Direct Conversion Of Syngas Research Articles

High Selectivity to Aromatics by a Mg and Na Co-modified Catalyst in Direct Conversion of Syngas.

The demand for aromatics, especially benzene, toluene, and xylene, has been increased in recent years as the crucial feedstocks of coatings and pharmaceutical industry. In this work, a modified Fischer–Tropsch synthesis (FTS) catalyst FeNaMg was fabricated via a sol-precipitation method and integrated with an HZSM-5 aromatization catalyst for the aromatics synthesis from syngas by a one-step process. Syngas was first converted to lower olefins as intermediates on the active component of the FeNaMg catalyst followed by aromatization on zeolite. Different characterization approaches, such as BET, XRD, XPS, hydrogen temperature-programmed reduction, temperature-programmed desorption of CO, TG, and SEM, revealed that Mg efficiently optimized physicochemical properties of the Fe-based catalyst by generating a MgFe2O4 spinel structure. Further investigation demonstrated that the MgFe2O4 spinel structure could increase the syngas adsorption area, facilitating the reduction and carburization of the Fe phase, while Mg decreased CO2 selectivity (31.26 to21%) by restraining the water–gas shift reaction and improved the utilization efficiency of carbon. At the same time, alkali metal Na changed the surface electronic environment of the FTS catalyst to enhance CO adsorption as an electronic promoter, which suppressed methane formation by restraining over hydrogenation. Therefore, the synergism that existed between Mg and Na during the reaction escalated the CO conversion and aromatics selectivity to 96.19 and 51.38%, respectively.

Role of nanosized sheet-like SAPO-34 in bifunctional catalyst for syngas-to-olefins reaction

Direct conversion of syngas to light olefins via oxide-zeolite strategy attracted extensive attention recently. Nanosized sheet-like SAPO-34, denoted as SAPO-34(NS), was synthesized and utilized as the zeotype in the bifunctional catalyst to enhance the activity of syngas-to-olefins (STO) reaction. SEM and Ar physisorption demonstrated that SAPO-34(NS) exhibited abundant outer cages and facilitated the diffusion of reactant and products. GC-MS revealed that the carbonaceous species in ZnCrOx + SAPO-34(NS) was lighter because of the enhancement of diffusion, thus ZnCrOx + SAPO-34(NS) was more active during STO reaction than the bifunctional catalyst containing micron-sized cubic SAPO-34. The evolution of carbonaceous species in the bifunctional catalyst proved that maintaining tetramethyl-benzenes as the majority of carbonaceous species was benefit to enhance CO conversion in STO reaction over bifunctional catalyst. 18.49% CO conversion and 88.18% light olefins selectivity (free of CO2) were achieved over ZnCrOx + SAPO-34(0.061NS) at 653 K, 1.0 MPa, GHSV = 6000 ml·g−1·h−1. The catalytic performance was stable after 6000 min of reaction.

Influential Role of Elemental Migration in a Composite Iron–Zeolite Catalyst for the Synthesis of Aromatics from Syngas

A composite catalyst of a metal oxide and a zeolite has been widely adopted for the direct conversion of syngas to aromatics (STAs). However, its stability along with higher conversion and selectiv...

Highly active ternary oxide ZrCeZnOx combined with SAPO-34 zeolite for direct conversion of syngas into light olefins

Direct conversion of syngas into light olefins over bifunctional catalysts (metal oxide and zeolite) has attracted great attention in recent years. For this reaction, the adsorption and activation of CO and H2 occur on metal oxide surface, thus the design of metal oxide is crucial. In this study, ternary oxides ZrCeZnOx with various CeO2 contents were prepared by parallel coprecipitation method, and SAPO-34 zeolite (Si/Al = 0.125) was hydrothermally synthesized. The metal oxides were characterized by XRD, BET, TEM, SEM, XPS, CO-TPD, H2-TPD, TGA and in-situ DRIFTS. The addition of CeO2 into Zr-Zn oxide shifted the diffraction peaks to lower values, and formed the Ce0.5Zr0.5O2 solid solution as the Zr/Ce/Zn atomic ratio reached 4/4/1. As the CeO2 content rose, the BET surface area increased while the metal oxide particle size decreased. Moreover, the addition of CeO2 greatly enhanced the concentration of oxygen vacancies and the adsorption ability of CO and H2. The in-situ DRIFTS confirmed that CH3O* was the intermediate. By optimizing the reaction conditions, ZrCeZnOx/SAPO-34 catalyst exhibited high CO conversion of 25.6 % and light olefins selectivity of 78.6 %. This study will contribute to the design of metal oxide for bifunctional catalyst for light olefins synthesis.

