Methanol Synthesis Catalyst Research Articles

Toward Carbon‐Negative Methanol Production from Biogas: Intensified Membrane Reactor

AbstractThe modern world's major challenges, such as global warming, air pollution, and increasing energy demands, escalate the importance of sustainable development and transition toward renewables using innovative and environmentally friendly solutions, such as intensifying chemical processes, to reduce carbon footprints effectively. Aiming to enhance the process toward negative carbon emissions, this perspective explores the intensified membrane reactors for reducing the energy intensity of converting biogas into methanol, a versatile chemical feedstock, and renewable liquid fuel. Syngas and methanol synthesis processes, catalysts, and membranes were explored, and novel reactor designs were proposed. Introduction of selective membranes into the catalytic reaction zone to combine synthesis separation steps could enhance the system efficiency and intensify the process by recycling energy and materials, besides reducing costs and required energy for the separation process: the continuous harnessing of products shifts reactions toward desired species while recycling energy and materials enhances the process efficiency, and separating water from methanol reduces the required energy and costs of extra processes for methanol separation. The successful implementation of this technology holds significant promise for sustainable developments in producing chemicals and renewable fuel from renewable biogas and reducing methane and carbon dioxide emissions toward achieving carbon‐negative technologies.

On the secondary promotion effect of Al and Ga on Cu/ZnO methanol synthesis catalysts

The structural and electronic effect of Al and Ga as ternary metals in Cu/ZnO catalysts for the methanol synthesis was examined. For this purpose, three zincian malachite-derived catalysts with the nominal Cu:Zn ratio of 70:30 were synthesized: an unpromoted binary catalyst (CZ) and two ternary catalysts with either 3 mol% Al (CZA) or Ga (CZG). Both Al and Ga showed a strong impact on the catalyst’s structure. Alongside the catalyst’s evolution from the co-precipitated precursors phase to the activated and reduced state, an improved microstructure and an increased BET surface area were found for the secondary promotor (Al or Ga) containing catalysts. Moreover, a sequence of chemisorption experiments allowed us to quantify and differentiate between Cusurf and Znred surface species in the activated catalysts. Considering the specific copper surface areas, DRIFTS data and catalytic results, an additional electronic promotion of Al and Ga is proposed. As demonstrated by Ga K-edge XANES, this promotion effect is related to doping of the ZnO support and enhances the reducibility of ZnO to form more Znred sites. This effect is stronger for Al leading to a more pronounced Znred overlayer on the Cu surface due to SMSI. In methanol synthesis, this results in a performance order CZA > CZG > CZ.

A Modified Two-Step Coprecipitation Method Provides Better CuZnO/Al2O3 Methanol Synthesis Catalyst with More Uniform Distribution of Alumina

A Modified Two-Step Coprecipitation Method Provides Better CuZnO/Al2O3 Methanol Synthesis Catalyst with More Uniform Distribution of Alumina

Effect of Mg modification on the catalytic performance of zinc malachite for methanol synthesis

The complex conditions of methanol production from coke-oven gas have brought challenges to the copper-based methanol synthesis catalyst. In this work, a series of zinc-malachite samples with different Mg contents were prepared. The zinc-malachite and calcined samples were characterized by in-situ X-ray diffraction (XRD), thermogravimetry-mass spectrometry (TG-MS), N2 physical adsorption, H2 programmed temperature reduction (H2-TPR), CO2 programmed temperature desorption (CO2-TPD) and other methods. The effects of Mg addition on the structure of zinc-malachite and its catalytic performance of methanol synthesis were investigated. The results showed that the addition of Mg increased the degree of Cu substitution inside the zinc-malachite structure and promoted the formation of high temperature carbonates in the catalyst after roasting. With the increase of Mg content, the specific surface area of the calcined catalyst increased gradually, and the Cu grain size decreased simultaneously. In-situ XRD results showed that a small amount of Mg could effectively inhibit the growth of copper grain size during the heat treatment. The evaluation showed that the initial activity of the catalyst increased first and then decreased with Mg addition, and the activity of the Mg-doped catalyst remained at a relatively high level after heat treatment. The appropriate Mg addition is beneficial to the initial activity and thermal stability of Cu-based methanol synthesis catalyst.

The impact of the porous structure on the efficiency of PdIn methanol synthesis catalysts

The characteristics of the porous structure and the specific surface area of the support have a significant impact on both the structure of the active sites and the efficiency of catalysts for the synthesis of methanol from CO2. The use of a complex of physicochemical methods of analysis in combination with the results of catalytic experiments has enabled the main tendencies in the development of productive and selective catalysts based on PdIn intermetallic nanoparticles to be established.

