Filters

2014 - 201812

More filters

2019 - 201922020 - 202310
Reset filters

Settings

Author: Martin, Andreas × End date: 2019 × Start date: 2010 × WGL Institute: LIKAT ×

Search Results

Now showing 1 - 10 of 12
  • Thumbnail Image
    Item
  • Thumbnail Image
    Item
  • Thumbnail Image
    Item
    Catalytic β-Bromohydroxylation of Natural Terpenes: Useful Intermediates for the Synthesis of Terpenic Epoxides
    (New York, NY [u.a.] : Hindawi, 2018) Oubaassine, Saadia; Köckritz, Angela; Eckelt, Reinhard; Martin, Andreas; Ait Ali, Mustapha; El Firdoussi, Larbi
    In a one-step procedure, various ß-bromoalcohols were synthesized from natural terpenes in good to excellent yields. Using different catalysts, the reaction was carried out at room temperature, with H 2 O as nucleophile and N-bromosuccinimide as a bromine source under mild reaction conditions. The synthesized ß-bromoalcohols were subsequently converted in situ to the corresponding epoxides in good yields. © 2019 Saadia Oubaassine et al.
  • Thumbnail Image
    Item
    Catalytic Performance of Lanthanum Vanadate Catalysts in Ammoxidation of 2-Methylpyrazine
    (Basel : MDPI, 2016) Kalevaru, Venkata; Dhachapally, Naresh; Martin, Andreas
    The influence of reaction conditions on the catalytic performance of lanthanum vanadate (La0.1V0.9Ox) catalyst in the ammoxidation of 2-methylpyrazine (MP) to 2-cyanopyarazine (CP) has been investigated. This novel catalytic material exhibited remarkably good performance with very high space-time-yields (STY) of CP. The reaction parameters such as the effect of temperature, gas hourly space velocity (GHSV) and all other reaction variables (e.g., NH3, air, and MP feed rates) on the catalytic performance were explored and optimized. For example, an increase in MP feed rate from 2 to >16 mmol/h led to decreased conversion of MP but increased the STY of CP significantly. Optimal performance was achieved when the reaction temperature was 420 °C and the molar ratio of 2-MP, ammonia, air, H2O and N2 in the feed gas was set to 1:7:26:13:22. Under these optimal reaction conditions, the catalyst showed a MP conversion of ~100%, CP selectivity of 86%, and STY of >500 gCP/(kgcat∙h). On the other hand, the formation of pyrazine (Py) as a by-product was found to be high when the NH3:MP ratio was lower at increased contact time. This suggests possible differences in the reaction mechanism pathways with respect to feed composition over La0.1V0.9Ox catalysts.
  • Thumbnail Image
    Item
    Bimetallic Catalysts Containing Gold and Palladium for Environmentally Important Reactions
    (Basel : MDPI, 2016) Alshammari, Ahmad; Kalevaru, Venkata Narayana; Martin, Andreas
    Supported bimetallic nanoparticles (SBN) are extensively used as efficient redox catalysts. This kind of catalysis particularly using SBN has attracted immense research interest compared to their parent metals due to their unique physico-chemical properties. The primary objective of this contribution is to provide comprehensive overview about SBN and their application as promising catalysts. The present review contains four sections in total. Section 1 starts with a general introduction, recent progress, and brief summary of the application of SBN as promising catalysts for different applications. Section 2 reviews the preparation and characterization methods of SBN for a wide range of catalytic reactions. Section 3 concentrates on our own results related to the application of SBN in heterogeneous catalysis. In this section, the oxidation of cyclohexane to adipic acid (an eco-friendly and novel approach) will be discussed. In addition, the application of bimetallic Pd catalysts for vapor phase toluene acetoxylation in a fixed bed reactor will also be highlighted. Acetoxylation of toluene to benzyl acetate is another green route to synthesize benzyl acetate in one step. Finally, Section 4 describes the summary of the main points and also presents an outlook on the application of SBN as promising catalysts for the production of valuable products.
  • Thumbnail Image
    Item
    Zeolite Catalysis
    (Basel : MDPI, 2016) Martin, Andreas
    [no abstract available]
  • Thumbnail Image
    Item
    Catalytic Cracking of Triglyceride-Rich Biomass toward Lower Olefins over a Nano-ZSM-5/SBA-15 Analog Composite
    (Basel : MDPI, 2015) Vu, Xuan Hoan; Nguyen, Sura; Dang, Tung Thanh; Phan, Binh Minh Quoc; Nguyen, Duc Anh; Armbruster, Udo; Martin, Andreas
    The catalytic cracking of triglyceride-rich biomass toward C2–C4 olefins was evaluated over a hierarchically textured nano-ZSM-5/SBA-15 analog composite (ZSC-24) under fluid catalytic cracking (FCC) conditions. The experiments were performed on a fully automated Single-Receiver Short-Contact-Time Microactivity Test unit (SR-SCT-MAT, Grace Davison) at 550 °C and different catalyst-to-oil mass ratios (0–1.2 g∙g−1). The ZSC-24 catalyst is very effective for transformation of triglycerides to valuable hydrocarbons, particularly lower olefins. The selectivity to C2–C4 olefins is remarkably high (>90%) throughout the investigated catalyst-to-oil ratio range. The superior catalytic performance of the ZSC-24 catalyst can be attributed to the combination of its medium acid site amount and improved molecular transport provided by the bimodal pore system, which effectively suppresses the secondary reactions of primarily formed lower olefins
