Journal of Non-Crystalline Solids 143 (1992) 14-20 North-Holland JOURNA L OF NON-CRYS LINESOLIDS Reactions of silica gel with alkylaluminum compounds and titanium tetrachloride Jan Kratochvfla, Zbynfik Kadlc, Anton~n Kazda and Zden~k Salajka Chemopetrol, Research Institute of Macromolecular Chemistry, Tkalcovskd 2, 656 49 Brno, Czechoslovakia Received 11 July 1991 Revised manuscript received 2 December 1991 The amount of gases (methane, ethane, isobutane and hydrogen chloride) evolved in a reaction of silica gel was measured. The gel was heated up to 20-900°C, with an excess of alkylaluminum compounds and titanium tetrachloride. A linear decrease of the amounts with activation temperature in the range 200-900°C was observed. These compounds can be used for OH determination as OH group signals in near infrared spectra are not detected after the reaction. Alkylaluminum deposition on silica gel from heptane solutions was measured. Besides the chemical reaction with OH groups a chemisorp- tion on silica gel surface was observed and its extent was measured. This phenomenon is discussed in terms of alkylaluminum chemisorption on surface siloxane bonds of silica gel. 1. Introduction Water free, granular silica gel with high sur- face area is widely used as a catalyst support for 1-alkene polymerization. According to the tem- perature of activation it contains varying amounts of free and hydrogen bonded hydroxyl groups, which enter into reactions with catalyst compo- nents. Their reactions, for example with organic compounds of aluminum, lithium, magnesium and zinc [1-5] and with aluminum, titanium, boron and silicon chlorides [1-3,6-9], were studied. Some of these compounds are proposed for di- rect hydroxyl group determination. The published results differ considerably, which may be caused by strong differences in structure and reactivity of these compounds, or by unsuitable reaction con- ditions. For such a study, a simultaneous determi- nation of OH group and H20 content in the near infrared region has been proposed [10,11] and further applied in this study. This communication presents reactions of sil- ica gel with various aluminum alkyls and titanium tetrachloride in heptane medium. Amounts of gases evolved and chemisorption equilibria were measured to ascertain the suitability of these extremely reactive compounds for hydroxyl group and siloxane bond determination. 2. Experimental Silica gel (Davison Chemical Co., USA, grade 952) was dehydrated in a quartz vessel in a puri- fied nitrogen stream at 200 to 900°C for 6 h. Samples of silica gel were also prepared by a 200 h evacuation in a glass vessel at 20°C and 1 x 10 -2 Pa. Specific surface area was measured using BET method and the following values were ob- tained for various temperatures of heat treat- ment: (285 + 2) mZ/g (20-600°C), (278 _+ 2) mZ/g (800°C), and (218_+ 4) m2/g (900°C). Pore vol- ume values were (1.8 _+ 0.1), (1.7 _+ 0.1) and (0.85 + 0.05) cm3/g, respectively, and the maximum of pore diameter distribution was 20 nm, indepen- dently of the activation temperature. Infrared spectra of silica gel in the range of 4000-8000 cm-1 were measured using a Perkin-Elmer 330 instrument. Silica gel was placed into a 1 cm diameter quartz cell and dry carbon tetrachloride 0022-3093/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved