Methanol Synthesis Catalyst Research Articles

Understanding the Enhanced Lifetime of SAPO-34 in a Direct Syngas-to-Hydrocarbons Process

In a hybrid catalyst process, syngas is converted, via a methanol intermediate, into a mixture of short-chain hydrocarbons over a combined methanol synthesis catalyst and molecular sieve. It operates under process conditions where the hydrogen partial pressure is relatively high vs the (intermediate) methanol partial pressure. We show that, under these conditions, the lifetime of the molecular sieve (SAPO-34) is greatly enhanced and the amount and type of carbon on the spent catalyst are vastly different as compared to those in a methanol to olefins (MTO) process. The impact of the hydrogen partial pressure, temperature, and methanol partial pressure is studied, leading to a conceptual model of coke deposition and removal. This allows the identification of process conditions that lead to a stable and long lifetime of SAPO-34 in a direct syngas-to-hydrocarbons process.

Dynamic changes of Au/ZnO catalysts during methanol synthesis: A model study by temporal analysis of products (TAP) and Zn LIII near Edge X-Ray absorption spectroscopy

Small gold nanoparticles supported on ZnO have been identified as highly active and selective catalysts for the green synthesis of methanol from CO2 and H2. Furthermore, they can serve also a model system for the mechanistic understanding of methanol synthesis on the industrial Cu/ZnO catalyst. The dynamic changes in the structure of Au/ZnO upon exposure to methanol synthesis gas mixtures were studied using a combination of TAP reactor and near edge X-ray absorption spectroscopy (XANES) measurements at the Zn LIII edge, both in CO2/H2 and CO/H2 gas mixtures. TAP measurements indicated that CO can create significant amounts of O-vacancy defects in ZnO at 240°C, while CO2 can re-oxidize a pre-reduced catalyst or maintain this state in the presence of strongly reducing gases (CO and H2). Furthermore, CO2 present as reactant or resulting from the reactive removal of surface lattice oxygen by interaction with CO can be deposited on the pre-reduced Au/ZnO surface as stable adsorbed carbon containing species, e.g., as surface carbonates, which decompose at T≥250°C. In situ XANES measurements at the Zn LIII edge revealed that ZnO is significantly reduced during reaction, both in CO2/H2 and CO/H2 gas mixtures, but with the extent of the reduction being more pronounced in CO/H2 than in CO2/H2. These results will be critically discussed in the light of previous findings on the role of ZnO reduction in the activity of methanol synthesis catalysts.

Highly active and selective Cu-ZnO based catalyst for methanol and dimethyl ether synthesis via CO2 hydrogenation

Highly active and selective Cu-ZnO based catalysts with high BET surface areas and Cu surface areas were prepared using the co-precipitation method. The Cu-ZnO based catalysts were systematically characterized and studied for methanol synthesis. Bifunctional catalysts, composed of Cu-ZnO based catalysts and HZSM-5 were studied for one-step dimethyl ether (DME) synthesis via CO2 hydrogenation. The effects of catalyst preparation conditions, reaction temperature, and pressure on methanol and DME synthesis were investigated and the optimum reaction conditions were determined. The optimized catalyst showed a BET surface area of 128 m2/g and a Cu surface area of over 59.3 m2/g, and demonstrated a high catalytic activity for CO2 hydrogenation. A bifunctional catalyst, prepared by a synthesized Cu-ZnO catalyst and HZSM-5, showed a high DME selectivity in one-step CO2 hydrogenation and methanol dehydration. The high activity and selectivity of the catalysts were attributed to the microstructure of the catalysts, which can be greatly affected by the catalyst preparation process. A long-term stability test showed a considerable decrease in activity within the first 20 h; however, the CO2 conversion (21.4%) and DME selectivity (55.5%) were still very high after 100 h.

