cu against CO2 oxidation. The results also suggest that the dehydration catalyst with higher acidity gives lower DME selectivity and yield. The higher the CO2 concentration in syngas, the lower the CO conversion and DME yield. The present study has provided comprehensive insights into DME synthesis which is conducive to DME production in industry.

Influence of Compound Additive CeO2-MxOy on Catalytic Performace of Pd/γ-Al2O3 Catalyst for One-step Synthesis of Dimethylether

A series of Pd/γ-Al2O3 catalysts with different types of compound additives were prepared by impregnation under microwave calcination; the physicochemical properties and catalytic performance of catalysts for one-step synthesis of dimethylether from sulfur-containing syngas were investigated. The results show that the catalysts added CeO2-ZrO2 showed much better catalytic performance and sulfur tolerance than those added CeO2-ZnO or CeO2-CaO in terms of CO conversion, methanol, and dimethylether selectivities and time space yield of dimethylether, which are closely related to higher pore volume and Pd dispersity, moderate CO adsorption, and moderate surface acidity of the catalyst. The optimum compound additive content was determined to be 2%CeO2-1%ZrO2. Under such optimum conditions, CO conversion, dimethylether selectivity, and time space yield of dimethylether are 63.2%, 68.5%, and 30.92 mmol·(ml·h)−1, respectively.

Performance of Cu-Zn-Si-Al Catalyst Prepared by a Complete Liquid-phase Techonology for Dimethyl Ether Synthesis

A series of Cu-Zn-Si-Al bifunctional catalysts for the synthesis of dimethyl ether( DME) was prepared by a liquid-phase technology. The catalysts were prepared with low-cost silica sol as the silica source. The addition of silica exhibits a strong promoting effect on the CO conversion and DME selectivity.When n( Si) / n( Al) is 2,the catalyst shows the best catalytic performance. The conversion of CO reaches58. 1% and the selectivity of DME is improved to 80. 2%. The catalysts were characterized by FTIR,XRD,TPR,TPD,BET,XPS and TEM. The results show that the addition of silicon components can promote the dispersion of active components on the catalysts and decrease the carbon deposition caused by heat treatment in the liquid phase. In addition, the Si components interact with Al, which significantly improves the performance of the catalyst for methanol dehydration and the selectivity of DME.

Enhanced catalytic performance of zeolite ZSM-5 for conversion of methanol to dimethyl ether by combining alkaline treatment and partial activation

Zeolite ZSM-5 (MFI) due to its excellent hydrothermal stability and high catalytic activity for methanol dehydration to dimethyl ether (MTD) has been considered for use in combination with a methanol synthesis catalyst, such as Cu/ZnO/Al2O3, in the conversion of syngas to dimethyl ether. However, the decline of dimethyl ether selectivity and catalytic activity over ZSM-5 by the formation of hydrocarbons and coke at optimum operation temperature of Cu/ZnO/Al2O3 catalyst impedes industrial application. In this work, for the first time the effects of alkaline treatment combined with partial activation on the catalytic performance of ZSM-5 catalysts with different Si/Al ratio have been studied for MTD reaction. The relationship between the physicochemical properties and catalytic performance has been assessed from the combined results of XRD, SEM, N2 physisorption, NH3-TPD, elemental analysis, online-GC and other characterization techniques. The results show that at a reaction temperature of 300°C and WHSV of 13gg−1h−1, all the parent and alkaline-treated ZSM-5 after full activation at 500°C exhibited a decline of dimethyl ether selectivity and methanol conversion over time. Alkaline treatment improved DME selectivity over ZSM-5 with an Si/Al ratio of 25, which could be ascribed to the formation of extra mesoporosity enhancing the diffusion capability and decreasing the probability of secondary reactions of DME to hydrocarbons. A decrease of the activation temperature led to a significantly improved DME selectivity for all parent and alkaline-treated ZSM-5 because ammonium cations were selectively retained in the structure and blocked the strong acid sites that brought about side-reactions. ZSM-5 with Si/Al ratio of 25 modified by combining alkaline treatment and partial activation, due to the synergy effect of moderated acidity and enhanced diffusion capability, exhibited improved catalytic performance with almost 100% DME selectivity, near 84% methanol conversion and excellent stability during 4 days of reaction.

