Physico-Chemical Modifications Affecting the Activity and Stability of Cu-Based Hybrid Catalysts during the Direct Hydrogenation of Carbon Dioxide into Dimethyl-Ether

The direct hydrogenation of CO2 into dimethyl-ether (DME) has been studied in the presence of ferrierite-based CuZnZr hybrid catalysts. The samples were synthetized with three different techniques and two oxides/zeolite mass ratios. All the samples (calcined and spent) were properly characterized with different physico-chemical techniques for determining the textural and morphological nature of the catalytic surface. The experimental campaign was carried out in a fixed bed reactor at 2.5 MPa and stoichiometric H2/CO2 molar ratio, by varying both the reaction temperature (200–300 °C) and the spatial velocity (6.7–20.0 NL∙gcat−1∙h−1). Activity tests evidenced a superior activity of catalysts at a higher oxides/zeolite weight ratio, with a maximum DME yield as high as 4.5% (58.9 mgDME∙gcat−1∙h−1) exhibited by the sample prepared by gel-oxalate coprecipitation. At lower oxide/zeolite mass ratios, the catalysts prepared by impregnation and coprecipitation exhibited comparable DME productivity, whereas the physically mixed sample showed a high activity in CO2 hydrogenation but a low selectivity toward methanol and DME, ascribed to a minor synergy between the metal-oxide sites and the acid sites of the zeolite. Durability tests highlighted a progressive loss in activity with time on stream, mainly associated to the detrimental modifications under the adopted experimental conditions

Silica-Related Catalysts for CO2 Transformation into Methanol and Dimethyl Ether

The climate situation that the planet is experiencing, mainly due to the emission of greenhouse gases, poses great challenges to mitigate it. Since CO2 is the most abundant greenhouse gas, it is essential to reduce its emissions or, failing that, to use it to obtain chemicals of industrial interest. In recent years, much research have focused on the use of CO2 to obtain methanol, which is a raw material for the synthesis of several important chemicals, and dimethyl ether, which is advertised as the cleanest and highest eciency diesel substitute fuel. Given that the bibliography on these catalytic reactions is already beginning to be extensive, and due to the great variety of catalysts studied by the dierent research groups, this review aims to expose the most important catalytic characteristics to take into account in the design of silica-based catalysts for the conversion of carbon dioxide to methanol and dimethyl ether

The impact of zeolite pore structure on the catalytic behavior of CuZnAl/zeolite hybrid catalysts for the direct DME synthesis

[EN] In this work, the influence of the pore structure of 10-ring zeolites used as the methanol dehydration func-tion in CuZnAl(CZA)/zeolite hybrid catalysts was studied for the direct dimethyl ether (DME) synthesis. Tothis purpose, six different 10-ring H-zeolites (ZSM-5, FER, IM-5, TNU-9, MCM-22, ITQ-2) with alike bulkSi/Al ratios (in the 9 14 range) were employed. Additionally, the effect of crystallite size (for ZSM-5) andselective surface dealumination by treatment with oxalic acid (for MCM-22) was also investigated. Whilethe initial activity of the zeolites for methanol dehydration was driven by the concentration of strongBrønsted acid sites, the extent of decay was dictated by the pore structure, which determined the amountand nature of the formed carbon species. When evaluated for direct DME synthesis under methanolsynthesis-controlled conditions, all CZA/zeolite hybrid catalysts (prepared by grinding, CZA:zeolite massratio of 2:1) experienced a decline of CO conversion (and DME yield) with time-on-stream (TOS) due toa gradual loss of the methanol synthesis activity of the Cu-based component. Interestingly, the stabilitywith TOS was the lowest for the hybrid catalysts comprising zeolites with large external surface areas(Sext) such as ITQ-2 and MCM-22. Moreover, for zeolites with similar Sext, the deactivation extent of thehybrid catalysts increased with the concentration of surface Al species (from XPS) in the zeolite. Thus,the delaminated ITQ-2 zeolite (Si/Alsurf= 10.6, Sext= 324 m2/g) produced the less stable hybrid while thatcomprising zeolite TNU-9 (Si/Alsurf= 17.9, Sext= 12 m2/g) displayed the highest stability during the syngas-to-DME experiments. These results suggest that the deterioration of the methanol synthesis activity ofthe CZA catalyst in the hybrid catalysts prepared by grinding is produced by detrimental interactionsbetween zeolitic Al species and Cu sites at the surface-contact between zeolite and CZA particleFinancial support by the Comision Interministerial de Ciencia y Tecnologia (CICYT) of Spain through the Project CTQ2010-17988/PPQ is gratefully acknowledged. A. Garcia-Trenco thanks the Ministerio de Economia y Competitividad (former Ministerio de Ciencia e Innovacion) of Spain for a predoctoral (FPI) scholarship.García Trenco, A.; Valencia Valencia, S.; Martinez Feliu, A. (2013). The impact of zeolite pore structure on the catalytic behavior of CuZnAl/zeolite hybrid catalysts for the direct DME synthesis. Applied Catalysis A General. 468:102-111. doi:10.1016/j.apcata.2013.08.038S10211146

