Surface Structure and Mechanisms of Gasification Catalysts Deactivation. Quarterly Report,August 1--October 31, 1977.

摘要

The vacuum and gas adsorption system which will be used to study adsorbed species via laser Raman spectroscopy is described. Preliminary Raman data from the Ni(111) plane show a forbidden mode which will be studied further in order to determine its origin. Raman and infrared spectra of a NiO/Cr sub 2 O sub 3 /MgSiO sub 3catalyst are presented and interpreted in terms of Si--O--Cr complexes with SiO sub 42-and CrO sub 42-coordination before methanation tests. After being exposed to typical methanation conditions,the spectra are closer to those expected for mixtures of NiO +Cr sub 2 O sub 3 + MgSiO sub 3 . Far-infrared studies on SiO sub 2 -,Al sub 2 O sub 3 -,and MgSiO sub 3 -supported catalysts are summarized. The interaction of CO with a sulfur-contaminated Ni(111) surface was studied by the Auger Technique at three different temperatures: -48exp 0 C; 30exp 0 C,and 100exp 0 C. Results have shown differences in the binding states at different temperatures. It has also shown that the presence of sulfur blocks the adsorption of CO. NiSiO sub 3and NiAl sub 2 O sub 4samples displayed ESCA spectra like those of the unreduced Ni/SiO sub 2and Ni/Al sub 2 O sub 3catalysts,but NiAl sub 2 O sub 4was reduced by argon ion etching,contrary to expectations. The etching procedure was evaluated and it was found that the form of the sample (pellet versus powder) influenced the degree of reduction observed for NiO. MgSiO sub 3supported catalysts appeared to show little interaction with the support. Sulfiding a reduced version of these catalysts leads to deactivation due to the formation of NiS deep in the sample. X-ray diffraction studies to determine the particle size distribution in reduced and passivated catalysts have been continued. A good correlation has been found between the crystallite sizes determined from hydrogen chemisorption surface area measurements and x-ray line broadening analyses. (ERA citation 03:046218)