Nanostructured KIT-6 materials functionalized with sulfonic groups for catalytic purposes

Efficient Self-Condensation of Cyclohexanone into Biojet Fuel Precursors over Sulfonic Acid-Modified Silicas: Insights on the Effect of Pore Size and Structure

Mesoporous silica materials with different pore structures and sizes have been used for supporting aryl sulfonic acid catalytic sites via a postsynthetic grafting approach. The synthesized materials have been evaluated in the solventless acid-catalyzed self-condensation of cyclohexanone (CHO) to obtain the corresponding C12 adducts. These compounds display great potential as oxygenated fuel precursors as they can be transformed into jet fuel range alkanes in a subsequent hydrodeoxygenation process. In this work, the synthesized catalysts have displayed high selectivity values toward monocondensed compounds (>95%), thus limiting the formation of undesired heavier condensation products, together with CHO conversion values in the range 20-40% after 2 h of reaction at 100 °C. The structural and textural properties of the supports play an important role in the catalytic performance. Moreover, the activity per acid center is correlated with the textural properties of the supports, indicating that a lower surface density of the anchored aryl sulfonic groups affords an improvement in their specific activity. Finally, the benefit of using supports with large pore sizes and open structures, which limit the fouling of the catalysts by organic deposits, is demonstrated in a stability and reusability test.

Dual Brønsted acidic-basic function immobilized on the 3D mesoporous polycalix [4]resorcinarene: As a highly recyclable catalyst for the synthesis of spiro acenaphthylene/indene heterocycles

In this study, a novel dual Brønsted acidic-basic nano-scale porous organic polymer catalyst, PC4RA@SiPr-Pip-BuSO3H, was synthesized through various steps: preparation of a 3D network of polycalix, modification with (3-chloropropyl)-trimethoxysilane, then functionalization of polymer with piperazine and n-butyl sulfonic acid under the provided conditions. The catalyst characterization was performed by FT-IR, TGA, EDS, elemental mapping, PXRD, TEM, and FE-SEM analyses, confirming high chemical stability, activity, recoverability, and excellent covalent anchoring of functional groups. So, the designed catalyst was utilized for preparing spiro-acenaphthylene and amino-spiroindene heterocycles, providing good performance with a high yield of the corresponding products. Accordingly, this catalyst can be used in different organic transformations. Necessary experiments were conducted for the recyclability test of the polymeric catalyst, and the results showed the PC4RA@SiPr-Pip-BuSO3H catalyst can be reused 10 times without any decrease in its activity or quality with excellent stability. The structure of resultant spiro heterocycles was confirmed using 1H NMR, 13C NMR, and FT-IR.

Sulfonic Acid-Functionalized Inorganic Materials as Efficient Catalysts in Various Applications: A Minireview

Acid catalysis is widely used in the chemical industry, and nowadays many efforts are being focused on replacing the more common homogeneous catalysts with heterogeneous ones in order to make greener the industrial processes. In this perspective, sulfonic solid acid materials represent a valid alternative to the homogenous mineral acid in several acid catalyzed reactions. In this minireview, an overview of the recent advances on the preparation, stability and application of these materials is reported. Special attention is addressed to the sustainability of the considered processes, starting from the catalyst’s preparation, the use of green solvents and reducing the possible reaction steps. Ways to tackle the main drawback represented by easy leaching of acid groups are described. For an easy catalyst recovery, the use of a magnetic core in a catalyst particle, with the related synthetic approaches, is also illustrated. Finally, a section is dedicated to the principal characterization techniques to identify the structural properties of the catalysts.