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

Platinum-Nanoparticles on Different Types of Carbon Supports: Correlation of Electrocatalytic Activity with Carrier Morphology

The electrocatalytic activity of Pt-nanoparticles used in fuel cells increases by 34% upon going from the usual Pt/Vulcan XC72 to support systems such as Pt/Printex XE2 which have a relatively rough surface structure

Supported palladium nanoparticles on hybrid mesoporous silica: Structure/activity-relationship in the aerobic alcohol oxidation using supercritical carbon dioxide

The preparation, characterization, and catalytic properties of Pd nanoparticles supported on mesoporous organic–inorganic hybrid materials are described for continuous-flow aerobic oxidation of alcohols using supercritical carbon dioxide (scCO2) as a mobile phase. The nanoparticles were generated “bottom-up” from molecular precursors that were precoordinated to the support through suitable anchor units. The most active material allows high single-pass conversions in scCO2 at temperatures as low as 60 °C. This high activity may be associated with the presence of small primary crystallites (approx. 2 nm) that conglomerate to ensembles about 25 nm in size, leading to a larger number of high-indexed planes in small volume units. These findings may provide useful guidelines for further catalyst design on the nanoscale for green oxidation methods

Gold on Different Manganese Oxides : Ultra-Low-Temperature CO Oxidation over Colloidal Gold Supported on Bulk-MnO2 Nanomaterials

Nanoscopic gold particles have gained very high interest because of their promising catalytic activity for various chemicals reactions. Among these reactions, low-temperature CO oxidation is the most extensively studied one due to its practical relevance in environmental applications and the fundamental problems associated with its very high activity at low temperatures. Gold nanoparticles supported on manganese oxide belong to the most active gold catalysts for CO oxidation. Among a variety of manganese oxides, Mn2O3 is considered to be the most favorable support for gold nanoparticles with respect to catalytic activity. Gold on MnO2 has been shown to be significantly less active than gold on Mn2O3 in previous work. In contrast to these previous studies, in a comprehensive study of gold nanoparticles on different manganese oxides, we developed a gold catalyst on MnO2 nanostructures with extremely high activity. Nanosized gold particles (2-3 nm) were supported on α-MnO2 nanowires and mesoporous β-MnO2 nanowire arrays. The materials were extremely active at very low temperature (-80 °C) and also highly stable at 25 °C (70 h) under normal conditions for CO oxidation. The specific reaction rate of 2.8 molCO·h(-1)·gAu(-1) at a temperature as low as -85 °C is almost 30 times higher than that of the most active Au/Mn2O3 catalyst

Highly Ordered Mesoporous Cobalt-Containing Oxides: Structure, Catalytic Properties, and Active Sites in Oxidation of Carbon Monoxide

Co₃O₄ with a spinel structure is a very active oxide catalyst for the oxidation of CO. In such catalysts, octahedrally coordinated Co³⁺ is considered to be the active site, while tetrahedrally coordinated Co²⁺ is assumed to be basically inactive. In this study, a highly ordered mesoporous CoO has been prepared by H₂ reduction of nanocast Co₃O₄ at low temperature (250 °C). The as-prepared CoO material, which has a rock-salt structure with a single Co²⁺ octahedrally coordinated by lattice oxygen in <i>Fm</i>3̅<i>m</i> symmetry, exhibited unexpectedly high activity for CO oxidation. Careful investigation of the catalytic behavior of mesoporous CoO catalyst led to the conclusion that the oxidation of surface Co²⁺ to Co³⁺ causes the high activity. Other mesoporous spinels (CuCo₂O₄, CoCr₂O₄, and CoFe₂O₄) with different Co species substituted with non/low-active metal ions were also synthesized to investigate the catalytically active site of cobalt-based catalysts. The results show that not only is the octahedrally coordinated Co³⁺ highly active but also the octahedrally coordinated Co²⁺ species in CoFe₂O₄ with an inverse spinel structure shows some activity. These results suggest that the octahedrally coordinated Co²⁺ species is easily oxidized and shows high catalytic activity for CO oxidation