The facile preparation of Cu–Zn–Al oxide composite catalysts with high stability and performance for the production of dimethyl ether using modified aluminum alkoxide

Modified aluminum alkoxide prepared by alcoholysis was used as an aluminum source in the complete liquid-phase technology for the preparation of slurry catalysts. The use of the modified aluminum alkoxide afforded control over the rate of the hydrolysis/condensation reactions during the preparation of the catalyst precursors, thereby generating catalysts with a fine nano-structured active metal and metallic oxide particles. Four types of Cu–Zn–Al (molar ratio is 2:1:4) catalysts were prepared using different procedures. These catalysts were tested for CO hydrogenation at 553K, 4.0MPa and H2/CO=1.0 in a kettle with a mechanical agitator. The results indicated that the activity of the catalysts was greatly dependent on the rate of the hydrolysis/condensation reactions, and the catalyst with the best catalytic performance was obtained by controlling the hydrolysis/alcoholysis rate during catalyst synthesis by pre-alcoholysis of AIP as the aluminum source, over which the CO conversion and dimethyl ether selectivity could reach 62.6% and 62.5%, respectively.

CO2 hydrogenation to methanol and dimethyl ether by Pd–Pd2Ga catalysts supported over Ga2O3 polymorphs

The production of methanol and dimethyl ether (DME) via CO2 hydrogenation was studied using Pd catalysts supported on α-Ga2O3, α-β-Ga2O3 and β-Ga2O3 polymorphs. The formation of a Pd2Ga intermetallic compound was observed using XRD and XPS. The catalytic activity improves with an increase in the content of the Pd2Ga intermetallic compound. The content of Pd2Ga on Pd/Ga2O3 depends on the Ga2O3 crystalline phase of the catalyst. A slight catalytic deactivation was observed for all samples studied. The Pd/α-β-Ga2O3 catalyst displayed the largest deactivation. The deactivation appears to be caused by a loss of basic sites. The selectivity to dimethyl ether is not dependent on the Pd2Ga content, but depends on the catalyst acidity. This assertion was tested by adding niobia to the catalysts, thus increasing the DME selectivity from 0 to 53%. The content of Pd2Ga over Pd/Ga2O3 catalysts was identified to be a crucial parameter for CO2 hydrogenation to methanol.

Dimethyl Ether Synthesis from Syngas over the Admixed Cu/ZnO/Al2O3 Catalyst and Alkaline Earth Oxide‐Modified HZSM‐5 Zeolite

AbstractHZSM‐5 zeolites modified with various alkaline earth oxides (MgO, CaO, and BaO) were prepared by using impregnation and mixed physically with Cu/ZnO/Al2O3 to perform the direct synthesis of dimethyl ether (DME) from syngas in a pressurized fixed‐bed under continuous flow conditions. The results indicated that the modification effectively enhanced the DME selectivity; MgO and CaO are more effective modifiers than BaO and they improved the DME selectivity up to 67 % as compared to only 54 % over the parent HZSM‐5. Moreover, the catalyst prepared from magnesium nitrate exhibits higher DME selectivity than those prepared from magnesium acetate and chloride. The enhancement in the DME selectivity resulted from the effective suppression of hydrocarbon and CO2 formation, which can be attributed to the significant decline in the amount of strong acid sites of the HZSM‐5 zeolite resulting from the modification.

The performance of chemically and physically modified local kaolinite in methanol dehydration to dimethyl ether

The catalytic activity of modified natural kaolinite as a solid acid catalyst for dimethyl ether (DME) preparation was investigated by following up the conversion% of methanol and the yield% of DME. Natural kaolinite (KN) was treated chemically with H2O2 (KT) followed by thermal treatment at 500°C (KC) and then mechano-chemically by ball milling with and without CaSO4 (KB-Ca and KB, respectively). These samples were characterized by XRD, FTIR, SEM, HRTEM, TGA and NH3-TPD techniques. The different techniques showed that the chemical treatment of kaolinite with H2O2 resulted in partial exfoliation/delamination of kaolinite, decreased the amount of acidic sites which is accompanied by increasing their strength. Calcination only decreased the acidic strength and slightly enlarged the particle size mostly due to heat effect. Ball milling resulted in multitude randomly-oriented crystals and increased the amount of acidic sites with the same strength of KT sample. CaSO4 mostly produced ordered monocrystalline kaolinite and created new acidic sites with slightly lower strength relative to KB. The catalytic activity and selectivity depend on the reaction temperature, the space velocity and the strength of acid sites. The most active sample is KB-Ca, which gives 84% DME due to its high amount and strength of acidic sites. The different modification methods resulted in 100% selectivity for DME.

