Hydrogénation du CO2 en produits C2+ en une seule étape sur des catalyseurs supportés sur TiO2

Les émissions humaines de CO2 provenant de la production d'énergie à partir de combustibles fossiles représentent la plupart des émissions mondiales de gaz à effet de serre, jouant un rôle central dans le changement climatique. Le captage et l'utilisation du carbone (CCU) représentent une stratégie prometteuse pour atteindre les objectifs énergétiques et climatiques mondiaux. Ce travail de recherche se concentre sur l'hydrogénation en une étape du CO2 en produits C2+ sur des catalyseurs supportés sur TiO2. Tout d'abord, l'état de l'art de l'hydrogénation en une seule étape, du CO2 en hydrocarbures à longue chaîne sur des catalyseurs à base de Co supportés par des oxydes, est présenté dans le Chapitre 1. Les aspects mécanistiques sont discutés en relation avec les limitations thermodynamiques et cinétiques. Les principaux paramètres à prendre en considération pour augmenter l'activité et la sélectivité vis-à-vis des produits C2+ sont détaillés. Ensuite, les conditions expérimentales utilisées pour la caractérisation des catalyseurs et les tests catalytiques CO2-FTS (synthèse CO2-Fischer Tropsch) sont présentées dans le Chapitre 2. Le Chapitre 3 présente la préparation en une étape de nouveaux supports à base de TiO2, riches en lacunes d'oxygène et en promoteurs (Na, B), pour assurer une bonne activation du CO2 et la formation d’une interface métal-support. Les catalyseurs à base de Co préparés sur de tels supports modifiés surpassent ceux préparés sur du TiO2-P25 commercial en termes de STY, C2+ et C5+ (YC2+, YC5+). En effet, la présence de promoteurs peut favoriser la formation de défauts de surface et de SMSI, améliore l'adsorption du CO2 et diminue l'activation de H2, entraînant un rapport XH2/XCO2 plus faible, qui à son tour favorise la croissance de chaîne. Le Chapitre 4 étudie l'utilisation du Pd comme co-catalyseur pour augmenter les performances des catalyseurs à base de Co pour la CO2-FTS. Deux systèmes sont étudiés : des catalyseurs bimétalliques et des mélanges de catalyseurs monométalliques. La séparation des deux phases métalliques sur deux supports différents profite fortement aux STY, YC2+ et YC5+. Enfin, le Chapitre 5 étudie la préparation de catalyseurs à base de Co et CoFe promus par des ions alcalins (Na, K) sur des supports modifiés pour promouvoir davantage la sélectivité en C2+ et C5+ durant la CO2-FTS. L'ajout de Fe à la phase active de Co renforce l'adsorption du CO2, favorisant ainsi la RWGS et diminuant la formation de CH4. En outre, la promotion alcaline augmente encore l'adsorption du CO2 et inhibe l'activation de H2, améliorant considérablement la sélectivité envers les produits désirés CO et C2+, et limitant la méthanation sur les catalyseurs Co et CoFe. Dans l'ensemble, la promotion alcaline de la phase métallique diminue significativement la méthanation et favorise la RWGS, mais diminue également l'activité du catalyseur par rapport aux catalyseurs Co non promus. En conséquence, les catalyseurs activés par les alcalins sont facilement surpassés par les catalyseurs Co non activés préparés sur les mêmes supports, en termes de rendements STY, C2+ et C5+.Anthropogenic CO2 emissions from fossil fuels-based energy generation account for most of the global greenhouse gas emissions, playing a central role in climate change. Carbon capture and utilization (CCU) represents a promising strategy to meet the global energy and climate goals. This research work focuses on the one-step CO2 hydrogenation to C2+ products over TiO2- supported catalysts. The state-of-the-art towards the single-step hydrogenation of CO2 to long-chain hydrocarbons over oxide-supported Co-based catalysts is presented in Chapter 1. Mechanistic aspects are discussed in relation to thermodynamic and kinetic limitations. The main parameters that must be taken into consideration to increase the activity and the selectivity towards C2+ products are discussed in detail. The experimental conditions employed for catalyst characterization and for CO2-FTS (CO2-Fischer Tropsch synthesis) catalytic tests are provided in Chapter 2. Chapter 3 presents the one-step preparation of new TiO2-based supports, rich in oxygen vacancies and promoters (Na, B), to ensure proper CO2 activation and metal-support interface formation. Co-based catalysts prepared on such modified supports outperform the ones prepared on commercial TiO2-P25 in terms of STY, C2+ and C5+ yields (YC2+, YC5+). Indeed, the presence of promoters can favor the formation of surface defects and SMSI, enhances CO2 adsorption and decreases H2 activation, resulting in a lower XH2/XCO2 ratio, which in turn favors chain growth. Chapter 4 investigates the utilization of Pd as a co-catalyst to increase the performance of Co-based catalysts for CO2-FTS. Two systems are investigated: bimetallic catalysts and mixtures of monometallic catalysts. The separation of the two metallic phases on two different supports strongly benefits STY, YC2+ and YC5+. Finally, Chapter 5 investigates the preparation of alkali (Na, K) promoted Co- and CoFe-based catalysts on modified supports to further promote C2+ and C5+ selectivity during CO2-FTS. Fe addition to the Co active phase strengthens CO2 adsorption, thus favoring RWGS and decreasing CH4 formation. Besides, alkali promotion further increases CO2 adsorption and inhibits H2 activation, significantly improving the selectivity towards CO and C2+ products, and limiting methanation on both Co and CoFe catalysts. Overall, alkali promotion of the metallic phase significantly decreases methanation and favors RWGS, but also decreases catalyst activity in comparison to the unpromoted Co catalysts. As a consequence, alkali promoted catalysts are easily outperformed by unpromoted Co catalysts prepared on the same supports, in terms of STY, C2+ and C5+ yields

