Low-temperature Methanol Synthesis Research Articles

Cu-supported nano-ZrZnOx as a highly active inverse catalyst for low temperature methanol synthesis from CO2 hydrogenation

Hydrogenation of CO2 into methanol at low-temperature on Cu-based catalysts is of great significance, but remains challenging to enhance activity. In this paper, we report an inverse catalyst constructed with nano-ZrZnOx supported on Cu particles with outstanding methanol synthesis performance at 220 ℃, two times higher than that of commercial Cu/ZnO/Al2O3 catalysts under the same conditions. Detailed structure characterization and performance evaluation demonstrate that the ZrZnOx mixed oxide serves as the most active oxide-metal interface site for CO2 hydrogenation. The ZrZnOx/Cu inverse catalyst increases the weak and medium CO2 adsorption sites which are further demonstrated responsible to the methanol productivity. In situ DRIFTs studies reveal that the inverse interface accelerates the reduction of asymmetric formate intermediates and prevents the generation of CO. The combination of enhanced CO2 activation capability and accelerated hydrogenation rate of intermediates over the ZrZnOx/Cu inverse catalyst probably contribute to the remarkable methanol synthesis performance from CO2.

Enhanced performance and stability of Cu/ZnO catalyst by hydrophobic treatment for low-temperature methanol synthesis from CO2

CO2 hydrogenation to methanol is an efficient way to utilize CO2 and store hydrogen. However, realizing high activity and methanol selectivity as well as excellent stability are still challenges due to the competitive reverse water-gas shift (RWGS) reaction and the accumulation of water on the catalyst surface. Herein, Cu/ZnO catalyst was prepared by oxalic acid-assisted solid-state grinding method and then was subjected to hydrophobic treatment using stearic acid as a functionalization agent. The effect of stearic acid concentration on the physicochemical properties of Cu/ZnO catalysts and the catalytic activity for low-temperature CO2 hydrogenation to methanol was investigated and discussed in detail. Detailed catalyst characterizations disclosed that hydrophobic treatment using suitable concentration of stearic acid removed residues from the decomposition of oxalic acid and also increased specific surface area, surface basicity, reducibility and hydrogen adsorption strength on Cu/ZnO catalysts, leading to the enhanced catalytic performance and methanol selectivity. Among all the catalysts, Cu/Zn-2 mM catalyst exhibited methanol selectivity and methanol space time yield (STY) of 78.8% and 87.17 g/kg·h−1 at 200 ℃, much higher than those of untreated Cu/ZnO catalyst (71.7% and 68.93 g/kg·h−1). The hydrophobic Cu/Zn-2 mM catalyst also exhibited outstanding stability for low-temperature CO2 hydrogenation to methanol, keeping its activity for 100 h without obvious deactivation when compared to untreated Cu/ZnO catalyst. This facile hydrophobic treatment using stearic acid not also enhanced catalytic activity, methanol selectivity and stability of Cu/ZnO catalysts for low-temperature methanol synthesis, but also enlightened the invention of more hydrophobic materials in the near future.

Alcohol Solvent Assisted Synthesis of Metallic and Metal Oxide Catalysts: As-Prepared Cu/ZnO/Al2O3 Catalysts for Low-Temperature Methanol Synthesis with an Ultrahigh Yield

Alcohol Solvent Assisted Synthesis of Metallic and Metal Oxide Catalysts: As-Prepared Cu/ZnO/Al₂O₃ Catalysts for Low-Temperature Methanol Synthesis with an Ultrahigh Yield

Rational Design of Novel Reaction Pathways and Tailor-Made Catalysts for Value-Added Chemicals Synthesis from CO2 Hydrogenation

