The use of the Boehm titration (BT) method as an analytical tool for the quantification of oxygen-containing surface groups is systematically investigated for oxidized carbon black, carbon nanotubes and two active carbons with specific surface areas between 60 and 1750 m2 g−1. The accuracy of the BT method is quantitatively compared with results from elemental analysis (EA), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). Overall, the results from TPD are in line with the values obtained by BT. Both show the equal ratio of the oxygen groups to each other. Within the series of carbon samples, all methods provide similar trends for the total oxygen content yet the absolute numbers are deviating significantly. Reasons for these discrepancies are discussed and linked to the specific characteristics of the different methods. As the BT method is a solution based method, it only probes the surface fraction of the carbon that is accessible to the base solution. That means, it probes the relevant fraction for applications where carbon is in contact to aqueous solutions. Overall, the BT method can be conveniently applied to a broad range of carbon materials as long as the samples are sufficiently hydrophilic and of the enough sample amount is provided.

Practical aspects of the Boehm titration method are evaluated for obtaining reliable results in the quantification of oxygen-containing surface groups in a short time. Analytical criteria such as accuracy, repeatability, precision, and robustness are applied. Oxidized multi-walled carbon nanotubes (MWCNTs) are used as the model substance. Different reaction bases (NaHCO3(aq), Na2CO3(aq), NaOH(aq)) are applied and treatment times are studied. We also show that smaller amounts of carbon material can be reliably analyzed by using an autotitrator combined with a pH electrode. We find that indirect titration with Na2CO3 results in the highest titration precision and accuracy despite the lower base strength compared with NaOH. Therefore, CO2 impurities do not have to be removed and only 7 min is necessary for one titration. The titration error with respect to the proposed method is 0.15% of the aliquot volume. The mixing method during the carbon treatment with bases (stirring, shaking, ultrasound treatment) has no influence on the result as long as one allows a few hours for the reaction to complete. Finally, we provide a standard operating procedure for obtaining results with high precision during Boehm titration.

Carbon Nanotubes (CNTs) have been oxidized with ozone in the gas phase and different Advanced Oxidation Processes (AOPs) in the aqueous phase such as H2O2/UV, Fenton reaction and ozonation, in order to functionalize them. A significant difference between the amounts and types of oxygen containing groups were generated using different oxidants. To investigate the efficiency of the oxidation methods, we monitored the depletion of the oxidants, using a titration of H2O2 with KMnO4 and an ozone analyzer for the ozonolysis experiments. Furthermore, we investigated the formation of hydroxyl radicals during the oxidation experiments by decolorization of methylene blue and depletion of salicylic acid.Boehm titration, Raman spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, elemental analysis, temperature programmed desorption and thermogravimetric analysis have been utilized to characterize the CNTs. Our results demonstrate that direct ozonolysis with water vapor produces the highest amount of oxygen containing surface in comparison to the other oxidation methods, and this by using only a small amount of the available oxidant. With our results we confirm different previous assumptions about the oxidation mechanisms and theoretical calculations for oxidation processes practically. (C) 2016 Elsevier Ltd. All rights reserved.

Platinum-group-metal materials were recovered from fuel cells and studied as catalysts for the total oxidation of propane as model reaction. Therefore a representative number of metal-foam catalysts containing platinum, palladium, and ruthenium in certain ratios were prepared and investigated. Interestingly, particularly active catalysts were observed with a high fraction of one metal and small amounts of the other two metals. This suggests a principal trend for preparing efficient catalysts using ternary-precious-metal systems. For the recycling of fuel-cell compounds the composition of the material could be varied by the substitution or addition of appropriate amounts of precious metals to achieve the highest performance.

Purification and ozonation protocols for the functionalization of multiwalled carbon nanotubes (MWCNT) were developed to modify the surface with respect to increasing the catalytic activity of the samples in the oxidative dehydrogenation of ethyl benzene (ODEB) to styrene. The modification processes drastically enhance the Brunauer-Emmett-Teller surface area and the number of oxygen-containing groups on the surface of the nanotubes. The modified MWCNT exhibit significantly improved conversion and styrene selectivity in the ODEB reaction. For instance, ozonation led to MWCNT-based catalysts revealing conversion and selectivity values of 80% and 92 %, respectively. An increase in surface oxygen accompanied by high catalytic activity observed on the catalysts suggests that oxygen-containing groups are the dominant active sites for the reaction.

