INSITU HIGH-TEMPERATURE AND HIGH-PRESSURE EXAFS STUDIES OF PT/AL2O3 CATALYSTS .2. CARBON REMOVAL

EXAFS has been used to follow in situ the structural evolution of a Pt/Al2O3 catalyst during removal of carbon by hydrogenation, after reduction and carbon deposition. After reduction at 350-degrees-C, the total hydrogen pressure was raised to 3 atm. and n-heptane was injected over the sample. EXAFS measurements at the Pt edge were carried out with simultaneous on-line EXAFS analysis of the spectra. After observing the rapid formation of a carbon-platinum bond which is unmodified with time, we stopped the heptane flow, raised the temperature to 450-degrees-C, and maintained hydrogen flow at 3 atm. The disappearance of the platinum-carbon bond during heat treatment in hydrogen was monitored via on-line analysis. No sintering of the metal particles was observed. EXAFS is thus proven to be an efficient tool to study not just structural changes of a catalyst during a hydrocarbon reaction [1], but also to use it as a technique to study other catalytic phenomena as well.