Intermetallic-Based Materials for Methane Dry Reforming (FWF WEAVE PIN1004125. 03/26-03/92)

The dry reforming of methane (DRM) is a viable heterogeneously catalyzed reaction to convert two harmful greenhouse gases carbon dioxide and methane into syngas (hydrogen and carbon monoxide) that can be further used to produce synthetic fuels. Much effort has been placed into the development of catalyst materials to overcome the coking and sintering limitations of the archetypical Ni-based catalysts. Several material classes have been screened and a common denominator of all systems is the highly dynamic nature of the catalytically active sites that must enable a full reversible methane and carbon dioxide activation-and-release cycle. The reactivity of carbon, due to reactant activation, is therefore crucial to obtain a highly active material. Intermetallic compound-based materials have evolved as particular promising catalyst materials in a variety of reactions due to their outstanding structural and electronic properties, including dry reforming of methane. A leading theme underscoring the highly dynamic nature is the use of intermetallic compounds as precursor materials to in situ form corresponding metal-oxide systems in either the dry reforming mixture or by pre-reduction in hydrogen. These metal-oxide systems then serve as the connector to other more common dry reforming catalysts. This steered decomposition pathway has been developed mostly on Zr-based intermetallic compounds. As such, studies on intermetallic materials mostly rely on materials that can be decomposed, but studies on stable intermetallic compounds are virtually non-existent. To fill this knowledge gap, the project provides a systematic assessment of the catalytic properties of intermetallic compounds in the dry reforming of methane. By comparing a set of cobalt-based intermetallic compounds in the cobalt-antimony, cobalt-gallium and cobalt-tungsten phase diagram, we span the entire stability region of DRM-stable (cobalt-antimony), DRM-unstable (cobalt-gallium, formation of a cobalt-gallium oxide interface) and carbide-forming (cobalt-tungsten) intermetallic compounds. This allows studying and comparing the intrinsic DRM properties of stable intermetallic compounds to those of a metal-oxide composite resulting from in situ decomposition and the reactivity of carbon within the same set of intermetallic compounds using a common leading element. Consequently, this approach enables addressing the teamwork between the different catalytically active components of intermetallic compounds and facilitates the establishment of reliable structure-property relationships in the dry reforming of methane.

If you are interested, please send your application to simon.penner@uibk.ac.at

In situ studies of catalyst deactivation and regeneration in methane dry reforming (ReMade@ARI 34204. 12/24-12/26)

By using Ni-Zr and Pd-Zr alloy catalyst precursors for methane dry reforming (DRM) applications, we study the initial activation, deactivation, and regeneration of the catalyst material by a combination of in situ high-resolution electron microscopy (HR-TEM), electron-energy loss spectroscopy (EELS), energy-dispersive X-ray spectroscopy (EDXS), and secondary electron imaging on a Hitachi 5000 electron microscope. Preliminary catalytic and structural studies by ex situ SEM have revealed that the initial Ni-Zr and Pd-Zr alloys transform into Ni-ZrO₂ and Pd-ZrO₂ with carbon filament formation, successively deactivating the catalyst by Ni and Pd particle encapsulation after several catalytic cycles. For Ni-Zr, we have preliminarily shown that regeneration by a CO₂ treatment is possible via the inverse Boudouard reaction (CO₂+C ↔ 2CO), which leads to carbon removal, partial encapsulation of the larger Ni particles by ZrO₂ layers, corrosion of larger Ni particles into smaller ones with enhanced coking resistance and, in turn, restoration and even improvement of catalytic DRM activity. The results prove that regeneration of coked catalysts by CO₂ is possible, but the structural prerequisites are yet largely unclear. To shed light on the structural transformations of the Ni-Zr alloys in the respective deactivation and regeneration steps, we want to focus on the proposed in situ experiments, especially in the regeneration step. To use the Hitachi 5000 microscope, it is necessary to FIB-cut lamellae parallel to the surface of the support material, as the Ni-Zr and Pd-Zr alloys are prepared on a Zr foil. Catalyst regeneration by CO₂ is a two-fold improvement in catalyst improvement: it avoids oxidative regeneration in oxygen, which often leads to particle sintering and provides an efficient additional means of re-using the harmful greenhouse gas carbon dioxide.

