Mixed Metal Phospho-Sulfates for Acid Catalysis
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Mat. Res. Soc. Symp. Proc. Vol. 497 © 1998 Materials Research Society
EXPERIMENTAL Synthesis & Characterization Catalysts were synthesized by reacting mixed-metal solutions with stoichiometric amounts of phosphoric acid and water, and an excess of sulfuric acid. The resultant precipitates were heated under flowing air at a ramp rate of 0.1 'C /minute to 300 'C and held at this temperature for 72 hours. The calcined materials were ground with a mortar and pestle afterwhich they were granulated by alternating 2000 PSI hydraulic loading, grinding, and sieving resulting in sample particles of 100-200 jtm. Powder X-ray diffraction data were collected at room temperature on a Siemens Model D500 diffractometer, with e-20 sample geometry and Cu Koa radiation, between 2(0 = 5 and 60'. BET measurements were performed on a Quantachrome Autosorb automated gas sorption system, with adsorbed and desorbed volumes of nitrogen in the relative pressure range of 0.05-1.0. Chemical analysis was performed via DCP using an ARL SS-7 DCP, with the exception of sulfur analysis, which was performed by Galbraith Laboratories. 3"P MAS NMR data were collected on a 9.4T system at 400 MHz for protons and 162 MHz for phosphorous, with a 900 pulse and spinning speeds between 6-7 KHz. The chemical shifts are relative to phosphoric acid as an external standard. De-convolution of spectra was performed using Peakfit 4.0 software (Jandel). The FTIR spectra of the samples were obtained using both transmission and diffuse reflectance modes. The transmission infrared spectroscopy was obtained with a Mattson Research Series 1 FTIR spectrometer equipped with an air-cooled source and a mercurycadmium-telluride detector. The spectra were obtained at a resolution of 4 cm' after 100-200 scans. The diffuse reflectance spectra were obtained using a Nicolet 20SXB FTIR spectrometer equipped with a water-cooled source and a mercury-cadmium-telluride detector. The spectra were obtained at a resolution of 4 cm-' after 250 scans. The IR cell was a Spectratech diffuse reflectance assembly. All spectra were taken at ambient temperature and in the N 2 purge of the IR chamber. The samples were diluted to a 5% sample in KBr mixture. Isomerization The materials were tested for activity toward 2-methyl-2-pentene isomerization and oxylene isomerization using a packed bed flow reactor. Approximately 50 mg of granulated sample was placed in a 6 mm O.D., 40 cm long fritted glass tube and held in place with glass wool. The samples were pretreated at elevated temperatures in ultra-high purity helium (99.999% Matheson) flowing at 40-60 cc/min. All pre-treatments and reactions were at atmospheric pressure. After pretreatment, the catalyst sample was cooled and the reaction was run isothermally at 150 'C. Flowing He was used to carry the 2-methyl-2-pentene and o-xylene from the 0 'C saturator to the reactor bed, at 10 cc/min and 1.5-2.0 cc/min, respectively. The products and reactants flowed through heated lines to a HP 5890 series II gas chromatograph (GC) equipped with a flame
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