Propane conversion on dry-air-calcined HZSM-5 zeolite
Propane conversion has been studied at high and low partial pressures on HZSM-5 based catalysts which had been dry-air calcined at temperatures between 773 and 1193 K. At a low partial pressure (36.5 Pa), where products at 808 K were restricted to methane, ethene and propene, attention is directed towards the relative contributions from cracking and dehydrogenation in the initial activation of propane. An excess of ethene over methane and differences in the activation energies for their formation suggest that cracking of both C3 and C6 carbenium ions contribute to ethene production. Both unbound and silica-bound HZSM-5 catalysts were used in these low-partial-pressure studies, where the rate of propane conversion expressed per g of zeolite was 25 ± 4% less for bound catalysts calcined at the same temperature. At a high partial pressure (101 kPa), where methane, ethane and various aromatics were the predominant products, activity measurements were restricted to silica-bound HZSM-5 at 808 K. In both pressure regimes the concentration of Al atoms occupying tetrahedral positions within the framework structure is fundamental in determining activity patterns.