Double Perovskites as Mixed Ionic-Electronic Conductors (FWF EINZEL P 35770. 09/22-10/26)

The main focus of the project “Double Perovskite-based Mixed Ionic-Electronic Conductors (MIEC)” lies on the synthesis and understanding of a new prospective class of double perovskite systems on strontium-iron-vanadium/niobium basis (Sr2Fe1+x(V/Nb)1-xO6-d) with controlled defect chemistry, and their in situ and operando characterization with respect to their use as prospective MIEC materials in solid oxide cells. Double perovskites belong to the class of complex oxides, which - due to their manifold physico-chemical properties – exhibit the potential to substitute to date used conventional materials with unfavorable behavior under extreme experimental conditions in fuel cell systems. To do so, the usual main obstacle of poor structural stability under relevant technological operating conditions has to be overcome. The focus of the project is the direct correlation of in situ/operando-determined redox chemistry and structural stability with catalytic properties in internal reforming reactions. The most important step hereby is the knowledge-based synthesis of the materials under controlled oxygen fugacity to directly steer the defect concentration and the redox behavior. In this respect, we will directly exploit the physico-chemical properties of the constituting elements to influence and trigger favorable material’s properties. Of equal and paramount importance is the structural and (electro-) chemical characterization of the materials under in situ and operando conditions, i.e. in the state of operation.

To achieve these goals, we utilize a portfolio of characterization methods capable of being operated under such close-to-real technological conditions. This includes in situ/operando structural characterization (X-ray diffraction, electron microscopy), electrochemical performance (electrochemical impedance spectroscopy), surface chemical characterization (FT-Infrared Spectroscopy), monitoring the electronic structure (in situ X-ray photoelectron spectroscopy) and quantitatively assessing the defect concentration. The scientific and methodological approach allows us to gain unprecedented insight into the structure-property relationships of double-perovskite materials in the working state of the materials and to optimize generalized synthesis routines to prospective new catalytic materials for SOC operation.

Optimization of Carbon Chemistry in Methane Dry Reforming  (FWF EINZEL P 36926-N. 03/23-07/27)

The main goal of the project “Optimization of the Carbon Chemistry in Methane Dry Reforming” is connected to the in situ/ operando experimental assessment and fundamental understanding of reactive carbon intermediates in different branches of the methane dry reforming network. In depth understanding of carbon reactivity and coke suppression will enable a focused, knowledge-based design of methane dry reforming. The central focus of the project is the direct correlation of the in situ/ operando determined reactivity of different carbon species with catalytic methane dry reforming activity. By exploiting the controlled in situ decomposition of selected intermetallic compounds towards active metal-oxide interfaces, we are able to quantify the reactivity of carbon bound in variable oxidation states between carbides and oxy-carbonates, including the suppression and re-mobilization of coke. The influence of material-specific redox chemistry, involving the the elementary carbon-forming and -converting reactions within the dry reforming network, will be scrutinized. To extract detailed structure-reactivity relationships, we will complement kinetic reactivity studies with in situ/ operando bulk and surface characterization under realistic reaction conditions. To accomplish these tasks, we rely on an exclusive portfolio of in situ and operando characterization methods capable of operation under close-to-technological conditions. This includes in situ/operando structural (X-ray diffraction, electron microscopy, Raman spectroscopy) and surface chemical characterization (X-ray photoelectron spectroscopy and FT-Infrared Spectroscopy), as well as integral quantification of carbon (thermo-gravimetry). We complement this characterization with kinetic reactor studies of important reactions within the dry reforming network and with theoretical assessment of the observed carbon reactivity trends. The controlled in situ decomposition of variable intermetallic precursors allows to induce a broad range of interfacial and bulk carbon species. Our methodological approach will provide novel material-specific insights into viable carbon reaction pathways within the methane dry reforming network.