Preparation And Characterization Of γ-Al2O3 Doped With Selected Elements and Correlating Surface Properties with the Catalytic Activity in Methanol Dehydration to Dimethyl Ether

The increasing demand for energy is associated with challenges that include environmental concerns and limited reserves. Dimethyl ether, DME, which can be obtained from different feedstocks, including natural gas and biomass, has recently been recognized as an ultra-clean environmentally friendly fuel due to the fact that it possesses unique characteristics that make it an efficient alternative fuel for diesel fuel engines. In addition, DME is an industrially important intermediate for a variety of chemicals. A promising potential route for dimethyl ether production is catalytic dehydration of methanol over solid acid catalysts. Therefore, exploring new solid acid catalytic materials and understanding the mechanistic steps of methanol adsorption on their surfaces is of great importance for developing modified efficient catalysts for this process. In the present work, solid acid catalysts based on modified γ-Al2O3 were prepared by the sol-gel method and were studied as catalysts for methanol to dimethyl ether conversion. The main focus of the present thesis is to investigate the effect of selected metal dopants on the surface chemical properties of γ-Al2O3, especially acid-base characteristics, and to correlate these effects with their catalytic activity in dehydration of methanol to DME. The selected dopants include transition metal ions with different d-configurations and different oxidation states, such as Ti(IV), V(III), and Ni(II) to elucidate any possible electronic effect on the alumina surface chemical behavior. The prepared catalysts were characterized by various physical and chemical techniques including adsorption of probe molecules, namely ammonia and methanol. The study showed very promising results where doping γ-Al2O3 resulted in significant textural and chemical modifications including an enhanced overall surface acidity. The catalytic activity study showed that the incorporation of certain concentrations of Ti(IV) and Ni(II) ions in the γ-Al2O3 matrix resulted in an enhanced catalytic activity. The catalytic activity of the catalysts was correlated with their textural, chemical, and structural modifications resulting from the presence of the dopant ions In addition, a comparison between the studied alumina-based solids and selected ZSM5 zeolites showed that the acidic character of the OH groups on their surfaces vary and therefore, different routes of methanol adsorption and dehydration were proposed for the two types of materials. Methanol adsorption and dehydration were proposed to be associative on the surface of ZSM5 zeolites, where Brønsted acid sites played a key role in adsorption and dehydration reaction. On the other hand, dissociative adsorption on Lewis acid-base pairs dominates the interactions with γ-Al2O3-based solids

Hydrogenation of Carbon Dioxide to Dimethyl Ether on CuO–ZnO/ZSM-5 Catalysts:Comparison of Powder and Electrospun Structures

The promising direct dimethyl ether (DME) production through CO2 hydrogenation was systematically analyzed in this research by synthesizing, characterizing, and testing several catalytic structures. In doing so, various combinations of precipitation and impregnation of copper- and zinc-oxides (CuO–ZnO) over a ZSM-5 zeolite structure were applied to synthesize the hybrid catalysts capable of hydrogenating carbon dioxide to methanol and dehydrating it to DME. The resulting catalytic structures, including the co-precipitated, sequentially precipitated, and sequentially impregnated CuO–ZnO/ZSM-5 catalysts, were prepared in the form of particle and electrospun fibers with distinguished chemical and structural features. They were then characterized using XRD, BET, XPS, ICP, TGA, SEM, and FIB-SEM/EDS analyses. Their catalytic performances were also tested and analyzed in light of their observed characteristics. It was observed that it is crucial to establish relatively small-size and well-distributed zeolite crystals across a hybrid catalytic structure to secure a distinguished DME selectivity and yield. This approach, along with other observed behaviors and the involved phenomena like catalyst particles and fibers, clusters of catalyst particles, or the whole catalytic bed, were analyzed and explained. In particular, the desired characteristics of a CuO–ZnO/ZSM-5 hybrid catalyst, synthesized in a single-pot processing of the precursors of all involved catalytically active elements, were found to be promising in guiding the future efforts in tailoring an efficient catalyst for this system.</p