Bimetallic NiSn supported on mesoporous carbon as an efficient catalyst for selective methanol synthesis from CO2

Global warming and climate change represent the most significant environmental challenges of the 21st century, primarily attributed to the rise in CO2 emission in the atmosphere. Efforts to mitigate this increase involve exploring various methods to reduce CO2 levels, with chemical reactions, such as hydrogenation, being a prominent approach. However, the stable and inert nature of CO2 necessitates the use of catalysts to facilitate its conversion. In this research, NiSn nanoparticles with varying atomic ratios were deposited onto a mesoporous carbon support and subsequently utilized as catalysts for CO2 conversion through hydrogenation reactions at ambient pressure. The diffraction patterns of NiSn/MC reveal peaks indicating the presence of a graphitic carbon structure and the existence of a nickel-tin alloy. SEM-EDX mapping and TEM characterization demonstrate the uniform dispersion of NiSn particles on the mesoporous carbon surface, without the formation of agglomerated particles. Catalytic hydrogenation reactions indicate that the atomic ratio of Ni:Sn significantly influences the catalyst activity and selectivity for methanol formation. Among the NixSny/MC catalysts and monometallic Ni/MC, Sn/MC, and NiSn NPs without support, Ni5Sn1/MC demonstrated the highest CO2 conversion of 39.9 %. Additionally, at a reaction temperature of 175 °C and a CO2:H2 gas ratio of 1:7, Ni5Sn1/MC exhibited a methanol yield of 86.31 mmol/gcat, outperforming other catalysts in the study.

Enhancing the catalytic performance of Cu/ZnO/Al2O3 catalyst in methanol synthesis from biomass‐derived syngas with CeO2, MnO2 and ZrO2 as promoters

AbstractThe performance of Cu/ZnO/Al2O3 (CZA) catalysts promoted by addition of CeO2, MnO2 or ZrO2 in direct methanol production from unconventional syngas was experimentally investigated. The unconventional syngas used in this study contain 25% H2, 25% CO, 20% CH4, 20% CO2 and 10% N2, representing biomass‐derived syngas cultivated from an industrial wood chips pyrolysis plant. The catalysts were synthesised using co‐precipitation technique and tested for methanol synthesis in a fixed‐bed reactor. The activity test of the catalysts showed that the addition of CeO2 or ZrO2 to the CZA catalyst improved the methanol yield, albeit with lower selectivity, whereas adding MnO2 enhanced methanol selectivity but decreased the methanol yield. ZrO2‐promoted catalyst showed the best‐improved activity and stability. The calcined and spent catalysts were characterised using X‐ray diffraction (XRD), N2 physisorption, N2O chemisorption, hydrogen temperature‐programmed reduction (H2‐TPR) and X‐ray photoelectron spectroscopy (XPS). The characterisation results indicate that the catalytic activity is dependent on Cu dispersion, Cu‐active surface area, the catalyst reducibility, Brunauer–Emmett–Teller (BET) surface area and the Cu0/Cu+ ratio. In contrast, catalyst stability was related to the proportion of Cu+ among all surface Cu species.

Dependence of the Fluidizing Condition on Operating Parameters for Sorption-Enhanced Methanol Synthesis Catalyst and Adsorbent

The fluidization of two different solids was investigated by varying the temperature and pressure conditions and the fluidizing gas. The solids are a novel catalyst and a water sorbent that could be used to perform sorption-enhanced methanol synthesis; the operating conditions were selected accordingly to this process. The aim of this investigation was to find an expression for predicting the minimum fluidization conditions of a methanol synthesis catalyst and an adsorbent in the presence of their process stream and operating conditions. The findings of this study highlighted how umf (STP) decreases with a rise in temperature and increases with a rise in pressure, according to other works in the literature with different solids. Furthermore, the type of gas was found to influence the minimum fluidization velocity significantly. The experimental results agreed well with a theoretical expression of the minimum fluidization velocity adjusted for temperature, pressure, and viscosity. The choice of the expression for viscosity calculation in the case of gas mixtures was found to be of key importance. These results will be useful for researchers aiming to calculate the minimum fluidization velocity of a catalyst or other solids under reaction conditions using results obtained at ambient conditions with air or inert gas.

