This Small Business Innovation Research (SBIR) Phase I project will demonstrate the technical and commercial viability of a novel four-way catalytic converter for lean burn diesel applications that is based on high-surface area nanomaterials applied directly to the inner walls of existing catalytic converter monoliths. While there is ongoing research to integrate diesel particulate filters and the oxidation catalyst, there is little research addressing the integration of all four components (oxidation of carbon monoxide, oxidation of hydrocarbons, capture and destruction of carbon particulate matter (PM) and reduction of NOx.
The broader/commercial impacts of this research are that in 2013 strict requirements for diesel emissions standards will become law. These new regulations will effect carbon emissions both in terms of particle size and number of particles. While there are proposals to meet impending PM regulations, none actively integrate all the required functions of a catalytic converter. Therefore the potential U.S. commercial value of the catalytic converter structure from this project is significant. The European market opportunity may be larger since diesel engines are more prevalent in Europe.
Summary: Under the auspices of this NSF SBIR Phase I/IB funding, GoNano Technologies, Inc. has been working on determining the viability and commercial feasibility of incorporating the company's silica Nanospring™ material into catalytic converter (CC) applications. This report describes in detail the progress made in this application. The Nanospring mat provides a high surface area (~ 400m2/g) support for the active catalyst, which can be easily deposited using solution-based techniques such as wet impregnation. The Nanospring support is stable at high temperatures maintaining its morphology and retaining its surface area up to 1025°C where it begins to sublime. The standard catalyst support in the CC industry is alumina, which has a surface area ~ 140m2/g, but when exposed to high temperatures over long periods of use it degrades and its surface area reduces eventually to ~ 20m2/g. During the period of this NSF award, GoNano Technologies was able to further analyze the practicality and develop some cost estimates regarding the deposition of Nanosprings inside CC cores. GoNano Technologies has worked on assessing the benefits of using Nanosprings in CC applications by first showing the ability of the silica Nanosprings to inhibit catalyst particle growth; a common problem seen when the catalyst is exposed to harsh environments over a long time. In previous work it was shown that the Nanosprings stabilized supported gold nanoparticles and prevented them from sintering even at elevated temperatures (600°C in the case of Au). Under the auspices of this grant it was found that both platinum and palladium nanoparticles supported on silica Nanosprings were able to resist sintering under hydrothermal aging (800oC at 10% relative humidity) for 16 hours and remain catalytically active. This result not only shows that Nanosprings offer a significant benefit over existing oxide supports, but also that silica Nanosprings do not poison the precious metal catalyst, which is often observed when these metals are supported on other forms of silica. The initial studies conducted by GoNano Technologies demonstrated that Nanosprings are a viable catalyst support. Experiments done in-house demonstrated that the Nanosprings could add some stability to catalyst particles during aging conditions. Both platinum and palladium nanoparticles were found to ripen very little and experiments showed that they were not "poisoned" by the silica during aging. Stainless steel foil substrates were found to be rather simple to grow the Nanosprings on. The configuration of rolling up the steel foil to make monoliths meshed well with the established procedures used at GoNano Technologies. For this reason GoNano Technologies decided to use metallic substrates for most of its investigations. It is highly expected that the Nanospring growth process could be configured to a roll-to-roll process using this metal foil, such that any size core could be made. The external collaborators we engaged all had different ideas of the configurations in which they would like to evaluate the Nanosprings. Most companies desired to first compare the Nanosprings as a support in a diesel oxidation catalyst (DOC) configuration against the standard alumina washcoat. GoNano Technologies coated both ceramic materials and metal substrates with the Nanosprings and even various thicknesses of Nanosprings to satisfy these evaluations. Most of these companies have not yet completed their evaluations and have asked GoNano Technologies for variations in the Nanospring configuration or for more samples. GoNano Technologies identified the potential of Nanosprings in DOC applications and realized that they should undertake some in-house experiments rather than rely on external partners to share all their data. GoNano Technologies coated 1" OD x 3" long metallic substrates (EcoCat 150cpsi) with Nanosprings and performed side-by-side comparison of those cores compared to equivalent washcoated cores. Unfortunately, none of the tests came back very promising. All of the cores with the standard washcoat out-performed the Nanospring cores. However, it became evident that the impregnation procedure was causing variation in the performance and needed to be improved. GoNano Technologies began to re-investigate some of the coating techniques and feels that there are improvements that can be made. It also became evident that the thickness of the Nanospring layer needs to be maximized to provide surface areas close to that of standard alumina washcoat loadings. GoNano Technologies has been able to maximize the Nanospring layer on planar substrates, and is attempting to translate this over to monoliths. GoNano Technologies continues to work on improving the problems seen during this grant and is hopeful that some of the data that has yet to be delivered from industrial partners comes back showing that the Nanosprings can be used to improve catalytic converters or diesel particulate filters.