Advanced zeolite and ordered mesoporous silica-based catalysts for the conversion of CO2 to chemicals and fuels

[EN] For many years, capturing, storing or sequestering CO2 from concentrated emission sources or from air has been a powerful technique for reducing atmospheric CO2. Moreover, the use of CO2 as a C1 building block to mitigate CO2 emissions and, at the same time, produce sustainable chemicals or fuels is a challenging and promising alternative to meet global demand for chemicals and energy. Hence, the chemical incorporation and conversion of CO2 into valuable chemicals has received much attention in the last decade, since CO2 is an abundant, inexpensive, nontoxic, nonflammable, and renewable one-carbon building block. Nevertheless, CO2 is the most oxidized form of carbon, thermodynamically the most stable form and kinetically inert. Consequently, the chemical conversion of CO2 requires highly reactive, rich-energy substrates, highly stable products to be formed or harder reaction conditions. The use of catalysts constitutes an important tool in the development of sustainable chemistry, since catalysts increase the rate of the reaction without modifying the overall standard Gibbs energy in the reaction. Therefore, special attention has been paid to catalysis, and in particular to heterogeneous catalysis because of its environmentally friendly and recyclable nature attributed to simple separation and recovery, as well as its applicability to continuous reactor operations. Focusing on heterogeneous catalysts, we decided to center on zeolite and ordered mesoporous materials due to their high thermal and chemical stability and versatility, which make them good candidates for the design and development of catalysts for CO2 conversion. In the present review, we analyze the state of the art in the last 25 years and the potential opportunities for using zeolite and OMS (ordered mesoporous silica) based materials to convert CO2 into valuable chemicals essential for our daily lives and fuels, and to pave the way towards reducing carbon footprint. In this review, we have compiled, to the best of our knowledge, the different reactions involving catalysts based on zeolites and OMS to convert CO2 into cyclic and dialkyl carbonates, acyclic carbamates, 2-oxazolidones, carboxylic acids, methanol, dimethylether, methane, higher alcohols (C2+OH), C2+ (gasoline, olefins and aromatics), syngas (RWGS, dry reforming of methane and alcohols), olefins (oxidative dehydrogenation of alkanes) and simple fuels by photoreduction. The use of advanced zeolite and OMS-based materials, and the development of new processes and technologies should provide a new impulse to boost the conversion of CO2 into chemicals and fuels.Velty, A.; Corma Canós, A. (2023). Advanced zeolite and ordered mesoporous silica-based catalysts for the conversion of CO2 to chemicals and fuels. Chemical Society Reviews. 52(5):1773-1946. https://doi.org/10.1039/d2cs00456a1773194652

Nanoporous Materials and Their Applications

This book is a special collection of articles dedicated to the preparation and characterization of nanoporous materials, such as zeolitic-type materials, mesoporous silica (SBA-15, MCM-41, and KIT-6), mesoporous metallic oxides, metal–organic framework structures (MOFs), and pillared clays, and their applications in adsorption, catalysis, and separation processes. This book presents a global vision of researchers from international universities, research centers, and industries working with nanoporous materials and shares the latest results on the synthesis and characterization of such materials, which have given rise to the special interest in their applications in basic and industrial processes

Design of novel well-defined organorhenium heterogeneous catalyst for unsaturated fatty acid derivatives self-metathesis

