Fumed oxides modified due to pyrolysis of cyclohexene

Mixed oxides such as fumed X/silica (X = Al2O3 (AS), TiO2 (TS)) and CVD-TiO2/fumed silica, initial and covered by carbon deposit formed on cyclohexene pyrolysis, were characterized by means of carbonization kinetics, nitrogen adsorption-desorption, water adsorption, and electrophoresis methods. Catalytic capability of AS (per gram of the adsorbent) in cyclohexene pyrolysis (973 K for 4 h) is greater at a low concentration of alumina, but for fumed TS, it is maximal at large C-TiO2. Concentration of pyrocarbon formed on AS or TS is 2-4 times larger than that on silica under the same pyrolysis conditions, and fumed TS can stronger catalyze pyrolysis than CVD-titania/silica does. A marked impact of the nature of X/SiO2 on cyclohexene pyrolysis results in variations of the structural, adsorptive, and electrokinetic properties of C/X/SiO2. Alterations in the pore size distributions (main maxima at Rp between 0.5 and 7 nm) &an be due to the availability of various channels between primary particles (5-50 nm) packed in relatively dense aggregates and between aggregates in more loose agglomerates of aggregates differently filled by grafted pyrocarbon. The dependencies of zeta potential of C/X/SiO2 particles on pH are closer to that of C/SiO2 than X/SiO2, i.e. carbon deposit covers mainly the X/SiO2 interface and X phase possessing catalytic activity in cyclohexene pyrolysis. (C) 2003 Elsevier Science B.V. All rights reserved.