Low-temperature Methanol Synthesis Research Articles

Formate Ester Is Not a Decisive Intermediate in the Low-Temperature Synthesis of Methanol from Carbon Dioxide Dissolved in Diethylaminoethanol

Alcohols are often discussed as suitable solvents for the low-temperature methanol synthesis. In particular, 2-(diethylamino)ethanol is seen as a promising solvent in this regard because it is already used as a carbon dioxide scrubbing agent. Often observed intermediates in the low-temperature methanol synthesis are alcohol formate esters. This study investigates the formation of 2-(diethylamino)ethanol formate ester and its conversion. Kinetic investigations with 2-(diethylamino)ethanol formate ester as the starting material reveal that the reduction of this ester to methanol is not the only reaction under typical reaction conditions. Two-thirds of the ester decomposes to carbon dioxide and hydrogen, while only one-third is reduced to methanol. Furthermore, it is shown that methanol is also produced in the related hydroxyl-group-free triethylamine. Hence, the formation of formate esters seems to be not a strict requirement for the low-temperature methanol synthesis.

Corrigendum: The Role of Solvent Polarity on Low-Temperature Methanol Synthesis Catalyzed by Cu Nanoparticles

Corrigendum: The Role of Solvent Polarity on Low-Temperature Methanol Synthesis Catalyzed by Cu Nanoparticles

Investigation of Active Center of Cu‐Based Catalyst for Low Temperature Methanol Synthesis from Syngas in Liquid Phase: The Contribution of Cu+ and Cu0

AbstractLaCuMn catalyst was prepared under different reduction temperature and passivation time, and used to catalyze CO hydrogenation to methanol in liquid phase. The effect of reductive copper species on the catalytic activity and the product distribution was studied. The results showed that the surface content of reductive copper species greatly affect the catalytic activity and the approximate molar ratio of Cu+ to Cu0 was important. The mixture of CuZn/AC‐N2 with only Cu+ and CuZn/AC‐H2 with only Cu0 was utilized for the low temperature methanol synthesis from syngas in liquid phase. It was confirmed that both of the reductive copper species of Cu+ and Cu0 were active species and Cu+ was superior to Cu0. Moreover, the synergic function of Cu+ and Cu0 led to the enhancement of the catalytic activity of Cu based catalyst, and the optimum molar ratio of surface Cu+ to Cu0 was in the range of 3.5 to 4.0.

The Role of Solvent Polarity on Low-Temperature Methanol Synthesis Catalyzed by Cu Nanoparticles

Methanol syntheses at low temperature in a liquid medium presents an opportunity for full syngas conversion per pass. The aim of this work was to study the role of solvents polarity on low temperature methanol synthesis (LTMS) reaction using 8 different aprotic polar solvents. A ‘once through’ catalytic system, which is composed of Cu nanoparticles and sodium methoxide, was used for methanol synthesis at 100 oC and 20 bar syngas pressure. Solvent polarity rather than the 7-10 nm Cu (and 30 nm Cu on SiO2) catalyst used dictated trend of syngas conversion. Diglyme with a dielectric constant (ɛ) = 7.2 gave the highest syngas conversion among the 8 different solvents used. Methanol formation decreased with either increasing or decreasing solvent ɛ value of diglyme (ɛ = 7.2). To probe the observed trend, possible side reactions of methyl formate, the main intermediate in the process, were studied. Methyl formate was observed to undergo two main reactions; (i) decarbonylation to form CO and MeOH and (ii) a nucleophilic substitution to form dimethyl ether and sodium formate. Decreasing polarity favoured the decarbonylation side reaction while increasing polarity favoured the nucleophilic substitution reaction. In conclusion, our results show that moderate polarity solvents, e.g. diglyme favour MF hydrogenolysis and hence, methanol formation, by retarding the other two possible side reactions.

