Ammonia Evaporation Method Research Articles

Influence of support on the performance of copper catalysts for the effective hydrogenation of ethylene carbonate to synthesize ethylene glycol and methanol

Cu/SBA-15 was successfully prepared by ammonia evaporation method and exhibited a high activity for the hydrogenation of ethylene carbonate to co-produce ethylene glycol and methanol.

Effect of Mn doping on the activity and stability of Cu–SiO2catalysts for the hydrogenation of methyl acetate to ethanol

A series ofxMn–Cu–SiO2catalysts with different manganese contents were prepared by an ammonia-evaporation method for methyl acetate hydrogenation.

Highly active and stable CeO2–SiO2 supported Cu catalysts for the hydrogenation of methyl acetate to ethanol

A series of Cu–CeO2–SiO2 catalysts for the hydrogenation of methyl acetate to ethanol with different CeO2 contents was prepared by an ammonia-evaporation method. Compared with the Cu–SiO2 catalyst, the catalytic activity and stability of the Cu–CeO2–SiO2 catalyst were greatly enhanced with an optimized CeO2 content of about 30wt.%. The structures of the catalysts were characterized by N2 physisorption, N2O chemisorption, X-ray diffraction, H2 temperature-programmed reduction, NH3-temperature programmed desorption and X-ray photoelectron spectroscopy. The results showed that adding an appropriate amount of cerium to Cu–SiO2 catalysts strengthened the interaction between the cupreous species and the support, diminished the copper crystallite size, improved the copper dispersion and enriched the surface Cu+ species. In addition, several characterizations were performed to investigate the structure changes of the catalysts after stability test, which demonstrated that the CeO2-modified Cu–SiO2 catalyst restrained the aggregation and valence change of cupreous species under reaction conditions.

Role of copper content and calcination temperature in the structural evolution and catalytic performance of Cu/P25 catalysts in the selective hydrogenation of dimethyl oxalate

A series of Cu-based P25-supported catalysts of copper weight loading ranging from 5% to 30% and calcinated at 623–923K were synthesized via a facile ammonia evaporation method for the selective hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG). Copper content and calcination temperature played significant roles in the catalytic process. The catalytic performance increases with growing copper loading, but excessively high copper contents would lead to metal aggregation and thus cause the deactivation of catalyst. Calcination effect illustrates that catalyst calcinated at lower temperature presents relatively weak metal-support interaction, while high temperature (923K) treatment results in collapse of microstructure and crystalline phase transformation of titania support, which further leads to low copper dispersion, metal aggregation and thus poor hydrogenation activity. The 20Cu/P25-823 catalyst with a 20wt.% copper loading and calcined at 823K displays superb catalytic performance and long-term stability of more than 96h, with DMO conversion of 100% and EG selectivity of 99% unchanged.

Effect of ammonia concentration on the catalytic activity of Pd-Cu supported on attapulgite clay prepared by ammonia evaporation in CO oxidation at room temperature

AbstractWith attapulgite clay (APT) as support, the Pd-Cu/APT catalysts were prepared by an ammonia evaporation method and characterized by N2-physisorption, XRD, FT-IR, TEM and H2-TPR. The effect of ammonia concentration on the catalytic performance of Pd-Cu/APT in CO oxidation at room temperature was investigated in a fixed-bed continuous flow microreactor. The results showed that CuO appears as the main Cu species in the Pd-Cu/APT catalysts prepared with over low or over high ammonia concentration, whereas the quantity of Cu2(OH)3Cl phase is much less. However, a proper concentration of ammonia is of benefits to forming stable Cu2(OH)3Cl species in Pd-Cu/APT; owing to its high dispersion, nano-platelet morphology and strong interaction with Pd species, the presence of stable Cu2(OH)3Cl can significantly promote the catalytic performance of Pd-Cu/APT in CO oxidation. Under a gas hourly space velocity (GHSV) of 6000 h−1 for a feed stream containing 1.5% CO and 3.3% water, the Pd-Cu/APT catalyst exhibits excellent activity and stability in CO oxidation even at room temperature.

Influence of the support composition on the hydrogenation of methyl acetate over Cu/MgO-SiO2 catalysts

A series of Cu/MgO-SiO2 catalysts with different support compositions of MgO and SiO2 were prepared using the ammonia-evaporation method and evaluated for methyl acetate hydrogenation reaction to synthesize ethanol. Physicochemical properties of these catalysts were investigated by N2 physisorption, N2O chemisorptions, X-ray diffraction, H2-temperature programmed reduction, CO2-temperature programmed desorption and X-ray photoelectron spectroscopy. It was found that the MgO content significantly influenced the chemical properties, then affected catalytic activities of Cu/xMgO-SiO2 catalysts. The optimal catalytic performance was obtained over Cu/9MgO-SiO2 catalyst with MgO/SiO2 mass ratio of 9 with the methyl acetate conversion of 80.3% and ethanol selectivity of 99.0%. The high catalytic performance of Cu/9MgO-SiO2 catalyst was attributed to the fine copper dispersion and large amount of weakly basic sites and Cu+ species.

