Ammonia Decomposition in the Process Chain for a Renewable Hydrogen Supply

This review article deals with the challenge to identify catalyst materials from literature studies for the ammonia decomposition reaction with potential for application in large-scale industrial processes. On the one hand, the requirements on the catalyst are quite demanding. Of central importance are the conditions for the primary reaction that have to be met by the catalyst. Likewise, the catalytic performance, i.e., an ideally quantitative conversion, and a high lifetime are critical as well as the consideration of requirements on the product properties in terms of pressure or by-products for potential follow-up processes, in this case synthesis gas applications. On the other hand, the evaluation of the multitude of literature studies poses difficulties due to significant varieties in catalytic testing protocols

Carbon Aerogel-Supported Iron for Gasification Gas Cleaning: Tars Decomposition

Tar removal from gasification gases is a determinant step to guarantee the operational feasibility of gasification-to-chemicals/energy systems. However, this is a very complex process requiring catalytic materials to proceed under reasonably low temperatures and to convert the tars into fuel gases (i.e., CHx). The use of Fe-based catalysts for application has been reported before, however, there are still unsolved questions related to its stability and interaction with some species of gasification gases. Therefore, we evaluated carbon-supported Fe for the decomposition of tar using simulated gasification gases, and toluene, naphthalene, and benzene as models for tar. The effects of temperature (565 < T < 665 °C) and co-feeding CO on the catalytic activity and stability were inspected at laboratory and bench scales. The activity of catalysts for decomposing tars was in the following order: benzene > toluene e > naphthalene. Moreover, there was evidence validating a reversible elemental step toluene⇔benzene over the Fe surface. The characterization of the spent catalysts evidenced the oxidation of the active phase and the carbon deposition on the surface. The formation of FexOy caused a marked loss of activity. Conversely, the carbides were stable and still active for tar decomposition

Carbon Aerogel-Supported Iron for Gasification Gas Cleaning: Tars Decomposition

Tar removal from gasification gases is a determinant step to guarantee the operational feasibility of gasification-to-chemicals/energy systems. However, this is a very complex process requiring catalytic materials to proceed under reasonably low temperatures and to convert the tars into fuel gases (i.e., CHx). The use of Fe-based catalysts for application has been reported before, however, there are still unsolved questions related to its stability and interaction with some species of gasification gases. Therefore, we evaluated carbon-supported Fe for the decomposition of tar using simulated gasification gases, and toluene, naphthalene, and benzene as models for tar. The effects of temperature (565 toluene e > naphthalene. Moreover, there was evidence validating a reversible elemental step toluene⇔benzene over the Fe surface. The characterization of the spent catalysts evidenced the oxidation of the active phase and the carbon deposition on the surface. The formation of FexOy caused a marked loss of activity. Conversely, the carbides were stable and still active for tar decomposition

Carbon Aerogel-Supported Nickel and Iron for Gasification Gas Cleaning. Part I: Ammonia Adsorption

Biomass gasification is a promising way to obtain “green energy”, but the gas composition makes it unsuitable for use in traditional technologies (i.e., IC engine). Gas purification over nickel and/or iron catalysts is an attractive alternative. Cellulose-based carbon aerogels (CAGs) have shown suitable physical chemical properties for use as catalyst supports. In this work, nickel and iron catalysts are supported on CAG made from cellulose microfibers. Microfibers were impregnated with (NH4)2SO4 to increase the mass yield. Carbonization was evaluated at different heating rates, maximum temperatures, and dwell times to generate CAGs. Resulting chars were characterized by N2 adsorption, X-ray diffraction (XRD), and Raman spectroscopy. The CAG with better properties (specific surface, pore size, thermal resistance) was impregnated with the metal precursor salt via incipient wetness and treated with H2. Catalysts were characterized by transmission electron microscopy (TEM), XRD, N2 adsorption, and inductively coupled plasma optical emission spectrometry (ICP-OES). Ammonia adsorption was studied over CAG and catalysts to estimate the thermodynamic parameters. The impregnation with ((NH4)2SO4 improves thermal resistance of the char obtained from carbonization. The catalysts exhibit higher adsorption capacity than CAG (without metal), indicating chemical interaction between ammonia and metals. The metal-ammonia interaction is stronger on Fe than on Ni catalyst, which is consistent with reported theoretical calculations