Catalysis of Organic..

Bacchini et al . 117Experimental SectionV/P/O samples were prepared according to the following procedure: the catalystprecursor, VOHPO 4 .0.5H 2 O, was precipitated starting from a suspension of 8.2 gV 2 O 5 (Aldrich, purity 99.6+%) and 10.1 g H 3 PO 4 (Aldrich 98+%) in 75 mlisobutanol (Aldrich, 99%+); the suspension was heated under reflux conditions for 6hours. The precipitate obtained was filtered, washed with a large excess ofisobutanol and dried at 125°C overnight. After a spray-drying conglomeration ofparticles into fluidizable material (20), the compound was thermally treated todevelop the VPP structure, following the hydrothermal-like procedure described indetail elsewhere (21). The thermal treatment was aimed at the development of awell-crystallized VPP, which took shorter time to reach the equilibrated state underreaction conditions, with respect to conventional thermal treatments. Then, thecatalyst was run in fluidized-bed pilot reactor for three months, under the followingconditions: temperature 400°C, feed 4% n-butane in air, pressure 3 atm. After thisperiod the catalyst was down-loaded by cooling the reactor under reaction feed. Thissample is denoted as sample eq. Sample eq was then oxidized for 4 h in flow of air,in a dedicated furnace, at different temperatures (see Table 1), in order to developdiscrete amounts of V 5+ . Samples obtained were denoted ox1, ox2 and ox3; theywere then used for catalytic tests in a lab reactor. Corresponding samples aftercatalytic tests are denoted with the suffix sp.Catalysts were characterized by means of X-ray diffraction (Phillipsdiffractometer PW3710, with CuKα as radiation source), UV-Vis-DR spectroscopy(Perkin-Elmer Lambda 19) and chemical analysis. Measurements of surface aciditywere carried out by recording transmission FT-IR spectra of samples pressed intoself-supported disks, after adsorption of pyridine at room temperature, followed bystepwise desorption under dynamic vacuum at increasing temperature (Perkin-Elmermod 1700 instrument). The procedure for chemical analysis is described in detail inref. (13).Catalytic tests of n-pentane oxidation were carried out in a laboratory glassflow-reactor, operating at atmospheric pressure, and loading 3 g of catalyst dilutedwith inert material. Feed composition was: 1 mol% n-pentane in air; residence timewas 2 g s/ml. The temperature of reaction was varied from 340 to 420°C. Theproducts were collected and analyzed by means of gas chromatography. A HP-1column (FID) was used for the separation of C 5 hydrocarbons, MA and PA. ACarbosieve SII column (TCD) was used for the separation of oxygen, carbonmonoxide and carbon dioxide.AcknowledgementsAcknowledgement is made to the Donors of the American Chemical SocietyPetroleum Research Fund, for the partial support of this activity.Dr Cristina Flego from EniTecnologie SpA is gratefully acknowledged forperforming FT-IR measurements.