The present work deals with the technology transfer from basic research on the microwave-assisted heterogeneous gas-phase catalysis into pilot plant scale. This enables a direct comparison of the novel microwave-assisted catalysis technology with conventional heating systems by means of ohmic losses. The work is focused on the technology and not on the catalyst material, which represents only one possible alternative. The electromagnetic radiation of 2.45 GHz gives the opportunity to transfer energy highly efficient by volumetric dielectromagnetic heating. This results in higher heating rates and lower energy losses compared to conventionally heated systems or other heating methods. The heat flow density in microwave systems can reach up to 35,000 W m−2 [1]. Operating under those conditions the utilized catalyst has to have a high catalytic activity as well as large dielectric and magnetic loss factors. The highest potential for those properties exhibit materials based on mixed metal oxides such as perovskites and spinels. Selected compounds of these substance classes have been prepared by various synthetic methods and were characterized with respect to their catalytic activity, complex permittivity, and complex permeability [2]. The experimentally determined values built the foundation for calculation and simulation of an optimized reactor and microwave absorber design. The constructed pilot plant includes both heating systems, magnetrons for microwave-assisted and resistance heaters for conventional gas-phase catalysis, and was used for a comparison of the heating methods.

This chapter contains sections titled: Introduction Liquid-Phase Synthesis Wet Air Oxidation Gas-Phase Synthesis Waste Gas Treatment Conclusion and Outlook References

Several stable iron-containing spinel oxides with the composition CuFe 2 O 4 or FeCr 2 O 4 were prepared by different methods including thermal nitrate decomposition, combustion synthesis, and mechano-chemical synthesis. Materials were compared to commercially available spinels produced by conventional ceramic route with respect to their structural properties and catalytic activity. Phase compositions and microstructures of the catalysts were studied in detail. The catalysts were tested in the Friedel–Crafts alkylation of various aromatic compounds with different alkyl halides as alkylating agents. Microstructural properties (microstrains) of the synthesized binary oxides have been identified as a reason for the increased reactivity. Even at low reaction temperatures of 50–70 °C catalysts maintained their high activity resulting in TOFs of up to 3000 h −1 and excellent selectivity with total heterogeneous behavior in catalysis.

The effect of hydroxyl radical (⁎OH)-assisted oxidation of multiwalled carbon nanotubes (MWCNTs) as catalysts for oxidative dehydrogenation of ethylbenzene (ODEB) to styrene was studied. Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) results indicated that the presence of hydroxyl radicals during UV/H2O2 oxidative treatment introduced significantly the amount of hydroxyl and carbonyl groups onto the surface of carbon nanotubes, leading to an improvement in the catalytic behavior. In the present work, UV/H35 MWCNTs obtained the best catalytic behavior with 91% styrene selectivity and 47% ethylbenzene conversion at 400°C under conventional heating. Transmission electron microscopy (TEM) of UV/H35 MWCNTs showed the formation of new sp2-carbon layers on the wall of nanotubes after the stability test.

With combustion synthesis it is possible to achieve catalytic active binary oxides of chromium, iron, cobalt, nickel and copper within a few seconds. The catalytic activity of combustion synthesized oxides was compared with commercially available spinel oxides and materials obtained by thermal nitrate decomposition in the selective liquid-phase oxidation of benzyl alcohol to benzaldehyde with a stoichiometric amount of tert-butyl hydroperoxide as the oxidant. The combustion synthesized materials revealed both higher reactivity and higher stability compared to those oxides available from high temperature ceramic processes or thermal nitrate decomposition. Crystallite sizes, microstrains, and phase compositions have been analyzed by X-ray powder diffractometry as important parameters for the catalytic activity. By applying combustion synthesis, it is possible to obtain several different low density oxides with smaller crystallites and higher values for microstrains compared to other methods of preparation. Thus, providing an explanation for the improved catalytic performance of those materials.

