PHYSICAL CHARACTERIZATION AND HYDROISOMERIZATION ACTIVITY OF A PLATINUM-RHENIUM/PILLARED CLAY CATALYST

[摘要] Montmorillonite is a clay mineral which when exchanged with hydroxyaluminum oligomers produces a pillared clay mineral. On calcination at 500(DEGREES)C the pillars are fixed, and a microporous structure having good thermal stability and high surface area (about 350 m(;;2)/g) is generated. The pillared interlayered clay (PILC) has a two dimensional pore network with a slit width of about 8.5 (ANGSTROM). By incorporating a (de)hydrogenation function such as Pt on the PILC, a bifunctional catalyst capable of catalyzing hydroisomerization of n-paraffins is obtained. Hydroisomerization of C(,5) to C(,7) n-paraffins on a Pt-Re/PILC catalyst was studied using an isothermal fixed bed reactor operated at 1 atmosphere pressure. The rate data fit a model based on bifunc- tional catalysis. The acid catalyzed isomerization of carbenium ions appears to be the rate controlling step. Single branched isomers are the dominant products. Poisoning experiments, using dimethyl sulfide to deactivate the metal sites and pyridine as a poison for the acid sites, support the bifunctional mechanism model. A temperature programmed reduction of PILC shows that during high temperature reduction almost all the iron in the clay lattice is reduced from Fe(;;+3) to Fe(;;+2). This was confirmed by Mossbauer spectroscopy. The presence of Pt and Re accelerates the reduction of iron as evidenced by temperature programmed reduction. When the iron in the lattice is reduced, the resulting increase in the negative charge of the clay lattice is balanced by H(;;+) ions on the surface which increase the Br(SLASHCIRC)nsted acidity. Infrared spectroscopy of adsorbed pyridine shows that reducing the PILC increases the Br(SLASHCIRC)nsted acidity. Temperature programmed desorption of butyl- amines showed that the acidity of PILC is comparable to silica-alumina cracking catalysis, in both amount and activity. It is evident from scanning and transmission electron microscopy that almost all the platinum is in the form of particles in the range of 100 (ANGSTROM) to 200 (ANGSTROM). The Re is finely dispersed in small clusters containing at most a few atoms and is evenly distributed. There is no significant alloy formation.

[发布机构] Rice University