No abstract

A platinum/alumina catalyst was sintered in oxygen and hydrogen atmospheres using two metal loadings of the catalyst: 0.3% Pt and 0.6% Pt. After sintering, the aromatization selectivity was investigated with the reforming of n-heptane as the model reaction at a temperature of 500• C and a pressure of 391.8 kPa. The primary products of n-heptane reforming on the fresh platinum catalysts were methane and toluene, with subsequent conversion of benzene from toluene demethylation. To induce sintering, the catalysts were treated with oxygen at a flow rate of 60 mL min −1 , pressure of 195.9 kPa and temperatures between 500 and 800• C. The 0.3% Pt/Al 2 O 3 catalyst exhibited enhanced aromatization selectivity at various sintering temperatures while the 0.6% Pt/Al 2 O 3 catalyst was inherently hydrogenolytic. The fact that aromatization was absent on the 0.6% Pt/Al 2 O 3 catalyst was attributed to the presence of surface structures with dimensionality between two and three as opposed to essentially 2-D structures on the 0.3% Pt/Al 2 O 3 catalyst surface. On the 0.3% Pt/Al 2 O 3 catalyst, the reaction product ranged from only toluene at a 500• C sintering temperature to predominantly cracked product at a sintering temperature of 650 • C and no reaction at 800• C. For sintering at about 650 • C, subsequent conversion of n-heptane was complete and dropped thereafter. The turnover number was observed to change from 0.07 to 2.26 s −1 as the dispersion changed from 0.33 to 0.09. The Koros-Nowark (K-N) test was used to check for the presence of internal diffusional incursions and Boudart's criterion was used for structural sensitivity determination. The K-N test indicated the absence of diffusional resistances while n-heptane reforming was found to be structure sensitive on the Pt/Al 2 O 3 catalyst.