Abstract The highly effective transformation of CO2 into targeted chemicals has attracted significant attention due to greenhouse gas utilization and value-added chemical synthesis functions. Among all of the proposed CO2 transformation pathways, e.g., electrolytic CO2 reduction, photocatalytic CO2 conversion, and thermal-catalytic CO2 utilization, the latter, especially the thermal-catalytic hydrogenation process with renewable energy-driven H2 supply, is the most promising strategy owing to its high efficiency, fast reaction rate, controllable product selectivity, and industrial application potential. In recent years, our research group has made great efforts to realize various chemical syntheses from CO2 hydrogenation technology, such as production of methanol, ethanol, liquid petroleum gas (LPG), alkenes, aromatics (especially para-xylene, PX), etc. In this account, we summarize the main achievements of our laboratory in the rational design of novel heterogeneous catalysts and innovative reaction pathways for CO2 hydrogenation, including reaction pathway design for new low-temperature methanol synthesis, catalytic metal-surface interaction tailoring to boost methanol synthesis performance, tandem reaction network fabrication for the synthesis of ethanol, LPG, or aromatics, a capsule catalyst concept for tandem reaction, etc. In this account, we want to inspire new ideas and methodologies for the rational design of novel catalysts and reaction pathways for CO2 hydrogenation into value-added chemicals.

Electronic Promotion of Methanol Synthesis over Cu-Loaded ZnO-Based Catalysts

Methanol, a raw material for C1 chemistry, is industrially produced under harsh conditions using Cu/ZnO-based catalysts. The synthesis of methanol under mild conditions is a challenging subject using an improved catalyst. Here, Zn1-xSixO (ZSO) nanoparticles were synthesized by a thermal plasma method, and their work function and carrier concentration could be tuned by the Zn:Si ratio. The electrically conductive ZSO nanoparticles with a low work function enhanced the donation of electrons to loaded Cu and significantly promoted hydrogenation of CO to methanol, whereas insulating ZSO nanoparticles with a similar low work function did not. These results reveal that efficient electronic promotion by the transfer of electrons from a support to loaded Cu plays a key role in low-temperature methanol synthesis.

Improved catalytic activity and stability of Cu/ZnO catalyst by boron oxide modification for low-temperature methanol synthesis

Surface modification is an efficient way for enhanced activity and stability in methanol synthesis over traditional Cu/ZnO catalyst. However, previous investigations mainly focused on different metal oxides or pure metals as additives to modify Cu-based catalysts. The influence of non-metal oxide incorporation on the catalytic activity and stability of Cu/ZnO catalyst lacks a deep study. In this work, we prepared a series of boron oxide (B2O3) modified Cu/ZnO catalysts (CZB-R-x) with tunable boron content to disclose the role of B2O3. With the increase of B/Cu molar ratio (x) from 0 to 0.10, there exists a volcano-shaped correlation between catalytic activity and B/Cu molar ratio, revealing a balance between the promotional effect of B2O3 and the negative influence caused by excessive B2O3. CZB-R-0.05 catalyst can increase methanol space time yield (STY) by 7.5 times and total carbon turnover frequency (TOF) by 5.8 times at 170 °C, when compared to unmodified Cu/ZnO, and also stabilizes for 700 h at 200 °C without obvious deactivation. Kinetic studies indicate that the apparent activation energy required for low-temperature methanol synthesis is remarkably decreased from 217.2 kJ/mol over Cu/ZnO to 121.4 kJ/mol over CZB-R-0.05. Importantly, STY of methanol correlates linearly with Cu0 surface area and the number of strongly acidic sites, suggesting that higher Cu0 surface area and stronger surface acidity are key prerequisites for achieving outstanding performance for low-temperature methanol synthesis.

Dimethyl ether (DME) synthesis from CO2 and H2 through ethanol-assisted methanol synthesis and methanol dehydration

Two steps of dimethyl ether (DME) synthesis from CO2 and H2 in a batch reactor were studied, including CO2 hydrogenation to methanol through ethanol-assisted method and methanol dehydration to DME. Additions of 10 wt% ZrO2, Al2O3 and ZrO2–Al2O3 into Cu/ZnO were investigated in low-temperature methanol synthesis using ethanol as catalytic solvent. Suitable zeolite (ZSM-5 and ferrierite) for methanol dehydration was also determined. Ethanol-assisted method offered high methanol yield and Cu/ZnO/ZrO2 catalyst provided the highest CO2 conversion (82.1%) and methanol yield (60.8%) at 150 °C and 50 bar since ZrO2 decreased CuO crystallite sizes and increased surface areas of the catalyst. For methanol dehydration to DME, zeolite's strong acidity related to DME formation. The Cu/ZnO/ZrO2 - Ferrierite provided the highest DME productivity at 0.44 mmolDME/gcat. In addition, DME synthesis from CO2 and H2 through ethanol-assisted methanol synthesis and methanol dehydration can be a potential method to simultaneously produce DME and ethylene. Under the operating conditions, ethylene was produced as a valued by-product of 5.65 mmolEthylene/gcat from dehydration of ethanol. In this study, rather high methanol yield was obtained from ethanol-assisted method. However, DME yield can be further improved by increasing synthesis temperature.

