•Almost complete one-pass conversion of CO2 into methanol under optimized process conditions.•The methanol stream rich in water and H2 can be directly used for further transformation.•One-step ...transformation of CO2 into dimethyl ether with >86% selectivity maintaining the high CO2 conversion.•Selective formation of alkane or alkene obtained by varying pressure of the secondary reactor with H-ZSM-5.•A commercial methanol synthesis catalyst delivers the highest yield of 7.7gMeOHgcat-1h-1 with good CO2 conversion and methanol selectivity.
The rising concerns about global warming and imbalance in the carbon cycle urge rapid development of efficient CO2 conversion processes. We report an exceptionally productive process for the synthesis of methanol via continuous catalytic hydrogenation of CO2 under high-pressure conditions (up to 360bar) over co-precipitated Cu/ZnO/Al2O3 catalysts. Outstanding one-pass CO2 conversion (>95%) and methanol selectivity (>98%) were achieved under an optimized range of reaction conditions. At a very high GHSV of 182,000h−1 over a commercial methanol synthesis catalyst, the process delivers 7.7gMeOHgcat-1h-1, which is by far the highest yield value reported to date, at the expense of lowered CO2 conversion (65.8%) and methanol selectivity (77.3%). Using a mixed bed consisting of the Cu/ZnO/Al2O3 and H-ZSM-5 catalysts, one-step conversion of CO2 into dimethyl ether with remarkable selectivity (89%) was attained at the equivalent or higher CO2 conversion level. Furthermore, we demonstrate that the effluent stream of methanol, rich in H2 and water, from the methanol synthesis reactor can be directly fed to a reactor containing the H-ZSM-5 catalyst for selective production of alkane (85%) or alkene (42%), depending on the operating pressure of the secondary reactor.
Methanol and carbon dioxide are continuously and efficiently converted to dimethyl carbonate (DMC) over a CeO2 catalyst using 2-cyanopyridine as a recyclable dehydrating agent in a fixed bed reactor. ...The process was operated over a wide range of pressure (1–300 bar) by feeding CO2 and the stoichiometric amount of methanol and 2-cyanopyridine mixture into the reactor. The study shows a successful demonstration of direct DMC synthesis mediated by a dehydrating agent with outstanding methanol conversion (>95%) and dimethyl carbonate selectivity (>99%) under optimized conditions. Remarkably higher reaction rates were achieved compared to those in batch operation.
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•High-pressure advantages are examined for stoichiometric CO2 hydrogenation to methanol.•Reaction temperature and space velocity are systematically investigated under high-pressure ...conditions (46–442bar).•High-pressure facilitates the reaction to enter thermodynamically controlled regime with excellent catalytic performance.•Strong interplay between kinetics and thermodynamics determines catalytic performance.•A remarkable methanol yield of 15.3gMeOHgcat−1h−1 can be achieved at 442bar at high space velocity.
Interplay between three important reaction parameters (pressure, temperature, and space velocity) in stoichiometric hydrogenation of carbon dioxide (CO2:H2=1:3) was systematically investigated using a commercial Cu/ZnO/Al2O3 catalyst. Their impacts on reaction performance and important ranges of process conditions toward full one-pass conversion of CO2 to methanol at high yield were rationalized based on the kinetics and thermodynamics of the reaction. Under high-pressure condition above a threshold temperature, the reaction overcomes kinetic control, entering thermodynamically controlled regime. Ca. 90% CO2 conversion and >95% methanol selectivity were achieved with a very good yield (0.9–2.4gMeOHgcat−1h−1) at 442bar. Such high-pressure condition induces the formation of highly dense phase and consequent mass transfer limitation. When this limitation is overcome, the advantage of high-pressure conditions can be fully exploited and weight time yield as high as 15.3gMeOHgcat−1h−1 could be achieved at 442bar. Remarkable advantages of high-pressure conditions in terms of reaction kinetics, thermodynamics, and phase behavior in the aim to achieve better methanol yield are discussed.