Direct conversion of syngas to DME over CuO-ZnO-Al2O3/HZSM-5 nanocatalyst synthesized via ultrasound-assisted co-precipitation method: New insights into the role of gas injection

In this study, direct synthesis of dimethyl ether (DME) is conducted over a bifunctional CuO–ZnO–Al2O3/H Zeolite Socony Mobil-5 (HZSM-5) nanocatalyst. A hybrid method of ultrasound-assisted co-precipitation is used for the synthesis of catalysts, and the effect of gas injection during sonication is investigated. The physicochemical characteristics of the catalysts are analysed by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), particle size distribution (PSD), energy dispersive X-ray (EDX), Brunauer–Emmett–Teller (BET) and Fourier-transformed infrared (FTIR) methods. In the absence of gas injection, the acetate-based catalysts have a better morphology and higher surface area than the nitrate-based catalyst. Gas injection significantly changes the morphology and structural properties of the acetate-based catalyst. High surface area, narrow PSD and better dispersion of small CuO crystals are obtained in a gas-injected synthesized sample. DME synthesis experiments showed that the CO conversion and DME selectivity are correlated with surface area, nanocatalyst particle size and its dispersion. The gas-injected CuO–ZnO–Al2O3/HZSM-5 nanocatalyst that has the highest surface area and the smallest dispersed particles showed more than 70% DME selectivity. The gas-injected CuO–ZnO–Al2O3/HZSM-5 nanocatalyst exhibited high stability in terms of CO conversion and DME yield over 1440-min time on a stream test at 275°C, 40 bar and 18 000 cm3 g.h−1. Copyright © 2014 John Wiley & Sons, Ltd.

Steam reforming of methanol over copper loaded anodized aluminum oxide (AAO) prepared through electrodeposition

In order to study the steam reforming of methanol (SRM) to produce hydrogen for fuel cells, porous γ-alumina support is developed on Al substrate using anodic oxidation process and copper catalyst particles are deposited homogeneously over anodic aluminum oxide (AAO) surface by electrodeposition method. We investigated the effect of electrodeposition time and hot water treatment (HWT) on the activity of catalysts for SRM reaction in the temperature range between 160 and 360 °C. The experimental results indicate that the SRM activity, CO2 and dimethyl ether (DME) selectivity's over Cu catalysts increased as the electrodeposition time increased from 30 to 120 s, further increment in deposition time of Cu have no significant effect on it. The rates of SRM conversion are found to be higher for the catalysts made from the supports obtained after HWT, which may be due to the enhancement in the surface area of AAO support. It is found that the SRM activity and CO2 selectivity strongly depended upon the free exposed copper sites available for methanol adsorption and reaction, and DME in products is mainly observed in the reaction temperature range between 300 and 350 °C and it is higher for the catalysts with low Cu content.

Dimethyl Ether Synthesis via Methanol Dehydration over Diatomite Catalyst Modified Using Hydrochloric Acid

The synthesis of dimethyl ether via methanol dehydration has been carried out over untreated-diatomite catalyst (DM) and hydrochloric acid modified treatment on diatomite catalyst (DMHC). The reactions were carried out in a fixed-bed reactor. The effects of hydrochloric acid modifications of diatomite on its catalytic performance were studied. The characterization such as XRD, SEM, FT-IR and FT-Raman had no deformation after HCl-modified treatment on catalysts. DMHC catalyst apparently gave the higher methanol conversion rate than DM due to the acidity while the selectivity of dimethyl ether from 250 to 350°C was slightly changed. The acidity was depended upon Al(IV) ions; nevertheless, both Al(V) and Al(VI) were affected and hence increasing the basic active sites. Not only was the competitively catalytic methanol dehydrogenation preferred with basic condition but also methanol-blocking water molecule interaction was the unwanted reaction. In this investigation, the chemical-bond arrangements of silicon and aluminium ions were proposed with solid MAS/NMR. The DMHC catalyst exhibited better DME yield than the DM catalyst, and it could be used as a selective catalyst for DME synthesis from methanol.

