Methanol Synthesis Catalyst Research Articles

CO2 Activation and Hydrogenation on Cu-ZnO/Al2O3 Nanorod Catalysts: An In Situ FTIR Study

CuZnO/Al2O3 is the industrial catalyst used for methanol synthesis from syngas (CO + H2) and is also promising for the hydrogenation of CO2 to methanol. In this work, we synthesized Al2O3 nanorods (n-Al2O3) and impregnated them with the CuZnO component. The catalysts were evaluated for the hydrogenation of CO2 to methanol in a fixed-bed reactor. The support and the catalysts were characterized, including via in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The study of the CO2 adsorption, activation, and hydrogenation using in situ DRIFT spectroscopy revealed the different roles of the catalyst components. CO2 mainly adsorbed on the n-Al2O3 support, forming carbonate species. Cu was found to facilitate H2 dissociation and further reacted with the adsorbed carbonates on the n-Al2O3 support, transforming them to formate or additional intermediates. Like the n-Al2O3 support, the ZnO component contributed to improving the CO2 adsorption, facilitating the formation of more carbonate species on the catalyst surface and enhancing the efficiency of the CO2 activation and hydrogenation into methanol. The synergistic interaction between Cu and ZnO was found to be essential to increase the space–time yield (STY) of methanol but not to improve the selectivity. The 3% CuZnO/n-Al2O3 displayed improved catalytic performance compared to 3% Cu/n-Al2O3, reaching a CO2 conversion rate of 19.8% and methanol STY rate of 1.31 mmolgcat−1h−1 at 300 °C. This study provides fundamental and new insights into the distinctive roles of the different components of commercial methanol synthesis catalysts.

Dry gel assisting crystallization of bifunctional CuO–ZnO–Al2O3/SiO2–Al2O3 catalysts for CO2 hydrogenation

A series of bifunctional catalysts CuO–ZnO–Al2O3/SiO2–Al2O3 (CZA/SA) with different SA/CZA ratios were prepared by dry gel assisting crystallization method. The catalytic performance of bifunctional catalysts for one-step synthesis of methanol (MeOH) and dimethyl ether (DME) from CO2 hydrogenation was investigated. The results showed that compared with Cu/ZnO/Al2O3, CZA/SA catalyst significantly improved the selectivity of DME and MeOH and reduced the CO selectivity with moderate CO2 conversion. The catalyst structure was characterized by X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (H2-TPR), which further confirmed that the active site of methanol generation was the Cu–ZnO interface with a strong interaction rather than solo Cu or ZnO crystallite, which could enhance the hydrogenation function and inhibit reverse water gas shift reaction. Compared with the physical mixing method, the dry gel assisting crystallization method could flexibly adjusted the acid strength and the amounts of acid sites, which was benefit for enhancing dehydration function to improve the selectivity of DME.

Influence of Si/Al ratio of MOR type zeolites for bifunctional catalysts specific to the one-pass synthesis of lower olefins via CO2 hydrogenation

Highly efficient CO2 utilization methodologies should be developed to reduce greenhouse gas emissions. Combining methanol synthesis (CO2-to-methanol) catalysts and methanol conversion (methanol-to-olefins) catalysts realizes one-pass hydrocarbon production via CO2 hydrogenation. We focused on ZnO/ZrO2 as metal-oxide-based catalysts for methanol synthesis and MOR zeolites as solid acid catalysts for methanol conversion. These catalysts were physically mixed to produce bifunctional catalysts which work at relatively low pressure (10 bars). Compositions of zeolite catalysts, especially Si/Al ratios, are important since composition influences on properties of zeolites, such as acid density and strength. MOR zeolites with varied Si/Al ratios were tested and found MOR zeolites with Si/Al ratio of 104 showed the best olefin selectivity. The relation between coke formation behavior and acid sites was discussed for explaining catalytic activities. The novel bifunctional catalysts and knowledge of selectivity provide a new methodology for CO2 utilization.

