Methanol Synthesis Catalyst Research Articles

Promoting CO2 hydrogenation to methanol by incorporating adsorbents into catalysts: Effects of hydrotalcite

CO2 hydrogenation, in which CO2 conversion to methanol plays a key role, is of increasing importance in mitigating the climate crisis. However, high reaction pressures are required to conduct methanol synthesis because of poor catalytic performance of conventional catalysts, leading to high energy consumption. In this study, a novel strategy was applied to promote methanol synthesis by adsorption-enhanced CO2 hydrogenation. Catalysts made from Cu-ZnO-Al2O3 mixed with different hydrotalcite contents (named CZA-HT) were prepared by physically mixing a commercial copper-based catalyst for methanol synthesis with hydrotalcite for high temperature CO2 adsorption. In these catalysts, only the commercial copper-based component contains the active part for CO2 hydrogenation and its copper surface area is 48.1 m2 g−1 with an optimal reaction temperature of 523 K. Hydrotalcite exhibits no catalytic activity, yet the catalytic performance of the CZA-HT catalysts were clearly facilitated by CO2 adsorption on HT. The sample containing 40 wt% hydrotalcite and 60 wt% CZA showed the highest methanol selectivity of 73.4% and a methanol yield of 4.4% among all samples. The reaction was conducted at a low reaction pressure of 30 bar (much lower than conventional pressure), so that the methanol yield was not high. However, it is observed that the methanol formation rate based on a unit mass of active CZA always increases as the hydrotalcite content in CZA-HT increases, confirming the promotion effects of CO2 adsorption on HT on catalytic performance. The mechanism of adsorption enhanced catalytic reaction was also analysed and discussed, in which the well mixed finer particles of CZA and HT perform better than CZA alone with a 73.9% higher methanol yield.

Influence of CO on the Activation, O-Vacancy Formation, and Performance of Au/ZnO Catalysts in CO2 Hydrogenation to Methanol.

The impact of CO on the activation and reaction characteristics of Au/ZnO catalysts in methanol synthesis from a CO2/H2 mixture was studied by kinetic, near ambient pressure X-ray photoelectron spectroscopy and X-ray absorption spectroscopy at the O K-edge, together with in situ Foureir transform infrared measurements. Transient measurements under up to industrial reaction conditions (50 bar, 240 °C) show a pronounced transient increase of the activity for methanol formation from CO2/H2 after exposure to a CO/H2 reaction gas mixture, while the steady-state activity is similar to that observed directly after oxidative pretreatment. For the reaction in CO/H2, the much longer activation phase is accompanied by formation of CO2 due to reaction of CO with the ZnO catalyst support. This leads to O-vacancy formation on the support at an extent significantly higher than in CO2/H2. The consequences of these findings on the mechanistic understanding of methanol formation from CO2/H2 on Au/ZnO and for ZnO-supported catalysts in general are discussed.

Zn and Si transport in dual-functioning catalyst for conversion of synthesis gas to dimethyl ether

Dimethyl ether (DME) is traditionally produced from synthesis gas, i.e., CO, CO2, and H2, with methanol as an intermediate before the final dehydration to DME. However, DME may also be produced in a one-stage synthesis from synthesis gas using a combi-catalyst with both methanol synthesis and methanol dehydration functionalities in a single catalyst. In this work, two combi-catalysts consisting of co-tableted methanol synthesis catalyst (Cu/ZnO/Al2O3) and methanol dehydration catalyst domains (silica-alumina) were tested in synthesis gas as 6 mm in diameter pellets in a single-pellet configuration for 700–850 h at 235–310 °C and 60 bar. The catalyst domain sizes were 50–100 μm in a fine particle catalyst A and 600–1000 μm in a coarse particle catalyst B. Surprisingly, the finer particle combi-catalyst A(fine) showed a markedly faster deactivation of the dehydration activity and slightly faster deactivation of the methanol activity than the coarser combi-catalyst B(coarse). Electron microprobe analysis of the spent catalyst B(coarse) showed that Zn had migrated from the methanol active material and 10 μm into the DME active particles. Similarly, silicon from the silica-alumina methanol dehydration catalyst particles had diffused several hundred µm into the methanol catalyst particles. Based on these experimental results, it is concluded that the methanol dehydration catalyst domains in combi-catalyst A(fine) were poisoned faster than those in combi-catalyst B(coarse) due to the larger contact area between the two catalyst materials, easing the transport of Zn and leading to a faster deactivation. Similarly, silicon migration from the silica-alumina catalyst to the methanol synthesis catalyst might decrease the formation rate of methanol in catalyst A(fine) more than in catalyst B(coarse).