  • Thumbnail Image
    Item
    Development of Active and Stable Low Nickel Content Catalysts for Dry Reforming of Methane
    (Basel : MDPI, 2017-5-16) Ha, Quan Luu Manh; Armbruster, Udo; Atia, Hanan; Schneider, Matthias; Lund, Henrik; Agostini, Giovanni; Radnik, Jörg; Vuong, Huyen Thanh; Martin, Andreas
    Methane dry reforming (DRM) was investigated over highly active Ni catalysts with low metal content (2.5 wt %) supported on Mg-Al mixed oxide. The aim was to minimize carbon deposition and metal sites agglomeration on the working catalyst which are known to cause catalyst deactivation. The solids were characterized using N2 adsorption, X-ray diffraction, temperature-programmed reduction, X-ray photoelectron spectroscopy, and UV-Vis diffuse reflectance spectroscopy. The results showed that MgO-Al2O3 solid solution phases are obtained when calcining Mg-Al hydrotalcite precursor in the temperature range of 550–800 °C. Such phases contribute to the high activity of catalysts with low Ni content even at low temperature (500 °C). Modifying the catalyst preparation with citric acid significantly slows the coking rate and reduces the size of large octahedrally coordinated NiO-like domains, which may easily agglomerate on the surface during DRM. The most effective Ni catalyst shows a stable DRM course over 60 h at high weight hourly space velocity with very low coke deposition. This is a promising result for considering such catalyst systems for further development of an industrial DRM technology.
  • Thumbnail Image
    Item
    Methanation of CO2 on Ni/Al2O3 in a Structured Fixed-Bed Reactor—A Scale-Up Study
    (Basel : MDPI, 2017-5-15) Türks, Daniel; Mena, Hesham; Armbruster, Udo; Martin, Andreas
    Due to the ongoing change of energy supply, the availability of a reliable high-capacity storage technology becomes increasingly important. While conventional large-scale facilities are either limited in capacity respective supply time or their extension potential is little (e.g., pumped storage power stations), decentralized units could contribute to energy transition. The concepts of PtX (power-to-X) storage technologies and in particular PtG (power-to-gas) aim at fixation of electric power in chemical compounds. CO2 hydrogenation (methanation) is the foundation of the PtG idea as H2 (via electrolysis) and CO2 are easily accessible. Methane produced in this way, often called substitute natural gas (SNG), is a promising solution since it can be stored in the existing gas grid, tanks or underground cavern storages. Methanation is characterized by a strong exothermic heat of reaction which has to be handled safely. This work aims at getting rid of extreme temperature hot-spots in a tube reactor by configuring the catalyst bed structure. Proof of concept studies began with a small tube reactor (V = 12.5 cm3) with a commercial 18 wt % Ni/Al2O3 catalyst. Later, a double-jacket tube reactor was built (V = 452 cm3), reaching a production rate of 50 L/h SNG. The proposed approach not only improves the heat management and process safety, but also increases the specific productivity and stability of the catalyst remarkably.
  • Thumbnail Image
    Item
    Continuous synthesis of diethyl carbonate from ethanol and CO2 over Ce–Zr–O catalysts
    (London : RSC Publ., 2015) Prymak, Iuliia; Kalevaru, Venkata Narayana; Wohlrab, Sebastian; Martin, Andreas
    CexZr1−xO2 (x = 0, 0.2, 0.5, 0.8 and 1.0) solids were prepared by a citrate method and characterized by various techniques such as N2-adsorption (BET-SA), XRD, XPS, TEM, H2-TPR, NH3- and CO2-TPD. The catalytic performance of these solids was evaluated for the direct synthesis of diethyl carbonate (DEC) from ethanol and CO2 in continuous mode using a plug-flow reactor (PFR). According to thermodynamic data, the reaction is favourable at low reaction temperatures and high reaction pressures. Thus, the catalytic experiments were carried out at reaction temperatures ranging from 80 to 180 °C and at reaction pressures from 80 to 180 bar. The CexZr1−xO2 catalysts exhibited significant differences in their performance mainly depending on (i) their Ce : Zr ratio and (ii) the different acid–base characteristics. Among the series Ce0.8Zr0.2O2 (C80Z) and Ce0.5Zr0.5O2 (C50Z) catalysts displayed the most efficient performance. Moreover, C80Z, pretreated at 700 °C, yielded DEC at the equilibrium conversion level of YDEC ~ 0.7% at 140 °C and 140 bar at a CO2 : ethanol ratio of 6 : 1 at a LHSV of 42 Lliq kgcat−1 h−1.