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Hanson, Jonathan C.

Publications and source records attributed to Hanson, Jonathan C..

5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Achieving Atomic Dispersion of Highly Loaded Transition Metals in Small‐Pore Zeolite SSZ‐13: High‐Capacity and High‐Efficiency Low‐Temperature CO and Passive NO x Adsorbers

Abstract The majority of harmful atmospheric CO and NO x emissions are from vehicle exhausts. Although there has been success addressing NO x emissions at temperatures above 250 °C with selective catalytic reduction technology, emissions during vehicle cold start (when the temperature is below 150 °C), are a major challenge. Herein, we show we can completely eliminate both CO and NO x emissions simultaneously under realistic exhaust flow, using a highly loaded (2 wt %) atomically dispersed palladium in the extra‐framework positions of the small‐pore chabazite material as a CO and passive NO x adsorber. Until now, atomically dispersed highly loaded (>0.3 wt %) transition‐metal/SSZ‐13 materials have not been known. We devised a general, simple, and scalable route to prepare such materials for Pt II and Pd II . Through spectroscopy and materials testing we show that both CO and NO x can be simultaneously completely abated with 100 % efficiency by the formation of mixed carbonyl‐nitrosyl palladium complex in chabazite micropore.

Khivantsev, Konstantin↗
DOE OSTI2018

Achieving Atomic Dispersion of Highly Loaded Transition Metals in Small-Pore Zeolite SSZ-13: High-Capacity and High-Efficiency Low-Temperature CO and Passive NO x Adsorbers

Synthesis of small-pore zeolitic materials with realistic loadings of transition metals atomically dispersed in the micropores has been a formidable challenge. Herein, we demonstrate a new simple and scalable route to high Pd and Pt loadings (>1 wt%) atomically dispersed in the micropores of a small-pore zeolite, SSZ-13. Unlike all previous methods that require addition of expensive transition metal precursor complexes into the synthesis gel and produce low loading of atomically dispersed species, this method does not require any complicated synthetic proce-dures. We determine the factors that govern the stabilization of M(II) species in the micropores of SSZ-13. Using a combined spectroscopic and DFT approach, we offer a unifying explana-tion for the discrepancies existing in available M-zeolite litera-ture. Moreover, we highlight the difference between the behavior of Pt and Pd during synthesis, and demonstrate that ionically dispersed Pd/SSZ-13 shows superior performance as a new class of environmentally important passive NOx Adsorber (PNA) material under practically relevant conditions. It thus represents the 2nd known metal-small pore zeolite material that has immediate industrial application, and the only known met-al-small pore zeolite material in which metal is close to 100 % utilized. In addition to NO x , the material performs remarkably for CO removal during cold start as well due to the formation of a mixed carbonyl-nitrosyl complex Pd(II)(CO)(NO).

Khivantsev, Konstantin↗
DOE OSTI2018

Structure and Thermal Stability of (H 2 O) 4 Tetrahedron and (H 2 O) 6 Hexagon Adsorbed on NaY Zeolite Studied by Synchrotron-Based Time-Resolved X-ray Diffraction

Water adsorption and desorption features play an important role in determining the adsorptive and catalytic properties of zeolites. In this study, the extraframework structure (water and cations) in NaY faujasite zeolite was studied by synchrotron-based in situ time-resolved X-ray diffraction (TR-XRD) in combination with the Rietveld refinement method. It was observed that Na cations locating at different sites migrated between each other during the dehydration process. Water molecules at three separate sites showed interesting geometries: (H 2 O) 4 tetrahedron W1, (H 2 O) 6 ice-like hexagonal W2, and disordered triangle W3. Interactions between each form of water and Na cations were deeply investigated. Here, the stability of the waters followed the sequence of W1 > W3 > W2. This work provides insights into both framework structure and cation positions of model zeolite under actual working conditions, which helps fully understand the properties of zeolites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Tailored multivariate analysis for modulated enhanced diffraction

Modulated enhanced diffraction (MED) is a technique allowing the dynamic structural characterization of crystalline materials subjected to an external stimulus, which is particularly suited for in situ and operando structural investigations at synchrotron sources. Contributions from the (active) part of the crystal system that varies synchronously with the stimulus can be extracted by an offline analysis, which can only be applied in the case of periodic stimuli and linear system responses. In this paper a new decomposition approach based on multivariate analysis is proposed. The standard principal component analysis (PCA) is adapted to treat MED data: specific figures of merit based on their scores and loadings are found, and the directions of the principal components obtained by PCA are modified to maximize such figures of merit. As a result, a general method to decompose MED data, called optimum constrained components rotation (OCCR), is developed, which produces very precise results on simulated data, even in the case of nonperiodic stimuli and/or nonlinear responses. The multivariate analysis approach is able to supply in one shot both the diffraction pattern related to the active atoms (through the OCCR loadings) and the time dependence of the system response (through the OCCR scores). When applied to real data, OCCR was able to supply only the latter information, as the former was hindered by changes in abundances of different crystal phases, which occurred besides structural variations in the specific case considered. To develop a decomposition procedure able to cope with this combined effect represents the next challenge in MED analysis.

Caliandro, Rocco↗