Low temperature methanol synthesis catalyzed by copper nanoparticles

A one pot catalytic system which involves Cu and an alkoxide co-catalyst has been used for methanol (MeOH) synthesis at low temperature. Up to about 92% syngas conversion per pass and more than 90% selectivity to MeOH (the rest is methyl formate) was obtained depending on the amount of catalyst employed at 100°C and 20bar syngas pressure. Low temperature methanol synthesis presents a good alternative to current technology for methanol production since the former is thermodynamically favored and gives a high yield per pass. Cu particles sized around 10±5nm were found to be involved in the catalytic process. Cu nanoparticles of increasing size was synthesized by varying temperature. However, methanol production decreased with increasing Cu nanoparticle size. Moreover, the maximum conversion at the end of each successive batch declined as a function of the number of cycles performed. Decrease in catalyst activity corresponded to Cu nanoparticle densification, suggesting agglomeration to be a major catalyst deactivation pathway.

Preparation and application of Cu/ZnO catalyst by urea hydrolysis method for low-temperature methanol synthesis from syngas

The Cu/ZnO catalyst prepared by urea hydrolysis method was investigated for low-temperature methanol synthesis from syngas containing CO2. Concurrently, the activity of the conventional Cu/ZnO catalyst prepared by co-precipitation method was also compared. The effects of precipitation temperature, urea content, stirring speed and the introduction of Al on the catalytic performance of Cu/ZnO were deeply studied. It was found that the total carbon conversion of the Cu/ZnO catalyst prepared by urea hydrolysis method was increased to 45.0% from 32.8%, comparing with that of the catalyst prepared by co-precipitation method. The structure, BET surface area, surface morphology of the catalyst were characterized by XRD, BET, EDX and SEM. The catalyst prepared by urea method obtained higher BET surface area and larger metallic surface area of Cu than those of the co-precipitation method. The crystals sizes of Cu by urea method were smaller than those of co-precipitation method. Surface structure prepared by urea method had needle shape, and it could increase the surface area, different from the catalyst by co-precipitation method. Both the increased BET surface area of the catalysts and the enhanced metallic surface area of Cu0 promoted the catalyst activity for the low-temperature methanol synthesis. The deactivation of the Cu-ZnO catalysts prepared by urea method was not observed in low-temperature methanol synthesis here.

Bifunctionality of Cu/ZnO catalysts for alcohol-assisted low-temperature methanol synthesis from syngas: Effect of copper content

Alcohol-assisted low-temperature methanol synthesis was conducted over Cu/ZnO_X catalysts while varying the copper content (X). Unlike conventional methanol synthesis, ethanol acted as both solvent and reaction intermediate in this reaction, creating a different reaction pathway. The formation of crystalline phases and characteristic morphology of the co-precipitated precursors during the co-precipitation step were important factors in obtaining an efficient Cu/ZnO catalyst with a high dispersion of metallic copper, which is one of the main active sites for methanol synthesis. The acidic properties of the Cu/ZnO catalyst were also revealed as important factors, since alcohol esterification is considered the rate-limiting step in alcohol-assisted low-temperature methanol synthesis. As a consequence, bifunctionality of the Cu/ZnO catalyst such as metallic copper and acidic properties was required for this reaction. In this respect, the copper content (X) strongly affected the catalytic activity of the Cu/ZnO_X catalysts, and accordingly, the Cu/ZnO_0.5 catalyst with a high copper dispersion and sufficient acid sites exhibited the best catalytic performance in this reaction.

Functional rice husk as reductant and support to prepare as-burnt Cu-ZnO based catalysts applied in low-temperature methanol synthesis

A novel method, that the precursor is burnt in argon without further reduction to directly prepare metallic catalyst, is developed using low-valued by-product. Rice husk not only contributed as catalyst support, but also as reductant and fuel. The XRD, TPR and TG-DTA analysis prove that Cu phase in the as-burnt catalyst is almost reduced to metallic Cu0. The as-prepared catalysts exhibit higher activity and methanol selectivity than those prepared by a conventional impregnation method. This method may open a new way to prepare metallic catalysts without further reduction, especially for some catalytic reactions promoted by K, Ca, Mg and Mn.