Low-temperature alcohol-assisted methanol synthesis from CO2 and H2: The effect of alcohol type

Carbon dioxide (CO2) conversion to higher-value products is a promising pathway to mitigate CO2 emissions. Methanol is a high-value-chain chemical in industries that can be produced through CO2 hydrogenation, which is an exothermic reaction. Due to thermodynamic limitations, a typical synthesis temperature between 250 °C and 300 °C results in a low conversion of CO2 at equilibrium. To enhance the CO2 conversion, high pressures of 50–100 bar are required, which inevitably causes the process to be energy-intensive. In this study, an alternative method called alcohol-assisted methanol synthesis is investigated. In this method, alcohol is used as a catalytic solvent and helps decrease the reaction temperature and pressure (150 °C and 50 bar) and significantly increases methanol yield. Ethanol is used as the alcohol due to its reactivity, providing a high methanol yield (47.80%) with 63.93% CO2 conversion and 67.54% methanol selectivity. However, due to unwanted side reactions, ethanol generates ethyl acetate as a byproduct that forms an azeotrope with methanol, leading to difficulty in product purification. The effects of alcohol type (molecular weight and structure), including ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, iso-butanol, tert-butanol and 1-pentanol, on CO2 conversion, methanol yield and byproducts are investigated. It is found that smaller-molecule alcohols provide a higher methanol yield. Moreover, n-alcohols provide a higher methanol yield than branched alcohols, and the byproducts of the reaction with n-alcohols do not form an azeotrope with methanol. Therefore, 1-propanol is compared with ethanol providing 26.55% methanol yield, 69.02% CO2 conversion and 70.82% methanol selectivity.

Integrated carbon capture and utilization to methanol with epoxide-functionalized polyamines under homogeneous catalytic conditions

Herein, a novel amine based integrated process is presented for CO2 capture and utilization (CCU) to synthesize methanol. Reaction of pentaethylenehexamine (PEHA) with selected epoxides led to a library of functionalized polyamines. In aqueous medium, the modified amines were efficient in capturing CO2 under ambient conditions. Subsequently, the CO2 loaded solutions were directly subjected to catalytic hydrogenation to CH3OH in presence of molecular H2 and Ru-PNP based molecular catalysts. While the epoxide-modified amines exhibited CO2 capture efficiencies comparable to those of unmodified PEHA, they displayed a notable enhancement in the hydrogenation step resulting in higher methanol yields of up to 93%. Furthermore, the integrated process was demonstrated in a water and 2-methyl-THF based biphasic solvent system. We believe that the improved amine-based system for CO2 capture and hydrogenation to methanol is key in advancing low temperature and renewable methanol synthesis processes.

Enhanced performance and stability of Cu/ZnO catalyst by introducing MgO for low-temperature methanol synthesis using methanol itself as catalytic promoter

Catalytic conversion of CO2-containing syngas to methanol is one of important processes in industry. However, realizing high space time yield (STY) of methanol at low reaction temperature remains a challenge. Herein, ternary Cu/ZnO/MgO catalysts were prepared via co-precipitation and tested for low-temperature methanol synthesis via autocatalysis of methanol. The effects of Mg2+ ion and MgO content on the formation and composition of the precipitated precursors, as well as on the physicochemical properties of the calcined and the reduced catalysts were systemically investigated and discussed. The structure–activity relationships were disclosed by detailed catalysts characterization. Compared to Cu/ZnO, the total carbon turnover frequency (TOF) and space time yield (STY) of methanol on Cu/ZnO/MgO remarkably increased from 17.8 to 20.0 h−1 and from 425.2 to 538.3 g/kg∙h−1, respectively. Besides, Cu/ZnO/MgO kept its activity for 180 h without deactivation, which was much more stable than Cu/ZnO. In comparison with commercial Cu/ZnO/Al2O3 and other Cu-based catalysts reported in the literatures for methanol synthesis from syngas, Cu/ZnO/MgO catalyst with Cu/Zn/Mg molar ratio of 1:1:0.05 displayed much higher space time yield (STY) of methanol. In addition, the reaction conducted in the presence of methanol promoter exhibited much lower apparent activation energy than that of the reaction carried out without methanol promoter, indicating a catalytic and promotional role of methanol during low-temperature methanol synthesis reaction. The current work provided not only a hopeful strategy for enhancing activity and stability of Cu/ZnO catalyst, but also a sustainable low-temperature methanol synthesis route using methanol itself as catalytic promoter.