Oxide Supported Cobalt Catalysts for CO 2 Hydrogenation to Hydrocarbons: Recent Progress

International audienceCarbon capture and utilization represents a promising strategy to meet the global energy and climate goals. Under specific conditions, CO2 catalytic hydrogenation with renewable H2 can transform waste CO2 into a chemical feedstock for added-value energy carriers and chemicals. CO2-Fischer–Tropsch synthesis-based-hydrocarbons should contribute to the creation of a circular carbon economy with a significant impact on anthropogenic emission into the atmosphere. This review summarizes the progress achieved toward the single-step hydrogenation of CO2 to long-chain hydrocarbons over oxide-supported Co-based catalysts. Mechanistic aspects are discussed in relation to thermodynamic and kinetic limitations. The main parameters that must be taken into consideration to increase the activity and the selectivity toward compounds of two or more carbon atoms (C2+) are discussed in detail: cobalt active phase, support and metal-support interfaces, and promoters. Finally, particular focus is dedicated to the role of reducible oxide supports and their surface defects on the activation of CO2, as well as on the regulation and evolution of metal-support interactions

CoOx and FeOx supported on ZrO2 for the simultaneous abatement of NOx and N2O with C3H6 in the presence of O2

MeOx/ZrO2 (Me = Co and Fe) catalysts were studied for the simultaneous selective catalytic reduction of NO and N2O in the presence of O2 using C3H6 as reducing agent (SCRsim). To give a better insight in the simultaneous process we investigated the reactions related to SCRsim (SCRN2O, SCRNO, N2O decomposition and C3H6 combustion) as well as the abatements in the absence of O2 (CRsim, CRN2O, CRNO). Catalytic results showed that, in the presence of O2 excess, CoOx/ZrO2 and FeOx/ZrO2 catalysts were scarcely active and unselective for the separate NO and N2O abatements with C3H6 and are ineffective for their simultaneous abatement. Because C3H6 preferentially reacted with O2, NO was poorly reduced and N2O was abated, at a temperature above that of complete C3H6 conversion, via both SCRN2O and decomposition. Conversely, in the absence of O2 in the feed, on both catalysts NO and N2O were efficiently reduced by C3H6, but undesired by-products formed. The activity for SCRsim strongly depended on the C3H6/O2 feeding ratio. With suitable feeding mixture O2 was completely consumed and the residual propene efficiently and simultaneously reduced NO and N2O, with negligible formation of by-products. In hydrothermal conditions both catalysts were slightly and reversibly deactivated. Characterization by XRD, UV–vis DRS and FTIR after catalytic experiments showed that dispersed Co2+ and Fe3+ species were stable on zirconia surface and that no significant segregation phenomena occurred in hydrothermal conditions

