Nano-Crystalline Powders and Suspensions Generated Using A Flow-Through Hydrothermal Process, Part II: Applications
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Pacific Northwest Laboratory [1], Richland, WA 99352 ABSTRACT Ultra-fine, nano-crystalline six-line ferrihydrite (5Fe 2O3-9H 2 0) and cubic zirconia (ZrO2) powders have been produced using the Rapid Thermal Decomposition of precursors in Solution (RTDS) technology. Nano-crystalline RTDS six-line ferrihydrite powder used as an in situ precursor for first-stage direct coal liquefaction catalysts increased the liquefied products from Blind Canyon Seam coal by 22% absolute over thermal background at 350'C. Initial sintering studies performed on nano-crystalline RTDS ZrO 2 powder have also been presented and compared to predictions made from theories derived for micro-crystalline powders. INTRODUCTION In a preceding paper [21 we outline the characteristics of selected nanocrystalline iron- and zirconium-oxide and oxyhydroxide powders produced using a flow-through hydrothermal technique referred to as the Rapid Thermal Decomposition of precursors in Solution (RTDS) process. RTDS was developed at Pacific Northwest Laboratory (PNL) and has been found to be useful for producing a variety of nano-crystalline oxide and oxyhydroxide suspensions and dried powders. RTDS-generated powders of various compositions are being evaluated as
heterogeneous catalysts in several industrial chemical processes where the large specific surface areas inherent to these powders (100-500 m 2/g) are of obvious benefit. Here we discuss the application of RTDS six-line ferrihydrite [2] as a catalyst precursor for the first-stage direct liquefaction of coal [3]. A potential application of RTDS zirconium oxide powder [2] is as a feedstock for the fabrication of fine-grained bulk products. The sintering behavior of relatively low green density compacts pressed from this powder have been investigated to test the applicability of typical processing schemes with RTDS powders. The often touted benefit of improved sintering characteristics (e.g., densification occurs at lower temperatures) associated with the use of such nano-crystalline powders was also explored. APPLICATIONS OF RTDS PRODUCTS Catalysts The high specific surface areas inherent to the ultra-fine, nano-crystalline powders produced by the RTDS process make them ideally suited for use as 505 Mat. Res. Soc. Symp. Proc. Vol. 346. 01994 Materials Research Society
heterogeneous catalysts. Several of the available RTDS powders are currently being tested by Pacific Northwest Laboratory (PNL) researchers and clients for their usefulness in industrial catalytic processes. Many of these catalytic applications have centered primarily around processes involving the hydrogenolysis, hydrogenation, and desulfurization of fossil fuels. We have extensively tested RTDS-generated nano-crystalline six-line ferrihydrite (5Fe2O3-9H 20) powder [2] as a heterogeneous first-stage coal liquefaction catalyst precursor [3]. Under liquefaction conditions and in the presence of a sulfur source, the active catalyst, which is an unidentified form of iron sulfide, forms in situ from the iron-based precursor powder. Catalys
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