Sustainable generation of fuels through the catalytic conversion of CO2 is an area of research that has the potential to enhance national energy security while simultaneously providing a mechanism to minimize direct CO2 emissions. Previous studies on CO2 photoreduction to fuels have utilized TiO2-based catalysts. A major challenge that exists with utilizing TiO2 as a photocatalyst for CO2 photoreduction is the fast recombination of electron-hole pairs which are formed by light irradiation. Electrons are needed to generate products via reduction of CO2. Efforts to minimize charge recombination are critical for enhancing product formation. Despite past efforts at modifying the TiO2-based catalysts using both metal and non-metal modifiers, published data shows relatively low production rates for useful products. Typical products include CO and valuable fuel products such as CH4 and CH3OH. Several of the catalysts resulted in the formation of multiple products, resulting in the need for gas separation technologies when the catalyst is implemented in a real-world scenario.
Preliminary experiments in the laboratories of Professor Jean Andino at Arizona State University have shown promise for a composite catalyst of RGO-TiO2, reduced graphite oxide and titania. The RGO can potentially assist in minimizing charge recombination when TiO2 is activated by light, thereby making more electrons available for a surface CO2 reduction reaction. A potential challenge with using reduced graphite oxide is whether the interlayer spacing would be sufficient to allow TiO2 to reside between the RGO layers. A modified RGO structure with increased interlayer spacing would alleviate this concern. Moreover, if the modifier for the RGO is capable of selectively attracting CO2 as compared to hydrocarbons, then this may allow for enhanced functionality. Published data show that CO2 is strongly attracted to ionic liquids. Andino hypothesizes that an ionic liquid (IL) functionalized RGO-TiO2 would result in the attraction of CO2, sufficient charge separation within the TiO2 (making electrons available for the CO2 photoreduction reaction), and rejection of the produced hydrocarbons, such as CH4, thus reducing separation needs.
Andino has performed preliminary work to synthesize the IL-RGO/TiO2 catalyst and to test the characteristics of the catalyst for the reduction of CO2 to hydrocarbons in the presence of water vapor. The DRIFTS studies showed the IL-RGO/TiO2 catalyst appears to lead to the selective and fast formation of CH4 in the absence of any CO. The CH4 production rate from CO2 photoreduction is more than 30 times higher than that which was published by any other research group. The results (taken in conjunction with literature data) suggest that the newly developed IL-RGO/TiO2 catalyst produces CH4 at a rate that is far superior to any other existing catalyst.
This is an ideal basis for this EAGER award. Researchers typically use GC techniques to quantify the data and not the DRIFTS IR spectroscopy technique. Furthermore the impact of oxygen presence on product yield needs to be known. The proposed EAGER award will provide the necessary data to confirm the observation and generate additional data to support a full investigation.
This EAGER is expected to have several broader impacts in the catalysis area and will broaden participation in the field. First, the data that will be generated will help to establish the usefulness of the IL-RGO/TiO2 catalyst in the direct and selective generation of a valuable fuel (CH4). This work could have significant impacts in the areas of national energy security and the control of CO2 emissions. The proposed project would be used to partially fund two traditionally underrepresented chemical engineering graduate students. The experience of working on the proposed project that has a strong connection to society?s grand challenges has already inspired these students, and is expected to help retain them in science and engineering. The expectation is that both students will make sufficient progress so that at least one peer-reviewed paper will be submitted and presentations made locally and also at annual meetings of either the American Chemical Society, the American Institute of Chemical Engineers, or the Air and Waste Management Association in 2013.
Intellectual Merit: Discussions, particularly over the last two years, on the development of new laws to restrict carbon emissions have increased the importance of developing new technologies for the control of carbon dioxide (CO2) emissions from stationary sources. Typically the public addresses the control of carbon emissions by considering carbon capture and geological sequestration. While there are advantages to geological sequestration, published research also suggests that there are still many uncertainties. This EAGER proposal provided preliminary studies to investigate an alternative method for dealing with CO2 emissions, i.e. the recycling of CO2 to useful fuels by reacting the CO2 in the presence of water vapor, a novel catalyst, and light. This method is particularly attractive since it serves as a technique for reducing CO2 emissions from sources while simultaneously generating useful compounds (e.g. methane), rather than simply storing the CO2. This NSF EAGER work specifically focused on further developing a catalytic material that could be used for the selective conversion of CO2 and water vapor to energy-rich compounds (e.g. methane). Several important accomplishments resulted from this preliminary work. Specifically, the project team was able to synthesize and test novel catalysts with different fractions of the active components. The novel composite materials exhibited optical properties (absorbance) in both the ultraviolet (UV) and the visible range. The absorbance of light in the visible range was at a level that was significantly different from the base material that was used in the syntheses. This suggested that the composite materials might have wider applicability as compared to the base material. The CO2 reaction with water vapor over different samples of the novel composite materials was examined upon activation of the surface with light. Different product distributions were noted depending on the fractions of raw materials used in the syntheses composites, as well as differences in the syntheses methods and analytical protocols that were used to monitor the products. Product distributions ranged from pure methane formation with no carbon monoxide to systems where predominantly carbon monoxide was formed with small amounts of methane. In all cases the absolute amount of CO2 that was converted was still very low. However, the work that was performed succeeded in (a) examining syntheses protocols, (b) analytical operating procedures, and (c) training new, diverse researchers. Moreover, the work established the need for new analytical approaches that could simultaneously monitor both surface bound and desorbed products, and led to a patent-pending technology. The technology that was developed in this project was licensed by Arizona State University to an Arizona small business (Next Potential, LLC). Preliminary data have been generated though this EAGER funding, and additional fundamental research questions as well as a path for follow on work have been determined. It is expected that the licensing activity will help to enhance additional fundamental development as well as accelerate the translation of university-based laboratory work to practical use. Two graduate students and one undergraduate student were trained, one conference proceeding was published, and additional collaborative work with new researchers to apply the technology in different ways was initiated. Broader Impacts: The generation of fuels from the recycling of carbon dioxide has the potential to further enhance domestic energy security. In the past the United States has been a net energy consumer. While the gap between the production and consumption of energy in the US has narrowed, having additional sources of fuels for energy production would significantly stabilize the US energy portfolio. This EAGER project has provided seed funding to gather additional data that will enable the project team to seek additional federal or private industry funding to enhance future development.
