Factors affecting aromatization functionality of n-heptane onto Cr[2]O[3]-Al[2]O[3] catalysts doped with K[2]O

ABSTRACT

CHROMIA/ALUMINA catalysts containing 2, 4, 8, 16 and 32 mol% Cr[2] O[3]. were prepared using the co-precipitation technique. Doping of the precipitated gels with 2 mol% K[2]O was made prior to calcinations at 500, 700 and 900 [degree sign] C. The structures of the calcinations products were determined from their XRD patterns and their textural properties were determined from the adsorption of nitrogen at 77 K. The dehydrocyclization of n-heptane was carried out at 520-580[degree sign] C. using helium as a gas carrier at a rate of 20-60 ml/min, in a pulse micro-reactor directly attached to a flame ionization detector. Samples containing 2 or 4 mol% Cr[2]O[3] did not show any crystalizied chromia phase, whereas those containing higher Cr[2]O[3] content showed gamma- and/or alpha- Cr[2]O[3] depending on their chromia content and calcination temperature. The surface area decreased and the pore size increased with increase of chromia content and with the rise of the calcinations temperature. Chromia/alumina catalysts calcined at 700 [degree sign] C exhibited the highest dehydrocyclization activities compared with the corresponding catalysts calcined either at 500 at 900 [degree sign] C. The conversion of n-heptane proceeded mainly via dehydrocyclization to toluene [major] and benzene [minor], with very low yield of cracking products of C[5]-naphthenes