Recent progress in understanding the nature of active sites for methanol synthesis over Cu/ZnO catalysts

Copper-zinc-alumina (Cu/ZnO/Al2O3) has been utilized as the leading catalyst for industrial methanol synthesis via hydrogenation of CO and CO2 for more than 50 years. Understanding the nature of active Zn sites at the atomic level is vital for gaining insight into the reaction mechanism and rational design of more efficient Cu/ZnO catalysts for methanol synthesis but remains greatly challenging and has been intensively debated for decades. In this mini-review, we first describe the fundamental insights obtained from well-defined model catalysts and then summarize the recent experimental evidence with respect to dynamic structural and electronic changes in the active Zn phase under realistic working conditions by in situ/operando microscopy/spectroscopy and surface site titration using probing molecules. In the following, we discuss the catalytic mechanism of diverse active structures by theoretical calculations and simulations. Therefore, the critical role of interfacial sites between metallic Cu and ZnO, especially those with oxygen defects, in methanol synthesis via CO2 hydrogenation is emphasized. Finally, we discuss the technical challenges and perspectives in understanding the origins of this Cu-ZnO synergy and rational design of next-generation Cu-based methanol synthesis catalysts.

The Pd/ZrO2 catalyst inversely loaded with various metal oxides for methanol synthesis from carbon dioxide

The selectivity and stability of catalysts for methanol synthesis from CO2 still remain to be enhanced. In this work, we synthesized a series of Pd/ZrO2 catalysts inversely loaded with various metal oxide promoters (ZnO, In2O3, and CeO2), those would partially cover Pd metal surface and form some new metal-promoter interface, to explore the nature in the performance of CO2 hydrogenation to methanol. The catalyst synthesized by this approach could limit the growth of Pd particles during the reduction and form new metal–metal oxide interfaces with different functions of CO2 hydrogenation, improving the reaction performance of Pd-ZrO2 catalysts. As a result, the ZnO-Pd/ZrO2 catalyst exhibited the highest CO2 conversion (12.0 %), methanol selectivity (95.6 %), and STY of methanol (472 gMeOHkgcat-1h−1), with excellent stability. The results of HRTEM, H2-TPR, XPS, and XAFS showed that the ZnO-Pd/ZrO2 catalyst had the typical Pd-ZnO interface with Pd2+ species after the H2 reduction, which could enhance the adsorption and activation of CO2. In addition, the in situ DRIFTS and NAP-XPS results implied that the Pd-ZnO interface significantly improved the formation of formate (HCOO*) and methoxy (H3CO*) species, which were considered to be the key intermediates of methanol generation, and thus greatly enhanced the selectivity of methanol.

Oxygen vacancy engineering in MOF-derived AuCu/ZnO bimetallic catalysts for methanol synthesis via CO2 hydrogenation

Three AuCu/ZnO bimetallic catalysts, AuCu/ZnO-BTC, AuCu/ZnO-BDC and AuCu/ZnO-MOF-74, were derived from various MOF precursors using facile hydrothermal methods. Among the resultant catalysts, the AuCu/ZnO-BTC catalyst possessed the best methanol synthesis activity, whose space time yield of methanol (STYMeOH) reached 359.0 gMeOH kgcat−1 h−1 at 250 °C under 3 MPa. Structural characterization reveals that in comparison with the AuCu/ZnO-BDC and AuCu/ZnO-MOF-74 catalysts, the AuCu/ZnO-BTC catalyst possessed higher specific surface area (SBET), tinier metal particle size, more oxygen vacancies, stronger metal-support interactions and larger amount of medium basic sites. In situ DRIFTS result demonstrates that formate (*HCOO) species were readily generated and bridged-methoxy (*b-OCH3) species were selectively formed on the AuCu/ZnO-BTC catalyst, which may be related with its abundant oxygen vacancies and responsible for its superior methanol synthesis activity. The present work derives high-performance AuCu/ZnO bimetallic catalysts from MOF precursors and provides new insight into structure-activity relationships for CO2 hydrogenation to methanol.

Theoretical investigation on the CO2 hydrogenation to methanol mechanism at electron-rich active interface over Cu/Ga-Ti-Al-O catalyst

Density functional theory investigations on CO2 hydrogenation to methanol mechanisms over Cu13 cluster loaded catalyst were performed. The results indicate that introducing TiO2 into Al2O3 promoted the residual electrons from Al2O3 surface directionally transmitted to the interface formed by the loaded Cu13 cluster and the support surface, thus created the electron-rich active interface. Incorporating single atom Ga promoter further gathered the residual electrons and stabilized the loaded Cu13 clusters. The electron-rich property of the active interface promoted the chemical adsorption and activation of both CO2 and the generated carbonyl species. Further favors the hydrogenating of carbonyl intermediates to methanol and effectively enhances the methanol selectivity. Moreover, CO2 priors to hydrogenated to methanol via reverse water gas shift pathway over Cu13/Ga-AT computational model with changed reaction rate controlling step with reduced activation energy. This work offers a simple approach for efficient copper-based methanol synthesis catalysts through control of interface electron structure.

