Hans-Josef Bongard

Structurally Designed Synthesis of Mechanically Stable Poly(benzoxazine-co-resol)-Based Porous Carbon Monoliths and Their Application as High-Performance CO2 Capture Sorbents

Porous carbon monoliths with defined multilength scale pore structures, a nitrogen-containing framework, and high mechanical strength were synthesized through a self-assembly of poly(benzoxazine-co-resol) and a carbonization process. Importantly, this synthesis can be easily scaled up to prepare carbon monoliths with identical pore structures. By controlling the reaction conditions, porous carbon monoliths exhibit fully interconnected macroporosity and mesoporosity with cubic Im3m symmetry and can withstand a press pressure of up to 15.6 MPa. The use of amines in the synthesis results in a nitrogen-containing framework of the carbon monolith, as evidenced by the cross-polarization magic-angle-spinning NMR characterization. With such designed structures, the carbon monoliths show outstanding CO(2) capture and separation capacities, high selectivity, and facile regeneration at room temperature. At ~1 bar, the equilibrium capacities of the monoliths are in the range of 3.3-4.9 mmol g(-1) at 0 °C and of 2.6-3.3 mmol g(-1) at 25 °C, while the dynamic capacities are in the range of 2.7-4.1 wt % at 25 °C using 14% (v/v) CO(2) in N(2). The carbon monoliths exhibit high selectivity for the capture of CO(2) over N(2) from a CO(2)/N(2) mixture, with a separation factor ranging from 13 to 28. Meanwhile, they undergo a facile CO(2) release in an argon stream at 25 °C, indicating a good regeneration capacity.

Toward Highly Stable Electrocatalysts via Nanoparticle Pore Confinement

The durability of electrode materials is a limiting parameter for many electrochemical energy conversion systems. In particular, electrocatalysts for the essential oxygen reduction reaction (ORR) present some of the most challenging instability issues shortening their practical lifetime. Here, we report a mesostructured graphitic carbon support, Hollow Graphitic Spheres (HGS) with a specific surface area exceeding 1000 m(2) g(-1) and precisely controlled pore structure, that was specifically developed to overcome the long-term catalyst degradation, while still sustaining high activity. The synthetic pathway leads to platinum nanoparticles of approximately 3 to 4 nm size encapsulated in the HGS pore structure that are stable at 850 °C and, more importantly, during simulated accelerated electrochemical aging. Moreover, the high stability of the cathode electrocatalyst is also retained in a fully assembled polymer electrolyte membrane fuel cell (PEMFC). Identical location scanning and scanning transmission electron microscopy (IL-SEM and IL-STEM) conclusively proved that during electrochemical cycling the encapsulation significantly suppresses detachment and agglomeration of Pt nanoparticles, two of the major degradation mechanisms in fuel cell catalysts of this particle size. Thus, beyond providing an improved electrocatalyst, this study describes the blueprint for targeted improvement of fuel cell catalysts by design of the carbon support.

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 Co(3+) is considered to be the active site, while tetrahedrally coordinated Co(2+) 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 Co(2+) octahedrally coordinated by lattice oxygen in Fm3̅m 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 Co(2+) to Co(3+) 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 Co(3+) highly active but also the octahedrally coordinated Co(2+) species in CoFe2O4 with an inverse spinel structure shows some activity. These results suggest that the octahedrally coordinated Co(2+) species is easily oxidized and shows high catalytic activity for CO oxidation.

A Polyphenylene Support for Pd Catalysts with Exceptional Catalytic Activity

We describe a solid polyphenylene support that serves as an excellent platform for metal-catalyzed reactions that are normally carried out under homogeneous conditions. The catalyst is synthesized by palladium-catalyzed Suzuki coupling which directly results in formation of palladium nanoparticles confined to a porous polyphenylene network. The composite solid is in turn highly active for further Suzuki coupling reactions, including non-activated substrates that are challenging even for molecular catalysts.

Fabrication of Magnetic Yolk–Shell Nanocatalysts with Spatially Resolved Functionalities and High Activity for Nitrobenzene Hydrogenation

In cracking from: Highly engineered bifunctional yolk-shell nanocatalysts with tailored structural configuration, that is, hollow carbon spheres as the matrix, entrapped magnetite nanoparticles in the core, and in situ formed and highly dispersed noble metal nanoparticles within the carbon shells as active catalytic sites, were prepared. These nanocatalysts show high activity, reusability, and good magnetic separation properties.

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.

Co3O4 Nanoparticles Supported on Mesoporous Carbon for Selective Transfer Hydrogenation of α,β-Unsaturated Aldehydes

A simple and scalable method for synthesizing Co3 O4 nanoparticles supported on the framework of mesoporous carbon (MC) was developed. Benefiting from an ion-exchange process during the preparation, the cobalt precursor is introduced into a mesostructured polymer framework that results in Co3 O4 nanoparticles (ca. 3 nm) supported on MC (Co3 O4 /MC) with narrow particle size distribution and homogeneous dispersion after simple reduction/pyrolysis and mild oxidation steps. The as-obtained Co3 O4 /MC is a highly efficient catalyst for transfer hydrogenation of α,β-unsaturated aldehydes. Selectivities towards unsaturated alcohols are always higher than 95 % at full conversion. In addition, the Co3 O4 /MC shows high stability under the reaction conditions, it can be recycled at least six times without loss of activity.

Chemical and morphological consequences of acidification of pure, phosphated, and phosphonated CaO: Influence of CO₂ adsorption

In situ Fourier transform infrared (FTIR) spectroscopy was employed to characterize the adsorption behavior (as a function of pressure or time) and surface species of CO2 molecules on pure, phosphated, and phosphonated CaO. Carbonate and bicarbonate species were found to form on the pure oxide, whereas on the phosphated and phosphonated oxide samples the carbonate species were found to substitute favorably some of the OH(-) and PO4(3-) groups thereon exposed, respectively. Before and after carbonation, the test samples were further examined by in situ FTIR spectroscopy of adsorbed pyridine species, scanning electron microscopy, and energy dispersive X-ray spectroscopy. Then they were in situ acidified by exposure to a wet atmosphere of HCl vapor at 673 K for 10 min and re-examined similarly to reveal the influence of CO2 adsorption on the chemical and morphological consequences of acidification. The results obtained show the carbonate substitution of PO4(3-) groups to enhance agglomeration of the otherwise fine, longitudinal material particles into much bulkier ones and to render the otherwise more stable phosphonate groups less stable to acid treatment than the phosphate groups. Moreover, the bulky particle agglomerates of the carbonated test samples were detectably eroded following the acid treatment.

Surface modification of PDMS microfluidic devices by controlled sulfuric acid treatment and the application in chip electrophoresis

Herein, we present a straightforward surface modification technique for PDMS‐based microfluidic devices. The method takes advantage of the high reactivity of concentrated sulfuric acid to enhance the surface properties of PDMS bulk material. This results in alteration of the surface morphology and chemical composition that is in‐depth characterized by ATR‐FTIR, EDX, SEM, and XPS. In comparison to untreated PDMS, modified substrates exhibit a significantly reduced diffusive uptake of small organic molecules while retaining its low electroosmotic properties. This was demonstrated by exposing the channels of a microfluidic device to concentrated rhodamine B solution followed by fluorescence microscopy. The surface modification procedure was used to improve chip‐based electrophoretic separations. Separation efficiencies of FITC‐labeled amines/amino acids obtained in treated and untreated PDMS‐devices as well as in glass chips were compared. We obtained higher efficiencies in H2SO4 treated PDMS chips compared to untreated ones but lower efficiencies than those obtained in commercial microfluidic glass devices.