Cu/ZnO Catalysts Derived from Bimetallic Metal-Organic Framework for Dimethyl Ether Synthesis from Syngas with Enhanced Selectivity and Stability.

Direct conversion of syngas to dimethyl ether (DME) through the intermediate of methanol allows more efficient DME production in a simpler reactor design relative to the conventional indirect route. Although Cu/ZnO-based multicomponent catalysts are highly active for methanol synthesis in this process, the sintering issue of Cu during the prolonged reaction generally deteriorates their performance. In this work, Cu/ZnO catalysts in a novel octahedron structure are prepared by a two-step pyrolysis of Zn-doped Cu-BTC metal-organic framework (MOF) in N2 and air. The catalyst CZ-350/A, hybrid of MOF-derived Cu/ZnO sample CZ-350 and γ-Al2 O3 for methanol dehydration, displays the best activity for DME formation (7.74% CO conversion and 70.05% DME selectivity) with the lowest deterioration rate over 40 h continuous reaction. Such performance is superior to its counterpart CZ-CP/A made via the conventional coprecipitation method. This is mainly due to the confinement of Cu nanoparticles within the octahedron matrix hindering their migration and aggregation. Besides, partial reduction of ZnO in the activated CZ-350 prompts the formation of Cu+ -O-Zn, further facilitating the DME production with the highest selectivity compared to literature results. The results clearly indicate that Cu and ZnO distribution in the catalyst architecture plays an important role in DME formation.

Exploring the Reaction Paths in the Consecutive Fe-Based FT Catalyst–Zeolite Process for Syngas Conversion

Direct conversion of syngas into aromatics with tandem catalysts containing Fe-based Fischer–Tropsch synthesis (FTS) catalysts and zeolites has been attracting significant attention because of the ...

A facile solvent-free synthesis strategy for Co-imbedded zeolite-based Fischer-Tropsch catalysts for direct gasoline production

A series of Co-imbedded zeolite-based catalysts were synthesized following a facile solvent-free grinding route. The catalytic performance for direct syngas conversion to gasoline range hydrocarbons was compared with their counterpart Co-impregnated zeolite-based catalysts. Successful transformation of solid raw materials to targeted zeolite was confirmed by XRD, SEM, STEM, and N 2 physisorption analysis. An in-depth study of acidic strength and acidic site distribution was conducted by NH 3 -TPD and Py-IR spectroscopy. Acidic strength showed a pivotal role in defining product range. Co@S1, with the weakest acidic strength of silicalite-1 among three types of zeolites, evaded over-cracking of product and exhibited the highest gasoline and isoparaffin selectivity (≈70% and 30.7%, respectively). Moreover, the solvent-free raw material grinding route for zeolite synthesis accompanies several advantages like the elimination of production of wastewater, high product yield within confined crystallization space, and elimination of safety concerns regarding high pressure due to the absence of the solvent. Facileness and easiness of the solvent-free synthesis route together with promising catalytic performance strongly support its application on the industrial scale. A facile and green solvent-free solid raw material grinding route was used to prepare Co-imbedded zeolite-based catalysts for direct gasoline production from syngas via Fischer-Tropsch synthesis.

Selective Conversion of Syngas into Higher Alcohols via a Reaction-Coupling Strategy on Multifunctional Relay Catalysts

Direct conversion of syngas (CO/H2) into higher alcohols is highly desirable but remains challenging due to the low C2+OH selectivity. Herein, an effective strategy was developed through the combin...