Experimental Investigation of the Application of Ionic Liquids to Methanol Synthesis in Membrane Reactors

In this study, a high-pressure membrane reactor (MR) was employed to carry out the methanol synthesis (MeS) reaction. Syngas was fed into the MR shell side where a commercial MeS catalyst was used, while the tube side was swept with a high boiling point liquid with good solubility toward methanol. A mesoporous alumina ceramic membrane was utilized after its surface had been modified to be rendered more hydrophobic. The efficiency of the MR was investigated under a variety of experimental conditions (different pressures, temperatures, sweep liquid flow rates, and types of sweep liquids). The results reveal improved per single-pass carbon conversions when compared to the conventional packed-bed reactor. An ionic liquid (IL), 1-ethyl-3-methylimidazolium tetrafluoroborate, was utilized in the MR as the sweep liquid. The experimental results are compared to those previously reported by our group (Li, Z.; Tsotsis, T. T. J. Membrane Sci. 2019, 570, 103) while using a conventional petroleum-derived solvent as swe...

Preparation of Catalyst Cu-ZnO-MgO-Al2O3 for Direct Synthesis of DME

Direct synthesis of DME catalyst was prepared using the co-precipitation method. The catalyst contained CuO/ZnO/Al2O3 about 40/27/33 (%-wt). Two types of catalyst were prepared, i.e. CZMA0 (Mg 0%-wt) and CZMA20 (Mg 20%-wt). Both of catalysts were activated using reducing gas (5% H2 and N2). The activity test was conducted by syngas model which contained (%-mole) 65% H2, 28% CO and 7% N2. The reaction was carried out in a fixed bed reactor at 5 bar, and temperature of 240, 250 and 260°C. Synthesis shown CZMA20 catalyst gave the highest catalytic activity with 73% of CO conversion and 66% of H2 conversion (5 bar and 260°C). Direct synthesis of DME was also carried out using a dual-catalyst, i.e. catalyst for methanol synthesis (M151, the commercial catalyst of methanol synthesis) and methanol dehydration (γ-Al2O3-ITB). The activity of dual catalyst shown 93% of CO conversion and 91% of H2 conversion. This activity was more stable than two other catalysts (CZMA0 and CZMA20).

Tuning adsorption properties of GaxIn2−xO3 catalysts for enhancement of methanol synthesis activity from CO2 hydrogenation at high reaction temperature

Abstract Light olefins can be produced from CO2 hydrogenation in a single reactor using a combination of a methanol synthesis catalyst and a methanol-to-olefin (MTO) catalyst. However, commercial methanol synthesis catalysts are active at low temperatures (200–260 °C), while MTO reaction is feasible at higher temperatures (>300 °C). Herein, we report the CO2 hydrogenation to methanol at high temperatures (320–400 °C) over GaxIn2−xO3 catalysts. By tuning the Ga/In ratios, phase, crystallinity, pore structure, morphology, electronic properties as well as adsorptive properties of GaxIn2−xO3 catalysts can be modified. At the lowest temperature (320 °C), the pure In2O3 shows the highest methanol yield. However, the maximum methanol yield declines significantly with increasing reaction temperatures. Incorporation of Ga into the In2O3 crystal lattices at x = 0.4 (Ga0.4In1.6O3) maximizes the methanol yield at higher reaction temperatures of 340–360 °C. This enhancement can be attributed to an increased binding energy of adsorptive molecules with the catalyst surface to promote the hydrogenation of CO2 to methanol. Further increasing Ga content (x > 0.4) leads to greatly strengthen the binding for adsorptive molecules, resulting in a lower methanol yield and the formation of methane. The surface chemisorbed oxygen is found to be a key factor determining the CO yield.