Thorium-promoted Cu/Zn/Al syngas catalyst for methanol synthesis with enhanced activity and stability

The traditional Cu/Zn/Al catalyst for methanol synthesis from syngas usually exhibits structural instability and carbon deposition. In this work, a trace of thorium (1–20 wt‰) was incorporated to a typical Cu/Zn/Al catalyst for structural modification. It was found that the Th-promoted (5 wt‰) Cu-based catalyst showed an obviously enhanced activity and stability for methanol production from syngas. Under identical testing circumstances, the activity after heat resistance of CatTh5 was 27.3% higher than the original catalyst (Cat0) and 23.8% higher than the commercial catalyst (Cat327). The 250-hour stability test revealed that the ideal CatTh5 catalyst presented good activity and stability in comparison to the original Cat0 catalyst. To the best of our knowledge, this result can significantly outperform Cu/Zn/Al benchmarks and rival the state-of-the-art systems. XRD, N2 physisorption, N2O titration, solid-state NMR, H2-TPR, semi-in-situ XPS and semi-in-situ XAES were used to comprehensively investigate the improved catalytic properties. Th was shown as a textural promoter and it can boost both metal dispersion and reduction property of reactive Cu species. Therefore, the created larger Cu surface area, smaller CuO particles and higher proportion of Cu+/Cu0 sites were demonstrated to be responsible for the superior catalytic performances.

A Ce-CuZn catalyst with abundant Cu/Zn-OV-Ce active sites for CO2 hydrogenation to methanol

CO2 hydrogenation to chemicals and fuels is a significant approach for achieving carbon neutrality. It is essential to rationally design the chemical structure and catalytic active sites towards the development of efficient catalysts. Here we show a Ce-CuZn catalyst with enriched Cu/Zn-OV-Ce active sites fabricated through the atomic-level substitution of Cu and Zn into Ce-MOF precursor. The Ce-CuZn catalyst exhibits a high methanol selectivity of 71.1% and a space-time yield of methanol up to 400.3 g·kgcat−1·h−1 with excellent stability for 170 h at 260 °C, comparable to that of the state-of-the-art CuZnAl catalysts. Controlled experiments and DFT calculations confirm that the incorporation of Cu and Zn into CeO2 with abundant oxygen vacancies can facilitate H2 dissociation energetically and thus improve CO2 hydrogenation over the Ce-CuZn catalyst via formate intermediates. This work offers an atomic-level design strategy for constructing efficient multi-metal catalysts for methanol synthesis through precise control of active sites.

Performance of Cu-Mn-Zn/ZrO2 catalysts for methanol synthesis from CO2 hydrogenation: The effect of Zn content

A series of Cu-Mn-Zn/ZrO2 catalysts with different Zn contents were prepared by sol-gel method and characterized by XRD, BET, TPR, N2O-adsorption, XPS, TPD and in-situ DRIFTS. It was found that by increasing a certain amount of Zn, the catalytic activity for CO2 hydrogenation increased. Among all samples, Cu3MnZn0.5Zr0.5 (CMZZ-0.5) possessed the best CO2 conversion (6.5%) and methanol selectivity (73.7%) at 250 °C and 5 MPa. Characterization results showed that Zn entered the Cu1.5Mn1.5O4 spinel structure, forming ZnOx and thus more surface OH groups. This increased the content of Cu0 and Cuα, which improved the activation of H2 and CO2. The pathway of CO2 to methanol was also clarified through in-situ DRIFTS.

M2X & SCGC enter into agreement for methanol synthesis catalysts R&D

M2X & SCGC enter into agreement for methanol synthesis catalysts R&D

Biomass-derived activated carbon catalysts for the direct dimethyl ether synthesis from syngas

The direct DME synthesis from syngas was studied by using activated carbon-based bifunctional catalytic beds. Two kinds of activated carbons, prepared by physical (by CO2 partial gasification) and chemical (with phosphoric acid) activation of olive stones, were used as supports for the preparation of the catalysts. The chemically activated carbon presented a considerable amount of thermally and chemically stable surface phosphorus complexes, which played an important role on the catalytic performance of the prepared catalysts. A Zr-loaded P-containing activated carbon presented a relatively high activity, selectivity and stability for the production of DME from methanol and was used as methanol dehydration catalyst. On the other hand, Cu-Zn was loaded on both P-containing and P-free activated carbon supports for the preparation of methanol synthesis catalysts. The presence of surface-phosphorus on the carbon support resulted in a strong metal-support interaction, hindering the catalytic activity for the hydrogenation of CO to methanol. However, the catalyst that did not contain phosphorus showed noticeable activity for this reaction. The physical mixing of the methanol synthesis and methanol dehydration catalysts resulted in the preparation of carbon-based bifunctional catalytic beds, which performed very efficiently in the direct DME synthesis from syngas in a fixed-bed reactor. Different mass ratios of the individual (metallic and acid) catalysts were studied. An acid/metallic catalyst mass ratio of 2 provided the catalytic bed with enough acid sites to promote methanol dehydration to its maximum extent and make the overall product distribution controlled by the methanol synthesis reaction on the metallic phase.

