HIGHLY DISPERSED METALS IN PILLARED CLAYS: PROPERTIES AS FISCHER-TROPSCH CATALYSTS (INTERCALATION, ELECTRON MICROSCOPY, METAL CARBONYLS)

Recently developed methods (1,2) were utilized for the synthesis of highly dispersed Fischer-Tropsch active metals in the microporous regions of pillared clays. The stability, activity, and distribution of hydrocarbons formed on the resulting catalytic sites were investigated.; The first method (1) involved intercalation of hydroxy-iron polycations into the clay galleries, followed by conversion of the polycations to Fischer-Tropsch active sites. The iron pillars produced primarily C(,1)-C(,7) paraffins and olefins, although minor amounts of branched hydrocarbons and C(,1)-C(,3) alcohols also were detected. Microanalysis in a scanning electron microscope indicated significant bulk iron inhomogeneities and iron enrichment at clay edges. X-ray diffraction revealed that even though the Fe-pillared clay was ordered and stable when calcined (air, 350(DEGREES)C), it was XRD amorphous after catalysis or after storage in air for a few months. This was most likely due to pillar hydrolysis.; In the second method (2), ruthenium carbonyls were selectively dispersed in the micropores of alumina pillared montmorillonite (APM). These Ru sites were catalytically active without prereduction and gave non Schulz-Flory hydrocarbon product distributions initially. Conversely, prereduced Ru/APM catalysts did not show significant Schulz-Flory deviations, but exhibited greater conversions and enhanced production of high molecular weight products.; High resolution electron microscope studies (3) of nonprereduced Ru/APM after 30 hrs of reaction proved that Ru aggregated into large crystallites located on the external surfaces of the pillared clay. In contrast, prereduced catalysts gave a narrow distribution of small Ru microcrystallites that were mainly retained inside the pillared clay particles. A model was proposed that explained the location of relatively large crystallites (6 nm) within void spaces created by layer packing disorders. Z-contrast imaging showed small microcrystallites in thicker regions of the clay which gave support for this model.; These Ru/APM catalysts exhibited high selectivities for internal olefins and branched hydrocarbons, an unusual result for Ru-based Fischer-Tropsch catalysts. The yields of these atypical isomer fractions were studied by variation of reaction variables and the addition of 1-olefin probe molecules. These experiments gave support to the proposal that this high isomerization selectivity is due to the strong intracrystalline acidity of alumina pillared clay.