Das Power-to-Gas-Konzept ist ein praktikabler Ansatz der chemischen Energiespeicherung, um die Herausforderungen der Energiewende zu meistern. Die heterogene Katalyse spielt bei der Umsetzung von CO2 eine entscheidende Rolle, welches beispielsweise bei Einsatz Ni-basierter Katalysatoren mit Wasserstoff zu Methan umgesetzt wird. Durch eine tiefgehende Charakterisierung ist es moglich, optimierte Katalysatorsysteme herzustellen. Das Bestimmen der Kinetik der Reaktion ermoglicht eine industrienahe Reaktorauslegung.The power-to-gas concept is a promising technology to chemically store energy and therefore a feasible approach to mitigate the challenges of energy transition. Heterogeneous catalysis plays a crucial role in CO2 conversion to methane using nickel based catalysts. A thorough catalyst characterization facilitates the synthesis of optimized catalyst systems. The determination of reaction kinetics is fundamental for industrial reactor design.

Deactivation behavior is an important topic in catalyst development. In case of methanol synthesis the conventional Cu/ZnO/Al2O3 system is commonly known to be prone to sintering, however, information about the structural development during deactivation or the sintering mechanism(s) are scarce. We present a systematic deactivation study on three different Cu/ZnO/Al2O3 catalysts which are aged under constant conditions and periodically analyzed using kinetic measurements and N2O chemisorption. A power law model for the catalyst activity with time on stream is derived. Furthermore it is found, that the presence of water provokes a steep loss in active surface area and specific activity. Also, the TEM particle size distributions generated during the aging treatment are evaluated and discussed. (C) 2015 Elsevier B.V. All rights reserved.

A series of NiAl(O)(x) catalysts with varying Ni/Al ratio has been prepared by coprecipitation of the metal nitrate solutions with NaOH/Na2CO3 at constant pH. The samples have been analyzed by XRD, N-2 physisorption, temperature programmed reduction and H-2 chemisorption. For kinetic characterization, apparent activation energies and reaction orders are determined. The correlation of the catalytic acitivity and metallic surface area indicates a linear relationship. A data set comprising over 200 data points with varying gas composition, temperature and pressure has been recorded as a basis to develop a kinetic model that captures the intrinsic kinetics of the methanation of carbon dioxide under process relevant conditions. As rate equations power laws, power laws with inhibition, for instance by water, and Langmuir-Hinshelwood-Hougen-Watson (LHHW) approaches are evaluated. Modeling results emphasize that the kinetics at differential conversions and pure H-2/CO2 feed markedly differ from the regime closer to equilibrium. Power laws with inhibition and adequate LHHW approaches are capable to reflect the kinetics over a wide range of conditions from differential conversion to thermodynamic equilibrium. (C) 2015 Elsevier B.V. All rights reserved.

By means of reactor modeling, externally cooled tubular reactors equipped with metallic honeycombs as catalyst supports are investigated. A 2D pseudo-continuous reactor model is adopted to study in particular heat transfer properties and to identify the influencing parameters as well as transport processes on the reactor performance. It is found that honeycomb reactors can indeed be operated isothermally up to higher cooling temperatures in comparison to fixed-bed reactors. The reduced catalyst inventory, however, prevents attaining thermodynamic equilibrium at low temperatures. Exceeding cooling temperatures adequate for isothermal operation, moderate hot spots can be maintained in a narrow range of cooling temperatures before transition to maximum temperatures in excess of 500 degrees C.

The power-to-gas concept is a promising technology to chemically store energy and therefore a feasible approach to mitigate the challenges of energy transition. Heterogeneous catalysis plays a crucial role in CO 2 conversion to methane using nickel based catalysts. A thorough catalyst characterization facilitates the synthesis of optimized catalyst systems. The determination of reaction kinetics is fundamental for industrial reactor design.

Conductive catalytic honeycombs of a low-void fraction have gained renewed interest for use in the production of bulk chemicals because of favorable heat transfer properties and a low pressure drop compared to fixed-bed reactors. In this work, a pseudocontinuous, heterogeneous 2D conductive honeycomb reactor model is compared to a detailed 3D computational fluid dynamics model for the case of an irreversible, exothermic first order reaction with emphasis on the description of heat transfer. Excellent agreement in terms of maximum temperature and conversion is found for moderate conditions preferable for technical purposes when using the symmetric model for calculation of the effective radial heat conductivity. Deviations of maximum temperatures at harsher conditions are attributed to the use of global heat and mass transfer coefficients in the 1D channel model and the inherent assumption of a radially fully segregated flow in the continuum approach.

The methanation of carbon dioxide has gained renewed interest during the last years as a possible technology to synthesize a feasible chemical energy carrier. This modeling study aims at a basic understanding of the aspects relevant for designing an externally cooled fixed-bed reactor for the methanation of a pure, stoichiometric feed gas. It is shown that the reaction rates and the exothermicity (Delta H degrees = -165 kJ/mol) prevent a fixed-bed reactor of technical dimensions to be operated at high conversions without runaway of the reactor. The model predictions of differently detailed pseudo-homogeneous reactor models and a heterogeneous reactor model where the intraparticle transport of mass is described according to a dusty-gas approach are compared to assess the needed level of detail in terms of modeling the heat transfer, fluid flow characteristics and transport resistances on the pellet scale. Under specific conditions, intraparticle mass transfer and external heat transfer need to be considered for describing the temperature and concentration profiles adequately. The study is completed by modeling a fixed-bed membrane reactor as an example of a structured reactor that offers improved temperature control by separated and controlled feeding. of hydrogen and carbon dioxide. (C) 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.