Evolution of intermetallic GaPd2/SiO2 catalyst and optimization for methanol synthesis at ambient pressure

ABSTRACT The CO2 hydrogenation to methanol is efficiently catalyzed at ambient pressure by nanodispersed intermetallic GaPd2/SiO2 catalysts prepared by incipient wetness impregnation. Here we optimize the catalyst in terms of metal content and reduction temperature in relation to its catalytic activity. We find that the intrinsic activity is higher for the GaPd2/SiO2 catalyst with a metal loading of 13 wt.% compared to catalysts with 23 wt.% and 7 wt.%, indicating that there is an optimum particle size for the reaction of around 8 nm. The highest catalytic activity is measured on catalysts reduced at 550°C. To unravel the formation of the active phase, we studied calcined GaPd2/SiO2 catalysts with 23 wt.% and 13 wt.% using a combination of in situ techniques: X-ray diffraction (XRD), X-ray absorption near edge fine structure (XANES) and extended X-ray absorption fine structure (EXAFS). We find that the catalyst with higher metal content reduces to metallic Pd in a mixture of H2/Ar at room temperature, while the catalyst with lower metal content retains a mixture of PdO and Pd up to 140°C. Both catalysts form the GaPd2 phase above 300°C, albeit the fraction of crystalline intermediate Pd nanoparticles of the catalyst with higher metal loading reduces at higher temperature. In the final state, the catalyst with higher metal loading contains a fraction of unalloyed metallic Pd, while the catalyst with lower metal loading is phase pure. We discuss the alloying mechanism leading to the catalyst active phase formation selecting three temperatures: 25°C, 320°C and 550°C.

Enhanced CO2 hydrogenation to methanol over TiO2 nanotubes-supported CuO-ZnO-CeO2 catalyst

TiO2 nanotubes (TNTs) have been extensively applied in many fields owing to their excellent porous structure and surface properties. Herein, a series of CuO-ZnO-CeO2/TNTs catalysts are synthesized through a deposition-precipitation method. The effects of TNTs content and support morphology on the catalyst physicochemical properties and catalytic performance are investigated. The incorporation of TNTs support into CuO-ZnO-CeO2 catalysts not only promotes CuO reducibility and improves the metallic Cu dispersion and specific surface area, but also enhances CO2 adsorption and increases the proportion of basic sites γ, thereby resulting in high CO2 conversion and CH3OH selectivity. It is also shown that CO2 conversion is positively correlated with the Cu specific surface area and that CH3OH selectivity is related to the proportion of basic sites γ. Due to the excellent reducibility, high metallic Cu surface area, superior CO2 adsorption and large proportion of basic sites γ, CuO-ZnO-CeO2/10 wt.% TNTs gives excellent catalytic performance and possesses a great potential as catalyst for methanol synthesis.

Role of Surface Species Interactions in Identifying the Reaction Mechanism of Methanol Synthesis from CO2Hydrogenation over Intermetallic PdIn(310) Steps

Considerable attention has been paid to the development of new catalysts for methanol synthesis from CO2 hydrogenation for a long period of time. The PdIn intermetallic catalyst was found recently ...

Density functional theory analysis of selective adsorption of AsH3 on transition metal-doped graphene.