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•CO2 capture and catalytic methanation can be performed in one process.•The process is based on isothermal unsteady-state operation.•K- and La-promoted Ni/ZrO2 show enhanced CO2 ...capture and conversion.•La promotes both CO2 capture and reduction in a wide temperature range.•Different promoters result in different active surface species and reaction mechanisms.
The recently demonstrated concept to combine CO2 capture and utilization in one process using isothermal unsteady-state operation, namely CO2 capture and reduction (CCR), was applied for CO2 methanation using unpromoted and K- or La-promoted Ni/ZrO2 catalysts. Both K and La promoters significantly improve CO2 capture capacity and also the selectivity of CO2 conversion to methane. The K-promoted catalyst (Ni-K/ZrO2) captures a larger amount of CO2 at high temperature but the capture capacity drops at low temperature due to incomplete catalyst regeneration during the cyclic unsteady-state reaction condition. In contrast, the La-promoted catalyst (Ni-La/ZrO2) shows temperature-independent CO2 capture capacity and rapid reduction of captured CO2, thus leading to stable CCR performance. The nature of the active sites and mechanistic details were gained by TPR, reductive CO2-TPD and space- and time-resolved operando DRIFTS, holistically elucidating the effects of the promoters and their impacts on CCR activity.
Methanol synthesis by CO2 hydrogenation is a key process in a methanol‐based economy. This reaction is catalyzed by supported copper nanoparticles and displays strong support or promoter effects. ...Zirconia is known to enhance both the methanol production rate and the selectivity. Nevertheless, the origin of this observation and the reaction mechanisms associated with the conversion of CO2 to methanol still remain unknown. A mechanistic study of the hydrogenation of CO2 on Cu/ZrO2 is presented. Using kinetics, in situ IR and NMR spectroscopies, and isotopic labeling strategies, surface intermediates evolved during CO2 hydrogenation were observed at different pressures. Combined with DFT calculations, it is shown that a formate species is the reaction intermediate and that the zirconia/copper interface is crucial for the conversion of this intermediate to methanol.
Interface matters: A combination of solid‐state NMR and IR spectroscopies with DFT calculations unravels the nature of reaction intermediates in the hydrogenation of CO2 to methanol on Cu/ZrO2 catalysts, pointing out the specific role of the metal–support interface in the formation and conversion of formate into methoxy species.
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•Visually looking into CeO2 catalyst in DMC synthesis from CO2 & methanol (≤30bar).•Using an organic dehydrating agent, thus a complex three-phase boundary was formed.•Rapid color ...change of the catalyst with slower deactivation.•Strong binding of 2-picolinamide over CeO2 causes the catalyst deactivation.•Mild temperature (300°C) calcination can reactivate the catalyst completely.
The high efficiency of 2-cyanopyridine (2-CP) as dehydrating agent in the direct dimethyl carbonate (DMC) synthesis from CO2 and methanol over CeO2 catalysts has been recently demonstrated with excellent DMC yields (>90%) in both batch and continuous operations. The catalytic reaction is expected to involve a complex three-phase boundary due to the high boiling points of 2-CP and also 2-picolinamide (2-PA) formed by hydration of 2-CP. The catalyst is also known to deactivate noticeably in the time-scale of days during the continuous operation. The aim of this work is to gain visual information of the catalyst under operando conditions by means of an optically transparent, fused quartz reactor to understand the behavior of catalyst deactivation and to learn about the phase behavior of the reaction mixture. The catalytic tests using the fused quartz reactor could reproduce the results observed in a common stainless steel reactor, and the effects of reaction temperature and pressure (up to 30bar) were examined in detail to show that there is an optimum condition (30bar, 120°C) to achieve the best catalytic performance. The visual inspection was further combined with IR and Raman spectroscopic studies to identify the origin of the catalyst deactivation and establish an efficient catalyst reactivation protocol. Interestingly, not coke but 2-PA surface adsorption was found responsible for the catalyst deactivation. The operando visual inspection evidenced that the surface of the CeO2 catalyst particles is constantly wet and also coated with some crystallites (likely of 2-PA) during the reaction, whereas the bulk of the CeO2 particle is still accessible for the reactants and thus available for the reaction.
