Kinetics of hydrolysis of carbon tetrachloride by acidic solids

Abstract

Carbon tetrachloride (CCl 4 ) has been catalytically hydrolysed to CO 2 + HCl over acidic solids ( 1 , TiO 2 (rutile); 2 , TiO 2 /SiO 2 ; 3 , γ-Al 2 O 3 ; 4 , Al 2 O 3 /SiO 2 ; 5 , 13% Al 2 O 3 –SiO 2 ) between 520 and 610 K without loss of activity. Rates have been measured as a function of water vapour pressure ( P H ) at various pressures of CCl 4 ( P C ) and temperatures, and the results modelled by simple Langmuir–Hinshelwood rate expressions. Over 1 , 2 and 4 CCl 4 adsorption is insignificant, and a satisfactory expression is r = kP C θ H (1 − θ H ) where θ H = fractional coverage by water. Water adsorption is defined by a Langmuir equation, and regression analysis of the linearised equation provides values for its adsorption coefficient b H and for k , the temperature dependence of which leads respectively to the heat of water adsorption q H and the true activation energy E t . Apparent activation energies are markedly dependent on P H , except on 1 where water is very strongly adsorbed. On 3 and 5 , adsorption of CCl 4 cannot be ignored, and a bimolecular rate expression: r = kθ C θ H ( θ C = coverage by CCl 4 ) works well; multilinear regression analysis of the linearised expression then gives values of k , b H and b C (the adsorption coefficient of CCl 4 ). Extensive structural and chemical characterisation has helped to explain certain aspects of catalytic performance. Dichloromethane (CH 2 Cl 2 ) and chloroform (CHCl 3 ) have also been hydrolysed over 1 and 3 ; rates increase with the number of chlorine atoms, and Arrhenius parameters are reported. CCl 4 has been hydrolysed by titania and alumina either unsupported or supported on silica to CO 2 + HCl between 520 and 610 K. Dependence of rate on H 2 O and CCl 4 pressures has been fitted to one or other Langmuir–Hinshelwood rate expressions, depending on whether the CCl 4 is chemisorbed or not. Water was strongly chemisorbed in all cases, especially on TiO 2 .