The removal of AsH3 from synthesis gas is crucial to prevent methanol synthesis catalyst from poisoning. In this work, Ti-, Mn-, Fe-, Co-, Ni-, Cu-, and Ag-doped graphene were proposed and their adsorption capabilities for AsH3 and CO were investigated by DFT method. The optimized structures, adsorption energies, electron transfers, electron density difference, and density of states were thoroughly discussed. It was found that pristine graphene had a slight interaction with AsH3 or CO, while doping Ti, Mn, Fe, Co, Ni, and Ag could greatly facilitate the AsH3 or CO adsorption with the adsorption energies of -0.95 to -1.45eV (AsH3) and - 1.00 to 2.02eV (CO). The partial density of states (PDOS) results showed that hybridizations between AsH3 orbitals, CO orbitals, and transition metals orbitals indicate that there were chemical interactions between them. The charge transfer and density of states (DOS) plots showed that AsH3 and CO have the same adsorption modes on transition metals-doped graphene. Among seven transition metals-doped graphene, Ni-doped graphene had the best selectivity for AsH3 but not for CO due to its larger adsorption energy discrepancy between AsH3 and CO than that of other transition metals-doped graphene, suggesting that Ni-doped graphene is a good candidate adsorbent for AsH3 removal in CO gas stream. Graphical abstract Seven transition metal (Ti, Mn, Fe, Co, Ni, Cu, Ag)-doped graphenes were investigated for AsH3 and CO adsorption by DFT method. Their most stable structure, adsorption energy, and electronic characters were thoroughly studied. The results showed that Ni-doped graphene was a good candidate for selective AsH3 adsorption.

The epitaxial growth of ZnO films on Cu(111) surface: Thickness dependence

ZnO ultrathin films supported on Cu, Ag or Au are attracting increasing interest because they can form under special conditions on commercial Cu/ZnO/Al2O3 catalysts for methanol synthesis, or can be used as alternative materials for catalysis, or as prototypes of the so-called inverse catalysts. In the present study, we have investigated the thickness dependence of the structure and electronic properties of free standing and Cu(111) supported ZnO ultrathin films by means of DFT + U calculations. On the free-standing films, a flat graphitic-like morphology is observed up to 10 layers, where a transition to wurtzite-like structures occurs. On Cu(111), a slightly corrugated graphitic structure is obtained for ZnO films up to 4 layers. From 5 layers on, the rumpling becomes substantial and a phase transition to wurtzite takes place. The driving force behind the destabilization of flat graphitic films on Cu(111) is the charge transfer from the underlying Cu support to the film. This finding rationalizes the experimental observations that the transformation from graphitic to wurtzite polymorph of ZnO films on Cu takes place above 5-layer thickness.

The effect of metal additives in Cu/Zn/Al2O3 as a catalyst for low-pressure methanol synthesis in an oil-cooled annulus reactor

• Annulus reactor minimising the influence of heat produced on the catalytic activity. • Zr addition to the commercial Cu/ZnO/Al 2 O 3 catalyst enhanced the methanol yield. • CO 2 conversion reduced for Zr modified Cu/ZnO/Al 2 O 3 catalyst. • The addition of Ga and Mg reduced the performance of the Cu catalyst. • Reducibility and copper crystallite size strongly influenced catalyst activity. The effect of metal additives, including Zr, Mg, and Ga, on the conventional Cu/ZnO/Al 2 O 3 (CZA) catalyst, was investigated for methanol synthesis using an oil-cooled annulus reactor. The annulus reactor was found to reduce the temperature gradient within the diluted catalyst bed by effective cooling and thus provide experimental data at steady-state and in kinetic regime allowing for the comparison of intrinsic activity between different catalysts. The addition of Zr enhanced the overall performance of methanol synthesis. However, the CZA-Zr catalyst displayed significantly reduced CO 2 conversion, possibly due to intensified water-gas shift reaction activity. The addition of Ga and Mg to CZA was found to be detrimental to the catalytic performance and is attributed to difficulties in reducibility and the increased crystalline size of copper particles. A relatively long induction period was observed for CZA-Zr sample in this study, which is attributed to the effective cooling imparted by the annulus reactor suppressing the r-WGS reaction.

