Catalytic dehydrochlorination of 2-chlorobutane

Abstract

The catalytic dehydrochlorination of 2-chlorobutane has been studied using promoted alumina catalysts. The modified alumina (AI2O 3-HCI, K-AI2O3), zirconia-alumina (Zr02-Al203) and silver-alumina (Ag/AC) catalysts were synthesized and characterised before being tested for catalyst activity. In addition, silver-silica (Ag/SiC) and silver-zirconia-alumina (Ag/ZrCVAhOs) were also prepared as different supported silver catalysts for dehydrochlorination of 2-chlorobutane. y-alumina catalysts were active for the dehydrochlorination reaction due to the presence of Lewis acid sites. The catalyst performance and the acid-base properties suggest the reaction was acid-catalysed. Doping K or Na on y-alumina inhibited the activity due to the loss of acidic sites from the alumina surface. Despite the inhibition effect of the alkaline doped catalyst, acid-base bifunctional catalysis was proposed over zirconia-alumina catalysts. The presence of Al-O-Zr surface structural defects on zirconia- alumina controlled the acid-base properties which relate to the catalytic activity. The role of basic sites is to stabilise the carbonium ion and activates the C-H bond, while the acid sites encourage the abstraction of CI-ions. A correlation between the ratio of base/acid sites and conversion is suggested, depending on the reaction conditions (i.e. space velocity). Finally, the silver-promoted catalysts were prepared, emphasis placed on the metal-support interaction. The results suggest that as well as the active species distribution which is important for the reaction, the acid-base properties of the support are vital