Hydrogen-Based Fuel Cells Will Reduce Diesel Emissions Using Novel Catalyst Technology

Professional truck drivers are mandated to rest for 10 hours after every 11 hours of driving, and they typically leave their engines idling to provide heating, ventilation, and air conditioning to the cabin where they sleep and to power other electrical devices. The 2.2 million diesel trucks that haul goods across the United States produce an estimated 11 million tons of carbon dioxide, 200,000 tons of nitric oxide, and 5,000 tons of particulate matter annually, while wasting more than 1 billion gallons of fuel. Auxiliary power units that incorporate solid oxide fuel cells (SOFCs) would allow drivers to obtain power from a cleaner, more efficient power source and could open the door for the use of similar units in large-scale commercial power plants.

SOFCs are high-efficiency devices that combine hydrogen and oxygen in an electrochemical reaction to produce electricity and water. The hydrogen can be produced by converting hydrocarbons into syngas, a gas mixture of hydrogen and carbon monoxide, in a process called reforming. Methods for generating syngas from simple hydrocarbons such as methane routinely involve the use of a catalyst, but the high sulfur and aromatic content of heavier more complex fuels such as diesel pose a challenge because these components can deactivate conventional catalysts. Unfortunately, no economically feasible catalyst is available to reform diesel and coal-based fuels into hydrogen-rich syngas for use in SOFCs.

Pyrochlores (A2B2O7) - A and B are metals incorporated into the structure in various combinations. This means the pyrochlore catalyst can be customized to reform a range of fuels under varying conditions.

To minimize catalyst deactivation, also called catalyst poisoning, National Energy Technology Laboratory (NETL) researchers developed the novel idea of incorporating active metals into the crystal structure of a thermally stable material: pyrochlore. The unique crystalline structure of pyrochlore allows for chemical modifications tailored to specific fuels and reaction conditions. Development of this technology has resulted in two patent-pending inventions: one for using pyrochlore catalysts in hydrocarbon-reforming processes, and the other for a method of optimizing the performance of pyrochlore catalysts for a particular application or specific operating condition. Together these inventions help overcome the limitations of current catalysts by efficiently reforming diesel fuel while maintaining thermal stability and resistance to sulfur, aromatics, and carbon formation.

Pyrochlore catalysts are less expensive and longer lasting then currently available catalysts for reforming heavy hydrocarbons. Moreover, pyrochlore catalysts can use either air or water (or both in varying proportions) as oxidants, making them extremely flexible to system design and consumer requirements. Because they can use air as the oxidant rather than water as most commercially viable catalysts do, pyrochlore catalysts will contribute to reducing the weight, operating size, complexity and system cost of mobile SOFCs while maintaining their high efficiency.

NETL's collaborative research to develop novel pyrochlore catalysts for reforming of hydrocarbon fuels was recently recognized with a 2012 Research Collaboration Award. This award, given each year by the Council for Chemical Research (CCR), honors a team of professionals in the field, whose combined efforts have made an outstanding contribution to the advancement of chemistry-related science or engineering. CCR is a nonprofit organization dedicated to advancing research in chemistry, chemical engineering and related disciplines. Representing a collaboration of industry, academia, and other government agencies, the award-winning team demonstrated superior function and value of the pyrochlore-based reforming catalyst, and has made significant advances in development and deployment of a commercially viable product.

A vial of diesel fuel and a vial of NETL's pyrochlore catalyst are pictured with a monolith structure to which the catalyst will be applied.

Developing stable catalysts for use in fuel reforming to produce hydrogen-rich synthesis gas is critical for enabling SOFC-based auxiliary power units (APUs) that can eventually be used in commercial power plants and in wide-scale commercialization. The potential of this technology has recently been recognized through the execution of an exclusive licensing agreement with the newly-formed Pyrochem Catalyst Corporation (PCC). NETL will continue to collaborate with PCC to further develop pyrochlore catalysts for use in fuel cell-based auxiliary power units and other commercial and military power applications.