John J. Low

Screening of Metal−Organic Frameworks for Carbon Dioxide Capture from Flue Gas Using a Combined Experimental and Modeling Approach

A diverse collection of 14 metal-organic frameworks (MOFs) was screened for CO(2) capture from flue gas using a combined experimental and modeling approach. Adsorption measurements are reported for the screened MOFs at room temperature up to 1 bar. These data are used to validate a generalized strategy for molecular modeling of CO(2) and other small molecules in MOFs. MOFs possessing a high density of open metal sites are found to adsorb significant amounts of CO(2) even at low pressure. An excellent correlation is found between the heat of adsorption and the amount of CO(2) adsorbed below 1 bar. Molecular modeling can aid in selection of adsorbents for CO(2) capture from flue gas by screening a large number of MOFs.

Sensitivity of Pt x-ray absorption near edge structure to the morphology of small Pt clusters

A theoretical study of the sensitivity of Pt L3 x-ray absorption near edge structure (XANES) to the size and shape in small Ptn clusters is reported. Calculations, based on a full multiple scattering, self-consistent field, real-space Green’s function approach implemented in the ab initio FEFF8 code, show that XANES provides a characteristic signature of cluster shape. For example, the calculated white line intensity exhibits a large variation for small cluster sizes and geometry, but becomes independent of cluster size for large clusters. A strong polarization dependence of the white line is predicted for two-dimensional clusters. For three-dimensional clusters the polarization dependence is smaller, but can be used as a measure of the “flatness” of a cluster. A series of semirelativistic all-electron, full potential density functional calculations was also performed for several Ptn clusters. These calculations show the existence of intrinsic static disorder in these clusters due to nonisotropic shrinkag...

Theoretical Interpretation of XAFS and XANES in Pt Clusters

This paper first briefly summarizes the dramatic progress over the past decade both in fundamental theory and in the interpretation of XAFS and XANES. These developments have led to several ab initio codes such as FEFF for simulating XAFS and XANES, together with compatible analysis codes which permit an interpretation of the spectra in terms of geometrical and electronic properties of a material. As an example of relevance to catalysis, we discuss recent work which interprets the Pt L-edge XANES of PtX clusters based on the self-consistent FEFF8 code. For pure Pt clusters, we find that self-consistency is important in determining the variation of XANES with cluster size. For PtCl clusters, we show that the presence of a Cl–Pt bond leads to a “hybridization peak,” i.e., a peak in the Cl d-density of states (dDOS) mixed with Pt d-states, which can be used as a measure of Cl content. For Pt–H clusters, we show that hydrogen addition is well correlated with the growth of a broad shoulder above the white line. We find that this feature can be attributed largely to AXAFS, i.e., to a change in the atomic background absorption. We also analyze the effect of a support, in terms of model calculations for a realistic Pt6 cluster within a zeolite-LTL pore.

Oxidative desulfurization of sulfur compounds: Oxidation of thiophene and derivatives with hydrogen peroxide using Ti-Beta catalyst

Oxidation of thiophene and its derivatives was studied using hydrogen peroxide (H2O2), t-butyl-hydroperoxide and Ti-Beta redox molecular sieve as selective oxidation catalysts. A new reaction pathway was discovered and investigated using C-13 NMR, GC, GC-MS, HPLC, ion chromatography, and XANES. The thiophene oxidized to thiophene-sesquioxide [3a,4,7,7a-tetrahydro-4,7-epithiobenzo[b]-thiophene 1,1.8-trioxide] and the sesquioxide oxidized mostly to sulfate. 2-Methyl-thiophene and 2,5 dimethylthiophene also oxidized to sulfate and sulfone products. The Benzothiophene oxidation product was sulfone. This proposed new reaction pathway is different from prior literature, which reported the formation of thiophene 1,1-dioxide (sulfone ) as a stable oxidation product

High Throughput Screening of Complex Hydrides for Hydrogen Storage

The discovery that dopants, such as Ti, cause NaAlH 4 to reversibly desorb H 2 at mild conditions has spurred a great deal of research into complex metal hydrides. However, no complex hydride meets the targets for automotive hydrogen storage. Our approach is to accelerate the rate of discovery of improved hydrides and dopants through the combination of Virtual High Throughput Screening (VHTS) and Combinatorial Synthesis and Screening (CSS). Our CSS methods will allow us to screen thousands of samples in a year. These samples will be prepared by ball milling mixtures of hydrides and dopants similar to the established method of preparing Ti doped NaAlH 4 . VHTS exploits a molecular mechanics method to screen a thousand phases in a month. The combination of combinatorial methods and VHTS will help us discover the most promising complex hydrides for hydrogen storage. We will show the results of our medium throughput CSS and VHTS as applied to the NaAlH 4 –LiAlH 4 – Mg(AlH 4 ) 2 mixed alanate compositions.

Carbon dioxide separation with novel microporous metal organic frameworks

The goal of this program was to develop a low cost novel sorbent to remove carbon dioxide from flue gas and gasification streams in electric utilities. Porous materials named metal-organic frameworks (MOFs) were found to have good capacity and selectivity for the capture of carbon dioxide. Several materials from the initial set of reference MOFs showed extremely high CO{sub 2} adsorption capacities and very desirable linear isotherm shapes. Sample preparation occurred at a high level, with a new family of materials suitable for intellectual property protection prepared and characterized. Raman spectroscopy was shown to be useful for the facile characterization of MOF materials during adsorption and especially, desorption. Further, the development of a Raman spectroscopic-based method of determining binary adsorption isotherms was initiated. It was discovered that a stronger base functionality will need to be added to MOF linkers in order to enhance CO{sub 2} selectivity over other gases via a chemisorption mechanism. A concentrated effort was expended on being able to accurately predict CO{sub 2} selectivities and on the calculation of predicted MOF surface area values from first principles. A method of modeling hydrolysis on MOF materials that correlates with experimental data was developed and refined. Complimentary experimental data were recorded via utilization of a combinatorial chemistry heat treatment unit and high-throughput X-ray diffractometer. The three main Deliverables for the project, namely (a) a MOF for pre-combustion (e.g., IGCC) CO{sub 2} capture, (b) a MOF for post-combustion (flue gas) CO{sub 2} capture, and (c) an assessment of commercial potential for a MOF in the IGCC application, were completed. The key properties for MOFs to work in this application - high CO{sub 2} capacity, good adsorption/desorption rates, high adsorption selectivity for CO{sub 2} over other gases such as methane and nitrogen, high stability to contaminants, namely moisture, and easy regenerability, were all addressed during this program. As predicted at the start of the program, MOFs have high potential for CO{sub 2} capture in the IGCC and flue gas applications.