An environmentally benign and low-cost approach to synthesis of thermally stable industrial catalyst Cu/SiO2 for the hydrogenation of dimethyl oxalate to ethylene glycol

This investigation focused on developing an environmentally benign approach to synthesis of nanostructured Cu/SiO2 catalysts for hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG). It was accomplished by using (NH4)2CO3, instead of the conventional ammonia evaporation method, for making nanostructured Cu/SiO2 exhibiting good performance for DMO conversion and EG selectivity in the desired temperature range, with increased temperature stability. The resulting catalysts were characterized for catalytic activity, optimal reaction temperature, specific surface area, crystalline structure, surface composition and the influence of sodium in support raw material. The new method generated active catalysts with improved thermal stability linked to better dimension control and more Cu2O content, together with improved morphology of the supported copper particles.

High-Performance and Long-Lived Cu/SiO2 Nanocatalyst for CO2 Hydrogenation

Cu-based nanocatalysts have been widely used for CO2 hydrogenation, but their poor stability is the bottleneck for further industrial applications. A high-performance and long-lived Cu/SiO2 nanocatalyst was synthesized by an ammonia-evaporation method for CO2 hydrogenation. The conversion of CO2 reaches up to 28%, which is close to the equilibrium conversion of CO2 (30%), and the selectivity to methanol is 21.3%, which is much higher than the equilibrium selectivity (6.6%) at 320 °C and 3.0 MPa. Furthermore, after 120 h of evaluation, the conversion can be still maintained at a high value (27%), which is much better than a Cu/SiO2 catalyst prepared by traditional impregnation. The Cu+ species has been demonstrated to be the active component for the activation and conversion of CO2. The higher ratio of Cu+/(Cu0 + Cu+) and interaction between the metal and support deriving from copper phyllosilicate are mainly responsible for the high catalytic activity and excellent stability, respectively.

Selective hydrogenation of dimethyl maleate to tetrahydrofuran over Cu/SiO2 catalyst: Effect of Cu+ on the catalytic performance

Abstract Cu/SiO 2 catalysts prepared by different methods have been investigated focusing on the influence of Cu + on the catalytic performance. The composition, structure and copper valence state were characterized by means of BET, XRD, XPS, FTIR, N 2 O-titration. It was found that the Cu/SiO 2 prepared by ammonia-evaporation (AE) method had much higher TOF value than that prepared by wetness-impregnation (WI) with the same THF selectivity. The higher TOF value was attributed to the coexistence of Cu + and Cu 0 species in the activated AE-Cu/SiO 2 , while only Cu 0 species existing in the activated WI-Cu/SiO 2 . Researches suggest that Cu + can adsorb and polarize the C O bond of DMM. It is concluded that Cu 0 could be the main active site and the synergistic effect between Cu 0 and Cu + could contribute to hydrogenation of DMM to THF.

Kinetics Study of Hydrogenation of Dimethyl Oxalate over Cu/SiO2 Catalyst

Gas-phase hydrogenation of dimethyl oxalate (DMO) on a copper-based catalyst is one of the crucial technologies in the production of ethylene glycol (EG) from syngas. Even though Cu/SiO2 catalyst is widely used in ester hydrogenation reactions, a kinetics study considering multiple active sites has not yet been reported. In this study, a series of experiments were carried out to investigate the heterogeneous catalytic reaction kinetics of the hydrogenation of DMO over Cu/SiO2 catalyst. Considering different situations of ester adsorption, H2 adsorption, and active sites, 34 possible kinetics models were proposed and screened to identify the one most appropriate to describe the hydrogenation of DMO over Cu/SiO2 catalyst. With the help of relevant thermodynamic theories and statistical evaluations, the optimal model was found to fit well to our experimental data. This model proved that the hydrogenation of DMO depends on the synergistic effect of two active sites, wherein hydrogen and the ester were adsorbed on two different active sites with dissociative states. The dissociative adsorption of the ester was found to be the rate-controlling step in the hydrogenation of DMO over Cu/SiO2 catalyst prepared by an ammonia-evaporation method.