Ethanol as a Binder to Fabricate a Highly‐Efficient Capsule‐Structured CuO−ZnO−Al2O3@HZSM‐5 Catalyst for Direct Production of Dimethyl Ether from Syngas

AbstractThis work reports a highly efficient capsule‐structured CuO−ZnO−Al2O3@HZSM‐5 (CZA@HZSM‐5‐EtOH) core‐shell catalyst for the direct conversion of syngas to dimethyl ether by a facile physical coating method with ethanol as a binder through coating micrometer‐sized HZSM‐5 shell on the prior‐shaped millimeter‐sized CZA core, it shows 2.9 times higher CO conversion with the 2.7 times higher turnover frequency and 9.2 times higher dimethyl ether space‐time yield of the CZA@HZSM‐5‐SS catalyst prepared by a similar process but with silica sol as a binder (315.5 vs 34.3 gDME kgcat−1 h−1). The relationship between the structure and performance was explored by a variety of characterization techniques including X‐ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X‐ray diffraction (XRD), ammonia temperature programmed desorption (NH3‐TPD), nitrogen adsorption‐desorption, H2‐temperature‐programmed reduction (H2‐TPR) and H2‐TPR after oxidation of the samples by N2O. CZA@HZSM‐5‐EtOH can be considered as a highly efficient and practical catalyst for dimethyl ether synthesis from syngas. This work presents a new avenue to design other bifunctional catalysts for the cascade reactions in which the raw materials can be converted into an intermediate over the core and then the as‐formed intermediate over the core can be subsequently converted into the final product.

Direct Conversion of Syngas into Light Olefins with Low CO2 Emission

Direct conversion of syngas into light olefins over bifunctional catalysts has made significant progress; the C2=–C4= selectivity in hydrocarbons reaches >80%. Nevertheless, a relatively harsh reac...

Direct conversion of syngas into aromatics over a bifunctional catalyst: inhibiting net CO2 release.

Tandem catalysis via methanol intermediate is a promising route for the direct conversion of syngas into aromatics. However, the simultaneous formation of CO2 is a serious problem. Here, we demonstrate that CO2 was formed by the water-gas shift (WGS) reaction (CO + H2O → CO2 + H2) over a ZnO-ZrO2/H-ZSM-5 catalyst, and the net CO2 formation could be inhibited without affecting the formation of aromatics by co-feeding CO2.

Direct conversion of syngas into light aromatics over Cu-promoted ZSM-5 with ceria–zirconia solid solution

Syngas conversion with 72.1% selectivity to aromatics and 40.8% CO conversion was achieved over a copper and silica-modified ZSM-5 and ceria–zirconia solid solution bifunctional catalyst.

Two-way desorption coupling to enhance the conversion of syngas into aromatics by MnO/H-ZSM-5

We herein report a composite catalyst containing partially reducible and highly active manganese oxide and nano-size H-ZSM-5 with short b-axis, prepared for the direct conversion of syngas into aromatics.

MODELING OF A RECTANGULAR CHANNEL MONOLITH REACTOR FOR SORPTION-ENHANCED WATER-GAS SHIFT

As CO2 concentration levels in the atmosphere are steadily reaching a point of no return, it is paramount that actions are taken towards mitigating emissions by improving the efficiency of existing processes. Sorption-enhanced water-gas shift (SEWGS) combines the water-gas shift reaction with in-situ adsorption of CO2 on potassium-promoted hydrotalcite (K-HTC). This enables a direct conversion of syngas into separate hot streams of H2 at feed pressure and CO2 at regeneration pressure, making the process attractive for pre-combustion carbon capture and storage (CCS) and reduction of greenhouse gas emissions. The current work is evaluating the high-temperature, high-pressure adsorption step of the SEWGS process enhanced by a novel technology which replaces common packed bed reactors with 3D-printed monolithic structures. This approach would enable an overall increase in process productivity. To this extent, innovative dynamic models based on validated competitive adsorption isotherms were developed in this work. COMSOL Multiphysics was used to develop a 1D computational fluid dynamics (CFD) model of adsorption for a fixed bed reactor in order to verify the model accuracy against existing studies. Subsequently, 2D CFD simulations were developed to describe adsorption inside monolith structures, both free and porous regions. The multi-component adsorption isotherm used in the simulations was validated with published breakthrough capacities for CO2 and H2O at different pressures. Model predictions are in agreement with expected behavior, as monolith reactors provide a more efficient mass transfer, and will be used to enhance the performance of experimental monolith structures used in SEWGS.