Effect of Different Chelating Agents on the Physicochemical Properties of Cu/ZnO Catalysts for Low-temperature Methanol Synthesis from Syngas Containing CO<sub>2</sub>

Nanostructured Cu/ZnO catalysts were prepared by a simple solid-state method, using cheap metal nitrates as raw materials. Special attention was paid to the influence of different chelating agents such as citric acid, formic acid and oxalic acid on the physicochemical properties of Cu/ZnO catalysts, which were characterized by detailed investigations. CuO crystallite size, oxygen vacancies and surface compositions were clearly affected by chelating agent types, leading to different CuO–ZnO interactions in the calcined catalysts as well as distinct reducibility. Different chelating agents also had significant effects on specific surface area, metallic Cu0 surface area, and Cu crystallite size, as well as ZnO (002) plane to ZnO (100) plane ratio (I(002)/I(100)) calculated based on the peak intensity of XRD patterns of the reduced samples, so influencing the catalytic activity for low-temperature methanol synthesis from syngas containing CO2. The structure-activity correlations, particularly the relationships between space time yield (STY) of methanol with Cu0 surface area and I(002)/I(100) ratio, were evaluated. Cu/ZnO catalyst prepared with oxalic acid showed the highest STY value, which was 2.3 and 5.3 times higher that of the catalysts obtained with citric acid and formic acid, respectively. The excellent catalytic performance was due to its greater Cu0 surface area, higher specific surface area and smaller Cu crystallite size. Stronger interactions between Cu and ZnO in the reduced samples were also favorable for enhancing catalytic activity for low-temperature methanol synthesis.

Effect 3A and 5A molecular sieve on alcohol-assisted methanol synthesis from CO2 and H2 over Cu/ZnO catalyst

Low-temperature methanol synthesis from CO2 and H2 was carried out using ethanol as a catalytic solvent. The alcohol-assisted method reduced synthesis temperature and enhanced methanol yield (33.80%) at 150 °C (5.0 MPa, Cu/ZnO catalyst). However, ethyl acetate and water were generated as byproducts from the reaction. The byproducts formed azeotrope mixture with methanol and led to a complex product purification. Therefore, in this study, molecular sieves (MS) were introduced to adsorb the byproducts. The effect of different MS (3A and 5A) was studied. It was found that MS helped enhancing methanol yield. The highest methanol yield (42.8%) was obtained when adding MS_3A to adsorb water. The MS_5A could separate methanol and ethyl acetate, providing high methanol purity. The effect of operating conditions was also investigated. When reducing temperature to 130 °C, methanol yield decreased but methanol selectivity (>98%) significantly increased. Controlling temperature and using MS could help enhance the yield and selectivity of methanol.

Structure-Performance Correlations over Cu/ZnO Interface for Low-Temperature Methanol Synthesis from Syngas Containing CO2.

Cu/ZnO catalysts with varied Cu/(Cu + Zn) molar ratios were prepared by a facile solid-state method. The Cu/(Cu + Zn) molar ratio displayed a significant effect on the oxygen vacancy formation of the calcined catalysts, thereby influencing the CuO-ZnO interaction and the reducibility of CuO. The Cu/(Cu + Zn) molar ratio also exhibited a significant effect on Cu0 surface area, oxygen vacancy, the ratio of ZnO(002) plane to ZnO(100) plane, as well as the basicity and acidity of the reduced catalysts, thereby affecting the catalytic performance for low-temperature methanol synthesis from syngas containing CO2. The correlations of methanol space time yield (STY) versus the physicochemical characteristics of Cu/ZnO catalysts were studied. The catalyst with equal amounts of Cu and Zn displayed the best catalytic activity owing to higher Cu0 surface area, more oxygen vacancy and ZnO(002) plane, as well as more moderately basic sites.