Green Methanol Production Process from Indirect CO2 Conversion: RWGS Reactor versus RWGS Membrane Reactor

Herein, two different scenarios for indirect CO2 conversion process to produce methanol via reverse water gas shift (RWGS) reaction were investigated and compared. In the first scenario, CO2 is converted to synthesis gas over Fe2O3/Cr2O3/CuO catalyst in a RWGS reactor and then after passing a condenser to eliminate water, as an inhibitor of methanol synthesis catalyst, the product is sent to the methanol production reactor. While in the second, although the process is totally as the same as the previous one, a water permselective membrane was applied in the RWGS reactor. In this scenario, the produced water during the RWGS reaction is separated by the membrane; therefore, the free of water product no longer needed a separator before the methanol synthesis reactor. Both processes were numerically modeled and differential evolution (DE) method was employed to optimize the processes in order to achieve high methanol productivity. Also, the methanol production reactor from these two scenarios were compared with the conventional route (CR), in which methanol is produced from coal and natural gas. The results indicate that, in addition to water removal in the RWGS membrane reactor, a higher CO2 conversion and CO yield and subsequently a more proper synthesis gas composition are obtained. More importantly, methanol production rate increases 13 ton/day (% 4.15 increase) and 109 ton/day (% 50.23 increase) in this scenario compared to the first scenario and CR. Also lower water is produced (17% reduction) in the methanol synthesis reactor of the second scenario respect to the first one.

Comprehensive theoretical analysis of the influence of surface alloying by zinc on the catalytic performance of Cu(1 1 0) for the production of methanol from CO2 selective hydrogenation: Part 1 – Thermochemical aspects

Open copper facets such as Cu(1 1 0) were recently reported to most likely act as an active center of commercial Cu/ZnO/Al2O3 methanol synthesis catalysts. Surprisingly, unlike other surfaces of the metal component, the Cu(1 1 0) facet suffers from severe deactivation by deposited reduced zinc adatoms under catalyst working conditions. Elucidating the catalytic behavior of the novel reactive site and the Zn poisoning effect in detail is highly desirable, however, very challenging. As the first paper of a series devoted to tackle these intriguing issues, we have performed density functional calculations and atomistic thermodynamic modeling to examine the mechanism of CO2 hydrogenation on a CuZn(1 1 0) surface alloy and, as a reference, its parent Cu(1 1 0) substrate. Based on the obtained formation free energies, guest Zn atoms were predicted to be enriched on the uppermost layer of CuZn(1 1 0), preferentially leading to Cu-based single-atom alloys. According to the computations of the authors, the methanol production on the two systems may proceed via formate (HCOO*) rather than both the CO* and carboxyl (HOCO*) species, laying pivotal foundations for future kinetic analysis. The structural insensitivity of the production process is traced back to slight improvement of the stability of most reaction intermediates by partial surface alloying. More in detail, there exist several thermodynamically viable intermediate-mediated strategies that convert bidentate HCOO* to another precursor formaldehyde (H2CO*), that is, bi-HCOO* → dioxymethylene (H2COO*) → hydroxymethoxy (H2COOH*) → H2CO*, bi-HCOO* → formic acid (HCOOH*) → H2COOH* → H2CO*, and bi-HCOO* → HCOOH* → formyl (HCO*) → H2CO*. Under the assistance of the semiempirical Brönsted–Evans–Polanyi (BEP) principle and previous published works, comparison of reaction free-energy data for key elemecntary steps indicates that on CuZn(1 1 0) and Cu(1 1 0), the rate-limting step of methanol synthesis is H3CO* hydrogeantion. Moreover, the Zn-contaminated surface renders the H3CO* + H* reaction thermodynamically and kinetically less favorable than on the latter one, which thus inhibits CO2 hydrogenation to H3COH. In summary, our finding is applicable in explaining the catalytic performance variation when Cu(1 1 0) is alloyed with Zn atoms.

A Highly Active Molybdenum Phosphide Catalyst for Methanol Synthesis from CO and CO2

AbstractMethanol is a major fuel and chemical feedstock currently produced from syngas, a CO/CO2/H2 mixture. Herein we identify formate binding strength as a key parameter limiting the activity and stability of known catalysts for methanol synthesis in the presence of CO2. We present a molybdenum phosphide catalyst for CO and CO2 reduction to methanol, which through a weaker interaction with formate, can improve the activity and stability of methanol synthesis catalysts in a wide range of CO/CO2/H2 feeds.

A Highly Active Molybdenum Phosphide Catalyst for Methanol Synthesis from CO and CO2.