Effect of the aging time of the precipitate on the activity of Cu/ZnO catalysts for alcohol-assisted low temperature methanol synthesis

Cu/ZnO_X catalysts were prepared by a co-precipitation method with various aging times of the precipitate (X=10min–10h). All prepared catalysts were evaluated in alcohol-assisted methanol synthesis through a low temperature liquid phase reaction using a batch type reactor under a reaction pressure of 50bar at a temperature of 150°C. Unlike the conventional low temperature methanol synthesis, ethanol was adopted as both the solvent and the reaction intermediate in this study. Variation of the aging time of the precipitate led to numerous changes in the surface properties of catalysts, resulting in the different catalytic activity in this reaction. This means that aging time of the precipitate should be precisely controlled for obtaining an efficient Cu/ZnO catalyst by a co-precipitation method. The results of catalytic activities and catalyst characterizations clearly demonstrated that the copper particle size, the morphology, and the strong acidity of the Cu/ZnO catalysts played key roles in this reaction. Small copper particle size, plate-like morphology, and high strong acidity of the catalysts were favorable for efficiently producing methanol in this reaction. Among the Cu/ZnO_X catalysts, the Cu/ZnO_5h catalyst showed the best catalytic activity. According to the proposed reaction pathway, not only the intrinsic activity of metallic copper but also the acid properties of catalysts were important factors to determine the activity of Cu/ZnO catalysts in this reaction.

Structural and kinetical studies on the supercritical CO2 dried Cu/ZnO catalyst for low-temperature methanol synthesis

The Cu/ZnO catalyst prepared by supercritical phase CO2 drying (denoted as CZS catalyst) and the conventional Cu/ZnO catalyst prepared by heating dry process (denoted as CZO catalyst) were comparatively investigated. The low-temperature methanol synthesis reaction from CO+CO2+H2 using 2-butanol as solvent was conducted over the CZS and CZO catalysts at 443K and 5.0MPa for continuous 20h in a flow-type reactor. It was found that the total carbon conversion of the CZS catalyst was increased from 35.1% to 46.4% and the methanol yield of the CZS catalyst was enhanced from 33.8% to 44.8%, comparing with those of the CZO catalyst. The results of kinetic analysis by in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS) revealed that the reaction rate of the low-temperature methanol synthesis on CZS catalyst was faster than that on CZO catalyst at 443K, in good accordance to the catalytic reaction performances. It was indicated that the supercritical fluid CO2, which was used to dry the catalyst precursor, suppressed the sintering of the Cu and ZnO particles and increased both the BET surface area of the catalysts and metallic surface area of Cu0, which further improved the reaction activity of the catalyst for the low temperature methanol synthesis.

Surface-Bound Intermediates in Low-Temperature Methanol Synthesis on Copper: Participants and Spectators

The reactivity of surface-adsorbed species present on copper catalysts during methanol synthesis at low temperatures was studied by simultaneous infrared spectroscopy (IR) and mass spectroscopy (MS) measurements during “titration” (transient surface reaction) experiments with isotopic tracing. The results show that adsorbed formate is a major bystander species present on the surface under steady-state methanol synthesis reaction conditions, but it cannot be converted to methanol by reaction with pure H2 or with H2 plus added water. Formate-containing surface adlayers for these experiments were produced during steady-state catalysis in (a) H2:CO2 (with substantial formate coverage) and (b) moist H2:CO (with no IR visible formate species). These reaction conditions both produce methanol at steady state with relatively high rates. Adlayers containing formate were also produced by (c) formic acid adsorption. Various “titration” gases were used to probe these adlayers at modest temperatures (T = 410–450 K) and...

Highly Active SiO<sub>2</sub>-supported Cu–ZnO Catalysts Prepared by Combustion Methods for Low-temperature Methanol Synthesis: Comparative Activity Test with or without SiO<sub>2</sub> Support

Nanostructured (Cu–ZnO/SiO2 and Cu/ZnO) catalysts are prepared by sol-gel and surface impregnation combustion methods with inexpensive raw materials and easily-operated conditions. The X-ray diffraction patterns and SEM analysis reveal that Cu crystallite and particle sizes prepared by surface impregnation combustion method are rather smaller. During the combustion process, the support SiO2 can absorb heat and promote heat transfer, realizing a significantly mild and smooth catalyst-preparation process. As-prepared catalysts are tested in low-temperature methanol synthesis from syngas containing CO2, with ethanol as a catalyst and solvent at 443 K and 5.0 MPa for 8 h. The activity and methanol selectivity of the supported Cu–ZnO/SiO2 catalyst are much higher, which are closely related the metallic Cu surface area and Cu crystalline sizes. The different properties of as-prepared catalysts are investigated by XRD, TG-DTA, FT-IR, Raman spectrum, SEM, BET and N2O chemisorption techniques in detail. Here, the support SiO2 has a function of heat transfer to make catalysts preparation process much smoother, besides the dispersion effect.

