1,721,019 research outputs found
Photocatalytic materials and light-driven continuous processes to remove emerging pharmaceutical pollutants from water and selectively close the carbon cycle
Full text linkPharmaceutical pollutants are increasingly being present in water effluents. Over the past decades, the emergence of advanced oxidation processes has provided a tool to catalytically remove organic pollutants and harmful pathogens. However, researchers have focused too often on increasing the degradation rate of the contaminants, without ensuring as well the formation of more biodegradable products. As a result, by-products that are more toxic than the initial substrate have frequently been formed, limiting the industrial and societal exploitation of this technology. In an attempt to urgently fill this gap, this minireview analyses in a holistic manner past and present technologies for water purification, outlining possible examples of ultraselective photocatalytic materials and reactor concepts to obtain biodegradable products. Based on the analysis conducted, guidelines for the rational design of catalytic materials and for the selection of emerging reactor concepts are put forward. We also highlight current technological barriers and future research needs that should be explored in greater depth in the quest for integrated and intensified continuous-flow operations. This journal i
Paired aluminum sites in zeolite catalysts enhance aromatics production
Full text linkIn this issue of Chem Catalysis, Ruiz-Martínez and co-workers investigate the effect of aluminum (Al) proximity and distribution on acid-catalyzed reactions in zeolites. They find that Al enrichment near the external surface results in paired acid sites that exhibit enhanced activity for aromatics formation
Beyond the use of modifiers in selective alkyne hydrogenation: Silver and gold nanocatalysts in flow mode for sustainable alkene production
Full text linkWe report on the excellent stereo and chemoselectivity of nanosized silver and gold catalysts in the three-phase hydrogenation of acetylenic compounds under flow chemistry conditions. The materials featuring metal nanoparticles in the range of 2-21 nm were prepared by spray deposition or incipient wetness impregnation of silver nitrate and sol immobilisation of gold chloride on different carriers (Al2O3, SiO2, TiO2, and carbon), followed by activation in various atmospheres. The samples were characterised by ICP-OES, N2 sorption, XPS, HAADF-STEM, and HRTEM, and evaluated in a continuous-flow flooded-bed micro-reactor. Both metals display optimal activities for particles below 5 nm, enabling stable operation at T = 373 K and P = 10 bar. While the performance of the silver catalysts is less influenced by the support, the gold nanoparticles exhibit significant activity only when deposited on TiO2, likely due to the strong metal-support interaction. Hydrogenations of functionalised alkynes reveal that silver and gold match, and in some cases exceed, the selectivity of benchmark palladium-based catalysts. Furthermore, in contrast to Pd, the Ag and Au samples require no modifiers, which brings fundamental and practical simplifications for their understanding and large scale manufacture. Therefore, these materials could be advantageously used for the continuous production of olefinic intermediates in the fine chemical and pharmaceutical industries. This journal i
Synthesis of surface-modified nanomaterials
No full textThis chapter deals with the synthesis of surface-modified nanomaterials. It presents an introduction to the materials surface chemistry, with an overview on those properties that are fundamental to control during synthesis. Various fabrication methods, including thermal and plasma treatment, silane chemical methods, ligand immobilization via grafting techniques, and atom anchoring for single-atom incorporation, are introduced. Several examples from the research literature are also presented during the discussion, to show how the synthesis can affect and tune catalytic properties
Sustainability assessment of single-atom catalysts in the transition to greener chemical processes
Full text linkFine chemical manufacturing is vital to the global economy, yet it faces growing pressure to address the environmental challenges inherent in its processes and products. In this study, we conducted a comprehensive analysis of various catalytic methodologies employed in the synthesis of fine chemicals by using the coupling of aryl halides and carboxylic acids to yield esters as a representative case. We compared the greenhouse gas emissions and criticality factors associated with the fabrication of various catalytic entities alongside the economic implications of different synthetic routes to yield the targeted ester compound. Our findings reveal key trends and guiding principles for the eco-design of single-atom catalyzed chemical processes, as well as the challenges and opportunities within this space. We emphasize the critical importance of integrating renewable energy sources for long-term sustainability and advocate for the adoption of heterogeneous catalysts over traditional homogeneous systems
Gram-Scale Domino Synthesis in Batch and Flow Mode of Azetidinium Salts
Full text linkAzetidinium salts are important motifs in organic synthesis but are difficult to obtain due to extremely long synthetic protocols. Herein, a rapid continuous-flow process for the on-demand synthesis of azetidinium salts is described. In particular, the nucleophilic addition of secondary amines and the subsequent intramolecular N-cyclization have been investigated in batch and continuous-flow modes, exploring the effects of solvent type, temperature, reaction time, and amine substituent on the synthesis of azetidinium salts. This has enabled us to quickly identify optimal reaction conditions and obtain microkinetic parameters, verifying that the use of a flow reactor leads to a reduction of the activation energy for the epichlorohydrin aminolysis due to the better control of mass and heat transfer during reaction. This confirms the key role of continuous-flow technologies to affect the kinetics of a reaction and make synthetic protocols ultrarapid and more efficient
Surface engineering of a Cu-based heterogeneous catalyst for efficient azide-alkyne click cycloaddition
Full text linkIn this work, we disclose that atomic-scale engineering of the active sites in copper-based catalysts can effectively tune the material performance for regioselective synthesis of triazoles, important building blocks for fine chemicals and pharmaceuticals. The copper catalysts have been prepared via impregnation of β zeolites with a Cu precursor, followed by post-synthetic modification with an organic ligand. The ligand is expected to partially cover the active sites, reducing the ensemble where the reaction takes place. The materials have been characterized by nitrogen adsorption, TEM, XRD, SEM-EDX, and FTIR spectroscopy to determine the structural, compositional, and textural properties of the samples. Catalyst testing in a one-pot three-component reaction of organic halides, terminal alkynes, and sodium azides in water shows that the presence of an organic layer on the catalyst surface favours the reaction. Leaching experiments in eight successive cycles have been conducted to prove the stability of the materials
Sustainability and Techno-Economic Assessment of Batch and Flow Chemistry in Seven Industrial Pharmaceutical Processes
Full text linkThe synthesis of active pharmaceutical ingredients (APIs) is commonly perceived as more efficient when performed using continuous-flow methods, whereas batch processes are often seen as less favorable due to their limitations in yield, heat and mass transfer, and safety. This perception largely stems from existing studies that focus on green metrics such as the E-factor and yield. However, a comprehensive comparison of batch and flow processes through full techno-economic analyses (TEA) and life-cycle assessments (LCA) remains underexplored, leaving key aspects of their environmental and economic impacts inadequately assessed. This work addresses this gap by presenting a detailed comparison of batch and flow syntheses of seven industrially relevant APIs, including amitriptyline hydrochloride, tamoxifen, zolpidem, rufinamide, artesunate, ibuprofen, and phenibut. Eleven environmental impact categories within the framework of nine planetary boundaries were assessed, and the study also included an evaluation of capital and operating costs for both production methods. The results demonstrated that, on average, continuous-flow processes are significantly more sustainable with improvements in energy efficiency, water consumption, and waste reduction. Flow processes also show a marked reduction in carbon emissions and up to a 97% reduction in energy consumption, highlighting their potential for greener API manufacturing. Despite these advantages, the study identified areas where the continuous-flow technology requires further development. Specifically, manufacturing certain APIs in flow show lower-than-average improvements in operating expenditure and land system changes, the latter being directly correlated with the consumption of organic solvents, that can be comparable to or even higher than in batch. These challenges highlight the need for further optimization of flow processes to fully realize their potential in API production
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