Catalysts Promoted with Niobium Oxide for Air Pollution Abatement

Pt-containing catalysts are currently used commercially to catalyze the conversion of carbon monoxide (CO) and hydrocarbon (HC) pollutants from stationary chemical and petroleum plants. It is well known that Pt-containing catalysts are expensive and have limited availability. The goal of this research is to find alternative and less expensive catalysts to replace Pt for these applications. This study found that niobium oxide (Nb2O5), as a carrier or support for certain transition metal oxides, promotes oxidation activity while maintaining stability, making them candidates as alternatives to Pt. The present work reports that the orthorhombic structure of niobium oxide (formed at 800 °C in air) promotes Co3O4 toward the oxidation of both CO and propane, which are common pollutants in volatile organic compound (VOC) applications. This was a surprising result since this structure of Nb2O5 has a very low surface area (about 2 m2/g) relative to the more traditional Al2O3 support, with a surface area of 150 m2/g. The results reported demonstrate that 1% Co3O4/Nb2O5 has comparable fresh and aged catalytic activity to 1% Pt/γ-Al2O3 and 1% Pt/Nb2O5. Furthermore, 6% Co3O4/Nb2O5 outperforms 1% Pt/Al2O3 in both catalytic activity and thermal stability. These results suggest a strong interaction between niobium oxide and the active component—cobalt oxide—likely by inducing an oxygen defect structure with oxygen vacancies leading to enhanced activity toward the oxidation of CO and propane

The Role of Ruthenium in CO2 Capture and Catalytic Conversion to Fuel by Dual Function Materials (DFM)

Development of sustainable energy technologies and reduction of carbon dioxide in the atmosphere are the two effective strategies in dealing with current environmental issues. Herein we report a Dual Function Material (DFM) consisting of supported sodium carbonate in intimate contact with dispersed Ru as a promising catalytic solution for combining both approaches. The Ru-Na2CO3 DFM deposited on Al2O3 captures CO2 from a flue gas and catalytically converts it to synthetic natural gas (i.e., methane) using H2 generated from renewable sources. The Ru in the DFM, in combination with H2, catalytically hydrogenates both adsorbed CO2 and the bulk Na2CO3, forming methane. The depleted sites adsorb CO2 through a carbonate reformation process and in addition adsorb CO2 on its surface. This material functions well in O2- and H2O-containing flue gas where the favorable Ru redox property allows RuOx, formed during flue gas exposure, to be reduced during the hydrogenation cycle. As a combined CO2 capture and utilization scheme, this technology overcomes many of the limitations of the conventional liquid amine-based CO2 sorbent technology

Part II: Oxidative Thermal Aging of Pd/Al2O3 and Pd/CexOy-ZrO2 in Automotive Three Way Catalysts: The Effects of Fuel Shutoff and Attempted Fuel Rich Regeneration

The Pd component in the automotive three way catalyst (TWC) experiences deactivation during fuel shutoff, a process employed by automobile companies for enhancing fuel economy when the vehicle is coasting downhill. The process exposes the TWC to a severe oxidative aging environment with the flow of hot (800 °C–1050 °C) air. Simulated fuel shutoff aging at 1050 °C leads to Pd metal sintering, the main cause of irreversible deactivation of 3% Pd/Al2O3 and 3% Pd/CexOy-ZrO2 (CZO) as model catalysts. The effect on the Rh component was presented in our companion paper Part I. Moderate support sintering and Pd-CexOy interactions were also experienced upon aging, but had a minimal effect on the catalyst activity losses. Cooling in air, following aging, was not able to reverse the metallic Pd sintering by re-dispersing to PdO. Unlike the aged Rh-TWCs (Part I), reduction via in situ steam reforming (SR) of exhaust HCs was not effective in reversing the deactivation of aged Pd/Al2O3, but did show a slight recovery of the Pd activity when CZO was the carrier. The Pd+/Pd0 and Ce3+/Ce4+ couples in Pd/CZO are reported to promote the catalytic SR by improving the redox efficiency during the regeneration, while no such promoting effect was observed for Pd/Al2O3. A suggestion is made for improving the catalyst performance

Part I: A Comparative Thermal Aging Study on the Regenerability of Rh/Al2O3 and Rh/CexOy-ZrO2 as Model Catalysts for Automotive Three Way Catalysts

