The conversions of 1,2-dichloropropane (12dcp), 1,3-dichloropropane (13dcp), and allyl chloride (3-chloropropene, 3cp) over a silica−alumina bed have been investigated. Both 12dcp and 13dcp undergo dehydrochlorination above 500 K, mainly resulting in the two 1-chloropropene (1cp) geometric isomers, which, above 650 K, further eliminate HCl to give propyne and burn in the presence of oxygen. Small amounts of 3cp were also observed. 12dcp was found to react more rapidly than 13dcp. The conversion of 3cp gives essentially COx above 700 K and small amounts of benzene in the range 600−700 K. The reaction order is zero. The activation energy for the conversion of 12dcp was found to be 14.4 kcal/mol (60.6 kJ/mol). IR data show that a reversible adsorption step is followed by a nucleophilic substitution by an active surface oxide species, giving rise to an alkoxide species. The slow step is likely the E1 elimination of the alkoxide. The conversion of the primary 3-chloro-1-propyl carbenium ion to a 1-chloro-2-propyl carbenium ion plays a relevant role. The catalyst deactivates progressively at 523 K, its activity being nearly halved after 4 h, but it attains a plateau after 7 h. At higher temperatures, the stable total conversion of 12dcp was obtained after 10 h.