Surface ZnOx on zirconia is highly active for high temperature methanol synthesis

Zinc containing mixed metal oxides and supported zinc oxide are stable and selective methanol synthesis catalysts at temperatures where a subsequent methanol to hydrocarbons reaction can occur directly. This work provides fundamental insights into ZnO-based high temperature methanol synthesis catalysts. A pronounced support effect was observed, where ZrO2 provided a beneficial effect while SiO2 exerted a detrimental effect compared to bulk ZnO. Preparing co-precipitated ZnO-ZrO2 catalysts showed that the initial activity correlated with the amount of amorphous ZnO on the surface of the support and that the catalytic activity increased with time on stream as zinc oxide migrated out of a solid solution with ZrO2 and onto the support surface. Hence the active phase appeared to be ZnO surface species and not zinc oxide in a solid solution with ZrO2. Operando XAS coupled with modulation excitation spectroscopy unravelled that the surface ZnO was partly reduced under operating conditions, as surface ZnOx, with x approximately equal to 0.98. In-situ DRIFTS further uncovered that the surface ZnOx activated CO2 and formed methanol via carbonate, formate and methoxide species. XPS finally showed that ZrO2 withdrew electrons from ZnO, facilitating oxygen abstraction to form the partly reduced ZnOx, which in turn facilitated the activation of CO2.

Development of Silicalite-1 encapsulated Cu-ZnO catalysts for methanol synthesis by CO2 hydrogenation

Converting CO2 into fuels and valuable chemicals such as methanol has been gaining significant attention as a favorable solution for reducing greenhouse gas emissions. Although Cu-ZnO-based catalysts are promising candidates for this reaction since methanol is selectively produced at the Cu-ZnO interface, Cu are not stable at elevated temperatures (500–600 K), leading to decrease in the surface areas of Cu and Cu-ZnO interface due to thermal aggregation of Cu. Furthermore, the generation of H2O as a by-product in the CO2 hydrogenation does not only accelerate the aggregation of Cu, but also inhibits an intermediate (formate species) formation for methanol. This paper reports the development of a novel catalyst, annotated as CuPS@S-1 by immobilizing Cu phyllosilicate (CuPS) as the Cu source within hydrophobic zeolite of Silicalite-1 particles (S-1). Cu@S-1 was obtained after the reduction CuPS@S-1 and the size of the Cu particles was approximately 2.4 nm. Cu@S-1 exhibited a higher CO2 hydrogenation activity and methanol selectivity than Cu/S-1 prepared by an impregnation method. To further improve the methanol production activity, ZnO was loaded onto Cu@S-1 to form a Cu-ZnO interface. ZnO/Cu@S-1 was obtained by the impregnation of CuPS@S-1 powder with an ethanol solution containing zinc acetate, followed by calcination and reduction. The obtained catalyst exhibited a better methanol production yield where the space–time yield for methanol based on the Cu weight exceeded 1200 mgmethanol gCu−1h−1.

Microrod networks CuO–ZnO–Al2O3 catalyst for methanol synthesis from CO2: Synthesis, characterization, and performance demonstration

Microrod-shaped CuO–ZnO–Al2O3 (CZA) catalysts are synthesized in a single-step hydrothermal method. Several characterization techniques, such as XRD, SEM, BET, XPS, H2-TPR, HR-TEM, and CO2-TPD, are used to investigate the physico-chemical properties of the prepared catalysts. A bench-scale high-pressure fixed-bed flow reactor is used to evaluate the performance of the synthesized catalysts. XRD analysis confirmed the presence of monoclinic CuO and hexagonal ZnO phases in the CZA catalysts. A uniform distribution of interconnected microrod-like morphology is observed in the CZA-4 catalyst. The metal dispersion, metal-support interactions, and surface basicity of CZA-4 are significantly improved during the hydrothermal synthesis under the continuous stirring and addition of CTAB, which positively impacts the CO2 conversion (14%) and methanol yield (7%). The CO2 conversion and methanol yield increases in the following order CZA-3 < CZA-1 < CZA-2 < CZA-4. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis confirmed the formate-methoxy pathway for methanol formation.