Frontiers in catalysis最新文献

{"title":"Speciality Grand Challenges in Organometallic Catalysis","authors":"A. Macchioni","doi":"10.3389/fctls.2021.704925","DOIUrl":"https://doi.org/10.3389/fctls.2021.704925","url":null,"abstract":"The interaction between a metal center (M) and a molecular moiety (substrate) is the basis of most catalytic processes. The chemical environment surrounding M can equally be a set of suitable ligands (Coordination Catalysis) (Crabtree, 2014), a set of properly engineered/functionalized ligands anchored onto a solid support (Single-Site Surface Coordination Catalysis) (Copéret et al., 2016), a small cluster of metal atoms as well as a lattice of a material (Heterogeneous Catalysis) (Friend and Xu, 2017), and an enzymatic framework (Biocatalysis) (Schwizer et al., 2018) (Figure 1). If at least one of the M-environment interactions involves an M–R bond (where R C and H), all types of catalysis listed above are by definition Organometallic Catalysis. Furthermore, even in the absence of a M–R bond in the starting molecule/material, the catalytic process may be still defined as of organometallic nature if a M–R fragment forms in any step of the catalytic cycle. These simple considerations clearly indicate the generality and importance of organometallic catalysis. Relevant examples of organometallic catalysis, for each of category illustrated above, are very well known and reported in the textbooks (Drauz et al., 2012; Bochmann, 2014). The success of organometallic catalysis may be ascribed to the capability of a metal to activate lowenergy reaction pathways along which the deformed substrate, stabilized through coordination at a properly designed LnM-fragment, is induced to react in a novel and original way. This explains why some reactions are exclusive of coordination/organometallic complexes. In this respect, a classical example is the reductive elimination, which is one of the fundamental steps of organometallic catalytic cycles (Hartwig, 1998; Chen et al., 2017; Chu and Nikonov, 2018; Wolczanski, 2018). It involves the release of R–X from a (LnMXR) complex, where oxidation state, coordination number and electron of the metal center are reduced by two units. As a result of this propensity to activate a substrate by opening low-energy reaction pathways, the activity of organometallic catalysts can be so high that a <10−6 M active metal concentration is sufficient for carrying out the reaction efficiently: in these cases, catalyst separation and recovery from the products might even be avoided, as it occurs in some industrial polymerization processes (Stürzel et al., 2016). This notwithstanding, catalyst recovery is still necessary is many cases, and typically more easily achievable with heterogenous rather than molecular systems. For this reason, industrially relevant molecular catalysts are often heterogenized onto suitable supports, as mentioned above, leading to heterogeneous catalysts with similar (ideally the same) activity and selectivity to the molecular counterpart, but with the additional advantage of being easy to separate from the reaction environment and recycle (Schwarz et al., 1995; McNamara et al., 2002; Witzke et al., 2020). Selectiv","PeriodicalId":73071,"journal":{"name":"Frontiers in catalysis","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44529299","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Promises and Challenges in Photocatalysis","authors":"Yi‐Jun Xu","doi":"10.3389/fctls.2021.708319","DOIUrl":"https://doi.org/10.3389/fctls.2021.708319","url":null,"abstract":"Photocatalysis is a Promising Technology for Energy and Environmental Protection The current rapid industrial development causes both a heavy reliance on non-renewable energy and a dramatic increase in atmospheric CO2 concentration, which in turn lead to severe energy and environmental crises (Zhang et al., 2015; Li et al., 2019; Li et al., 2020; Li et al., 2021). Therefore, it is urgent to consider how to develop new energy to meet the sustainable development of society. Nowadays, direct solar-to-fuel conversion through green photocatalysis technology has received increasing research interests due to its potential for solar energy utilization and storage to relieve the growing energy demands and greenhouse effect (Habisreutinger et al., 2013). With the expansion and deepening of the research, photocatalysis technology has been extended to many fields, such as energy, health, environment, pollution control and value-added chemicals synthesis (Lu et al., 2020). As a result, the relevance of photocatalysis and human life has been increasing steadily. The grand challenge of photocatalysis today is to further expand the practical application of photocatalytic technology in the industrial field, which