Elucidation of Cu-Zn Surface Alloying on Cu(997) by Machine-Learning Molecular Dynamics.

The Cu-Zn surface alloy has been extensively involved in the investigation of the true active site of Cu/ZnO/Al2O3, the industrial catalyst for methanol synthesis which remains under controversy. The challenge lies in capturing the interplay between the surface and reaction under operating conditions, which can be overcome given that the explicit dynamics of the system is known. To provide a better understanding of the dynamic of Cu-Zn surface at the atomic level, the structure and the formation process of the Cu-Zn surface alloy on Cu(997) were investigated by machine-learning molecular dynamics (MD). Gaussian process regression aided with on-the-fly learning was employed to build the force field used in the MD. The simulation reveals atomistic details of the alloying process, that is, the incorporation of deposited Zn adatoms to the Cu substrate. The surface alloying is found to start at upper and lower terraces near the step edge, which emphasize the role of steps and kinks in the alloying. The incorporation of Zn at the middle terrace was found at the later stage of the simulation. The rationalization of alloying behavior was performed based on statistics and barriers of various elementary events that occur during the simulation. It was observed that the alloying scheme at the upper terrace is dominated by the confinement of Zn step adatoms by other adatoms, highlighting the importance of step fluctuations in the alloying process. On the other hand, the alloying scheme at the lower terrace is dominated by direct exchange between the Zn step adatom and the Cu atom underneath. The alloying at the middle terrace is dominated by the wave deposition mechanism and deep confinement of Zn adatoms. The short propagation of alloyed Zn in the middle terrace was observed to proceed by means of indirect exchange instead of local exchange as proposed in the previous scanning tunneling microscopy (STM) observation. The comparison of migration rate and activation energies to the result of STM observation is also made. We have found that at a certain distance from the surface, the STM tip significantly affects the elementary events such as vacancy formation and direct exchange.

Hydrogenation of CO and CO2 Catalyzed by Potassium Chloride F Centers

The role of F centers on the KCl (100) surface in the hydrogenation of carbon monoxide and carbon dioxide was investigated theoretically at density-functional theory level. The surface defect was found to reduce all carbon-containing species involved in the reactions. In all cases, the defect electron occupies the lowest antibonding orbital of the molecules which weakens at least one of the C–O bonds. All reaction barriers of the hydrogenation on the defect are significantly reduced in comparison with the gas-phase reactions. The thermodynamic and kinetic parameters of the reaction pathways were computed, allowing for a comparison with the industrially established Cu/ZnO catalyst for methanol synthesis. It was found that methanol synthesis from CO2 is thermodynamically and kinetically hindered, yielding formate as a product that blocks the F center. The reaction rate for the rate limiting step of the methanol synthesis from CO on the F center is about 10 times higher than that for the conventional catalyst. However, the end product methanol further dissociates into methanolate and free radical hydrogen with only a small activation barrier. Furthermore, it was found that water dissociates into OH– and H• on the defective surface, so that even trace amounts can deactivate the F center.

Insight into the Nature of the ZnO x Promoter during Methanol Synthesis.

Despite the great commercial relevance of zinc-promoted copper catalysts for methanol synthesis, the nature of the Cu–ZnOx synergy and the nature of the active Zn-based promoter species under industrially relevant conditions are still a topic of vivid debate. Detailed characterization of the chemical speciation of any promoter under high-pressure working conditions is challenging but specifically hampered by the large fraction of Zn spectator species bound to the oxidic catalyst support. We present the use of weakly interacting graphitic carbon supports as a tool to study the active speciation of the Zn promoter phase that is in close contact with the Cu nanoparticles using time-resolved X-ray absorption spectroscopy under working conditions. Without an oxidic support, much fewer Zn species need to be added for maximum catalyst activity. A 5–15 min exposure to 1 bar H2 at 543 K only slightly reduces the Zn(II), but exposure for several hours to 20 bar H2/CO and/or H2/CO/CO2 leads to an average Zn oxidation number of +(0.5–0.6), only slightly increasing to +0.8 in a 20 bar H2/CO2 feed. This means that most of the added Zn is in a zerovalent oxidation state during methanol synthesis conditions. The Zn average coordination number is 8, showing that this phase is not at the surface but surrounded by other metal atoms (whether Zn or Cu), and indicating that the Zn diffuses into the Cu nanoparticles under reaction conditions. The time scale of this process corresponds to that of the generally observed activation period for these catalysts. These results reveal the speciation of the relevant Zn promoter species under methanol synthesis conditions and, more generally, present the use of weakly interacting graphitic supports as an important strategy to avoid excessive spectator species, thereby allowing us to study the nature of relevant promoter species.