Influence of Reaction Temperature on CO2-to-methanol Hydrogenation over MZrOx (M = Al, Mn, Cu, Zn, Ga, and In)

Abstract To open up the possibility of synthesizing useful substances from CO2, we have developed new catalysts that hydrogenate CO2 to methanol with high yield at 300 °C and higher. In this study, methanol synthesis via CO2 hydrogenation at 250–350 °C and 10 bar was investigated using Zr-based metal oxide catalysts, MZrOx (M = Al, Mn, Cu, Zn, Ga, and In). The different metals (M) determined the suitable reaction temperature wherein the maximum yield of methanol was obtained. CuZrOx was a suitable catalyst for low-temperature methanol synthesis because the yield decreased with increasing reaction temperature from 250 °C to 350 °C. In contrast, ZnZrOx, GaZrOx, and InZrOx were suitable for methanol synthesis at 300 °C and higher. In particular, ZnZrOx afforded the highest yield of methanol (60 mLSTP h−1 g−1 at 300 °C) among the prepared MZrOx catalysts.

Copper-zirconia interfaces in UiO-66 enable selective catalytic hydrogenation of CO2 to methanol

Molecular interactions with both oxides and metals are essential for heterogenous catalysis, leading to remarkable synergistic impacts on activity and selectivity. Here, we show that the direct link between the two phases (and not merely being together) is required to selectively hydrogenate CO2 to methanol on catalysts containing Cu and ZrO2. Materials consisting of isolated Cu particles or atomically dispersed Cu–O–Zr sites only catalyze the reverse water-gas shift reaction. In contrast, a metal organic framework structure (UiO-66) with Cu nanoparticles occupying missing-linker defects maximizes the fraction of metallic Cu interfaced to ZrO2 nodes leading to a material with high adsorption capacity for CO2 and high activity and selectivity for low-temperature methanol synthesis.

Vapor-phase low-temperature methanol synthesis from CO2-containing syngas via self-catalysis of methanol and Cu/ZnO catalysts prepared by solid-state method

Binary Cu/ZnO catalysts were prepared by solid-state method and tested for vapor-phase low-temperature methanol synthesis from CO2-containing syngas. The influence of H2C2O4/(Cu + Zn) molar ratio on the physicochemical properties and the corresponding catalytic activity was systematically studied. The space time yield (STY) of methanol exhibited a linear relationship with the Cu0 surface area, and increased linearly by enhancing the number of strongly acidic sites or moderately basic sites. The effects of various parameters on the methanol synthesis reaction were also investigated. C4-Red catalyst (H2C2O4/(Cu + Zn) = 4/1) exhibited the maximum turnover frequency (TOF, 11.4 × 10−3 s−1) and STY values (456.3 g/kg h−1), due to the larger Cu0 surface area, greater specific surface area, more strongly acidic sites and moderately basic sites. The strengthened Cu-ZnO interaction, superior CO and H2 adsorption capability as well as higher adsorbed CO and H2 amount also contributed to increasing the catalytic performance of C4-Red catalyst.

Urea-derived Cu/ZnO catalyst being dried by supercritical CO2 for low-temperature methanol synthesis

Methanol synthesis from syngas is a crucial process in the transformation of coal, natural gas and biomass into high-value added products. The high CO conversion and methanol yield are challenging in low-temperature methanol synthesis, thus improving catalyst activity is necessary. Cu/ZnO nanoparticles with a narrow size distribution were synthesized via homogeneous precipitation method using urea as the precipitant, being followed by supercritical CO2 drying treatment (named as CZhp-S). The analysis results rendered that CZhp-S had a lower reduction temperature, higher Cu0 specific surface area and smaller crystal sizes compared with those of the catalyst prepared by co-precipitation method with conventional drying process (named as CZcp-H). Due to the large specific surface area and the enhanced amount of active sites, the CZhp-S with optimized supercritical CO2 drying treatment condition demonstrated a maximum CO conversion of 52.7% and STY of methanol 87.6 gMeOH/kgcatalyst.h−1 for low-temperature methanol synthesis from syngas, which were much higher than those of CZcp-H (CO conversion 36.5%, STY of methanol 62.9 gMeOH/kgcatalyst.h−1).