Effects of Pd and Co intimacy in Pd-modified Co/TiO 2 catalysts for direct CO 2 hydrogenation to fuels: the closer not the better

International audienceDirect CO2 hydrogenation to liquid fuels is a sustainable approach to decarbonize the future air transport. This reaction proceeds through a tandem pathway involving the reverse water gas shift reaction (RWGSR) to produce CO and the subsequent traditional CO-Fischer–Tropsch synthesis. On Co-based catalysts, the introduction of dopants can improve CO2 activation, enhance the RWGSR activity and decrease the methanation side reaction. We reported that alkali-promoted Co/TiO2 catalysts outperform the unpromoted ones in terms of activity and selectivity towards C2+ (C. Scarfiello, K. Soulantica, S. Cayez, A. Durupt, G. Viau, N. Le Breton, A. K. Boudalis, F. Meunier, G. Clet, M. Barreau, D. Salusso, S. Zafeiratos, D. P. Minh and P. Serp, J. Catal., 2023, 428, 115202). To further improve the catalytic performances, we doped an alkali-promoted Co/TiO2 catalyst with palladium, which is active for the RWGSR and promotes hydrogen spillover. The effect of noble metal location in relation to cobalt, a rarely studied parameter, was investigated by using bimetallic and mixtures of monometallic catalysts. This study demonstrates that whatever the location of Pd and its loading (0.03–0.9 wt%), doping with this metal leads to an improvement in catalytic activity. Furthermore, we show that the proximity between Co and Pd has a pronounced effect on the selectivity of the reaction. The best configuration to achieve higher activity and C2+ selectivity is obtained using mixtures of monometallic catalysts

Preparation of Supported Metal Single-Atom Catalysts on Metal Oxides and Hydroxides

International audienceDuring the last decade, great attention has been devoted to supported metal single-atom catalysts (SACs), due to the maximal metal utilization and the unique reactivity of such materials. The preparation of high-loading, stable isolated metal atoms with the desired local environments remains the main challenge for the industrial application of SACs. In this chapter, we discuss in detail the most representative methods for the preparation of SACs on oxide and hydroxide supports to give to the reader a complete idea of the different steps of each procedure employed and the final stability of the deposited single atoms. Moreover, we focus our attention on the “bottom-up” methods, which represent a facile and universal route for the direct preparation of SACs on metal oxides and hydroxides

Supported catalysts for induction-heated steam reforming of methane

International audienceNi60Co40 nanoparticles supported on γ-Al2O3 capable of simultaneously catalysing the steam reforming reaction of methane and supplying in-situ the heat necessary to activate the reaction by induction heating, have been synthesized and characterized. Energy is remotely and promptly supplied by an alternating radiofrequency magnetic field (induction heating system) to supported nanoparticles that act as dissipating agents by virtue of their ferromagnetic properties. The temperature reached on the Ni–Co based catalyst surface is high enough to obtain good catalytic performances for the steam methane reforming (SMR). By varying synthesis conditions, samples with two different metal loading (17 wt% and 30 wt%) and different particle size distribution were prepared and characterized. Experimental results evidence that the temperature reached on the catalyst surface is related to the metal loading and to the particles size distribution that strongly affect the ability of ferromagnetic nanoparticles to convert the externally applied radio frequency field into heat. Catalyst pellets proved their effectiveness reaching the temperature of 720 °C during SMR reaction and 80% methane conversion

Direct Evidence of Dynamic Metal Support Interactions in Co/TiO2 Catalysts by Near-Ambient Pressure X-ray Photoelectron Spectroscopy