High metal containing wastes from the aluminium industry, the tannery industry and the electroplating industry were tested as precursors for catalysts. These waste materials were processed using various treatments and tested for the total oxidation of volatile organic compounds employing propane as a model gas. Comparisons were made with unprocessed counterparts in certain cases. Investigations were made in the temperature range of 100–500°C with a GHSV of 5000h−1. Characterization of fresh and used catalysts was performed using techniques like BET analysis, X-ray diffraction (XRD), X-ray fluorescence (XRF), inductively coupled plasma optical emission spectrometry (ICP-OES) and thermal analyses (DTA/TG). The results showed that the catalyst obtained from combination of red mud with tannery shavings mixed in high ratio followed by thermal treatment and the unprocessed red mud were the most active. A 50% conversion in the range of 320–380°C was achieved. In comparison, the other wastes showed lower activity, requiring much higher temperatures for the same conversion.In view of the low cost involved and easy availability of such materials, their utilization as a source of catalyst can be of interest.

The influence of microwave heating on the catalytic performance of oxidized multi-walled carbon nanotubes (OMWCNTs) in oxidative dehydrogenation of ethylbenzene (ODEB) was investigated. OMWCNTs were characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) before and after the catalytic reaction. The highest yield of ∼60% styrene was achieved under microwave-assisted reaction conditions. The significant amount of high disordered amorphous carbon was observed on the surface of OMWCNTs after the conventionally-heated reaction, while the treatment of the catalyst under microwave-assisted reaction conditions resulted in the formation of new layers of surface sp2-carbon. Moreover, the formation of carbonyl groups which are responsible for the dehydrogenation power of the catalyst was observed on the surface of OMWCNTs after the reaction in microwave oven only.

Gel-combustion synthesis (GCS) in self-sustaining mode was used for preparation of mixed oxide with spinel structure AB2O4 (where A=Co, Cu and B=Cr, Co). To support these mixed oxides on CeO2 and ZrO2 powders, the GCS technique in self-propagating mode was developed. The synthesized materials were characterized by IR-spectroscopy, X-ray diffraction and transmission electron microscopy. The GCS preparation leads to the formation of nanocrystalline, single-phase spinel catalysts, which showed high activity in VOCs (hexane) elimination. The best catalytic performance was obtained over copper cobaltite catalyst prepared by GCS from glycerin-chelated precursor.

The catalytic performance of multi-walled carbon nanotubes (MWCNTs) modified by iron oxide has been investigated for oxidative dehydrogenation of ethylbenzene in an integral fixed-bed reactor conventionally-heated and under microwave-assisted conditions. The morphology and microstructural characteristics of the obtained composites before and after the catalytic reaction were characterized by transmission electron microscopy and X-ray diffraction. The content 3wt.% of iron oxide supported on MWCNTs was found optimal in respect of the ethylbenzene conversion and styrene selectivity. All prepared composites were found more selective in a microwave field in the temperature range 380–450°C. The transformation of Fe2O3 into Fe nanocrystals encapsulated by polyhedral graphite shells was observed only under microwave-assisted reaction conditions.

Carbon dioxide was incorporated into various oxirane-containing compounds. The starting materials include natural products with epoxy groups (1-4), glycidyl compounds (5-9) and epoxidized polymers (9, 10). It could be shown that the crosslinking side reaction is not significant for internal epoxides but important for terminal glycidyl compounds.