Simple strategy synthesizing stable CuZnO/SiO2 methanol synthesis catalyst

The metal particle size distribution of a catalyst can affect the rate of deactivation in many chemical reaction. This work developed a facile method to prepare a well dispersed CuZnO/SiO2 catalyst via rotary evaporation assisted deposition-precipitation method (RE-CZS). By comparison, conventional deposition-precipitation method and ultrasound assisted deposition-precipitation method were applied to synthesize other catalysts (Im-CZS and Ul-CZS), in order to clarify the influence of Cu particle size distribution of the catalyst on catalytic stability of methanol synthesis via CO2 hydrogenation. RE-CZS catalyst possessed the narrowest Cu particle distribution (ca. 4.9–9.1 nm) and thus exhibited the best catalytic stability because of the least Cu particle growth. Im-CZS catalyst showed the broadest Cu particle distribution (ca. 5.3–28.7 nm) and suffered from the most serious particle growth resulting in the least catalytic stability. The Cu particle distribution and the related catalytic stability of the Ul-CZS catalyst lied between RE-CZS catalyst and Im-CZS catalyst. The origin of the tremendous effect of the Cu particle size distribution on the catalytic stability was studied via XRD, N2 adsorption/desorption, N2O chemisorption, ICP-AES, XPS, TEM and temperature-programmed techniques, which suggested that catalyst deactivation was mainly attributed to the growth of Cu particles originating from Ostwald ripening effect.

In situ investigations on the amorphous to crystalline phase transformation of precursors for methanol synthesis catalysts

Two in situ methods are presented to study phase transformations in the synthesis of Cu/Zn hydroxycarbonates as catalyst precursors for industrial methanol production. In contrast to the well-established application of in situ FTIR probes in the detection of liquid phase concentrations, we evaluated spectra arising from the structural changes in the solid phase during the transformation of amorphous georgeite to nanocrystalline zincian malachite. Further, a novel microreaction system is employed to gain statistical insight on the scattering of the reaction time as a function of various process parameters. The obtained transformation kinetics during aging are described by a model based on the theory of solvent-mediated phase transformations showing excellent agreement with experimental results. The quantitative impact of temperature, concentration and zinc content on dissolution, nucleation and growth of the respective phases is discussed.

Revealing the Synergy between Oxide and Alloy Phases on the Performance of Bimetallic In–Pd Catalysts for CO2 Hydrogenation to Methanol

In2O3 has recently emerged as a promising catalyst for methanol synthesis from CO2. In this work, we present the promotional effect of Pd on this catalyst and investigate structure–performance rela...

Industrial and scientific directions of methanol catalyst development

This article provides a brief overview of methanol synthesis with emphasis on commercial catalysts and some of the relevant literature on this subject. Firstly, industrial production of this very applicable molecule, as well as a summary of manufacturing trends and challenges are presented. Secondly, requirements for methanol synthesis catalysts and recent advances in catalyst synthesis and compositions are examined and finally, reaction mechanism and the Cu-ZnO synergy in industrial methanol synthesis catalysts are discussed together with literature tendencies and possible future developments in this classic, but lively research area.

Stability of mesocellular foam supported copper catalysts for methanol synthesis

Mesocellular foam is a well-defined mesoporous silica comprising large cages (˜20 nm), connected by small windows (2–10 nm). Here, we used mesocellular foam as a support material in the preparation of Cu based model catalyst for methanol synthesis at high temperature and pressure. To this end, we synthesized two types of mesocellular foam, with the same cage size, but a different window size of 8 and 2.3 nm, and compared them to the use of a silica gel support. Cu particles were deposited by impregnation with a copper nitrate precursor solution and decomposition in either N2 or H2-containing gas stream. We followed the phase evolution in situ, and identified a method using direct reduction in H2 to deposit 3 nm Cu particles on all different supports. The catalysts prepared on the mesocellular foam displayed a much higher stability than the silica gel supported catalysts. The impact of the window size of the MCF was small, but significant: the catalysts supported on the small window mesocellular foam were more stable on the long term. However, they also had a lower activity due to embedment of the Cu particles in the windows, as revealed with electron tomography. A higher metal loading on the small window mesocellular foam resulted in enhanced coalescence of the Cu particles, which was attributed to smaller interparticle distances. Increasing the loading on this support even further increased the size and polydispersity of the Cu nanoparticles, leading to a higher deactivation rate due to Ostwald ripening. Hence, the loading and size polydispersity are important parameters in determining the catalyst stability. We also found that the nature of the SiO2 support has more impact on the catalyst stability than the restricting pore sizes, probably due to the fact that Ostwald ripening dominates particle growth on the longer time scales.