Synthetic Routes to Crystalline Complex Metal Alkyl Carbonates and Hydroxycarbonates via Sol–Gel Chemistry—Perspectives for Advanced Materials in Catalysis

Metal alkoxides are easily available and versatile precursors for functional materials, such as solid catalysts. However, the poor solubility of metal alkoxides in organic solvents usually hinders their facile application in sol–gel processes and complicates access to complex carbonate or oxidic compounds after hydrolysis of the precursors. In our contribution we have therefore shown three different solubilization strategies for metal alkoxides, namely the derivatization, the hetero-metallization and CO2 insertion. The latter strategy leads to a stoichiometric insertion of CO2 into the metal–oxygen bond of the alkoxide and the subsequent formation of metal alkyl carbonates. These precursors can then be employed advantageously in sol–gel chemistry and, after controlled hydrolysis, result in chemically defined crystalline carbonates and hydroxycarbonates. Cu- and Zn-containing carbonates and hydroxycarbonates were used in an exemplary study for the synthesis of Cu/Zn-based bulk catalysts for methanol synthesis with a final comparable catalytic activity to commercial standard reference catalysts.

Structuring of Methanol Synthesis Catalyst CuO/ZnO/γ-Al2O3 During Mechanochemical Synthesis

Structuring of Methanol Synthesis Catalyst CuO/ZnO/γ-Al2O3 During Mechanochemical Synthesis

Insight into the structural sensitivity of CuZnAl catalysts for CO hydrogenation to alcohols

The catalytic conversion of CO hydrogenation is a structure-sensitive reaction over Cu-based catalyst. It is very important to distinguish the structural differentiation and possible reaction pathway of Cu-based catalysts in methanol synthesis and ethanol/C2+OH synthesis. Herein, the activity of four types of CuZnAl catalysts is evaluated, and their structural differentiation is investigated. The CuZnAl catalyst (CZA) prepared by a complete liquid-phase (CLP) method after solid–liquid separation directly applied in the fixed bed reactor also shows the ability to synthesize ethanol and higher alcohols (C2+OH), with the selectivity of C2+OH in liquid product reaching up to 31.6% at the CO conversion of 10.6%. However, commercial methanol synthesis catalyst (CMC) displays the highest CO conversion (28.2%) and the poorest C2+OH selectivity (7.8%). After characterized by ICP, XRD, CO-TPD, N2O adsorption, XPS, SEM, TEM and in-situ DRIFTS techniques, it is discovered that the dispersion of Cu and the exposed Cu surface area significantly influences CO conversion. The selectivity of ethanol and C2+OH is related to the size and distribution of Cu, the architectural feature, and the chemical environment of Cu and Al. In-situ DRIFTS indicates that CHxO* species can be formed over different CuZnAl catalysts. However, the formed CHxO* species will be rapidly hydrogenated to produce methanol on CMC catalyst, while the step is inhibited on CZA catalyst. Additionally, a bridge-type adsorbed CO is only observed on CZA catalyst, which is beneficial for the formation of CHx intermediates, leading to the formation of ethanol and higher alcohols.