Preparation of Cu/ZnO catalyst using a polyol method for alcohol-assisted low temperature methanol synthesis from syngas

A polyol method was used to prepare Cu/ZnO catalysts for alcohol-assisted low temperature methanol synthesis from syngas. Unlike conventional low temperature methanol synthesis, ethanol was employed both as a solvent and a reaction intermediate. Catalyst characterization revealed that Cu/ZnO catalysts were successfully and efficiently prepared using the polyol method. Various preparation conditions such as PVP concentration and identity of ZnO precursor strongly influenced the catalytic activity of Cu/ZnO catalysts. Copper dispersion and catalyst morphology played key roles in determining the catalytic performance of the Cu/ZnO catalyst in alcohol-assisted low temperature methanol synthesis. A high copper dispersion and platelike Cu/ZnO structure led to high catalytic activity. Among the catalysts tested, 5_Cu/ZnO_Zn(Ac)2 had the best catalytic performance due to its high copper dispersion.

Alcohol-assisted low temperature methanol synthesis from syngas over Cu/ZnO catalysts: Effect of pH value in the co-precipitation step

Alcohol-assisted low temperature methanol synthesis from syngas was conducted in a batch type reactor using ethanol as both a solvent and a reaction intermediate. Cu/ZnO_X catalysts were prepared by a co-precipitation method with different co-precipitation pH values (X=6–10), with an aim of investigating the effect of pH value on the catalytic activity of Cu/ZnO_X catalysts in this reaction. The co-precipitation pH value had a strong influence on the Cu crystallite size, the surface morphology, and the surface acidity, leading to the different activities of Cu/ZnO_X catalysts depending on the pH value (X). Catalyst characterization and reaction mechanism clearly revealed that Cu crystallite size and strong acidity of Cu/ZnO_X catalysts played key roles in determining their catalytic activity in this reaction. Yield for methanol showed a tendency to increase with decreasing Cu crystallite size and with increasing strong acidity of Cu/ZnO_X catalysts. Among Cu/ZnO_X catalysts, Cu/ZnO_8 catalyst prepared at pH 8 showed the best catalytic performance due to the finely dispersed Cu particles and the high strong acidity. In addition, the catalytic activity of Cu/ZnO_8 catalyst maintained at the same level even after a 60h-catalytic reaction, leading to the high feasibility of application of Cu/ZnO_8 catalyst to the continuous reaction system along with the batch reaction system for methanol production from syngas.

Performance of Cu-Based Catalysts in Low-Temperature Methanol Synthesis

The reactions of the methanol synthesis were conducted from the CO/CO2/H2 on the Cu-based catalysts using different solvent at 443 K and 3.0 MPa. The alcohol solvent had the activity in the low-temperature methanol synthesis reaction. The activity of the Cu-based catalyst with ZnO as carrier was higher than that of the catalyst with CeO2, Al2O3, or TiO2 as carrier separately in the reaction. The addition of the CeO2 to the Cu/ZnO catalysts improved the copper species dispersion, so that it was easier for the reduction of the Cu/CeO2-ZnO catalyst than that of the Cu/ZnO catalyst according to the TPR analysis. The variation trend of the BET surface area and the copper surface area was consistent with those of the activity for the Cu/ZnO and the Cu/CeO2-ZnO catalysts in the reaction. The activity of the Cu/CeO2-ZnO catalyst was higher than that of the Cu/ZnO catalyst in the reaction.