Synthesis of dimethyl ether from syngas over core–shell structure catalyst CuO–ZnO–Al2O3@SiO2–Al2O3

A core–shell structure catalyst, CuO–ZnO–Al2O3@SiO2–Al2O3, with commercial methanol synthesis catalyst CuO–ZnO–Al2O3 as the core and amorphous SiO2–Al2O3 as the shell, was prepared by facile hydrothermal treatment. In the synthesis procedure, the core–shell catalyst was synthesized using tetraethylorthosilicate, silica sol, or water glass as the silica source, aluminum nitrate as the aluminum source, and without using any aid, alkali or amine template to avoid etching of core material, CuO–ZnO–Al2O3. The core–shell structure and acidic property of the catalyst materials were characterized by XRD, SEM and NH3-TPD. The results indicated that an amorphous SiO2–Al2O3 shell coated the surface of the core materials. The thickness of shell and acidity of the catalysts could be altered by adjusting the quantity of silicon source added. The core–shell structure catalysts were utilized as bifunctional catalysts in the syngas to dimethyl ether reaction (STD). The acidity and the thickness of the shell affect the catalytic performance in the STD reaction. The conversion of CO and the selectivity of dimethyl ether on the core–shell catalyst, with moderate acidity and suitable shell thickness, are 71.1% and 61.9%, respectively.

Fabrication of active Cu–Zn nanoalloys on H-ZSM5 zeolite for enhanced dimethyl ether synthesis via syngas

One-step conversion of CO and H2 to dimethyl ether (DME) is still challenging to date. This work describes a promising bifunctional Cu/ZnO/H-ZSM5 catalyst prepared by a novel bimetallic sputtering method for such conversions. The sputtered catalyst consisted of well-dispersed Cu–ZnO nanoparticles of about 5 nm, which were physically anchored on an acidic zeolite support. The weak interaction between the deposited metal and zeolite clearly lowered the reduction temperature by 50 °C. After H2 reduction, a unique Cu–Zn nanoalloy layer was observed on the surface of the Cu–ZnO nanoparticles, reducing the activation energy of CO adsorption. The surface alloy layer and inner Cu–ZnO sites play a cooperative catalytic role in improving the CO conversion and promoting DME selectivity. Compared to conventional impregnated catalysts, the CO conversion was enhanced by almost four times and the DME selectivity was promoted to as high as 92.1%. The proposed concept is beneficial for developing highly-active catalysts with bimetallic components supported on a functional support.

Methanol to dimethylether on H-MFI catalyst: The influence of the Si/Al ratio on kinetic parameters

A series of H-MFI zeolites at different Si/Al ratio were prepared and characterised in terms of physical and chemical properties and morphology. The zeolites were tested in the methanol dehydration reaction to Dimethyl Ether (DME), aiming at investigate the catalyst stability as a function of the reaction temperature. According to literature the temperature interval was set in the way of keeping a DME selectivity close to one and this required a lower temperature when increasing the catalyst acidity. Conversion data were measured at different catalyst amount/reactant flow rate ratios and the initial rate was extrapolated from the early points. Arrhenius plot of these initial rates as a function of temperature allowed to estimate the (apparent) activation energy as a function of the catalyst acidity (from 50 to 70kJ/mol). Main findings were the confirmation that the catalyst performance is favoured by the higher acidity, but also samples at the lower is the Si/Al ratio exhibited the higher activation energy, revealing as the more sensitive to temperature variation.

The Dehydration of Methanol to Dimethyl Ether over a Novel Solid Acid-base Catalyst

A novel polymer solid acid-base catalyst Cat-AAA (Al + aminoacetic acid) with aluminum and nitrogen was prepared from aminoacetic acid and Al by using triblock copolymer Pluronic F127 as a template via evaporation induced organic–organic assembly method. Cat-AAA was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectra. The acid-base properties of the catalysts were determined by temperature programmed desorption using CO2 and NH3 as probe molecules. The dehydration of methanol to dimethyl ether over Cat-AAA had been studied; the results showed that the conversion of methanol and selectivity of dimethyl ether is higher at a high reaction temperature. The key requirements for a good catalyst for dehydration of methanol to dimethyl ether are: (i) weak acid-sites activate O in a methanol molecule; (ii) at the same time, weak base-sites activate H of hydroxy group in another methanol molecule.

