This work is motivated by the need to find a controllable preparation method of high surface area metal/oxide catalysts for the production of hydrogen from the oxidative reforming of methanol (ORM) for small fuel cell applications. The objective of the research is twofold: 1) to study a novel method for catalyst preparation based on solution combustion synthesis, referred to as Impregnated Layer Combustion Synthesis, or ILCS, and, 2) develop structure-activity correlations of catalysts prepared by the ILCS method for the ORM reaction along with spectroscopic studies to identify active sites and links those with surface and material properties.
Preliminary studies conducted in the PIs groups' show that Pd/Cu/ZnO/ZrO2 catalysts prepared by co-precipitation are active and selective for the ORM reaction. The PIs have also identified the Cu metal surface area and oxidation state as determining factors of activity and selectivity. The ILCS method has shown to yield high surface area oxides as well as metals supported onto high area oxides. The ILCS method involves the controlled propagation of a reaction front in a narrow area for a short time, which along with the evolution of gases, inhibits particle size growth leading to the formation of oxides of high surface area (50-200 m2/g), high purity and crystallinity, which do not require additional calcination. A proof of concept is provided that by using ILCS they were able to synthesize a catalyst that has high area and activity and selectivity similar to co-precipitated catalyst. Further studies of the ILCS method are expected to yield even higher active areas and increase activity and selectivity.
On the basis of the above results they hypothesize that i) Fundamental understanding of how preparative variables of ILCS affect material properties will lead to the design of active and selective catalysts for the ORM reaction, ii) Establishing structure-activity correlations for ORM reactions could lead to the rational design of more active and selective oxidation catalysts.
A detailed program is planned to study how the preparative variables used in ILCS (solution concentration, fuel composition, substrate impregnation, ignition temperature) affect the bulk material and surface properties such as total and active surface area, degree of crystallinity, phase composition, dispersion of promoters, and oxidation state under different environments. Activity and selectivity results for various catalysts prepared by ILCS will be evaluated by various advanced techniques. The kinetics of selected catalysts will be measured in detail for correlation with the material properties and preparative variables. EXAFS and IR spectroscopy of selected catalysts will be used to determine the catalysts' oxidation state and type of adsorbates under reaction conditions (operando) and to determine the key surface variable(s) responsible for activity and selectivity. The rate constants from the kinetics studies will be then correlated with the key surface properties and these in turn with the ILCS preparative variables.
The results obtained will provide new knowledge of the novel ILCS as a method for the rational design of oxidation catalysts as well as the factors determining hydrogen production from the ORM. The intellectual merit is that through the combined expertise of the PIs, new knowledge will be gained in the field of catalysts synthesis applied to the problem that is currently of considerable societal importance and could have a broad technical impact. The comprehensive program proposed will integrate research at both the graduate level, and at undergraduate level via REU grants. A broader educational impact is planned by setting aside funds for supporting the effort of the minority engineering program at Notre Dame to help increase recruiting of underrepresented groups in engineering. The funds will support an outreach program to bring prospective students to Notre Dame and have them participate on experiments related to this proposal.
The objective of the studies funded by this grant was to investigate a new method to prepare catalysts for the production of hydrogen from alcohols obtained from biomass (methanol and ethanol). The hydrogen thus produced is to be used in a fuel cell to produce electricity. The new method of catalysts preparation is based on the so-called Solution Combustion Synthesis (SCS) approach in which a reaction propagates in a form of a steady-state self-sustained combustion wave leading to the formation of the desired solid-state products. First we studied variation of SCS referred as Impregnated Layer Combustion Synthesis or ILCS , but later we used a controlled mode of SCS for the preparation of catalysts and metal nano-particles We first studied the preparation of catalysts by ILCS for hydrogen production from methanol using materials that were known to be good catalyst for that reaction including copper and zinc oxides. A comprehensive investigations of the thermal profiles of the ILCS reaction wave combined with detailed studies of the microstructural transformations of reactants and products allowed us precisely control of the SCS process and yielded catalysts that were more active and selective than the ones prepared by standard co-precipitation methods. A detailed theoretical model was developed for the first time including the main reactions and processes experimentally observed during the preparation. This model helped to understand better the ILCS method to prepare catalysts, and to extend it to a controlled SCS method for preparing catalysts active for the conversion of ethanol to hydrogen. We found that a catalyst containing several components including copper, nickel, and iron prepared by SCS, was among the most active and selective when compared with literature reports. Detailed studies of the effect of operating variables on the combustion synthesis reaction led to determining conditions to prepare for the first time metal nano-particles using combustion synthesis. The complex multi-metallic catalysts were studied by a multi-technique approach, of which the use of the Advanced Photon Source using X-rays generated from a synchrotron, was the most powerful and advanced application. These studies led to the discovery of the oxidation state of the catalyst that was the most active and selective for the production of hydrogen. The studies are summarized in nine publications. It can be concluded that the main objectives of the proposed research program were fully accomplished, allowing us to develop the fundamental bases for using SCS for catalyst’s preparation. Based on the fundamental knowledge gained we succeeded in controlling the synthesis of variety of effective catalysts, which showed high activities for hydrogen production from both methanol and ethanol. Furthermore, the results obtained increased the scope of materials that can be produced by the SCS approach, which now also includes pure metals and alloys. The methods developed can be used for designing controllable technologies for production of novel nano-materials for a variety of applications including pigments, fuel cells, catalysts, and solar cells. The broader impact of this project was the formation of the 2 PhDs that worked in this project, who are now gainfully employed in the US, and one undergraduate student (REU grant). In addition, a startup company, Nanosyntek, to produce nano-powders was founded by the coPIs. The results obtained will help the development of more effective catalysts for hydrogen generation, and thus of environmentally friendly alternative fuels contributing to our society future energy needs.
