Studies on the Pyrolysis of the Surface-Treated Silica Gels through the Gas Chromatograph-Quadru-Pole Mass Spectrometer I. Silica Gels Treated with C1
1980 Volume 53 Issue 1 Pages 2-14
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1980 Volume 53 Issue 1 Pages 2-14
The pyrolysis of silica gels surface-treated with (A) methanol, (B) ethanol, (C) n-propanol and (D) isopropanol has been investigated by means of QPMS or GC-QPMS. The thermal decomposition takes place on the following three ranges, i. e., (i) in the vicinity of ca. 150°C, (ii) in the range of 200-300°C and (iii) 300-500°C. The amount of gas evolved showed the most appreciable rate in the range of (iii) and had the maximum in the vicinity of 400-450°C. In the case of silica gels surface-treated with (A) methanol, the range of (iii) was extended over 300-800°C and the amount of gas evolved had the maximum rate in the vicinity of 550-600°C which was higher than the ones of silica gels surface-treated with other alcohols. The mass spectra of vapors evolved in the respective temperature range were observed and their constituents were analysed. The followings were found from them that (1) the physisorbed water and unreacted alcohol were released in the range of (i); (2) the released water in the ranges of (ii) and (iii) was regarded as the water due to condensation of unreacted surface silanols ; (3) vapors evolved in the range of (ii) was mainly alcohol due to hydrolysis of surface groups with the water arised from the condensation of unreacted surface silanols ; (4) vapors evolved in the range of (iii) included the alcohol, but principal constituents were confirmed to be CO with minute amount of CH4 and H2 in the case of (A), CH2=CH2 with a small amount of CH3CHO in the case of (B), CH3CH=CH2 with small amount of CH2=CH2 and CH4 in the case of (C) and only CH3CH=CH2 in the case of (D), respectively ; (5) these constituents were also confirmed by using GC-QPMS ; (6) the mechanisms were suggested to account for thermal decomposition of the surface groups ; (7) from these results, the surface groups thus formed were confirmed not to be the alcohol chemisorbed on the silica gel, but to the alkoxy groups formed by the condensation of the surface silanol with alcohols.