CO2 Activation over Catalytic Surfaces Álvarez, Andrea; Borges, Marta; Corral‐Pérez, Juan José ...
ChemPhysChem,
November 17, 2017, Letnik:
18, Številka:
22
Journal Article
Recenzirano
Odprti dostop
This article describes the main strategies to activate and convert carbon dioxide (CO2) into valuable chemicals over catalytic surfaces. Coherent elements such as common intermediates are identified ...in the different strategies and concisely discussed based on the reactivity of CO2 with the aim to understand the decisive factors for selective and efficient CO2 conversion.
Activation and transformation of CO2 are enabled by catalytic surfaces with various forms of energetic inputs inducing characteristic reactivities. The authors summarize the physicochemical properties of CO2 and its activated forms. They also discuss key elements to be considered for efficient CO2 activation and its selective transformation to targeted products.
Iridium based materials are state-of-the-art anode catalysts for polymer electrolyte membrane (PEM) water electrolysis thanks to their unmatched stability and performance in the acidic environment of ...common PEMs like Nafion registered . However, their cost restricts their use in large-scale operations. To improve their utilization, identifying a synthesis method of nano-structured iridium oxide with a high active surface area, possibly in a supported form, is of great importance. For this aim, we developed a one-step and cost-effective solution combustion synthesis (SCS) method to prepare nano-structured IrO2 and IrO2-based materials suitable for PEM electrolysis. Among various materials prepared, the iridium oxide incorporated and dispersed in amorphous alumina showed a high surface area (131 m2 g-1) and the current density of 1.78 A cm-2 at 1.8 V which is comparable to the performance of the state-of-the-art commercial membrane electrode assembly (MEA) made of IrRuOx (1.8 A cm-2 at 1.8 V) under PEM water electrolysis. Importantly, the dispersion of the material in the catalyst ink used for the preparation of the MEA was significantly superior compared to that of commercial IrO2 nanoparticles and the amount of the precious metal in the catalyst made by SCS could be reduced by 45 wt% compared to that in the commercial MEA.
A desirable process for realizing a low-carbon society is the direct conversion of dilute CO2 from flue gases or air into highly concentrated hydrocarbons without a need for separate CO2 capture and ...purification processes. In this study, we investigated the performance of integrated CO2 capture and reduction to CH4 over Ni-based dual-functional catalysts promoted with Na, K, and Ca. Ni/Na-γ-Al2O3 exhibited the highest activity for integrated CO2 (5% CO2) capture and reduction, achieving high CO2 conversion (>96%) and CH4 selectivity (>93%). In addition, very low-concentration CO2 (100 ppm CO2) was successfully converted to 11.5% CH4 at the peak point (>1000 times higher concentration than that of the supplied CO2) over Ni/Na-γ-Al2O3. The Ni-based dual-functional catalyst exhibited a high CO2 conversion exceeding 90%, even when 20% O2 was present during CO2 capture. Furthermore, an increased operation pressure had positive impacts on both CO2 capture and CH4 formation, and these advantageous effects were also observed when CO2 concentration was at the level of atmospheric CO2 (100–400 ppm). As the pressure increased from 0.1 to 0.9 MPa, CH4 production capacity with 400 ppm CO2 was enhanced from 111 to 160 μmol gcat –1. This approach in combination with the efficient catalyst shows encouraging potential for CO2 utilization, enabling direct air capture-conversion to value-added chemicals.
Modulation excitation spectroscopy (MES) allows sensitive and selective detection and monitoring of the dynamic behavior of species directly involved in a reaction. The method, combined with proper
...in situ spectroscopy, is powerful for elucidating complex systems and noisy data as often encountered in heterogeneous catalytic reactions at solid–liquid and solid–gas interfaces under working conditions. The theoretical principle and actual data processing of MES are explained in detail. Periodic perturbation of the system by an external parameter, such as concentration and temperature, is utilized as stimulation in MES. The influence of stimulation shape upon response analysis is explained. Furthermore, an illustrative example of MES, enantioselective hydrogenation at a solid-liquid interface, is presented.
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