ABSTRACT The interplay between analytical technique and industrial practice has been central in t... more ABSTRACT The interplay between analytical technique and industrial practice has been central in the development of catalytic materials for processing petroleum. This article presents reviews of key aspects of two of the most important classes of catalytic materials: noble-metal Pt nanoparticles (NPs) on alumina, which are the basis of catalytic reforming; and layered sulfides of Mo and W, which catalyze hydrogenation and hetero-atom removal in hydroprocessing. The state of understanding of Pt cluster growth and resulting structures, as developed using X-ray absorption spectroscopy and STEM, is reviewed. Influences of both Pt reduction temperature in hydrogen gas, and oxidizing pretreatment conditions prior to Pt reduction, are considered. Recent work by the present authors on Pt NP structure evolution is presented in the context of the previous work. A review is subsequently presented of layered sulfide based NPs, summarizing contributions from a range of analytical techniques. Work on active site structures of sulfide NPs is reviewed, focusing particularly on the critical interactions of active edge sites with sulfur and hydrogen in chemisorption, physisorption, and spillover interactions. New temperature programmed reduction (TPR) results are presented for supported and unsupported sulfide NPs. Structural changes in TPR of alumina-supported MoS2 are investigated using extended X-ray absorption fine structure and density functional theory modeling, and are determined to arise from removal of identifiable edge-site sulfur species.
Nature International Weekly Journal of Science, 2002
One strategy that is being pursued to tackle the international problem of actinide contamination ... more One strategy that is being pursued to tackle the international problem of actinide contamination of soils, sediments and water is to use microbial activity to 'fix' these radionuclides into an insoluble form that cannot be readily dispersed. Here we show that uraninite (UO(2)) particles formed from uranium in sediments by bacterial reduction are typically less than 2 nanometres across and that the small size has important implications for uraninite reactivity and fate. Because these tiny particles may still be transported in an aqueous environment, precipitation of uranium as insoluble uraninite cannot be presumed to immobilize it.
An x-ray absorption fine structure study is being made of the pressure induced changes in the loc... more An x-ray absorption fine structure study is being made of the pressure induced changes in the local structure about Ag and Br in AgCl, AgBr and the AgCl_xBr_1-x mixture at T=77K. At ambient pressure and 18 Kbar the AgCl data show the expected NaCl-type structure. Above 60 Kbar the data are no longer consistent with the NaCl-type structure and above
ABSTRACT The interplay between analytical technique and industrial practice has been central in t... more ABSTRACT The interplay between analytical technique and industrial practice has been central in the development of catalytic materials for processing petroleum. This article presents reviews of key aspects of two of the most important classes of catalytic materials: noble-metal Pt nanoparticles (NPs) on alumina, which are the basis of catalytic reforming; and layered sulfides of Mo and W, which catalyze hydrogenation and hetero-atom removal in hydroprocessing. The state of understanding of Pt cluster growth and resulting structures, as developed using X-ray absorption spectroscopy and STEM, is reviewed. Influences of both Pt reduction temperature in hydrogen gas, and oxidizing pretreatment conditions prior to Pt reduction, are considered. Recent work by the present authors on Pt NP structure evolution is presented in the context of the previous work. A review is subsequently presented of layered sulfide based NPs, summarizing contributions from a range of analytical techniques. Work on active site structures of sulfide NPs is reviewed, focusing particularly on the critical interactions of active edge sites with sulfur and hydrogen in chemisorption, physisorption, and spillover interactions. New temperature programmed reduction (TPR) results are presented for supported and unsupported sulfide NPs. Structural changes in TPR of alumina-supported MoS2 are investigated using extended X-ray absorption fine structure and density functional theory modeling, and are determined to arise from removal of identifiable edge-site sulfur species.
Nature International Weekly Journal of Science, 2002
One strategy that is being pursued to tackle the international problem of actinide contamination ... more One strategy that is being pursued to tackle the international problem of actinide contamination of soils, sediments and water is to use microbial activity to 'fix' these radionuclides into an insoluble form that cannot be readily dispersed. Here we show that uraninite (UO(2)) particles formed from uranium in sediments by bacterial reduction are typically less than 2 nanometres across and that the small size has important implications for uraninite reactivity and fate. Because these tiny particles may still be transported in an aqueous environment, precipitation of uranium as insoluble uraninite cannot be presumed to immobilize it.
An x-ray absorption fine structure study is being made of the pressure induced changes in the loc... more An x-ray absorption fine structure study is being made of the pressure induced changes in the local structure about Ag and Br in AgCl, AgBr and the AgCl_xBr_1-x mixture at T=77K. At ambient pressure and 18 Kbar the AgCl data show the expected NaCl-type structure. Above 60 Kbar the data are no longer consistent with the NaCl-type structure and above
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