Valorization of steel-work off-gases: Influence of impurities on the performance of Cu-based methanol synthesis catalyst

The use of steel-work off-gases as CO2 source for methanol production is a promising strategy for the decarbonization of the steel industry. In this work, we show that typical impurities, namely S, N, Na, Ca and Fe, reduce the activity of a commercial CuO/ZnO/Al2O3 catalyst by blocking part of the Cu active sites. The extent of the activity loss is proportional to the poison-induced decrease in the exposed Cu surface area, suggesting that the poisons do not modify the nature, but rather the number of active sites. The only deviation is observed for Na, as its strong basicity leads to stronger binding of CO2 on the catalyst surface. Moreover, all catalysts suffer from methanol selectivity losses with time, due to thermal sintering that occurs similarly over the untreated and poisoned samples. Industrial CO2 off-gases can thus be exploited for methanol production after appropriate purification targeted primarily at the removal of metal impurities. The presence of sulfur and nitrogen is less critical to the catalyst performance.

Novel layered triple hydroxide sphere CO2 adsorbent supported copper nanocluster catalyst for efficient methanol synthesis via CO2 hydrogenation

Copper-based catalysts are playing important roles in CO2 hydrogenation to methanol. Active copper provides sites for H2 dissociation, whereas CO2 adsorption and activation cannot be ignored either. Accordingly, novel Cu/LTH catalysts with copper nanoclusters supported on layered triple hydroxide (LTH) sphere CO2 adsorbent were developed to improve microstructures and CO2 adsorption capabilities simultaneously. The results show increasements in copper content enlarge crystallite sizes yet reduce surface areas and pore volumes. All Cu/LTH catalysts consist of uniformly dispersed copper nanoclusters on external surfaces of LTH. Catalytic tests reveal remarkable properties of Cu/LTH catalysts compared with conventional catalysts. Further mechanism analyses demonstrate LTH can boost CO2 adsorption capability at reaction conditions. Due to metal-support interactions, copper species in Cu3/LTH are more easily reduced mainly in the form of Cu+, benefiting directional CO2 conversion to methanol. Thus, it is feasible and efficient to ameliorate catalyst by incorporating adsorbent for enhanced CO2 adsorption process.

The role of CO2 over different binary catalysts in methanol synthesis

A small amount of CO2 in syngas (CO/H2) is beneficial to methanol synthesis over Cu-based catalysts. To obtain more information on the CO2 effect, a series of binary Cu-based catalysts including Cu/ZnO and Cu/MgO were prepared and evaluated under feed gas (CO/H2/Ar) with or without CO2. Evaluation results show that when CO2 was added, the CO conversion of Cu0.6ZnO0.3 catalyst jumped from ~4% to ~68%, while the activity of Cu/MgO catalyst decreased from ~15% to ~0% (230 °C, 4 MPa, 8000 h−1 with 78.5% H2, 12.75% CO, 1.75% CO2 and 7% Ar). In situ X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were employed to examine the states of catalysts under different treatment conditions. The migration and transformation of metal species on the catalysts surface should be a reason that caused the opposite change of catalysts activity with and without CO2.

Hazardous spent methanol synthesis catalyst waste and ground cooled ferrous slag application to produce sustainable ceramics

Hazardous spent methanol synthesis catalyst waste and ground cooled ferrous slag application to produce sustainable ceramics

Insights of precursor phase transition of (Cu-Zn-Al)/γ-Al2O3 hybrid catalyst for one step dimethyl ether synthesis from syngas