Catalytic performance of hierarchical H-ZSM-5/MCM-41 for methanol dehydration to dimethyl ether

Micro-mesoporous composite molecular sieves H-ZSM-5/MCM-41 were prepared by the hydrothermal technique with alkali-treated H-ZSM-5 zeolite as the source and characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, N2 adsorption-desorption measurement and NH3 temperature-programmed desorption. The catalytic performances for the methanol dehydration to dimethyl ether over H-ZSM-5/MCM-41 were evaluated. Among these catalysts, H-ZSM-5/MCM-41 prepared with NaOH dosage (nNa/nSi) varying from 0.4 to 0.47 presented excellent catalytic activity with more than 80% methanol conversion and 100% dimethyl ether selectivity in a wide temperature range of 170–300 °C, and H-ZSM-5/MCM-41 prepared with nNa/nSi = 0.47 showed constant methanol conversion of about 88.7%, 100% dimethyl ether selectivity and excellent lifetime at 220 °C. The excellent catalytic performances were due to the highly active and uniform acidic sites and the hierarchical porosity in the micro-mesoporous composite molecular sieves. The catalytic mechanism of H-ZSM-5/MCM-41 for the methanol dehydration to dimethyl ether process was also discussed.

Catalytic performance of metal ion doped MCM-41 for methanol dehydration to dimethyl ether

Metal ion doped MCM-41 mesoporous molecular sieves (M-MCM-41, M = Al, Ga, Sn, Zr and Fe) were prepared using a hydrothermal synthesis method, with metal chlorides serving as the dopant sources. The M-MCM-41 structures were characterized by Fourier transform infrared spectroscopic (FTIR) analysis, X-ray diffraction, energy dispersive spectroscopy and N2 adsorption–desorption measurement. The surface of M-MCM-41 acidities were determined by NH3 temperature-programmed desorption and pyridine-adsorption FTIR analysis, and their catalytic performance for methanol dehydration to dimethyl ether (DME) was evaluated. The results showed that the prepared M-MCM-41, which exhibited a structure similar to that of MCM-41 with long-range ordered mesoporous structure, contained weak acidic sites. The number of weak acid sites in Al-MCM-41 increased as the Al content increased. The Al content in Al-MCM-41 had an important effect on its catalytic performance, where the highest catalytic activity was 80 and 100 % DME selectivity was achieved at a Si/Al molar ratio of 10. For MCM-41 doped with various types of metal ions, M-MCM-41 (M = Al, Ga, Sn and Zr) also presented a similar wide distribution of acidity, and their catalytic activities were ranked in the following order: Al-MCM-41 > Ga-MCM-41 > Zr-MCM-41 > Fe-MCM-41 > Sn-MCM-41, which were related to the coordination of the metal ions.

Determination of Dimethyl Ether in Air by Cataluminescence-Based Gas Sensor

A rapid and sensitive cataluminescence-based gas sensor utilizing nanosized Y2MnO5as the sensing materials for determining dimethyl ether in air was proposed. The luminescence characteristics and the optimal conditions were investigated in detail. The gas sensor showed high selectivity for dimethyl ether at 620 nm and satisfying activity at 210°C under the optimized conditions. The linear range of cataluminescence intensity versus concentration of dimethyl ether was 5~120 mg/m3, and the detection limit (3σ) was 3 mg/m3. No or weak interference was observed while the foreign substances, such as formaldehyde, ammonia, ethanol, benzene, carbon monoxide and sulfur dioxide, were passing through the sensor under selected conditions. The gas sensor displayed good stability for continuously introducing dimethyl ether over 100 h, and allowed real-time monitoring of dimethyl ether in air.

Hierarchical mesoporous ZSM-5 for the dehydration of methanol to dimethyl ether

Hierarchical mesoporous ZSM-5 zeolites were synthesized using small organic cations of tetrapropylammonium and meso-sized cationic polymers of dimethyldiallyl ammonium chloride acrylamide copolymer as templates. The zeolites were used for the dehydration of methanol to dimethyl ether (DME). Characterization results showed that the basic MFI-type structure was still obtained after adding the cationic polymers, while their nitrogen isotherms exhibited a broad hysteresis loop at relative pressures higher than 0.4, which proved the presence of mesopores. The mesoporosity of the hierarchical mesoporous ZSM-5 can be adjusted simply by adding different amounts of the cationic polymer. Catalytic tests showed that the hierarchical mesoporous HZSM-5 zeolites exhibited better stability than conventional HZSM-5 and excellent DME selectivity. The activity for methanol dehydration strongly depended on the textural property and acidity of the catalyst. The synthesized hierarchical mesoporous HZSM-5 zeolites exhibited better catalytic activity than conventional HZSM-5, indicating that hierarchical mesopores play an important role in the methanol to dimethyl ether process.