International audienceThe interaction between metal particles and the oxide support, the so-called metal–support interaction, plays a critical role in the performance of heterogenous catalysts. Probing the dynamic evolution of these interactions under reactive gas atmospheres is crucial to comprehending the structure–performance relationship and eventually designing new catalysts with enhanced properties. Cobalt supported on TiO2 (Co/TiO2) is an industrially relevant catalyst applied in Fischer−Tropsch synthesis. Although it is widely acknowledged that Co/TiO2 is restructured during the reaction process, little is known about the impact of the specific gas phase environment at the material’s surface. The combination of soft and hard X-ray photoemission spectroscopies are used to investigate in situ Co particles supported on pure and NaBH4-modified TiO2 under H2, O2, and CO2:H2 gas atmospheres. The combination of soft and hard X-ray photoemission methods, which allows for simultaneous probing of the chemical composition of surface and subsurface layers, is one of the study’s unique features. It is shown that under H2, cobalt particles are encapsulated below a stoichiometric TiO2 layer. This arrangement is preserved under CO2 hydrogenation conditions (i.e., CO2:H2), but changes rapidly upon exposure to O2. The pretreatment of the TiO2 support with NaBH4 affects the surface mobility and prevents TiO2 spillover onto Co particles

Stabilization of Metal Single Atoms on Carbon and TiO2 Supports for CO2 Hydrogenation: The Importance of Regulating Charge Transfer

Supported single atoms constitute excellent models for understanding heterogenous catalysis and have achieved breakthroughs during the past years. How to prevent the aggregation and modulate activity of these species via metal-support interaction should be considered for practical applications. This work presents simple methods involving the creation of carbon- (on carbon nanotube (CNT)) or oxygen-vacancies (on TiO2) to stabilize nickel and ruthenium single atoms. The defective supports and the resulting catalysts are characterized by a large variety of techniques. These analyses show that this strategy is efficient for the preparation of ultra-dispersed catalysts. Comparison of the catalytic performances of these catalysts for the CO2 hydrogenation reaction is also reported. Catalysts supported on TiO2 are more active and sometimes more stable than those deposited on CNT. Nickel catalysts are very selective for the production of CO, and ruthenium catalysts are more selective for the production of methane. Most importantly, it is shown that, in the case of Ru, a direct correlation exists between the electronic density on the metal and the selectivity; electron-rich species produce selectively methane, while electron-deficient species orientate the selectivity toward CO. This work may figure a new way for the synthesis of ultra-dispersed catalysts for various applications.C.R.C. thanks CONICYT for the financial support (Becas de doctorado en el extranjero Becas Chile – no. 72170200). CNRS is acknowledged for financial support (PEPS Energie program 2019). Part of this work was supported by the Agence Nationale de la Recherche (ANR project ANR-19, COMET), which is gratefully acknowledged.Peer reviewe

Modified Co/TiO2 catalysts for CO2 hydrogenation to fuels

International audienceThe direct CO2 conversion to liquid fuels by catalytic hydrogenation (CO2-based Fischer-Tropsch synthesis, FTS), is a sustainable approach to reduce CO2 emissions. This challenging reaction proceeds through tandem catalysis involving reverse water gas shift reaction to produce CO and subsequent traditional CO-FTS. Unmodified Co-based catalysts allow performing the reaction at low temperatures (< 250 °C), albeit producing mainly methane. In this study, we modified a commercial TiO2-P25 support by NaBH4 reduction so as to introduce controlled amounts of promoters and oxygen vacancies (Ov). The modified and unmodified supports were used to prepare Co-based catalysts, which were evaluated for CO2-based FTS at 220-250 °C and 20 bar. The promoted catalysts outperform the one prepared on commercial TiO2 in terms of activity and selectivity towards C5+. Detailed characterizations of the catalysts were performed to decipher the role of promoters. We show that, besides improving CO2 activation and limiting H2 activation, the presence of alkali on the support allows a modulation of hydrogen spillover in the system. The best catalyst in terms of activity and selectivity is the one for which sodium is deposited in sufficient amount to modulate the hydrogen spillover, which allows an optimal surface C/H ratio on cobalt