La formation des liaisons C-C est parmi les cibles les plus élevés de la science et de la technologie de la catalyse. Dans ce cadre, la réaction de métathèse catalytique a gagné une importance considérable en raison de l'efficacité du processus de transformation. Par conséquent, un grand progrès a été réalisé dans ce domaine avec le développement de plusieurs catalyseurs homogènes et hétérogènes, ainsi que les différentes approches de métathèse. Cette formule a permis une conception plus facile et plus durable de diverses stratégies de synthèse dans différents domaines, y compris la synthèse organique, la science des polymères, etc. Cependant, le développement des catalyseurs de métathèse robustes pour les applications à grande échelle est encore une tâche difficile. Tenant compte de cela, les résultats de recherche présentés dans cette thèse de doctorat se concentrent sur la synthèse d'un nouveau catalyseur hétérogène de métathèse. Par conséquent, le méthyltrioxorhénium (MTO) a été supporté sur différents matériaux à base d'alumine. La performance des catalyseurs synthétisés a été étudié par l'auto-métathèse de l'oléate de méthyle, choisi comme substrat modèle; volumineux et fonctionnalisé, afin d'évaluer la tolérance des espèces actives aux groupements fonctionnels, ainsi que d'évaluer sa diffusion à l'intérieur des canaux mésoporeux. Tout d'abord, des supports très organisés à base alumine mésoporeux organisée modifiée avec le chlorure de zinc (ZnCl2-AMO) ont été préparés avec succès grâce à un procédé sol-gel puis une imprégnation post-synthèse. Le MTO supporté sur ces supports catalytiques est très actif pour l'auto-métathèse de l'oléate de méthyle, avec des vitesses de réaction plus élevées et une meilleure sélectivité par rapport aux catalyseurs à base d'alumine classiques. Cette amélioration est attribuée à des meilleurs phénomènes de transfert de masse à l'intérieur du réseau mésoporeux organisé. Ensuite, nous avons développé une voie de synthèse efficace en une seule étape pour la préparation des matériaux ZnCl2-AMO. Cette approche a permis l'accès à des supports ZnCl2-AMO très ordonnés avec de meilleurs rendements de synthèse ainsi que de meilleures propriétés physiques et de surface. En outre, ces fonctionnalités améliorées ont permis aux catalyseurs à base de MTO supportés sur ces matériaux préparés en une seule étape de manifester une meilleure performance catalytique par rapport à celle de ZnCl2-AMO préparé par le processus en plusieurs étapes. Toutefois, des études spectroscopiques ont révélé la formation d'espèces actives semblables sur la surface pour tous les supports catalytiques préparées. Ces caractérisations nous ont guidés pour étudier et proposer un mécanisme complet pour les voies de formation des produits de métathèse, ainsi que le cycle catalytique de métathèse, démontrant l'effet d'encombrement stérique sur l'interface de catalyseurs qui contrôle la sélectivité de la réaction. La synthèse des catalyseurs de métathèse MTO/ZnCl2-AMO nous a permis d'effectuer efficacement les transformations de métathèse utilisant des matières premières renouvelables (par exemple des acides gras estérifiés provenant des huiles végétales), offrant un accès à une variété de monomères fonctionnalisés, qui pourraient éventuellement être utilisés pour d'autres transformations telles que la synthèse des bio-polymères à valeur ajoutée à base (par exemple, les bioplastiques, biosurfactants).Sustainable C-C bond forming reactions have been among the highest target of catalysis science and technology. In this scope, metathesis reaction has been gaining enormous attention due to the efficiency of the transformation process. Therefore, a great progress has been made in this area by developing several homogeneous and heterogeneous catalysts as well as distinct metathesis reaction approaches. This allows an easier and more sustainable design for various synthesis strategies in different fields including organic synthesis, polymer science, etc. However, the development of robust metathesis catalysts for large scale applications is still a challenging task. Taking this into account, this research presented in this doctoral dissertation is focusing on the synthesis of new heterogeneous metathesis catalysts. Therefore, methyltrioxorhenium (MTO) was supported on various alumina-based materials. The synthesized catalysts' performance was studied though methyl oleate self-metathesis, chosen as a model bulky functionalized substrate, in order to evaluate the active species tolerance to functional groups as well as to evaluate its diffusion inside the mesoporous channels. First, highly organized ZnCl2-modified OMA supports were successfully prepared through a sol-gel method followed by a post-synthesis modification via wet-impregnation process. MTO supported on these catalytic supports were found o be highly active for methyl oleate self-metathesis, displaying higher reaction rate and products selectivity compared to the conventional wormhole-like alumina-based catalysts. This improvement is ascribed to enhanced mass transfer phenomena inside the organized mesoporous network. Afterwards, we have developed efficient one-pot synthesis route ZnCl2-modified OMA supports. Interestingly, this approaches allowed access to numerous highly ordered ZnCl2-modified OMA supports with better synthesis yields and improved textural and surface properties. Moreover, these enhanced features allowed the MTO-based catalyst supported on these one-step prepared materials to exhibit higher metathesis reaction performance compared to ZnCl2-modified OMA supports prepared via the two-steps processes. However, spectroscopic investigations revealed the formation of similar surface active species for all the prepared catalytic supports. These characterizations guided us to study and propose a comprehensive mechanism of metathesis products formation pathways as well as the metathesis catalytic cycle, demonstrating the steric hindrance effect on the catalysts interface that governed the reaction selectivity. The synthesis of the 3 wt.% MTO/ZnCl2-OMA catalysts allowed us to efficiently perform metathesis reaction using renewable feedstock (e.g. fatty acid esters derived from vegetable oils), offering access to a variety of functionalized monomers which could be used for further transformations such as the synthesis of value-added bio-based polymers (e.g. bioplastics, biosurfactants)