Methanol is a major fuel and chemical feedstock currently produced from syngas, a CO/CO2 /H2 mixture. Herein we identify formate binding strength as a key parameter limiting the activity and stability of known catalysts for methanol synthesis in the presence of CO2 . We present a molybdenum phosphide catalyst for CO and CO2 reduction to methanol, which through a weaker interaction with formate, can improve the activity and stability of methanol synthesis catalysts in a wide range of CO/CO2 /H2 feeds.

Methanol synthesis in a high-pressure membrane reactor with liquid sweep

Membrane reactors (MR) are known for their ability to improve the selectivity and yield of chemical reactions. In this paper, a novel high-pressure MR employing a liquid sweep was applied to the methanol synthesis (MeS) reaction, aiming to increase the per single-pass conversion. For carrying-out the reaction, an asymmetric ceramic membrane was modified with a silylating agent in order to render its pore surface hydrophobic. A commercial MeS catalyst was used for the reaction, loaded in the MR shell-side, while the tube-side was swept with a high boiling point organic solvent with high solubility towards methanol. The membrane reactor was studied under a variety of experimental conditions (different pressures, temperatures, space times, and liquid sweep flow rates) and showed improved carbon conversion when compared to the conventional packed-bed reactor operating under the same conditions.

Atomic-emission determination of the macro composition of the catalyst of methanol synthesis with a photoelectric spectrum analyzer

The possibility of atomic-emission determination of the main components in powder samples with spectra excitation in an AC arc is studied. An arc source of excitation is actually used mainly in approximate-quantitative emission spectral analysis of geological objects for determination of the main components. The goal of the study is to reduce the error of determination of the macro components of the samples when using the aforementioned procedure. The object of the study is a zinc-aluminum-copper catalyst. The spectra are recorded on a DFS-458Cautomated atomic-emission spectrometer. A photoelectron attachment FEP-454 with a CCD-array (Toshiba) is used as a radiation detector in the spectrometer. FEP-454 boasts a system of dynamic accumulation which provides more efficient simultaneous determination of the impurity and sample base components. A calibration curve was constructed using model mixtures for quantitative determination of the matrix elements in real samples. It is shown that the mutual impact of the matrix elements in the arc discharge is almost completely leveled by 16-fold dilution of the samples with a spectrographic buffer. The results of the study prove the possibility of using arc atomic emission analysis for determination both micro- and macro-components in powder samples with a satisfactory accuracy.

Component ratio dependent Cu/Zn/Al structure sensitive catalyst in CO2/CO hydrogenation to methanol

A set of 16 series CuO/ZnO/Al2O3 ternary catalysts in four different groups with various compositions were systematically synthesized through co-precipitation route and employed for the production of methanol from a mixture of H2, CO and CO2 at 50 bar and 250 °C. In each group, CuO/Al2O3 ratio was fixed in specific and constant value and CuO/ZnO ratio varied from 1.8 to 2.7. The ratio of CuO/Al2O3 was also varied from 5 to 11. The prepared samples were characterized and analyzed to understand the relation between the catalytic activity and textural properties to develop a high active and stable catalyst for methanol synthesis. It was observed that the sample with CuO/ZnO = 2.7 and CuO/Al2O3 = 9 as well as the samples having CuO/ZnO = 1.8 possessed the best productivity and selectivity. The smallest Cu crystal sizes and the highest BET and Cu surface areas were observed for the samples with a CuO/Al2O3 ratio of 9. Furthermore, the largest Cu crystal size and the lowest Cu surface area were observed on the samples with CuO/ZnO = 1.8. Nevertheless, higher activities were observed at CuO/ZnO = 1.8. It was also found that some interwoven nano-twins are formed at CuO/ZnO = 1.8, which in turn accelerate the methanol productivity and improve the catalytic stability. Finally, the active catalysts were compared with the commercial catalyst and the results showed a better catalytic performance for the prepared samples in this article.