requires future research to pay attention to the following aspects:","PeriodicalId":73071,"journal":{"name":"Frontiers in catalysis","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-05-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45485473","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Conversion of Cyclohexane to 6-Hydroxyhexanoic Acid Using Recombinant Pseudomonas taiwanensis in a Stirred-Tank Bioreactor","authors":"L. Bretschneider, Ingeborg Heuschkel, Martin Wegner, M. Lindmeyer, Katja Bühler, R. Karande, B. Bühler","doi":"10.3389/fctls.2021.683248","DOIUrl":"https://doi.org/10.3389/fctls.2021.683248","url":null,"abstract":"6-hydroxyhexanoic acid (6HA) represents a polymer building block for the biodegradable polymer polycaprolactone. Alternatively to energy- and emission-intensive multistep chemical synthesis, it can be synthesized directly from cyclohexane in one step by recombinant Pseudomonas taiwanensis harboring a 4-step enzymatic cascade without the accumulation of any intermediate. In the present work, we performed a physiological characterization of this strain in different growth media and evaluated the resulting whole-cell activities. RB and M9* media led to reduced gluconate accumulation from glucose compared to M9 medium and allowed specific activities up to 37.5 ± 0.4 U gCDW −1 for 6HA synthesis. However, 50% of the specific activity was lost within 1 h in metabolically active resting cells, specifying growing cells, or induced resting cells as favored options for long-term biotransformation. Furthermore, the whole-cell biocatalyst was evaluated in a stirred-tank bioreactor setup with a continuous cyclohexane supply via the gas phase. At cyclohexane feed rates of 0.276 and 1.626 mmol min−1 L−1, whole-cell biotransformation occurred at first-order and zero-order rates, respectively. A final 6HA concentration of 25 mM (3.3 g L−1) and a specific product yield of 0.4 g gCDW −1 were achieved with the higher feed rate. Product inhibition and substrate toxification were identified as critical factors limiting biocatalytic performance. Future research efforts on these factors and the precise adjustment of the cyclohexane feed combined with an in situ product removal strategy are discussed as promising strategies to enhance biocatalyst durability and product titer and thus to enable the development of a sustainable multistep whole-cell process.","PeriodicalId":73071,"journal":{"name":"Frontiers in catalysis","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-05-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47672210","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Grand Challenges in Computational Catalysis","authors":"F. Studt","doi":"10.3389/fctls.2021.658965","DOIUrl":"https://doi.org/10.3389/fctls.2021.658965","url":null,"abstract":"Catalysis is a cornerstone of modern societies as over 90% of processes in the chemical industry are facilitated by catalysts, with the majority requiring a homogeneous or heterogeneous catalyst (Hagen, 2015). Future renewable energy scenarios also rely heavily on the utilization of electro-catalysts, e.g., for the production of clean hydrogen. This shift towards new feedstocks and benign processes entails the development of new generations of catalysts. While the discovery of catalysts has often relied on trial and error in the first half of the last century, the establishment of (design) rules has significantly improved the speed with which new catalysts are being discovered. To this end, the knowledge-based improvement and design of new catalysts is increasingly supported by quantum chemical calculations of reaction mechanisms and kinetic modeling of corresponding reaction rates. In fact, first examples of catalyst design by means of computational screening have already emerged (Nørskov et al., 2009; Medford et al., 2015; Zhao et al., 2019). The extent to which computational modeling becomes a dominant factor in the catalysis community in the 21st century depends crucially on the accuracy with which predictions can be made, but also on the development of a reductionist approach, where the main contributing factors to the performance of a given class of catalysts are reduced to a few selected key parameters that can be used efficiently for computational screening. Perhaps the most challenging issue in computational catalysis is the fact that the rate constant of a reaction step changes drastically with minor changes of the reaction barrier (e.g., for a reaction occurring at 500 K by a factor of about 120 for typical errors of ±20 kJ/mol, or a factor of approximately 3 for an error ±5 kJ/mol, that is commonly referred to as chemical accuracy) and that only approximate methods are computationally feasible for the calculation of enthalpy and entropy