The rhodium (Rh) component in automotive three way catalysts (TWC) experiences severe thermal deactivation during fuel shutoff, an engine mode (e.g., at downhill coasting) used for enhancing fuel economy. In a subsequent switch to a slightly fuel rich condition, in situ catalyst regeneration is accomplished by reduction with H2 generated through steam reforming catalyzed by Rh0 sites. The present work reports the effects of the two processes on the activity and properties of 0.5% Rh/Al2O3 and 0.5% Rh/CexOy-ZrO2 (CZO) as model catalysts for Rh-TWC. A very brief introduction of three way catalysts and system considerations is also given. During simulated fuel shutoff, catalyst deactivation is accelerated with increasing aging temperature from 800 °C to 1050 °C. Rh on a CZO support experiences less deactivation and faster regeneration than Rh on Al2O3. Catalyst characterization techniques including BET surface area, CO chemisorption, TPR, and XPS measurements were applied to examine the roles of metal-support interactions in each catalyst system. For Rh/Al2O3, strong metal-support interactions with the formation of stable rhodium aluminate (Rh(AlO2)y) complex dominates in fuel shutoff, leading to more difficult catalyst regeneration. For Rh/CZO, Rh sites were partially oxidized to Rh2O3 and were relatively easy to be reduced to active Rh0 during regeneration

Parametric and laboratory aging studies of direct CO2 air capture simulating ambient capture conditions and desorption of CO2 on supported alkaline adsorbents

Alkali and alkaline earth metal oxides dispersed on high surface area γ-alumina were studied for the selective adsorption of CO2 under simulated ambient direct air capture (DAC) and subsequent temperature programmed desorption. Thermogravimetric analysis showed Na2O/γ-Al2O3 had superior adsorption and desorption via temperature programed desorption (TPD) relative to other supported metal oxides. Parametric and laboratory aging studies were conducted under simulated direct air capture of 400 ppm CO2, reflecting seasonal and locational ambient temperature and humidity conditions. Initial studies were performed on granular carriers and subsequently on washcoated ceramic monoliths. Aging studies were conducted on sample compositions of 10% Na2O/γ-Al2O3 granules and 10% Na2O + PX-80 γ-Al2O3 washcoat, deposited on a cordierite automotive-catalytic converter type monolith designed for low pressure drop in high air flow rates. Both selective adsorption and desorption of CO2 showed high stability with no signs of deactivation after 400+ hours of cyclic testing under a wide variety of simulated ambient conditions

Ceria-based palladium zinc catalysts as promising materials for water gas shift reaction

The production of hydrogen for fuel cell applications requires several fuel processing steps, including CO removal by means of the water gas shift (WGS) and CO preferential oxidation reactions. In this work we investigate the behavior of palladium\u2013zinc supported on CeO2, Ce0.5Zr0.5O2 and ZrO2 as a promising alternative to low temperature WGS catalysts for fuel processing.WGS activity is optimized when the PdZn alloy is formed. Ceria-containingmaterials showlittle deactivation during startup\u2013shutdown cycles in reformate gas and for palladium\u2013zinc supported on pure ceria the activity can be fully recovered by an in situ reduction treatment

The Role of Ruthenium in CO2 Capture and Catalytic Conversion to Fuel by Dual Function Materials (DFM)

Development of sustainable energy technologies and reduction of carbon dioxide in the atmosphere are the two effective strategies in dealing with current environmental issues. Herein we report a Dual Function Material (DFM) consisting of supported sodium carbonate in intimate contact with dispersed Ru as a promising catalytic solution for combining both approaches. The Ru-Na2CO3 DFM deposited on Al2O3 captures CO2 from a flue gas and catalytically converts it to synthetic natural gas (i.e., methane) using H2 generated from renewable sources. The Ru in the DFM, in combination with H2, catalytically hydrogenates both adsorbed CO2 and the bulk Na2CO3, forming methane. The depleted sites adsorb CO2 through a carbonate reformation process and in addition adsorb CO2 on its surface. This material functions well in O2- and H2O-containing flue gas where the favorable Ru redox property allows RuOx, formed during flue gas exposure, to be reduced during the hydrogenation cycle. As a combined CO2 capture and utilization scheme, this technology overcomes many of the limitations of the conventional liquid amine-based CO2 sorbent technology