Bifunctional Capsule Catalyst of Al2O3@Cu with Strengthened Dehydration Reaction Field for Direct Synthesis of Dimethyl Ether from Syngas

Direct conversion of syngas to dimethyl ether (DME) using bifunctional catalysts is a promising way to meet the current industrial demands. However, the spatial design of the bifunctional catalyst ...

Direct conversion of syngas to light olefins (C2–C3) over a tandem catalyst CrZn–SAPO-34: Tailoring activity and stability by varying the Cr/Zn ratio and calcination temperature

A series of CrZn oxide catalysts with different Cr/Zn ratios were synthesized by co-precipitation and calcined at different temperatures. The catalysts were tested in a physical mixture with SAPO-34 in the direct conversion of syngas to olefins. X-ray diffraction, x-ray photoelectron and absorption spectroscopy, and electron microscopy were used to evaluate the impact of the Cr/Zn ratio and calcination temperature on the physicochemical properties of the resultant materials. CrZn–SAPO-34 catalysts were able to selectively convert syngas to C2–C3 hydrocarbons with a high olefin/paraffin ratio and low methane yield. However, the catalytic performance of these systems exhibited a trade-off between activity and stability in the olefin yield over time. By tuning the Cr/Zn ratio, it is possible to improve the olefin production stability, but with some compromise in the overall activity. The nonstoichiometric and inversed ZnCr2O4 spinel phase was considered to be the active phase for CO hydrogenation, while the decay in olefin production over time is correlated with abundance of ZnO on the resultant catalyst. Spectroscopic analysis demonstrated that the inversed spinel evolves toward its normal form under reaction conditions, which is accompanied by the formation of segregated ZnO; this phase may also increase the olefin hydrogenation activity.The challenge for the rational design of an optimal CrZn–SAPO-34 system is the stabilization of inversed ZnCr2O4, while minimizing the presence of the ZnO phase in the catalyst formulation.

Understanding Structure-Property Relationships of MoO3-Promoted Rh Catalysts for Syngas Conversion to Alcohols.

Rh-based catalysts have shown promise for the direct conversion of syngas to higher oxygenates. Although improvements in higher oxygenate yield have been achieved by combining Rh with metal oxide promoters, details of the structure of the promoted catalyst and the role of the promoter in enhancing catalytic performance are not well understood. In this work, we show that MoO3-promoted Rh nanoparticles form a novel catalyst structure in which Mo substitutes into the Rh surface, leading to both a 66-fold increase in turnover frequency and an enhancement in oxygenate yield. By applying a combination of atomically controlled synthesis, in situ characterization, and theoretical calculations, we gain an understanding of the promoter-Rh interactions that govern catalytic performance for MoO3-promoted Rh. We use atomic layer deposition to modify Rh nanoparticles with monolayer-precise amounts of MoO3, with a high degree of control over the structure of the catalyst. Through in situ X-ray absorption spectroscopy, we find that the atomic structure of the catalytic surface under reaction conditions consists of Mo-OH species substituted into the surface of the Rh nanoparticles. Using density functional theory calculations, we identify two roles of MoO3: first, the presence of Mo-OH in the catalyst surface enhances CO dissociation and also stabilizes a methanol synthesis pathway not present in the unpromoted catalyst; and second, hydrogen spillover from Mo-OH sites to adsorbed species on the Rh surface enhances hydrogenation rates of reaction intermediates.

