Low-Temperature Oxidation/ Reduction Catalysts

In conjunction with academia and industry, NASA's Glenn Research Center has developed a range of microelectromechanical systems (MEMS)-based and Silicon Carbide (SiC)-based microsensor technologies that are well-suited for many applications. The suite of technologies includes hydrogen and hydrocarbon leak detection sensors; emissions sensor arrays; and high-temperature contact pads for wire bond connections. Currently used to protect astronauts on the International Space Station, the hydrogen and leak detection sensors have many Earth-based applications as well. They can function as a single-sensor unit or as part of a complete smart sensor system that includes multiple sensors, signal conditioning, power, and telemetry. The system can comprise sensors for hydrogen, hydrocarbons, oxygen, temperature, and pressure. The emissions sensor array features a gas-sensing structure that detects various combustion emission species (carbon monoxide, carbon dioxide, oxygen, hydrocarbons, and nitrogen oxides) over a wide range of concentrations. In addition, the emissions sensor array remains highly sensitive and stable while providing gas detection at temperatures ranging from 450 to 600°C. These new sensors provide a combination of responsiveness and durability that offers great value for a wide range of applications and industries.

The NASA cement innovation describes a method to make solid carbon material from CO2 captured during the cement-making process, and for using that carbon material in the mixture to improve cement properties. Doing so provides a direct use for the captured CO2, eliminating any CO2 storage/disposal issues and providing an improved cement product. The innovation employs a chemical reaction, known as the Bosch process, which uses hydrogen gas and catalysis to reduce the CO2 to solid carbon and water. Cement manufacturing is uniquely suited to the use of the Bosch process. Cement manufacturing requires high temperatures, and harnessing this excess heat limits the total energy required to maintain a Bosch process at a cement plant. Also, cement contains iron, a metal shown to be an exceptional catalyst for the Bosch process. Thus, the cement product itself can be used as the catalyst for the reaction, also serving as a carbon sink. This eliminates any requirements for the storage or disposal of the waste carbon captured from CO2 emissions. Test evaluations at the bench scale have provided encouraging indications of enhanced mechanical properties for the carbon-containing cement materials. In particular, the findings suggest that the carbon in the concrete might delay the environmental breakdown of concrete due to the blocking effect of the carbon on harmful ions (e.g., chlorine).

NASA's Supercritical Water Oxidation - Flame Piloted Vortex (SCWO-FPV) Reactor implements a unique design where heating is primarily supplied by the energetics of the waste stream through the control of a hydrothermal flame in the core of the reactor with the injection of fuel and oxidizer. Once the hydrothermal flame is initiated and stabilized, an outer-core "wash" stream, consisting primarily of water, is injected near the walls at the base of the reactor. This "wash" stream maintains subcritical conditions at the reactor walls, while also dissolving and/or flushing from the reactor any precipitate and non-soluble inorganic materials generated from the supercritical reactor core. Mixing between the core region and the outer subcritical flow region is largely eliminated due to the great differences in density and viscosity. The flow configuration is further stabilized by the generation of a vortex using internal structures on the inside of the reactor wall. An aspirator assembly is positioned at the top of the supercritical core region to extract treated water and un-extracted material is recirculated through the reactor. The rate and amount of aspiration will be determined by product monitoring and will depend on waste stream content and overall operating conditions. Key aspects of the technology have been demonstrated and a prototype reactor is under development.

Current bulk or thick film solid electrolyte CO2 sensors are expensive, difficult to batch fabricate, and large in size. In contrast, this new amperometric, solid-state, oxide-based electrolyte CO2 microsensor is affordable, easy to fabricate, and is so small that it could easily be integrated onto a substrate the size of a postage stamp. The basic composition of the sensor is identical to a previously designed NASA Glenn technology in which a solid electrolyte of Na3Zr2Si2PO12 is deposited between interdigitated electrodes on an alumina substrate and is covered by Na2CO3/BaCO3. Unlike its predecessor, however, this innovation includes an additional layer of nanocrystalline SnO2 sol gel, an electron donor type (N-type) semiconductor, on top of the Na2CO3/BaCO3 . This new layer provides a greater number of electrons for reduction reaction at the working electrode to detect CO2. As a result, overall performance is enhanced, and this new state-of-the-art sensor has the ability to operate at temperatures as low as 375°C. This low temperature capability significantly decreases the amount of power required to operate the sensor, opening the door to a multitude of new applications that were previously unattainable.

This technology consists of a photoelectrochemical cell composed of thin metal oxide films. It uses sunlight (primarily the ultraviolet (UV), visible and Infrared (IR) portions)) and inexpensive titanium dioxide composites to perform the reaction. The device can be used to capture carbon dioxide produced in industrial processes before it is emitted to the atmosphere and convert it to a useful fuel such as methane. These devices can be deployed to the commercial market with low manufacturing and materials costs. They can be made extremely compact and efficient and used in sensor and detector applications.