Continuous synthesis of methanol: heterogeneous hydrogenation of ethylene carbonate over Cu/HMS catalysts in a fixed bed reactor system.

Continuous fixed-bed catalytic hydrogenation of ethylene carbonate (EC) to methanol and ethylene glycol (EG), an emerging synthetic process of methanol via indirect conversion of CO2, was successfully performed over Cu/HMS catalysts prepared by the ammonia evaporation (AE) method. The catalysts possessed superb performance with a conversion of 100% and a selectivity to methanol of 74%.

A stable Ni/SBA-15 catalyst prepared by the ammonia evaporation method for dry reforming of methane

Coking and sintering were inhibited simultaneously by the strong metal–support interactions.

The direct transformation of ethanol to ethyl acetate over Cu/SiO 2 catalysts that contain copper phyllosilicate

Cu/SiO2 catalysts that contain copper phyllosilicate, were successfully prepared using the ammonia-evaporation method. The catalysts were characterized via XRD, ICP, BET, FTIR, TPR, XPS, NH3-TPD and FTIR of Pyridine Adsorption techniques. The results demonstrated that the formation of the copper phyllosilicate species significantly affected the structural properties and caused the CuO nanoparticles to become highly dispersed, and the copper phyllosilicate would provide access to the Lewis acidic Cu+ species. It was found that the catalyst with a 23.7 wt% copper loading exhibited the best ethanol conversion and ethyl acetate selectivity. When compared to a catalyst with the same copper loading which was prepared with the impregnation method, the higher activity and selectivity of catalysts might be ascribed to the homogenous distribution of copper nanoparticles, which was the active site for the dehydrogenation, and the amount of Lewis acidic Cu+ sites active for esterification. The synergetic effect between the Cu0 and Lewis acidic sites was the key factor to achieve direct transformation of ethanol to ethyl acetate.

Insight into the Tunable CuY Catalyst for Diethyl Carbonate by Oxycarbonylation: Preparation Methods and Precursors

Three different methods were used to prepare CuY catalysts, which play an important role in Cu loading and ion-exchange level during the oxidative carbonylation of ethanol to synthesize diethyl carbonate. Of the prepared CuY catalysts, those synthesized by the ammonia evaporation method exhibited a significantly enhanced activity compared to those obtained by the other two methods. In addition, under optimized conditions, four different copper precursors were applied to adjust the textural properties and chemical states of the CuY catalysts. To obtain a deep understanding of their structure–performance relationship, XRD, XPS, CO adsorption, DRIFTS, and NH3 TPD were conducted to characterize the CuY catalysts. The experimental results indicated that the catalytic performances were in line with the proportions of Cu+ in CuY catalysts, which can be regulated by cupric precursors. In addition, the textural structures of the catalysts and the acidity and type of Cu+ species influenced by the precursors were al...

Enhanced catalytic performance for SiO2–TiO2 binary oxide supported Cu-based catalyst in the hydrogenation of dimethyloxalate

Copper based catalyst with Si–Ti binary-oxide support is synthesized via a facile ammonia evaporation method for selective hydrogenation of dimethyloxalate (DMO) to ethylene glycol (EG). 100% conversion of DMO and 90% selectivity to EG could be obtained over the Cu/SiO2–TiO2 catalyst at high liquid hourly space velocity (LHSV). Catalytic stability is greatly enhanced when the Si–Ti binary oxide is used as support because of the intimate interaction between copper species and the support. The improved catalytic performance compared to the unitary oxide-supported catalysts SiO2 and TiO2 could be attributed to the highly dispersed copper species stabilized by the binary support. Also, the electron transfer from TiO2 to Cu-species is found to play an important role in improving the surface charge density of the metallic copper, which is helpful to improve the catalytic activity.

Hydrogen Production via Steam Reforming of Ethanol on Phyllosilicate-Derived Ni/SiO2: Enhanced Metal–Support Interaction and Catalytic Stability

This paper describes the design of Ni/SiO2 catalysts obtained from a phyllosilicate precursor that possess high activity and stability for bioethanol steam reforming to sustainably produce hydrogen. Sintering of metal particles and carbon deposition are two major issues of nickel-based catalysts for reforming processes, particularly at high temperatures; strong metal–support interaction could be a possible solution. We have successfully synthesized Ni-containing phyllosilicates by an ammonia evaporation method. Temperature programmed reduction results indicate that the metal–support interaction of Ni/SiO2 catalyst prepared by ammonia evaporation method (Ni/SiO2P) is stronger due to the unique layered structure compared to that prepared by conventional impregnation (Ni/SiO2I). With the phyllosilicate precursor nickel particles highly disperse on the surface, remaining OH groups in the unreduced phyllosilicates promote nickel dispersion and carbon elimination. We also show that high dispersion of Ni and strong metal–support interaction of Ni/SiO2P significantly promote ethanol conversion and H2 production in ethanol steam reforming. Ni/SiO2P produces less carbon deposition compared to Ni/SiO2I; for the latter, a surface layer of Ni3C formed during the deactivation.