AbstractMikroreaktoren werden in der chemischen Industrie bei der Miniaturisierung verfahrenstechnischer Prozesse bereits seit langem erfolgreich eingesetzt. Forschungsseitig leisteten dazu Hochschulen und Universitäten im Rahmen von Schwerpunktprogrammen einen großen Beitrag. Auf dieser Grundlage und der Auswertung neuester Literatur wurde im Institut für Technische Chemie und Umweltchemie eine Mikroreaktorversuchsapparatur entwickelt und aufgebaut. Ausgehend von den theoretischen Grundlagen lernen die Studierenden am Beispiel eines T‐Mischers den Einfluss der wichtigsten technologischen Parameter auf den Ablauf eines durch den Stofftransport limitierten Reaktionsprozesses kennen. Besonderer Wert wurde dabei auf die Visualisierung und die mathematische Auswertung der Qualität des Mischvorgangs gelegt. Dieses gelang unter Verwendung eines Stereomikroskops, einer handelsüblichen Videokamera und der Anwendung eines dafür angepassten Computerprogramms. Die erzielten Ergebnisse werden dargestellt und ausführlich diskutiert.

Perovskite powders of the types La(0.5)Ca(0.5)Al(y)M(1-y)O(3-delta) (y = 0-0.8), M = Fe, Cr, Mn, Co and La(x)Sr(1-x)Mn(y)Co(1-y) (x = 0.5-1, y = 0-1) were prepared via a sol-gel route according to the modified Pechini method. Incineration of the resins was performed before final sintering at 1000 degrees C for 6 h. The phase composition of the samples was established by X-ray powder diffraction analysis, and the lattice parameters were calculated using Rietveld analysis. The shape and size of the particles were determined via scanning electron microscopy and the specific surface area of the powder perovskites was established by the BET method. The principal particles were ca. 100 nm in size and formed agglomerates larger than 1.0 mu m. The composition of the perovskites was established by EDX analysis. Following this, the catalytic behavior was tested by means of total oxidation of propane. The catalytic performance was measured at atmospheric pressure with 3 g of catalyst in a fixed-bed quartz reactor (i.d. = 18 mm) under thermal-assisted and microwave-assisted conditions. Initial results show a strong dependence of the catalytic and heating behavior on the nature of the M-atom and its number of unpaired d-electrons as well as on the particle size and its specific surface area. No significant difference in the results could be detected from comparison of the two heating methods.

Chemie Ingenieur TechnikVolume 79, Issue 9 p. 1300-1300 PosterFree Access Combustion Synthesized Nanocrystalline Mixed Oxide Catalysts for Elimination of Volatile Organic Compounds U. Zavyalova Dr., u.zavyalova@uni-jena.de Institut für Technische Chemie und Umweltchemie, Friedrich-Schiller-Universität Jena, Lessingstraße 12, D-07743 JenaSearch for more papers by this authorK. Pollok Dr., Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, Burgweg 11, D-07749 JenaSearch for more papers by this authorF. Langenhorst Prof. Dr., Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, Burgweg 11, D-07749 JenaSearch for more papers by this authorP. Scholz Dr., Institut für Technische Chemie und Umweltchemie, Friedrich-Schiller-Universität Jena, Lessingstraße 12, D-07743 JenaSearch for more papers by this authorB. Ondruschka Prof. Dr., Institut für Technische Chemie und Umweltchemie, Friedrich-Schiller-Universität Jena, Lessingstraße 12, D-07743 JenaSearch for more papers by this author U. Zavyalova Dr., u.zavyalova@uni-jena.de Institut für Technische Chemie und Umweltchemie, Friedrich-Schiller-Universität Jena, Lessingstraße 12, D-07743 JenaSearch for more papers by this authorK. Pollok Dr., Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, Burgweg 11, D-07749 JenaSearch for more papers by this authorF. Langenhorst Prof. Dr., Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, Burgweg 11, D-07749 JenaSearch for more papers by this authorP. Scholz Dr., Institut für Technische Chemie und Umweltchemie, Friedrich-Schiller-Universität Jena, Lessingstraße 12, D-07743 JenaSearch for more papers by this authorB. Ondruschka Prof. Dr., Institut für Technische Chemie und Umweltchemie, Friedrich-Schiller-Universität Jena, Lessingstraße 12, D-07743 JenaSearch for more papers by this author First published: 18 September 2007 https://doi.org/10.1002/cite.200750337AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume79, Issue9Special Issue: ProcessNet Jahrestagung 2007September, 2007Pages 1300-1300 ReferencesRelatedInformation