Enhanced performance of the CuO-ZnO-ZrO2 catalyst for CO2 hydrogenation to methanol by WO3 modification

A series of WO3 modified CuO-ZnO-ZrO2 mixed oxides with different WO3 contents (0–20 at.%) were prepared by co-precipitation method and used as catalyst for methanol synthesis from CO2 hydrogenation. The effects of WO3 content on the physicochemical and catalytic properties of the CuO-ZnO-ZrO2-WO3 catalysts were investigated by X-ray diffraction, X-ray photoelectron spectra, temperature-programed reduction of hydrogen, temperature-programed desorption of CO2, N2 adsorption and desorption, reactive N2O adsorption, and activity testing. The results indicated that both CO2 conversion and methanol selectivity of the CuO-ZnO-ZrO2 catalyst was enhanced by the addition of small amounts (2 and 5 at.%) of WO3. However, the activity was significantly decreased by the addition of excessive WO3 (20 at.%). The activity was closely related to the specific surface area of metallic Cu (SCu), amount of weak basic sites, and reducibility of the catalyst.

OXIDIZING REACTIVATION OF COPPER CATALYST FOR METHANOL SYNTHESIS

The change in phase composition and catalytic properties of a copper-containing catalyst for methanol synthesis which was deactivated under industrial operation was studied at its redox treatment. The possibility of catalyst partial reactivation was shown. Conditions of reactivation were choosen at the increase in catalyst running time.

Effect of Al-containing precursors on Cu/ZnO/Al2O3 catalyst for methanol production

Aluminum is an essential ingredient in the ternary Cu/ZnO/Al2O3 catalyst for methanol synthesis from syngas. This work investigated the effect of Al-containing precursors on Cu/ZnO/Al2O3 catalysts during catalyst preparation. A series of Cu0.6Zn0.3Al0.1 catalysts with various Al-containing precursors, including Cu-Zn-Al hydrotalcite, aluminum hydroxide and Zn-Al hydrotalcite, were prepared by co-precipitation and fractional-precipitation, respectively. The catalysts were characterized with XRD, TG, XRF, N2 physisorption, N2O chemisorption, SEM, TEM/EDS and TPR. Results show that the Al-containing precursor has an important effect on the Cu substitution by Zn in malachite lattice, leading to various performances of the obtained catalysts. The catalyst with Al existing as aluminum hydroxide performed high Cu substitution in the co-precipitated zinc malachite, and exhibits better catalyst performance compared to its counterparts. Aluminum hydroxide can be a suitable Al-containing precursor for preparing the Cu/Zn/Al methanol-synthesis catalyst.

Understanding methanol synthesis from CO/H2 feeds over Cu/CeO2 catalysts

Understanding copper-based methanol synthesis catalysts as a function of catalyst type and applied reaction conditions is an area of active industrial and academic research. In this work, results of a methanol synthesis study over a Cu/CeO2 catalyst using CO/H2 feeds are presented, using catalyst performance data combined with catalyst characterisation information (DRIFTS, XPS, TPR, XRD) obtained during start-up and under steady state methanol synthesis conditions. The results indicate that the active site and reaction mechanism for methanol synthesis over Cu/CeO2 are different from the conventional Cu/ZnO/Al2O3 catalyst, with CO, rather than CO2, being the carbon source for methanol. Fixed-bed micro reactors were employed to obtain catalyst performance data in discrete bed sectors using experimental spatial discretisation methods. Methanol synthesis activity over Cu/CeO2 from CO/H2 is preceded by transient CO2 formation, with the onset of methanol synthesis activity observed when the CO2 formation reaches its peak. Considerable differences between reactor bed sectors are observed during start-up, with CO2 formation, CO2 re-adsorption (as surface carbonates and formates), methanol formation and transient methanol decomposition occurring to different degrees and at different time scales.The interfaces of defective CeO2−x in contact with highly dispersed copper particles form the active site of the catalyst under steady-state methanol synthesis conditions, with the copper oxidation state being a combination of 0 and +1 states. The CeO2−x defect sites are formed during start-up upon reaction of CeO2 with CO. The CO2 thus formed leads to catalyst deactivation due to build-up of carbonate and formate species on the catalyst surface. A gradient of progressive poisoning/deactivation is observed going further down the catalyst bed, where the level of deactivation can be controlled by modifying the CO content in the feed. CO2 thus acts as a poison for the Cu/CeO2 catalyst, and addition of even low levels of CO2 to the feed leads to an evenly deactivated catalyst. During start-up in CO/H2, transient CO2 and H2O formation is also observed in the case of Cu/ZnO/Al2O3, ascribed to partial reduction of ZnO, similar to the partial reduction of CeO2 as seen in Cu/CeO2. The key difference between the two systems is the absence of CO2 and H2O re-adsorption on Cu/ZnO/Al2O3, resulting in stable methanol production distributed equally over the catalyst bed. Introduction of CO2 to the CO/H2 feed in case of Cu/ZnO/Al2O3 leads to reduction of Cu+ to Cu0 and a change in methanol synthesis mechanism from CO to CO2 hydrogenation.