The concerns on environmental pollution and climate change, along with ever-growing energy demands, have driven interest in dimethyl ether (DME) as a clean fuel alternative and a versatile chemical intermediate. Due to the advantages of single-step synthesis of DME, we investigated the influence of precursor phase transition of methanol synthesis catalyst from hydrotalcite to zincian malachite on the hybrid catalyst’s activity for direct syngas to DME process by varying its Cu/Al content. A series of Cu-Zn hybrid catalysts were prepared via a kneading extrusion process by physical mixing of methanol synthesis catalyst (CuO:ZnO:Al2O3) prepared via facile forward precipitation route with CuO/Al2O3 ratios 1.5–6 and the dehydration component boehmite (γ-AlO(OH)). The physicochemical aspects of prepared hybrid catalysts were studied in detail by BET, XRD, N2O chemisorption, H2-TPR, NH3-TPD, SEM, and TEM. The activity studies revealed that the catalyst with a lower CuO/Al2O3 (1.5) ratio derived from the phase pure hydrotalcite precursor showed enhanced catalytic activity with a high CO conversion 60.5% and DME selectivity 71.5%. Whereas the catalyst with a high CuO/Al2O3 (6) ratio showed relatively lower DME selectivity, although it was derived from the phase-rich zincian malachite, which is a preferred active phase for methanol synthesis. The higher yield of DME with hydrotalcite-derived hybrid catalyst was most likely attributed to the well dispersed nanostructured active Cu sites and the higher number of weak and medium strength acidic sites. Moreover, the phase transition of dehydration component boehmite to γ-Al2O3 helps in methanol dehydration with its characteristic Lewis acidity.

Inside Cover: Drastic Events and Gradual Change Define the Structure of an Active Copper‐Zinc‐Alumina Catalyst for Methanol Synthesis (Angew. Chem. Int. Ed. 15/2022)

Copper and zinc oxide are a dream team in transforming carbon dioxide and carbon monoxide together with hydrogen into the valuable base chemical methanol. Inspired by the cover art of the music masterpiece “Wish you were here” by Pink Floyd, the picture featuring the Research Article (e202200301) by Jeroen A. van Bokhoven and co-workers highlights the fundamental collaboration of the copper and zinc oxide phase in methanol catalysts for a sustainable future.

Innentitelbild: Drastische Ereignisse und langsame Transformation definieren die Struktur eines aktiven Kupfer‐Zink‐Aluminiumoxid‐Katalysators für die Methanol Synthese (Angew. Chem. 15/2022)

Kupfer und Zinkoxid sind ein Dreamteam bei der Umwandlung von Kohlendioxid und Kohlenmonoxid mit Wasserstoff in die wertvolle Basischemikalie Methanol. Inspiriert vom Cover von Pink Floyds Meisterwerk “Wish you were here” illustriert das Titelbild, das zum Forschungsartikel (e202200301) von Jeroen A. van Bokhoven et al. gehört, das Zusammenspiel der Kupfer- und Zinkoxidphase in Methanolkatalysatoren für eine nachhaltige Zukunft.

Drastische Ereignisse und langsame Transformation definieren die Struktur eines aktiven Kupfer‐Zink‐Aluminiumoxid‐Katalysators für die Methanol Synthese

AbstractDer Kupfer‐Zink‐Aluminiumoxid‐Katalysator (CZA) ist einer der wichtigsten industriellen Katalysatoren. Jedoch versteht man die komplexe CZA‐Struktur nur teilweise und das bremst seine Weiterentwicklung. Um einen sehr aktiven und stabilen Katalysator zu erzeugen sind optimale Aktivierungsbedingungen in Wasserstoff essentiell. In dieser Arbeit folgen wir mithilfe von operando Röntgenadsorptionspektroskopie und ‐diffraktion der Entwicklung eines industriellen CZA‐Katalysatorvorläufer zum arbeitenden Katalysator. Zwei Ereignisse während der Aktivierung führen zu drastischen Veränderung in den kupfer‐ und zinkhaltigen Komponenten des CZA‐Katalysators und bestimmen die Struktur des fertigen Katalysators: Erstens, die Reduktion des ursprünglichen Kupfer(II)oxids und, zweitens, das Kristallwachstum und Reoxidierung von Zinkoxid während des Wechsels zu katalytischen Bedingungen. Diese drastischen Ereignisse werden von anderen graduellen Transformationen begleitet. Um maßgeschneiderte Aktivierungsprotokolle, die die maximale Lebensdauer und Aktivität des Katalysators erzielen, zu entwickeln, müssen wir diesen Transformationen verstehen.

Drastic Events and Gradual Change Define the Structure of an Active Copper-Zinc-Alumina Catalyst for Methanol Synthesis.