Unveiling the Structure Sensitivity for Direct Conversion of Syngas to C2-Oxygenates with a Multicomponent-Promoted Rh Catalyst

Mn and Li promoted Rh catalysts supported on SiO2 with a thin TiO2 layer were synthesized by stepwise incipient wetness impregnation approach. The thin TiO2 layer on the surface of SiO2 was proved to stabilize those small Rh nanoparticles and hinder their agglomeration. The reducibility of Rh on these catalysts depends on Rh particle size as well as the position of manganese oxide, and large Rh nanoparticles with MnO on Rh nanoparticles can be only reduced at an elevated temperature. Catalyst with large Rh particles exhibits a higher CO conversion and higher products selectivity towards long chain hydrocarbons and C2-oxygenates at the expense of decreasing methane formation than a similar catalyst with smaller Rh particles. This was attributed to the synergistic effect of Mn and Li promotion and molar ratio between Rh0 and Rhδ+ sites on the surface of Rh nanoparticles. Moreover, Rh nanoparticles on MnO are proved to be more efficient in promoting hydrogenation of acetaldehyde to ethanol than its counterpart with MnO on Rh nanoparticles. Finally, in order to target high C2-oxygenates selectivity, low reaction temperature together with a low H2/CO ratio in the feed is recommended.Graphic

Operando monitoring of temperature and active species at the single catalyst particle level

The development of improved catalysts requires insights into the relationship between catalytic activity and catalyst structure, including the underlying reaction mechanism. Here, we demonstrate a unique set of catalyst extrudate sensors that allow for the simultaneous detection of local temperature by luminescence thermometry, and of surface species by shell-isolated nanoparticle-enhanced Raman spectroscopy. This sensing approach was applied to the characterization of direct conversion of syngas into hydrocarbons and C2+ oxygenates over supported Rh and RhFe catalysts. Luminescence thermometry demonstrated a mismatch between the set temperature and the local catalyst temperature, with variations up to 40 °C. Furthermore, by investigating the surface species on varying extrudate and catalyst compositions, we identified tilted carbonyl species on the Rh/SiO2 interface that are probable precursors for the hydrogen-assisted CO dissociation. The implementation of extrudate catalyst sensors as a characterization tool provides a unique approach towards the further understanding of the relevant parameters in catalysis. Multi-modal approaches to simultaneously characterize different aspects of a reaction in situ are not readily accessible. Here, catalyst extrudates equipped with both luminescence thermometry and Raman spectroscopy sensors are introduced, providing an in-depth picture for the conversion of syngas on a supported rhodium catalyst.

Design and synthesis of spherical-platelike ternary copper-cobalt-manganese catalysts for direct conversion of syngas to ethanol and higher alcohols

Novel CuCoMn ternary catalyst with a “spherical-platelike” (CuMn-Co) nanosized particles structure was designed and successfully performed in ethanol and higher alcohols (HA) production via heterogeneous CO hydrogenation. The “spherical-platelike” CuCoMn catalyst, achieved through a simple co-precipitation (CP) route followed by a calcination-reduction process, contained a CuMn-rich sphere structure and a Co-dominated nanosheet. The catalyst demonstrated a total alcohols selectivity of 46.2%, and the fraction of ethanol reached up to 45.4% among the total alcohols products, which is superior to the classical modified CuCo-based catalysts. The outstanding catalytic performance was attributed to the unique “spherical-platelike” structure, which altered the surface Cu+/Cu0 distribution and the dispersion of Co species. As revealed by in situ XRD, H2-TPR, in situ XPS, HAADF-STEM and in situ DRIFT spectra techniques, a strong electronic and geometric interaction between Cu and Mn species in optimized CuCoMn catalyst modified the chemical states of Cu species to present a higher proportion of surface Cu+/(Cu0 + Cu+) and, especially, enhanced the linear CO adsorption on Cu+ active sites, which provided a higher probability of CO insertion, and eventually contributed to promotion of catalytic performance. In addition, a higher probability of bridge CO adsorption on metallic Co was also observed over the CuCoMn catalyst, which was beneficial for the formation of CHx intermediates. It is concluded that a synergistic effect between Cu+ and Co species, promoted by the presence of manganese species, was responsible for CO hydrogenation to produce ethanol.