Hydrogenation of Dimethyl Oxalate Using Extruded Cu/SiO2 Catalysts: Mechanical Strength and Catalytic Performance

In this work, the extrusion process of Cu/SiO2 catalysts prepared by the ammonia-evaporation (AE) method has been investigated and optimized in order to obtain materials with convenient catalytic and mechanical properties for their application in the gas-phase hydrogenation reaction of dimethyl oxalate (DMO) to ethylene glycol (EG). Thereby, a variety of Cu/SiO2 extrudates were prepared with different Cu loading. It has been observed that a special microstructure including defects, flaws, and discontinuities plays a significant role on the mechanical strength. Larger CuO grains may act as fracture origins, which negatively affect the mechanical strength. The 20Cu/SiO2 extrudate with high Cu dispersion and high porosity is optimized for hydrogenation of DMO to EG, achieving a 98% conversion of DMO and 85% selectivity of EG under the liquid hourly space velocity (LHSV) of 1.0 h–1.

Synthesis and High Photocatalytic Activity of Zn-doped TiO2Nanoparticles by Sol-gel and Ammonia-Evaporation Method

Photocatalysis has been applied to decompose the waste and toxic materials produced in daily life and in the global environment. Pure TiO2 (Zn-TiO2-0) and Zn-doped TiO2 (Zn-TiO2-x, x = 3-10 mol %) samples were synthesized using a novel sol-gel and ammonia-evaporation method. The Zn-doped TiO2 samples showed high photocatalytic activity for the degradation of methylene blue (MB). The physicochemical properties of the samples were investigated using XRD, SEM, ICP, DLS and BET methods. In addition, the most important measurement of photocatalytic ability was investigated by a UV-vis spectrophotometer. The effects of the mol % of zinc ion doping in TiO2 on photocatalytic activity were studied. Among the mol % Zn ions investigated, the Zn-TiO2-9 sample showed the highest photoreactivity. This sample removed 91.4% of the MB after 4 h, while the pure TiO2 only removed 46.4% of the MB.

Hydrogenation of dimethyl oxalate to ethylene glycol on a Cu/SiO2/cordierite monolithic catalyst: Enhanced internal mass transfer and stability

AbstractThe design and application of a Cu/SiO2‐based monolithic catalyst for hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG) is presented. The catalyst was dip‐coated on cordierite with highly dispersed Cu/SiO2 slurry prepared by ammonia evaporation method. This structure guarantees high dispersion of copper species within the mesopores of silica matrix in the form of copper phyllosilicate. The catalyst is low cost, stable, and exhibits high activity in the reaction of hydrogenation of DMO, achieving a 100% conversion of DMO and more than 95% selectivity to EG. Notably, STYEG over the monolith is significantly enhanced compared to the packed bed Cu/SiO2 catalysts in both forms of pellet and cylinder. It is primarily due to the relatively short diffusive pathway of the thin wash‐coat layer and high efficiency of the active phase derived from the monolithic catalyst. Theoretical results indicated that the internal mass transfer is dominated on the catalysts of pellet and cylinders. Moreover, the monolithic catalyst possessed excellent thermal stability compared to the pellet catalyst, which is attributed to the regular channel structure, uniform distribution of flow. © 2011 American Institute of Chemical Engineers AIChE J, 2012

Self-assembled synthesis of hierarchically porous NiO film and its application for electrochemical capacitors

A hierarchically porous NiO film on nickel foam substrate is prepared by a facile ammonia-evaporation method. The self-assembled film possesses a structure consisting of NiO triangular prisms and randomly porous NiO nanoflakes. The pseudocapacitive behaviors of the porous NiO film are investigated by cyclic voltammograms and galvanostatic charge–discharge tests in 1 M KOH. The hierarchically porous NiO film exhibits a high discharge capacitance and excellent rate capability with 232 F g −1, 229 F g −1, 213 F g −1 and 200 F g −1 at 2, 4, 10, and 20 A g −1, respectively. The specific capacitance of 87% is maintained from 2 A g −1 to 20 A g −1. The porous NiO film also shows rather good cycling stability and exhibits a specific capacitance of 348 F g −1 after 4000 cycles.