Methanol synthesis from CO2 hydrogenation over CuO-ZnO-ZrO2-MxOy catalysts (M=Cr, Mo and W)

Three CuO-ZnO-ZrO2-MxOy (CZZM, M = Cr, Mo and W) mixed oxides were prepared by a co-precipitation method and tested as catalysts for methanol synthesis from CO2 hydrogenation. The catalysts were characterized by XRD, N2 adsorption/desorption, XPS, reactive N2O adsorption, H2-TPR, and CO2-TPD techniques. The results indicated that the methanol selectivity and yield of the CuO-ZnO-ZrO2 catalyst noticeably increased by the additions of MoO3 and WO3, but slightly decreased by Cr2O3 doping. Combining with the characterization results, the difference in methanol yield over the three catalysts can be attributed to the differences in their BET specific surface areas (SBET) and adsorption capacities for CO2, while the methanol selectivity is closely correlated to the ratio of surface contents of Zn to Cu, as well as the fraction of strong basic sites in the total basic sites of the investigated catalysts.

Synthesis of dimethyl ether using a fixed bed of dual catalyst for methanol synthesis and its dehydration

Experimental study on direct synthesis of DME (dimethyl ether) has been conducted using tubular reactor. The synthesis of DME was performed with two commercial catalysts, ie methanol synthesis catalyst (M151, Cu-based) and methanol dehydration catalyst (γAl2O3). A mixture of H2, CO, and N2 was used as a model for synthesis gas. Gas flow rate was set at 20 mL/min (5 bar and 240oC). The reaction held at: pressure of 5 bar and a temperature of 240°C. This experiment was conducted by arranging a series of two types of catalysts in a fixed bed reactor. The methanol synthesis catalyst was placed in the upstream to ensure the reaction of methanol formation, then proceed with dehydration of methanol to DME. The objective of this experiment was to find out the best dual catalyst composition to produce a high concentration of DME. The experiment has shown that the best combination of methanol catalyst to dehydration catalyst was a mixture of 20% methanol catalyst (ratio 1/4). CO conversion was 62% and the product ratio of DME/methanol was 40%.

CO hydrogenation on M1/W6S8 (M = Co and Ni) single-atom catalysts: Competition between C2 hydrocarbons and methanol synthesis pathways

Comprehensive density functional theory (DFT) calculation of methanol synthesis and C2 hydrocarbons formation in Fischer-Tropsch synthesis (FTS) on M1/W6S8 (M = Co and Ni) Single-Atom Catalysts have been carried out. The activation barriers and reaction energies for CO dissociation, CHx hydrogenation, CHx + CHy coupling and C(HO) insertion into CHx, and CHxCHy-O bond scission involved in C2 hydrocarbons formation have been examined. Methanol production (CO* + 4H* → CHO* + 3H* → CH2O* + 3H* → CH3O*+ H* → CH3OH*) is highly favored by Ni1/W6S8 catalysts. In contrast, Co1/W6S8 catalysts strongly favor C2 hydrocarbons production. The rate constant of the step for the subsequent transformation of CH3O* species on the Co1/W6S8 and Ni1/W6S8 was determined with the harmonic transition state theory (TST). The results of rate constant are in line with our kinetic results. Simultaneously, we use the d-band center to prove the correctness of the previous steps, the d-band center value of Co1/W6S8 is closer to EF than that of Ni1/W6S8; the result indicates that the catalytic activity of Co1/W6S8 is the best. The present study provides the basis to understand and develop novel M1/W6S8 (M = Co and Ni) single-atom catalysts for C2 hydrocarbons and methanol synthesis.