Start | Grid View | Browse by Day OR Group/Topical | Author Index | Personal Scheduler

CO,Sub>x-Free Hydrogen Via NH3 Decomposition On K-Promoted Ru Catalysts Derived From KRu4O8

Monday, November 9, 2009: 4:40 PM
Tennessee A (Gaylord Opryland Hotel)

Elizabeth D'Addio, University of Delaware, Newark, DE
William D. Pyrz, Chemical Engineering, University of Delaware, Newark, DE
Hua Yang, Chemical Engineering, University of Delaware, Newark, DE
Douglas Buttrey, Chemical Engineering, University of Delaware, Newark, DE
Jochen Lauterbach, Chemical Engineering, University of Delaware, Newark, DE

Discovery of an ammonia decomposition catalyst that is active at low temperatures is essential to ensuring the viability of ammonia for use as a chemical carrier for on-board hydrogen production.  Toward this end, an extensive search of materials and synthesis conditions was undertaken to identify promising catalysts. The most dramatic improvement in NH3 conversion was achieved by promoting Ru supported on g-Al2O3 with K; at 350°C and GHSVNH3=4,000 g·mL/h, NH3 conversion was increased from 10% with unpromoted Ru to 65% with K promotion.

             Extensive characterization of this catalyst throughout the synthesis process revealed the formation of an mixed-metal Ru oxide phase after calcination of the catalyst. XRD, EDS, bright field TEM and HAADF imaging were used to identify this crystalline phase as hollandite (KRu4O8), which manifested itself as a network of “whiskers” dispersed on the surface of the g -Al2O3 support. Upon exposure to NH3, the hollandite whiskers reduced to Ruo particles. NH3 decomposition was observed, however it was unknown if or how the hollandite contributed to the active sites.  KRu4O8 whiskers were isolated from the supported catalyst and tested for activity; the whiskers were reduced to Ruo particles that showed significant NH3 conversion.

            Based on these results, we proposed that the reduction of the oxide hollandite to a well-dispersed Ru phase was the mechanism by which the K-promoted Ru catalyst was able to achieve high NH3 conversion. Recent high resolution microscopy provides strong supporting evidence; atomic scale images of the hollandite after initiation of the degradation process show the onset of formation of Ruo particles with high dispersion. Furthermore, by exploring preparation treatments to the K-promoted Ru system, a correlation was found between hollandite formation after calcination and high NH3 conversion in reaction conditions. The behavior of hollandite as a sacrificial structure to a well-dispersed active phase may indicate a novel method of achieving nanoparticle catalysts derived from a unique precursor material.

 

Extended Abstract: File Not Uploaded
See more of this Session: Catalytic Hydrogen Generation for Fuel Cell Applications II
See more of this Group/Topical: Catalysis and Reaction Engineering Division