Effect of modifiers on the performance of Cu-ZnO-based catalysts for low-temperature methanol synthesis

A series of Cu-ZnO-based catalysts modified with Al, Zr, and Ce for the low-temperature methanol synthesis were prepared through co-precipitation and characterized by N2 sorption, H2-TPR, CO2-TPD, N2O titration, XRD, and high-resolution TEM; the effect of various modifiers and calcination temperature on their catalytic performance in methanol synthesis at 170°C was investigated. The results showed that the Cu-ZnO-based catalyst modified with ZrO2, among the various modifiers, exhibits the highest activity. Meanwhile, a lower calcination temperature is propitious to get a higher Cu dispersion, a smaller Cu crystal size, and a higher low temperature activity for methanol synthesis; as a result, the uncalcined catalyst exhibits excellent catalytic performance, with a productivity of 106.02 g/(kg·h) and a selectivity of 87.04% to methanol.

Low-Temperature and Low-Pressure Methanol Synthesis in the Liquid Phase Catalyzed by Copper Alkoxide Systems

We report a new very low temperature methanol catalyst system that is produced in situ by the reaction of Cu(CH3COO)2, NaH, and methanol. The catalytic reaction is assumed to proceed in two steps: (i) formation of methyl formate from syngas and (ii) hydrogenation of methyl formate to two molecules of methanol. When the catalyst system is tested in a batch reactor, syngas conversion of 50–75% is achieved at a temperature of 60–120 °C and a pressure of 10–20 bar. Syngas generation is a major cost factor in current commercial methanol technology. Very high conversion per pass (low reaction temperature) in the methanol reactor would allow for the use of air for syngas generation (autothermal reforming or partial oxidation reaction) and thereby contribute to potential cost reduction.

Nitrate Combustion Methods to Prepare Highly Active Cu/ZnO Catalysts for Low-Temperature Methanol Synthesis: Comparative Behaviors of Citric Acid in Air or Argon Atmosphere

Abstract A citric acid-assisted solid-state method is developed to prepare highly active Cu/ZnO catalysts in different atmospheres (air and argon). The entire catalyst preparation process is accomplished with inexpensive raw materials. It is environmentally friendly in that no water is used and no waste water is produced during the entire process. These as-prepared catalysts are investigated in low-temperature methanol synthesis with CO2-containing syngas. The properties of these catalysts are systematically studied by thermogravimetry differential thermal analysis, X-ray diffraction, Fourier transform-infrared spectroscopy, Raman spectroscopy, temperature-programmed reduction, Brunauer–Emmett–Teller, and N2O chemisorption techniques. The activity and methanol selectivity of Cu/ZnO catalysts are closely related to the metallic Cu0 surface areas and Cu crystalline sizes. Compared with traditional solid-state or sol–gel autocombustion methods, the catalysts prepared by this citric acid-assisted solid-state method exhibit much higher activity and methanol selectivity.

Liquid-Phase Low-Temperature and Low-Pressure Methanol Synthesis Catalyzed by a Raney Copper-Alkoxide System

Current CuZnO methanol synthesis technology may be improved by development of a catalyst allowing a “once through” methanol synthesis step. A Raney copper/alkoxide catalyst has been reported in the patent literature operating at 50 bar and 120 °C. We report here the effect of temperature, pressure, Raney copper concentration and CH3OK concentration by orthogonal array design on this catalyst system. A synergistic effect on catalyst activity and methanol formation has been observed between CH3OK and Raney copper.

Formic acid directly assisted solid-state synthesis of metallic catalysts without further reduction: As-prepared Cu/ZnO catalysts for low-temperature methanol synthesis

Metallic catalysts (Cu/ZnO) and pure metals (Co, Ni, and Ag) without any impurities are directly prepared by a novel formic acid-assisted solid-state method without further reduction. During the decomposition of metal–formic acid precursors at 523K under argon, H2 and CO are liberated and act in situ as reducing agents to obtain pure metals and metallic catalysts (Cargon). X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive spectroscopy, and temperature-programmed reduction analysis reveal that the as-prepared catalyst Cargon without further reduction is converted into metallic Cu0 and ZnO species. TPR analysis results, Fourier transform infrared analysis, and the thermal decomposition behavior in air illustrate that no amorphous carbon or carbonic residues are left in Cargon when formic acid is used as the chelating agent and reductant, because formic acid is the simplest organic acid. The as-prepared Cu/ZnO catalyst is tested for low-temperature methanol synthesis at 443K from syngas containing CO2 and using ethanol as a solvent and catalyst; it exhibits much higher activity and methanol selectivity than catalysts prepared by conventional solid-state methods.