The copper‐zinc‐alumina (CZA) catalyst is one of the most important catalysts. Nevertheless, understanding of the complex CZA structure is still limited and hampers further optimization. Critical to the production of a highly active and stable catalyst are optimal start‐up procedures in hydrogen. Here, by employing operando X‐ray absorption spectroscopy and X‐ray diffraction, we follow how the industrial CZA precursor evolves into the working catalyst. Two major events in the activation drastically alter the copper‐ and zinc‐containing components in the CZA catalyst and define the final working catalyst structure: the reduction of the starting copper(II) oxide, and the ripening and re‐oxidation of zinc oxide upon the switch to catalytic conditions. These drastic events are also accompanied by other gradual, structural changes. Understanding what happens during these events is key to develop tailored start‐up protocols that are aimed at maximal longevity and activity of the catalysts.

Methanol mediated direct CO2 hydrogenation to hydrocarbons: Experimental and kinetic modeling study

Carbon dioxide can be utilized as a feedstock to produce chemicals and renewable fuels sustainably. CO2 hydrogenation to hydrocarbons through a methanol mediated pathway requires a more detailed study, examining interactions between reaction processes leading to different product selectivities. In this particular work, we propose a kinetic model for the direct CO2 hydrogenation to different hydrocarbon products over an In2O3/HZSM-5 bifunctional catalytic bed. The model includes a CO2 hydrogenation to methanol model based on a Langmuir Hinshelwood Hougen Watson (LHHW) reaction mechanism over In2O3 catalyst combined with a lump-type methanol to hydrocarbon (MTH) model over the HZSM-5 zeolite. Interestingly, the combined model could largely predict the suppression of the reverse water gas shift (RWGS) reaction and an increase in the yield of hydrocarbons compared to the formation of methanol in case of the same reaction conditions carried out with only the methanol synthesis catalyst (In2O3). Further, by varying the mass ratio of the individual components of the bifunctional catalytic bed, it was demonstrated that a higher outlet concentration of methanol achieved with a higher mass ratio of the methanol synthesis catalyst caused less suppression of the RWGS reaction and shifted the hydrocarbon product distribution to a slightly larger share of higher hydrocarbons. These changes in product selectivity caused by variation of the catalyst mass ratio were both also successfully reproduced by the model. Therefore, a comparison between the experimental results and the model predictions shows that this model, including equilibrium effects for the reactions, can accurately predict the trends of the experimental findings for direct CO2 hydrogenation to hydrocarbons over the In2O3/HZSM-5 catalyst.

Comprehensive review of Cu-based CO2 hydrogenation to CH3OH: Insights from experimental work and theoretical analysis

Developing the technology of CO 2 hydrogenation into methanol can not only alleviate environmental problems such as greenhouse effect, but also effectively promote the utilization of CO 2 resources. In general, Cu-based catalysts have been extensively studied due to its low cost and the effective synthesis of methanol. Thus, this review is to be reported based on Cu-based catalysts for methanol synthesis from CO 2 hydrogenation. The specific goal of this review is to provide some insights into the structural and surface properties of Cu-based catalysts and their functions on the reaction mechanisms, and further affecting on the catalytic selectivity, stability, and activity for the CO 2 hydrogenation to methanol. A vital issue discussed is the fundamental understanding of active sites, reaction mechanisms, and interactions (active metal-support, active metal-promoter, bimetal) in determining the catalytic performance. Through a comprehensive overview on Cu-based systems for CO 2 hydrogenation to methanol from both experimental and theoretical perspectives, it could provide some useful information to go into CO 2 hydrogenation to methanol for the outsider, and promote the design and synthesis of novel and efficient catalysts. • CO 2 hydrogenation to methanol could alleviate environmental problems. • Cu catalyst plays a vital role in the CO 2 hydrogenation. • The low yield of methanol is the major obstacle. • Combining experiment with DFT calculation is a promising strategy to accelerate the development of new catalysts.