CuO–ZnO anchored on APS modified activated carbon as an enhanced catalyst for methanol synthesis—The role of ZnO

Abstract

Development of highly selective PdZn/CeO2 and Ca-doped PdZn/CeO2 catalysts for methanol synthesis from CO2 hydrogenation

Effect of Pd, Zn, PdZn alloy and Ca-doped PdZn on CeO2 for CO2 hydrogenation to methanol was investigated. CeO2-supported PdZn and Ca-doped PdZn nanoparticles (NPs) proved to be highly selective, fairly active and quite stable for CH3OH synthesis at reasonably low temperature conditions. In the case of Ca-doped PdZn/ CeO2, methanol selectivity of ∼100% was achieved at low temperature (T = 220 °C, P = 30 bar and GHSV = 2400 mL g−1h−1) with reasonable CO2 conversion (7.7%). CeO2-supported PdZn nanoparticles (NPs) (3–6 nm, measured from HR-TEM) were successfully prepared by the chelating method using citric acid as a chelating agent. The developed catalysts were investigated using a range of characterization techniques (BET, CO-Chemisorption, CO2-TPD, H2-TPR, XRD, XPS, STEM-EDS and HR-TEM). XPS results revealed the presence of Ce+3 ions implying the generation of oxygen-vacant sites over the surface of CeO2-supported catalysts which aided in increased CO2 dissociation resulting in higher methanol rates. An in situ diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) study was also carried out for the best performing catalyst at actual reaction conditions to determine the intermediate species and a probable reaction mechanism. Characterization results revealed the significance of CeO2 interaction with PdZn nanoparticles for selective CH3OH formation over ceria-supported PdZn nanoparticles. Addition of Ca, to the CeO2-supported PdZn catalysts, as a promoter, slightly improved the selective conversion of CO2 to methanol by raising the amount of oxygen-vacant sites as revealed by XPS results. DRIFT studies revealed the emergence of monodentate, bidentate formates, CH2O and methoxy species and their subsequent conversion to methanol and CO, steering the reaction mechanism towards formate route for selective formation of methanol.

A review of research progress on heterogeneous catalysts for methanol synthesis from carbon dioxide hydrogenation

Catalytic transformations of carbon dioxide (CO2) to methanol with the help of hydrogen (H2), originates directly from renewable energy sources, is considered as one of the economic ways to alleviate the global warming and drive chemical and energy companies towards a more sustainable use of resources. Recently, a wide variety of heterogeneous catalysts have been evaluated in the CO2 hydrogenation to methanol. The focus of this perspective article is discussing three catalyst categories: (1) Metal-based catalysts, including modified Cu-based methanol catalysts and noble metals such as Au, Ag, Pd and Pt; (2) Oxygen deficient materials; (3) Other catalytic system with novel reaction mechanism and catalytic structure. In addition, this review tries to provide a current understanding of catalyst design, catalytic performance and reaction mechanism over various types of heterogeneous catalysts with an emphasis on practical aspects for the direct production of methanol from CO2 hydrogenation to methanol. We also provide an overview of the challenges and opportunities for future research associated with CO2 hydrogenation to methanol.

Mechanism and microkinetics of methanol synthesis via CO2 hydrogenation on indium oxide

Indium oxide has emerged as a highly effective catalyst for methanol synthesis by direct CO2 hydrogenation. Aiming at gathering a deeper fundamental understanding, mechanistic and (micro)kinetic aspects of this catalytic system were investigated. Steady-state evaluation at 5 MPa and variable temperature indicated a lower apparent activation energy for CO2 hydrogenation than for the reverse watergas shift reaction (103 versus 117 kJ mol−1), which is in line with the high methanol selectivity observed. Upon changing the partial pressure of reactants and products, apparent reaction orders of −0.1, 0.5, −0.2, and −0.9 were determined for CO2, H2, methanol, and water, respectively, which highlight a strong inhibition by the latter. Co-feeding of H2O led to catalyst deactivation by sintering for partial pressures exceeding 0.125 MPa, while addition of the byproduct CO to the gas stream could be favorable at a total pressure below 4 MPa but was detrimental at higher pressures. Density Functional Theory simulations conducted on In2O3(1 1 1), which was experimentally and theoretically shown to be the most exposed surface termination, indicated that oxygen vacancies surrounded by three indium atoms enable the activation of CO2 and split hydrogen heterolytically, stabilizing the polarized species formed. The most energetically favored path to methanol comprises three consecutive additions of hydrides and protons and features CH2OOH and CH2(OH)2 as intermediates. Microkinetic modeling based on the DFT results provided values for temperature and concentration-dependent parameters, which are in good agreement with the empirically obtained data. These results are expected to drive further optimization of In2O3-based materials and serve as a solid basis for reactor and process design, thus fostering advances towards a potential large-scale methanol synthesis from CO2.

Preparation of a highly active ternary Cu-Zn-Al oxide methanol synthesis catalyst by supercritical CO2 anti-solvent precipitation

Methanol synthesis using Cu/ZnO/Al2O3 catalysts is a well-established industrial process. Catalyst development is always an important factor and this has resulted in the current fully optimised commercial catalyst that is prepared by co-precipitation via hydroxycarbonate precursors. Recently, the synthesis of a CuZn hydroxycarbonate precursor, analogous to the rare mineral georgeite, was reported to produce a high activity methanol synthesis catalyst. Here we report the addition of Al3+, the third component found in industrial catalysts, to the zincian georgeite-derived catalyst prepared using a supercritical CO2 anti-solvent precipitation methodology. The co-addition of an AlO(OH) sol to the Cu/Zn precursor solution was found to not disrupt the formation of the CuZn georgeite phase, while providing efficient mixing of the Al3+ within the material. The catalyst derived from the CuZn georgeite precursor phase doped with Al3+ showed a high level of methanol synthesis productivity, which was comparable to that of the binary CuZn georgeite derived catalyst. This material also exhibited enhanced stability during an accelerated ageing test compared to the non-Al doped zincian georgeite material. Performance was benchmarked against an industrially relevant Cu/ZnO/Al2O3 standard catalyst.

The effect of lanthanide promoters on NiInAl/SiO2 catalyst for methanol synthesis

The addition of lanthanides, or rare earth elements, as promoters to NiInAl/SiO2 methanol synthesis catalysts was investigated. The promoters studied are the light rare earth elements (La to Gd) and all but La and Ce were shown to improve methanol synthesis activity. A comparison of the synthesis method for introduction of Pr as a promoter found that addition during the deposition-precipitation synthesis of the catalyst is superior to incipient wetness impregnation introduction after synthesis. The heaviest lanthanides tested (Sm, Eu, Gd) showed the greatest improvement in methanol synthesis activity and selectivity, with a concomitant decrease of CO produced. The Gd-promoted catalyst showed the greatest increase in methanol synthesis activity at 0.51 mmol gcat−1 h−1 which is a 27% increase over the catalyst with no promoter. Examination of the basic characteristics of the catalysts by CO2 TPD and in situ FTIR revealed a negative correlation between basicity and methanol synthesis activity. FTIR methanol synthesis tests also revealed a larger proportion of the key intermediate, bidentate formate, with the addition of the Gd promoter. STEM micrographs and particle size distributions show that the incorporation of the Gd promoter results in smaller diameter metallic particles and higher resistance to sintering. EELS mapping revealed that the location of Ni and Gd correlates well with the metallic particles observed with STEM, and while the In is also found in these particles, small amounts are also observed to be dispersed outside of the particles.