contributions of a transition states free energy as the catalytic systems are often large and complex. In all fields discussed here (homogeneous, heterogeneous and electro-catalysis) density functional theory (DFT) has become the workhorse of computational studies as it exhibits the best compromise between accuracy and computational cost. In homogeneous catalysis for example, the enthalpy related to the active site of a transition-metal complex can be determined quite accurately with advanced hybrid functionals (Jiang et al., 2012). However, homogeneous catalysts often exhibit large ligands raising the issue of conformational complexity that is difficult to model. This is often getting even more problematic with solvation and leads to difficulties in determining the active conformational space and corresponding enthalpy and particularly entropy contributions to the free energy (Harvey et al., 2019). A balanced description of interand intramolecular interactions during solvation is similarly challenging","PeriodicalId":73071,"journal":{"name":"Frontiers in catalysis","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46623261","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Tailoring Noble Metal-Free Ti@TiO2 Photocatalyst for Boosting Photothermal Hydrogen Production","authors":"Sara El Hakim, T. Chave, A. Nada, S. Roualdès, S. Nikitenko","doi":"10.3389/fctls.2021.669260","DOIUrl":"https://doi.org/10.3389/fctls.2021.669260","url":null,"abstract":"In this work, we provide new insights into the design of Ti@TiO2 photocatalyst with enhanced photothermal activity in the process of glycerol reforming. Ti@TiO2 nanoparticles have been obtained by sonohydrothermal treatment of titanium metal nanoparticles in pure water. Variation of sonohydrothermal temperature allows controlling nanocrystalline TiO2 shell on Ti0 surface. At 100 < T < 150°C formation of TiO2 NPs occurs mostly by crystallization of Ti(IV) amorphous species and oxidation of titanium suboxide Ti3O presented at the surface of Ti0 nanoparticles. At T > 150°C, TiO2 is also formed by oxidation of Ti0 with overheated water. Kinetic study highlights the importance of TiO2 nanocrystalline shell for H2 generation. Electrochemical impedance spectroscopy points out more efficient electron transfer for Ti@TiO2 nanoparticles in correlation with photocatalytic data. The apparent activation energy, Ea = (25–31) ± 5 kJ·mol−1, assumes that photothermal effect arises from diffusion of glycerol oxidation intermediates or from water dynamics at the surface of catalyst. Under the heating, photocatalytic H2 emission is observed even in pure water.","PeriodicalId":73071,"journal":{"name":"Frontiers in catalysis","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-04-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44840759","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Heterogeneous Catalysis: Enabling a Sustainable Future","authors":"Xijun Hu, A. Yip","doi":"10.3389/fctls.2021.667675","DOIUrl":"https://doi.org/10.3389/fctls.2021.667675","url":null,"abstract":"","PeriodicalId":73071,"journal":{"name":"Frontiers in catalysis","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-03-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44895668","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Grand Challenges in Biocatalysis","authors":"F. Hollmann, R. Fernández-Lafuente","doi":"10.3389/fctls.2021.633893","DOIUrl":"https://doi.org/10.3389/fctls.2021.633893","url":null,"abstract":"Biocatalysis Is an Enabling Technology for Chemical Synthesis Biocatalysis comprises the use of nature’s catalytic repertoire to facilitate chemical reactions (Sheldon and Woodley 2018; Sheldon and Brady 2019). Enzymes catalyze a broad range of chemical transformations, generally under very mild reaction conditions and with high selectivity. These features make enzymes attractive catalysts for industrial chemical transformations, enabling less resource-consuming and waste-generating synthesis routes. Therefore, biocatalysis is already today an important pillar of chemistry and continues gaining relevance in academic research and in industrial application. The last two decades have seen an exponential expansion of biocatalytic tools ranging from new catalysts with tailored properties to new reaction engineering concepts. As a result, the relevance of biocatalysis in the chemical industry has been also increasing steadily. Today’s grand challenge in biocatalysis is to keep this impetus up and further consolidate and expand the toolbox of biocatalysis. A few aspects will be highlighted in the following:","PeriodicalId":73071,"journal":{"name":"Frontiers in catalysis","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47273400","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}