Fabrication of a CuZn-based catalyst using a polyethylene glycol surfactant and supercritical drying

We employed PEG treatment and supercritical CO2 drying to improve the traditional co-precipitation method for fabrication of CuZn-based catalysts for alcohol-assisted low-temperature methanol synthesis.

Integrated CO2 Capture and Conversion to Formate and Methanol: Connecting Two Threads.

The capture of CO2 from concentrated emission sources as well as from air represents a process of paramount importance in view of the increasing CO2 concentration in the atmosphere and its associated negative consequences on the biosphere. Once captured using various technologies, CO2 is desorbed and compressed for either storage (carbon capture and storage (CCS)) or production of value-added products (carbon capture and utilization (CCU)). Among various products that can be synthesized from CO2, methanol and formic acid are of high interest because they can be used directly as fuels or to generate H2 on demand at low temperatures (<100 °C), making them attractive hydrogen carriers (12.6 and 4.4 wt % H2 in methanol and formic acid, respectively). Methanol is already produced in huge quantities worldwide (100 billion liters annually) and is also a raw material for many chemicals and products, including formaldehyde, dimethyl ether, light olefins, and gasoline. The production of methanol through chemical recycling of captured CO2 is at the heart of the so-called "methanol economy" that we have proposed with the late Prof. George Olah at our Institute. Recently, there has been significant progress in the low-temperature synthesis of formic acid (or formate salts) and methanol from CO2 and H2 using homogeneous catalysts. Importantly, several studies have combined CO2 capture and hydrogenation, where captured CO2 (including from air) was directly utilized to produce formate and CH3OH without requiring energy intensive desorption and compression steps. This Account centers on that topic. A key feature in the combined CO2 capture and conversion studies reported to date for the synthesis of formic acid and methanol is the use of an amine or alkali-metal hydroxide base for capturing CO2, which can assist the homogeneous catalysts in the hydrogenation step. We start this Account by examining the combined processes where CO2 is captured in amine solutions and converted to alkylammonium formate salts. The effect of amine basicity on the reaction rate is discussed along with catalyst recycling schemes. Next, methanol synthesis by this combined process, with amines as capturing agents, is explored. We also examine the system developments for effective catalyst and amine recycling in this process. We next go through the effect of catalyst molecular structure on methanol production while elucidating the main deactivating pathway involving carbonylation of the metal center. The recent advances in first-row transition metal catalysts for this process are also mentioned. Subsequently, we discuss the capture of CO2 using hydroxide bases and conversion to formate salts. The regeneration of the hydroxide base (NaOH or KOH) at low temperatures (80 °C) in cation-conducting direct formate fuel cells is presented. Finally, we review the challenges in the yet unreported integrated CO2 capture by hydroxide bases and conversion to methanol process.

Insight into activation of CO and initial C2 oxygenate formation during synthesis of higher alcohols from syngas on the model catalyst K2O/Cu(111) surface

Alkali-metal-modified Cu-based catalysts are important in low-temperature synthesis of methanol and higher alcohols from syngas. Spin-polarized density functional theory calculations with periodic slab models were performed for a K2O/Cu(111) model catalyst to investigate the interactions between K2O and the Cu(111) surface, and activation of CO. The results show that K2O interacts strongly with the Cu(111) surface via electron transfer between K2O and the Cu(111) surface. This changes CO activation and modulates the mechanism of formation of the initial C2 oxygenates. Although K2O significantly promotes CO direct dissociation, H-assisted dissociation of CO is still the most energetically favorable route. The optimal reaction pathway for C2 oxygenate formation is proposed based on a climbing-image nudged elastic band calculation. The reactions starts with CO hydrogenation to yield the preferred monomers, i.e., CHO, CH2O, and CH2, through the pathways CO + H → CHO + H → CH2O + H → CH2 + OH, with reaction barriers of 0.92, 0.97, and 0.58 eV. The reaction of CH2 with CH2O is the main C2 oxygenate formation route on the K2O/Cu(111) surface. These results clarify the effects of K2O on Cu-based catalysts and elucidate the mechanism of C2 oxygenate formation during alcohol synthesis from syngas.