Synthetic ferripyrophyllite: preparation, characterization and catalytic application

[EN] Sheet silicates, also known as phyllosilicates, contain parallel sheets of tetrahedral silicate built up by [Si2O5](2-) entities connected through intermediate metal-oxygen octahedral layers. The well-known minerals talc and pyrophyllite are belonging to this group based on magnesium and aluminium, respectively. Surprisingly, the ferric analogue rarely occurs in nature and is found in mixtures and conglomerates with other materials only. While partial incorporation of iron into pyrophyllites has been achieved, no synthetic protocol for purely iron-based pyrophyllite has been published yet. Here we report about the first artificial synthesis of ferripyrophyllite under exceptional mild conditions. A similar ultrathin two-dimensional (2D) nanosheet morphology is obtained as in talc or pyrophyllite but with iron(iii) as a central metal. The high surface material exhibits a remarkably high thermostability. It shows some catalytic activity in ammonia synthesis and can serve as catalyst support material for noble metal nanoparticles.The authors gratefully acknowledge the following people for support with analytical measurements and data analysis: Hans-Josef Bongard (SEM-EDX), Silvia Palm (EDX bulk), Adrian Schluter (TEM), Norbert Pfander (STEM), Jan Ternieden and Jan Nicolas Buscher (XRD and XPS), Prof. Dr Osamu Terasaki and Dr Yanghang Ma (3D electron diffraction tomography: failed due to the poor crystallinity and stability under strong beam irradiation), Dr Nicolas Duyckaerts (NH3-TPD measurements), Kai Jeske (GC gas analysis), Dr Yuxiao Ding (ATR-IR) and Dr Zhengwen Cao (titration). The authors also would like to thank Prof. Dr Robert Schlogl, Dr Thomas Lunkenbein, Fabian Pienkoss and Dr Gaetano Calvaruso for helpful and enthusiastic discussions, as well as Niklas Fuhrmann and Lars Winkel for technical support. The studies were carried out as part of our activities in the Cluster of Excellence "Tailor-Made Fuels from Biomass" (EXC 236) and "The Fuel Science Center" funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy -Exzellenzcluster 2186 "The Fuel Science Center" ID: 390919832. Open Access funding provided by the Max Planck Society.Qiao, Y.; Theyssen, N.; Spliethoff, B.; Folke, J.; Weidenthaler, C.; Schmidt, W.; Prieto González, G.... (2021). Synthetic ferripyrophyllite: preparation, characterization and catalytic application. Dalton Transactions. 50(3):850-857. https://doi.org/10.1039/d0dt03125aS85085750

Selektive Oxidationsreaktionen mit molekularem Sauerstoff in komprimiertem Kohlendioxid

The present dissertation is divided into two research projects. In the first one the possibility for a synthesis of organic carbonates starting from alkenes, oxygen, carbon dioxide and aldehydes as coreductants was investigated. The first part of the consecutive reaction sequence-the stainless steel initiated synthesis of epoxides using O2/aldehyde mixtures in supercritical carbon dioxide-was successively performed by Loeker.[1] This result bares the potential for an in situ synthesis of organic carbonates by the addition of suitable catalysts. However, established catalysts of different structure and mode of operation for CO2 insertion proved not to be compatible with the reaction conditions of the epoxidation reaction. The coexistence of Lewis-base and a Brönsted-acid sites was identified as a main difficulty for the development of active and resistant catalysts. In the second project the coupled oxidation of cycloalkanes or alkylarenes with acetaldehyde (2.0 equiv.) and molecular oxygen (2.1 equiv.) was for the first time found to occur effectively in compressed carbon dioxide (16 equiv.) under mild multiphase conditions.[2] No catalyst is required but high pressure ATR-FT-IR online measurements show that the free radical reaction is heterogeneously initiated by the stainless steel of the reactor walls. Since experiments in a titanium autoclave led to comparable conversions, the initiation seems to be relative independent in terms of the reactor material. For secondary carbon atoms a high keto to alcohol ratio is observed (3.5-7.9), most probably due to the fast consecutive oxidation of alcoholic intermediates. Since C-C-scission reactions are detected only to a very small extend, tertiary carbon atoms are transformed to the corresponding alcohols with high selectivity. The obtained product distributions suggest that the strong influence of acetaldehyde is related to its function not only the determining oxygen activator and an efficient H-atom donating agent for peroxo and oxo radicals, but also a crucial reductant for hydroperoxo intermediates. In comparison with compressed N2 or Ar carbon dioxide was proven to increase the yields of alkane oxygenates under identical reaction conditions. Although the experimental results allow at present no full explanation for the enhanced conversion in CO2, a set of exclusive effects in CO2 as a reaction medium were described which are believed to play an important role for the enhanced performance in this medium. [1] F. Loeker, W. Leitner, Chem. Eur. J., 2000, 6, 2011-2015. [2] N. Theyssen, W. Leitner, Chem. Commun., 2002, 410-411

Kaolin: A Natural Low-Cost Material as Catalyst for Isomerization of Glucose to Fructose

Kaolin was identified as an effective catalyst for isomerization of glucose to fructose in methanol. The methyl-fructoside is obtained as main product through <i>in situ</i> etherification at the anomeric carbon atom, reflecting the bifunctionality of the layered alumosilicate. Using this exceptionally cheap and abundant natural clay (0.16 $/kg), methyl-fructoside is produced with up to 52% yield